**Functional Biomimetic Dental Restoration**

**Functional Biomimetic Dental Restoration**

DOI: 10.5772/intechopen.69534

#### Elham M. Senan and Ahmed A. Madfa Elham M. Senan and Ahmed A. Madfa Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69534

#### **Abstract**

Bioinspired functionally graded approach is an innovative material technology, which has rapidly progressed both in terms of materials processing and computational modeling in recent years. Bioinspired functionally graded structure allows the integration of dissimilar materials without formation of severe internal stress and combines diverse properties into a single material system. It is a remarkable example of nature's ability to engineer functionally graded dental prostheses. Therefore, this novel technology is designed to improve the performance of the materials in medical and dental fields. Thus, this chapter book reviews the current status of the functionally graded dental prostheses and biomimetic process inspired by the human bone, enamel and dentin-enamel junction (DEJ) structures and the linear gradation in Young's modulus of the human bone, enamel and dentin-enamel junction, as a new material design approach, to improve the performance compared to traditional dental prostheses. Notable research is highlighted regarding application of biomimetic prostheses into various fields in dentistry. The current chapter book will open a new avenue for recent researches aimed at the further development of new dental prostheses for improving their clinical durability.

**Keywords:** functionally graded materials, dental restorations, dental implant, dental post, dental crown

## **1. Introduction**

The biomechanical behavior of biologic structures as well as restorative systems is influenced by several factors that interact with one another other [1, 2]. In the oral environment, several variables contribute to the long term success of restorations. Some of them are dependent on the individual, just like occlusion, load intensity and direction, temperature, moisture, wear, presence of sound tooth structure and quality of supporting tissues, whereas other factors are not controllable, such as structural integrity, microleakage, fatigue and time. Furthermore,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

teeth and restorative materials are characterized by intrinsic physical characteristics which are responsible for their mechanical performances during functions over time [3].

Biomaterials are essential for life and health in certain cases. They generally have a high added value for their size. Biomaterials should simultaneously satisfy many requirements and possess properties such as non-toxicity, corrosion resistance, thermal conductivity, strength, fatigue durability, biocompatibility and sometimes aesthetics. However, a single composition with a uniform structure may not satisfy all such requirements. Therefore, materials scientists increasingly aim to engineer materials that are more damage-resistant than their conventional homogeneous counterparts. This is particularly important at surfaces or at interfaces between dissimilar materials, where contact failure commonly occurs.

Learning from nature, natural biomaterials often possess the structure of functionally graded materials (FGMs) which enables them to satisfy these requirements. Many engineered materials are graded in some manner, but FGMs are often characterized by a gradient purposefully formed using compositional or microstructural design. FGMs provide the structure with which synthetic biomaterials should essentially be formed.

Bioinspired functionally graded approach is an innovative material technology, which has rapidly progressed both in terms of materials processing and computational modeling in recent years [4]. Bioinspired functionally graded structure allows the integration of dissimilar materials without formation of severe internal stresses and combines diverse materials properties into a single material system. The graded structure eliminates the sharp interface resulting from traditional core-veneer fabrication, thus, eliminating the potential for delamination between layers. Reduced stress concentration at the intersection between an interface and a free surface is another advantage of this graded transition. Likewise, the local driving force for crack growth across an interface can be increased or decreased by altering the gradients in elastic and plastic properties across the interface [5, 6].

Many applications of this innovative technology are found in medical and dental fields [7–15]. Thus, this chapter book will review the current status of the functionally graded dental prostheses and biomimetic process inspired by the human bone, enamel and dentin-enamel junction (DEJ) structures and the linear gradation in Young's modulus of the human bone, enamel and DEJ, as a new material design approach, to improve the performance compared to traditional dental prostheses.

## **2. Dental implant**

#### **2.1. Overview**

Dental implants are an effective treatment to replace the root part of the missing natural tooth [16], in order to restore patients' appearance, speech and health [17]. They are completely placed into the jaw bone and give support to a dental prosthesis [18].

During the last 10 years, dental implants had received an increasingly growing interest and focus worldwide. They are used to treat about one million individual per year around the globe [19]. Complete restoration of dentition, rise in the mean age of population, higher number of elderly individuals in population along with increased public awareness are all causes for the increasing demand for dental implants [19].

teeth and restorative materials are characterized by intrinsic physical characteristics which

Biomaterials are essential for life and health in certain cases. They generally have a high added value for their size. Biomaterials should simultaneously satisfy many requirements and possess properties such as non-toxicity, corrosion resistance, thermal conductivity, strength, fatigue durability, biocompatibility and sometimes aesthetics. However, a single composition with a uniform structure may not satisfy all such requirements. Therefore, materials scientists increasingly aim to engineer materials that are more damage-resistant than their conventional homogeneous counterparts. This is particularly important at surfaces or at interfaces between

Learning from nature, natural biomaterials often possess the structure of functionally graded materials (FGMs) which enables them to satisfy these requirements. Many engineered materials are graded in some manner, but FGMs are often characterized by a gradient purposefully formed using compositional or microstructural design. FGMs provide the structure with

Bioinspired functionally graded approach is an innovative material technology, which has rapidly progressed both in terms of materials processing and computational modeling in recent years [4]. Bioinspired functionally graded structure allows the integration of dissimilar materials without formation of severe internal stresses and combines diverse materials properties into a single material system. The graded structure eliminates the sharp interface resulting from traditional core-veneer fabrication, thus, eliminating the potential for delamination between layers. Reduced stress concentration at the intersection between an interface and a free surface is another advantage of this graded transition. Likewise, the local driving force for crack growth across an interface can be increased or decreased by altering the gradients in

Many applications of this innovative technology are found in medical and dental fields [7–15]. Thus, this chapter book will review the current status of the functionally graded dental prostheses and biomimetic process inspired by the human bone, enamel and dentin-enamel junction (DEJ) structures and the linear gradation in Young's modulus of the human bone, enamel and DEJ, as a new material design approach, to improve the performance compared to tradi-

Dental implants are an effective treatment to replace the root part of the missing natural tooth [16], in order to restore patients' appearance, speech and health [17]. They are completely

During the last 10 years, dental implants had received an increasingly growing interest and focus worldwide. They are used to treat about one million individual per year around the

placed into the jaw bone and give support to a dental prosthesis [18].

are responsible for their mechanical performances during functions over time [3].

dissimilar materials, where contact failure commonly occurs.

146 Insights into Various Aspects of Oral Health

which synthetic biomaterials should essentially be formed.

elastic and plastic properties across the interface [5, 6].

tional dental prostheses.

**2. Dental implant**

**2.1. Overview**

Basically, implants should be fabricated from biomaterials congruous with the human body environmental conditions. Titanium and its alloys have been reported as the materials of choice for most dental implants because of their inertness, biocompatibility and distinguished mechanical properties [20]. However, the Young's modulus of titanium alloys is higher than that of mineralized tissues. Moreover, the dense structure of titanium for biomedical implants can result in a divergence among the titanium implant Young's modulus (110 GPa) and that of human cortical (17–20 GPa) and cancellous bones (about 4 GPa) [21, 22].

The increased stiffness of titanium implants causes stress shielding with improper loading of the underlying bone tissue [23]. Human bone is a dynamic vital tissue that undergoes continuous modifications by bone-forming and bone-eating cells in response to applied external signals. This results in a reduced mechanical loading of bone which in turn leads to bone resorption, implant loosening and ultimate failure which has been a problem for implants in the past [9]. Overloading, on the other hand, also creates high stresses in local regions of bone which can also stimulate resorption [24]. For that reason, many trials have been performed to improve the mechanical properties of different biomaterials to be compatible with those of bone tissue. Most of these efforts have directed to develop certain significant interaction features at the implant surface and bone tissue interface. Recent developments in dental implant designs, and bone tissue engineering scaffolds, have all added to manufacturing novel porous titanium structures, and these fields utilize and benefit from each other's technologies.

Other issue is configuration of implant that represents an essential factor in bone-implant interface and can promote the process of osseointegration. For promotion of dental implant stability, various implant surface adjustments have been suggested to adapt the properties of dental implants [25]. Modifying the implant surface can upgrade the interaction of implant to bone; however, there is not always a clear explanation for the mechanism of interface improvement. For example, a morphological modification, such as roughening the implant surface, can also create alterations in the chemistry of dental implant surface [26]. Sand blasting with stiff particles such as alumina, TiO<sup>2</sup> and ceramic has also been proposed to roughen dental implant surface [19]. Chemical modification, such as plasma spraying with different powder particles such as titanium oxide, calcium phosphate and hydroxyapatite, has been used to coat dental implants surface [27]. In spite of being very successful, there are number of disadvantages related to the previous procedures; the bulk structure is still high-density titanium, the coating materials can dissolve away over a long period of time. Furthermore, coating particles that break away from the surface spray layer could have a negative biological effect on the adjacent tissue such as peri-implantitis [27]. Thus, various alternative approaches have been employed to overcome these shortcomings of coating materials by producing porous biomaterials as an alternative for the classical solid structure. Cellular structures can create a suitable biological environment for the host tissues to grow into these porous designs [28], establishing improved early implant stability. However, this technology is an expensive which may not be affordable to many individuals seeking dental implant treatments and, therefore, methods of providing a porous structure in titanium or a titanium alloy is of strong interest to the dental implant community [29].

#### **2.2. Dental implant based on functionally graded concept**

Presence of a porous surface or rough surface with macroscopic grooves and threads is one of the basic requirements of dental implants to establish a primarily mechanical stabilization between implants and bone tissues [30]. In addition, adequate support should be present mechanically between the radicular part of dental implant and its superstructure coronal part. This should be accomplished by forming a solid inner core and porous outer shell as a replacement to a completely porous structure [30]. A problematic issue is that high magnitude of stress could form at the implant shell and core junction area where the mechanical properties alter quickly [31]. Consequently, the bond between the implant covering layer and its core is weakened. Cook et al. [32] have suggested a post-sintering heat treatment in order to reduce the aforementioned problem that is related to residual accumulated stresses. This method showed an improvement in the fatigue strength of titanium alloy by about 15%. However, the concept of designing and manufacturing functionally graded structures can be useful to prevent stress concentrations between the interface layers where the elastic modulus changes suddenly [33].

Development of implants based on biocompatible FGMs for various applications in medical and dental fields has been emphasized [7–15]. FGM permits the integration of different materials without creating severe internal stresses and combines various unlike properties into a single material system (**Figure 1**). Materials in nature, such as bones and teeth, are the source to the development of FGM concept with its origin in regard to their sophisticated

**Figure 1.** FGM dental implant with graded material composition.

properties [34, 35]. For example, bone design which gradually changes from a dense, stiff external structure (the cortical bone) to a porous internal one (the cancellous bone) reflects the idea that functional gradation has been utilized by biological adaptation [34]. This unique bony structure demonstrates biologic revolution and enhances the material's reaction to extrinsic loads. Thereby, improved structure for a synthetic implant must exhibit alike gradation. A similar trend has been noticed in the development of functionally graded dental implants with the suggestion of placing surface layer coatings, adding porosity gradients and composite materials formed basically of metal and ceramics (e.g. hydroxyapatite), which ought to promote implant performance with regard to stress distribution and biocompatibility issues [36, 37].

individuals seeking dental implant treatments and, therefore, methods of providing a porous structure in titanium or a titanium alloy is of strong interest to the dental implant

Presence of a porous surface or rough surface with macroscopic grooves and threads is one of the basic requirements of dental implants to establish a primarily mechanical stabilization between implants and bone tissues [30]. In addition, adequate support should be present mechanically between the radicular part of dental implant and its superstructure coronal part. This should be accomplished by forming a solid inner core and porous outer shell as a replacement to a completely porous structure [30]. A problematic issue is that high magnitude of stress could form at the implant shell and core junction area where the mechanical properties alter quickly [31]. Consequently, the bond between the implant covering layer and its core is weakened. Cook et al. [32] have suggested a post-sintering heat treatment in order to reduce the aforementioned problem that is related to residual accumulated stresses. This method showed an improvement in the fatigue strength of titanium alloy by about 15%. However, the concept of designing and manufacturing functionally graded structures can be useful to prevent stress concentrations between the interface layers where the elastic modulus changes

Development of implants based on biocompatible FGMs for various applications in medical and dental fields has been emphasized [7–15]. FGM permits the integration of different materials without creating severe internal stresses and combines various unlike properties into a single material system (**Figure 1**). Materials in nature, such as bones and teeth, are the source to the development of FGM concept with its origin in regard to their sophisticated

**2.2. Dental implant based on functionally graded concept**

**Figure 1.** FGM dental implant with graded material composition.

community [29].

148 Insights into Various Aspects of Oral Health

suddenly [33].

Hydroxyapatite/titanium FGM, based on the criterion of minimum residual thermal stress, was optimally designed and fabricated by Chu et al. [38]. Due to the gradual increase of the thermal expansion coefficient from the substrate to the coating outer layer, the titanium component enhanced the mechanical properties of the coating and also assisted in decreasing the residual stresses in the final coating. Additionally, Khor et al. [39] produced hydroxyapatitetitanium functionally graded coatings which result in improvements related to microstructure, density, porosity, micro-hardness, and Young's modulus. Hedia and Mahmoud [7] utilize the finite element method (FEM) to optimize the hydroxyapatite/titanium functionally graded dental implant, based on the criterion of minimum von Mises' stress. Improved analysis by including this effect in another numerical investigation was later made by Hedia [8]. Yang and Xiang [12] used FEM to study the biomechanical behavior of a threaded functionally graded biomaterials dental implant/surrounding bone system under both static and harmonic occlusal forces. They found that functionally graded biomaterials dental implant effectively diminishes the stress difference at the implant-bone interfaces where maximum stresses occur. Furthermore, Wang et al. [11] investigated the thermal-mechanical performance of hydroxyapatite/titanium functionally graded dental implants with the FEM. They concluded that the functionally graded implants with different hydroxyapatite fraction perform almost equally well, while the titanium yields much higher von Mises' stress. Functionally graded coatings containing hydroxyapatite and glass also were prepared by Yamada et al. [40].The concentration of glass increased from the innermost to the outermost. The glass phase was noticed to improve adhesion of the coating to the titanium substrate.

The concept of creation of functionally graded structures in porous materials by changing the structure of the lattice has also been investigated [41]. Tolochko et al. [30] used Laser-forming techniques with continuous wave and pulsed lasers to produce dental implants from Ti powders with two different zones. They made a compact core and irregular porous shell by incorporating selective laser sintering (SLS) for the porous surface and selective laser melting (SLM) for the solid core. Microscopical examination showed that the average pore size was 100–200 μm and the porosity 40–45%. Traini et al. [42] used a laser metal sintering technique to construct Ti alloy dental implant incorporating a gradient of porosity, from the inner core to the outer surface. The functionally graded materials were proven to give better approximate to the elastic properties of the bone (**Figure 2**). Mangano et al. [43] used direct laser fabrication that has potential to produce dental implants with irregular and narrow intercommunicating crevices and shallow depressions using Ti alloy powder. However, they noticed a residue of metal

**Figure 2.** FGM implant with porous Ti alloy.

particles on the implant surface under stereo-scanning electron microscopy. As a result, they proposed acid etching procedure as a treatment to remove the surface adherent particles [43].

Murr et al. [44] used electron beam melting to produce Ti-6Al-4V open cellular foams with different cell wall structures (solid and hollow). The elastic moduli were decreased with increased porosity as widely known for porous metals of all types. On the other hand, the micro indentation hardness of the hollow cell wall structure was higher than that of the solid cell wall. Long term stability and mechanical properties of two types of porous dental implants were investigated under both dynamic and static circumstances [23]. Implants were coated by porous layers made from ammonium hydrogen-carbonate (NH4 ) HCO3 as space holder particles. Then testing these coated implant samples was performed in fatigue and finite element analysis was used to predict their fatigue behavior. It was determined that the melting process of the electron beam has the potential to process Ti-6Al-4V implants with wide range of pore geometry [45]. The compressive properties of porous implants varied with pore structure and can resemble those of human bone [46]. To improve the surface wear resistance of the titanium structures, Laoui et al. applied laser gas nitriding using a CW Nd:YAG laser, and consequently, the coating layer withstand more cycles without fracture [46].

Nomura et al. [47] recommended the vacuum infiltration technique with sintering to generate porous titanium/hydroxyapatite composites. The elastic modulus was rated utilizing the porosity percentage and then tailored to be in the scale of bone tissue (given by 24–34% porosity). Porosity can be specified by adjusting and controlling the applied temperature and pressure in a hot-pressing stage. Likewise, Hanks' buffered salt solution was applied to reduce the elastic modulus of the sintered porous titanium/hydroxyapatite composites. The bone implant contact and removal torque of dental implants with a porous layer produced by laser sintering were measured and compared with sandblasted-acid etched implant (i.e., those with a rough, but not porous, surface) [48]. It was decided that resultant porous dental implants fabricated by the sintering process are better in terms of biocompatibility and biomechanical properties.

Basically, adequate combination of both mechanical properties and biocompatibility constitute important factors in the application of any biomaterial within the medical or dental field. Surface characteristics govern the material biocompatibility, while its mechanical strength is determined by the average mechanical strength of the materials. According to Chenglin et al. [49] and Lim et al. [50], the combinations of hydroxyapatite and Ti-6Al-4V can results in an excellent functionally graded material. Although the surface layer is essentially hydroxyapatite, the resultant functionally graded material exhibits excellent properties with regards to biocompatibility and bone-bonding ability or dental-bonding ability. Superior mechanical strength in the functionally graded material is accomplished by Ti-6Al-4V phase. Yokoyama et al. [51] analyzed the biocompatibility and mechanical properties of hydroxyapatite/titanium functionally graded implant synthesized by spark sintering technique and found that much enhancement was accomplished by this technique. Miyao et al. [52] manufactured titanium/hydroxyapatite functionally graded material utilizing spark plasma sintering method, and both biocompatibility and mechanical properties as an implant were investigated. They reported that the titanium/hydroxyapatite functionally graded material implants made by the spark plasma sintering method showed strength, excellent biocompatibility, and controllability for graded bioreaction. Watari et al. [53] fabricated the hydroxyapatite/titanium functionally graded dental implant and tested its biocompatibility in Wistar strain rat. They noticed that hydroxyapatite/titanium functionally graded dental implant had better biocompatibility than titanium implant. Foppiano et al. [54] evaluated in vitro the biocompatibility of functionally graded bioactive coating of novel glasses utilizing mouse osteoblast-like cells. Their results exhibited that functionally graded bioactive coating performed at least as well as tissue culture polystyrene and Ti-6Al-4V alloy in the performed biocompatibility tests. Also, functionally graded bioactive coating may influence gene expression favorably promoting osseointegration. Animal implantation tests have exhibited that the coexistence of the hydroxyapatite component in both titanium/hydroxyapatite implants and bone accelerates new bone formation from earlier stage without inflammation [55]. Hedia [9] introduced the optimal design of functionally graded material dental implant in the form of thin layer of cancellous bone around the implant. When compared with conventional titanium implants, stresses concentration in the cortical bone, cancellous bone, and implant were shown to be reduced with the optimal design of collagen/hydroxyapatite functionally graded material implant. In terms of biocompatibility and controllability, collagen/hydroxyapatite functionally graded material was excellent. Hedia claimed that the use of functionally graded material concept in dental implant materials achieve full integration of the implant with living bone, thus increasing the life span of implant. The computational results showed that the use of a functionally graded implant effectively reduces the stress difference at the implant-bone interfaces where the maximum stresses occurred.

particles on the implant surface under stereo-scanning electron microscopy. As a result, they proposed acid etching procedure as a treatment to remove the surface adherent particles [43]. Murr et al. [44] used electron beam melting to produce Ti-6Al-4V open cellular foams with different cell wall structures (solid and hollow). The elastic moduli were decreased with increased porosity as widely known for porous metals of all types. On the other hand, the micro indentation hardness of the hollow cell wall structure was higher than that of the solid cell wall. Long term stability and mechanical properties of two types of porous dental implants were investigated under both dynamic and static circumstances [23]. Implants were

holder particles. Then testing these coated implant samples was performed in fatigue and finite element analysis was used to predict their fatigue behavior. It was determined that the melting process of the electron beam has the potential to process Ti-6Al-4V implants with wide range of pore geometry [45]. The compressive properties of porous implants varied with pore structure and can resemble those of human bone [46]. To improve the surface wear resistance of the titanium structures, Laoui et al. applied laser gas nitriding using a CW Nd:YAG laser, and consequently, the coating layer withstand more cycles without fracture [46].

Nomura et al. [47] recommended the vacuum infiltration technique with sintering to generate porous titanium/hydroxyapatite composites. The elastic modulus was rated utilizing the porosity percentage and then tailored to be in the scale of bone tissue (given by 24–34% porosity).

) HCO3

as space

coated by porous layers made from ammonium hydrogen-carbonate (NH4

**Figure 2.** FGM implant with porous Ti alloy.

150 Insights into Various Aspects of Oral Health

#### **2.3. Biomimetic process and biological interaction**

Different biomimetic strategies were established to manufacture new materials, which are thought to promote the levels of biological and mechanical performance of biomaterials [56, 57].

A number of researchers utilized bovine and human sera in vitro to investigate protein adsorption on biomaterials [58, 59]. The observed reactions on the biomaterials surface which is in contact with these protein-containing solutions have also been studied using Dulbecco's Modified Eagle's minimum essential medium supplemented with 10% Nu-Serum [60], which includes growth factors, hormones and vitamins within their composition. Immersion in cellcontaining solutions is a step further regarding *in vitro* method to mimic the real condition of biomaterials immersed into body fluids.

Most dental implant materials aim to support cell attachment by conferring a suitable an area for cell adhesion [61]. Mangano et al. seeded human dental pulp stem cells on direct laser metal sintered titanium scaffolds and acid etched surfaces. They observed that gene expression and protein secretion were faster on laser sintered scaffolds [62]. Cheng et al. proposed using a template from human trabecular bone to produce porous Ti-6Al-4V materials using particularly laser sintering method as additive manufacturing technology. Different porosities (low, medium and high) ranging from 15–70% with interconnected structure were manufactured to produce structures that simulated the human body trabecular bone. After certain surface treatment with calcium phosphate particles and acid etching, the trabecular bone structure revealed micro and nanoscale porosities which were able to boost osteoblast cell differentiation. Therefore, well-suited devices for dental and orthopedic implants can be produced using the potential of this trabecular structure [18].

Incorporation of a modified sponge replication method and anodization process represents another trial to promote the mechanical and biological properties of porous titanium structures as well. Titanium scaffolds with elongated pores were produced by coating a stretched polymeric sponge template with TiH2 . The anodization of the titanium can produce a nanoporous surface that can stimulate osteoblast cell proliferation and enhance attachment on implant surfaces [23]. Pore geometry has probably a potential strong effect on cell attachment and matrix formation [63]. However, different pore geometries within a single material and manufacturing process are rarely investigated by researchers. Recently, Markhoff et al. [64] evaluated the viability and proliferation of human osteoblast cells in porous Ti-6Al-4V using various scaffold designs and cultivation methods. They applied additive manufacturing technology to produce different pore geometries (cubic, diagonal, pyramidal), using both static and dynamic culture techniques which interestingly showed no significant differences in their results, however, the pyramidal pore design with a 400–620 μm pore size and 75% porosity showed the best results in regard to cell activity and its migration.

Crucial steps in the discovery of novel implant materials and structures include many in vitro studies. However, various inherent limitations are present in relation to the use of different cell culture methods to estimate the long-term service of an implant. Such limitations involve the lack of a three-dimensional environment that properly simulate both chemical and mechanical bone properties, the absence of exerted mechanical loads at the bone-implant interface after implantation procedure, the lack of proteins intricate matrix and different types of bone cells that are present at the bone-implant interface in vivo and the difficulty of preserving the culture for long time periods. Despite the researchers' efforts to improve the different in vitro studies using 3D environments and bioreactors, the in vivo studies represent the source to the current information regarding long-term implant stability.

Designing titanium dental implants with intertwined pores and irregular crevices using a laser sintering process was performed by Mangano et al *in vivo* studies [65] which showed 95% success rate on clinical observation after 1 year postoperatively. On the other hand, histological evaluations made by Shibli et al. who measured human bone tissue response to three types of dental implants: direct laser fabrication, sand-blasted acid-etched and machined commercially pure titanium under unloaded circumstances. Their results revealed that eight weeks post implant insertion, the bone-implant contact produced by the direct laser and sandblasted acid-etched processes was not significantly different but was higher than that of the machined implant, and there were no significant differences between the three types. These findings are explained and attributed to the surface roughness that was produced in both laser and sandblasting techniques, which improved the osseointegration process [66]. Another study using male Sprague-Dawley rats indicated that the biological fixation was affected by the percentage of titanium implants porosity (25, 11, 3%). Examinations after sixteen weeks showed that calcium ions concentration increased proportionally with increased percentage of porosity [67]. Laoui et al. inserted a Ti implant into a dog's lower jaw and their result showed a clear bone growth into the porous structure within the porous surface layer with no observed inflammation at the interface [46]. Tolochko et al. [30] inserted a prototype porous dental implant into the lower jaw of a cadaver which demonstrated a firm integration of the implant into the alveolar ridge of the lower jaw with a maximum gap width of 200–300 μm at the bone-implant interface. Another trial was made to decrease the required healing time for the dental implant and bone by covering a titanium dental implant with a layer of TiO2 nanotubes, which was tested in a rat femur. Various diameter sizes of these nanotubes were used (30, 50, 70, and 100 nm), with the highest removal torque and osseointegration rate seen in the 30 nm implants after two weeks while the 70 nm implants exhibited the highest value after six weeks for both tests [23].

## **3. Dental restorations**

The dental restorations categorize as dental post and crown.

#### **3.1. Dental post**

**2.3. Biomimetic process and biological interaction**

152 Insights into Various Aspects of Oral Health

biomaterials immersed into body fluids.

polymeric sponge template with TiH2

produced using the potential of this trabecular structure [18].

Different biomimetic strategies were established to manufacture new materials, which are thought to promote the levels of biological and mechanical performance of biomaterials [56, 57].

A number of researchers utilized bovine and human sera in vitro to investigate protein adsorption on biomaterials [58, 59]. The observed reactions on the biomaterials surface which is in contact with these protein-containing solutions have also been studied using Dulbecco's Modified Eagle's minimum essential medium supplemented with 10% Nu-Serum [60], which includes growth factors, hormones and vitamins within their composition. Immersion in cellcontaining solutions is a step further regarding *in vitro* method to mimic the real condition of

Most dental implant materials aim to support cell attachment by conferring a suitable an area for cell adhesion [61]. Mangano et al. seeded human dental pulp stem cells on direct laser metal sintered titanium scaffolds and acid etched surfaces. They observed that gene expression and protein secretion were faster on laser sintered scaffolds [62]. Cheng et al. proposed using a template from human trabecular bone to produce porous Ti-6Al-4V materials using particularly laser sintering method as additive manufacturing technology. Different porosities (low, medium and high) ranging from 15–70% with interconnected structure were manufactured to produce structures that simulated the human body trabecular bone. After certain surface treatment with calcium phosphate particles and acid etching, the trabecular bone structure revealed micro and nanoscale porosities which were able to boost osteoblast cell differentiation. Therefore, well-suited devices for dental and orthopedic implants can be

Incorporation of a modified sponge replication method and anodization process represents another trial to promote the mechanical and biological properties of porous titanium structures as well. Titanium scaffolds with elongated pores were produced by coating a stretched

porous surface that can stimulate osteoblast cell proliferation and enhance attachment on implant surfaces [23]. Pore geometry has probably a potential strong effect on cell attachment and matrix formation [63]. However, different pore geometries within a single material and manufacturing process are rarely investigated by researchers. Recently, Markhoff et al. [64] evaluated the viability and proliferation of human osteoblast cells in porous Ti-6Al-4V using various scaffold designs and cultivation methods. They applied additive manufacturing technology to produce different pore geometries (cubic, diagonal, pyramidal), using both static and dynamic culture techniques which interestingly showed no significant differences in their results, however, the pyramidal pore design with a 400–620 μm pore size and 75%

Crucial steps in the discovery of novel implant materials and structures include many in vitro studies. However, various inherent limitations are present in relation to the use of different cell culture methods to estimate the long-term service of an implant. Such limitations involve the lack of a three-dimensional environment that properly simulate both chemical and mechanical bone properties, the absence of exerted mechanical loads at the bone-implant interface after implantation procedure, the lack of proteins intricate matrix and different types

porosity showed the best results in regard to cell activity and its migration.

. The anodization of the titanium can produce a nano-

#### *3.1.1. Overview*

The primary role of teeth in the oral cavity is to serve as a mechanical device for mastication. Restoration of endodontically treated tooth presents a great challenge in everyday practice of dental clinicians. Despite the numerous developments in materials and techniques, patients' demand for improved aesthetics, function and longevity of such restoration drives researchers and practitioners to make further developments. This challenge is even greater in cases where there is massive tooth damage due to caries or trauma. This is explained by less fracture resistance of damaged tooth due to reduction in the number of cross-linked collagen fibers and loss of moisture within the tooth [68]. In such cases, there is often a need to compensate for the lack of tooth substance by additional restoration, which is achieved by placing a post in the root canal and core build up [69].

The main role of a post is to provide retention of the core of an endodontically treated tooth. When an occlusal force is applied coronally, the force is transferred to dentine through the core and post system. In such cases, stress tends to be concentrated at the coronal and apical regions (**Figure 3**). Stress concentrations at the coronal region of the root are likely to be due to the increased flexure of the compromised root structure, while stress concentrations at the apical region (**Figure 4**) are generally due to the root canal taper and post characteristics [70]. The regions of high stress concentration were also observed at the apical termination of the post [71]. In such cases, stress concentration which occurred at the apical end, could initiate a root fracture. This phenomenon is dependent on post geometry, material choice of the post and the adhesion between post and dentine. Considerable controversy exists with regards to the ideal choice of material and design of post and core.

Furthermore, as enamel and dentine reveal slightly mismatch coefficient of thermal expansion, thermal loads may even generate stresses in intact sound tooth [72].This problem is increased if the tooth is restored with various restorative materials. The effect of thermal stimuli may be further amplified during mastication as functional load could create tensile stresses on the buccal side of the teeth and compressive stresses on the lingual side.

Endodontically treated teeth are at higher risk of biomechanical failure than vital teeth [73]. The placement of a dental post creates an unnatural restored structure since it fills the root canal space with a material that has a defined stiffness unlike the pulp. Hence it is difficult to recreate the original stress distribution within the tooth in order to avoid fractures. Therefore, post systems must be carefully selected to reduce the incidence of root fractures and to preserve the root if failure occurs. Generally, there are significant mismatch between material properties of these types of posts, e.g. stiffness, and surrounding dental tissues resulting in the poor stress distribution and root fracture.

A widely discussed issue in the literature up to date is the most appropriate material for posts construction [74]. Flexible material that has a flexible dentine-like quality with a low Young's modulus, such as fiber-reinforced composite posts is the most highly recommended material for reducing the risk of root fracture [75, 76]. However, de-bonding of the post and movement of the core can occur due to stress concentrations focused at the post-dentine interface, which consequently results in microleakage [77]. On the other hand, rigid posts require minimal tooth preparation due to their smaller diameters but this may lead to root fracture [78, 79]. For the previous reasons, dental practitioners are left with two options: either continuing to use posts with a high modulus, which could lead to an irreparable failure or choosing low modulus posts that can result in a reparable failure [74].

#### *3.1.2. Dental post based on functionally graded concept*

Needless to say, dental post should be high modulus of elasticity at coronal part which is approximately similar to the crown/s and bridge abutment/s and it gradually reduced towards

fibers and loss of moisture within the tooth [68]. In such cases, there is often a need to compensate for the lack of tooth substance by additional restoration, which is achieved by placing

The main role of a post is to provide retention of the core of an endodontically treated tooth. When an occlusal force is applied coronally, the force is transferred to dentine through the core and post system. In such cases, stress tends to be concentrated at the coronal and apical regions (**Figure 3**). Stress concentrations at the coronal region of the root are likely to be due to the increased flexure of the compromised root structure, while stress concentrations at the apical region (**Figure 4**) are generally due to the root canal taper and post characteristics [70]. The regions of high stress concentration were also observed at the apical termination of the post [71]. In such cases, stress concentration which occurred at the apical end, could initiate a root fracture. This phenomenon is dependent on post geometry, material choice of the post and the adhesion between post and dentine. Considerable controversy exists with regards to

Furthermore, as enamel and dentine reveal slightly mismatch coefficient of thermal expansion, thermal loads may even generate stresses in intact sound tooth [72].This problem is increased if the tooth is restored with various restorative materials. The effect of thermal stimuli may be further amplified during mastication as functional load could create tensile

Endodontically treated teeth are at higher risk of biomechanical failure than vital teeth [73]. The placement of a dental post creates an unnatural restored structure since it fills the root canal space with a material that has a defined stiffness unlike the pulp. Hence it is difficult to recreate the original stress distribution within the tooth in order to avoid fractures. Therefore, post systems must be carefully selected to reduce the incidence of root fractures and to preserve the root if failure occurs. Generally, there are significant mismatch between material properties of these types of posts, e.g. stiffness, and surrounding dental tissues resulting in

A widely discussed issue in the literature up to date is the most appropriate material for posts construction [74]. Flexible material that has a flexible dentine-like quality with a low Young's modulus, such as fiber-reinforced composite posts is the most highly recommended material for reducing the risk of root fracture [75, 76]. However, de-bonding of the post and movement of the core can occur due to stress concentrations focused at the post-dentine interface, which consequently results in microleakage [77]. On the other hand, rigid posts require minimal tooth preparation due to their smaller diameters but this may lead to root fracture [78, 79]. For the previous reasons, dental practitioners are left with two options: either continuing to use posts with a high modulus, which could lead to an irreparable failure or choosing low

Needless to say, dental post should be high modulus of elasticity at coronal part which is approximately similar to the crown/s and bridge abutment/s and it gradually reduced towards

stresses on the buccal side of the teeth and compressive stresses on the lingual side.

a post in the root canal and core build up [69].

154 Insights into Various Aspects of Oral Health

the ideal choice of material and design of post and core.

the poor stress distribution and root fracture.

modulus posts that can result in a reparable failure [74].

*3.1.2. Dental post based on functionally graded concept*

**Figure 3.** Schematic diagram obtained from FEM analysis showing the typical distribution of (A) shear and (B) tensile, compressive and von Mises stresses in a post and core restored teeth..

the apical part of the tooth (**Figure 5**). Ramakrishna et al. [80] suggested that ideal dental post should be stiff at the coronal region, i.e. in the region of the core, so that the core is not stressed excessively when occlusal force is applied to the crown and its stiffness should be reduced apically. The high stiffness eradicates the stress from the core and the gradual reduction of stiffness along the post would dissipate the stress from the post to the dentine uniformly. The gradual dissipation of stress would also help to eliminate local stress concentration areas and reduce the interfacial shear stress growth.

The problem of materials' properties mismatch can possibly be solved by compositional gradient of multilayer materials achieved in FGMs. Drake et al. The power distribution law was utilized to prove that significant stress and plastic strain reduction can be accomplished through increasing the ceramic materials thickness gradient and tailoring the exponent to create a compositional change gradient close to the parts showing high modulus and little plasticity [81].

**Figure 4.** Stress concentration due to commercial dental post.

Matsuo et al. [82] fabricated functionally graded dental post (FGDP) using laser lithography, one of the photo-curing type computer-aided design/computer-aided manufacturing (CAD/ CAM). The elastic modulus of the post could be changed longitudinally at its apical end by decreasing the filler content of ceramic powders from 64 to 0% in polymer matrix. They used FEM and showed that stress was reduced further by 30% in functionally graded dental post compared with the uniform one. Fujihara et al. [83] fabricated functionally graded dental post and analyzed the stress distribution by FEA. They showed that the peak tensile and shear stresses for a functionally graded dental post were less than that of stainless steel post. They suggested that the modulus of elasticity of post material should be as close as possible to the modulus of elasticity of dentine and crown at the apical part and the coronal part respectively, in order to minimize the chance of interfacial debonding. Lately, Abu Kasim et al. [84] patented three types of multilayered composite materials that were produced using powders of zirconia (ZrO2 ), alumina (Al2 O3 ), hydroxyapatite (HA), and titanium (Ti) to develop newly designed functionally graded dental post. The stress distribution of a newly constructed functionally

**Figure 5.** Uniform stress distribution due to functionally graded dental post [15].

Matsuo et al. [82] fabricated functionally graded dental post (FGDP) using laser lithography, one of the photo-curing type computer-aided design/computer-aided manufacturing (CAD/ CAM). The elastic modulus of the post could be changed longitudinally at its apical end by decreasing the filler content of ceramic powders from 64 to 0% in polymer matrix. They used FEM and showed that stress was reduced further by 30% in functionally graded dental post compared with the uniform one. Fujihara et al. [83] fabricated functionally graded dental post and analyzed the stress distribution by FEA. They showed that the peak tensile and shear stresses for a functionally graded dental post were less than that of stainless steel post. They suggested that the modulus of elasticity of post material should be as close as possible to the modulus of elasticity of dentine and crown at the apical part and the coronal part respectively, in order to minimize the chance of interfacial debonding. Lately, Abu Kasim et al. [84] patented three types of multilayered composite materials that were produced using powders of zirconia

functionally graded dental post. The stress distribution of a newly constructed functionally

), hydroxyapatite (HA), and titanium (Ti) to develop newly designed

(ZrO2

), alumina (Al2

O3

**Figure 4.** Stress concentration due to commercial dental post.

156 Insights into Various Aspects of Oral Health

graded dental post that is comprised of multiple layer design of ZrO2 -Ti-HA was studied in Ref. [85]. The results were evaluated in comparison to those of posts constructed from a single homogeneous material such as titanium and zirconia. In terms of stress distribution, it was concluded that the new multilayered dental post showed better results and advantages in comparison to homogenous posts with a better stress distribution at the post-dentine interface of functionally graded dental post (FGDP). Therefore, it is important to ascertain the thermal behavior of FGDP in order predict their performance in the oral environment. Madfa et al. [86] examined thermal stress in endodontically treated teeth restored with FGDP under cold and hot conditions using finite element analysis. They found that the magnitude of thermal stresses at the post and surrounding structures interface were greater in the zirconia and titanium posts especially at the middle third of the posts. In this study, thermal analysis showed that thermal stress level is closely related to the amount of temperature gradient. The peak stress by thermal stimuli for the zirconia and titanium posts are approximately three times higher than FGSP. This is due to that the FGDP possibly improved the heat flow into dentine because of the gradual change in thermal conductivity. Madfa [15] also investigated the shear stress distribution of a newly designed functionally graded dental post which consisted of multilayer design of ZrO2 -Ti-HA and was compared to posts fabricated from homogeneous material such as titanium and zirconia. They reported that shear stress of FGDP at posts and surrounding structures was lower than titanium and zirconia posts when tooth loaded obliquely. It was observed that the peak shear stress for the FGSP reduced approximately three times of those for titanium and zirconia posts. Moreover, Madfa [15] analyzed the strain distribution pattern in the natural tooth and endodontically treated teeth restored within either FGDP or titanium and zirconia posts. Strain mainly occurred at the coronal third of the root and gradually diminished towards the apical third. This strain may result from the increased displacement of the alveolar bone in the cervical region, relieving the apical third from any undue strain. The same authors found that FGDP and natural tooth models distributed strain uniformly in the tooth structure, the strain found to concentrate at the coronal third of the root, where the cementoenamel junction (CEJ) creates a physiological discontinuity of the mechanical properties of natural tissue.

Furthermore, Madfa et al. [87] compared the fracture resistance and failure modes of endodontically treated bovine teeth restored with FGDP prototype, prefabricated titanium and cast posts. Their results found that there was no significant difference in the mean fracture resistance (N) for endodontically treated teeth restored with FGDP, titanium and cast posts. Surprisingly, the failure mode evaluation results exhibited significant differences between the groups. Most typically, fracture of the sample in all groups occurred initially at the crown margin on the palatal side where loading was applied. The fracture line then progressed towards the buccal surface of the root, above, below or at the simulated bone level. If the fracture terminates above or at the simulated bone level, this fracture mode was considered to be

**Figure 6.** Relationship between failure mode and the finite element analysis [15].

repairable. The FGDP and the endodontically treated teeth without post showed more repairable failures compared to titanium and cast posts. The stress were concentrated at middle and apical thirds for endodontically treated teeth restored with titanium and cast posts compared to FGSPs and endodontically treated teeth without posts [15] as shown in **Figure 6**.

#### **3.2. Dental crown**

#### *3.2.1. Overview*

**Figure 6.** Relationship between failure mode and the finite element analysis [15].

than FGSP. This is due to that the FGDP possibly improved the heat flow into dentine because of the gradual change in thermal conductivity. Madfa [15] also investigated the shear stress distribution of a newly designed functionally graded dental post which consisted of multilayer

as titanium and zirconia. They reported that shear stress of FGDP at posts and surrounding structures was lower than titanium and zirconia posts when tooth loaded obliquely. It was observed that the peak shear stress for the FGSP reduced approximately three times of those for titanium and zirconia posts. Moreover, Madfa [15] analyzed the strain distribution pattern in the natural tooth and endodontically treated teeth restored within either FGDP or titanium and zirconia posts. Strain mainly occurred at the coronal third of the root and gradually diminished towards the apical third. This strain may result from the increased displacement of the alveolar bone in the cervical region, relieving the apical third from any undue strain. The same authors found that FGDP and natural tooth models distributed strain uniformly in the tooth structure, the strain found to concentrate at the coronal third of the root, where the cementoenamel junction (CEJ) creates a physiological discontinuity of the mechanical properties of

Furthermore, Madfa et al. [87] compared the fracture resistance and failure modes of endodontically treated bovine teeth restored with FGDP prototype, prefabricated titanium and cast posts. Their results found that there was no significant difference in the mean fracture resistance (N) for endodontically treated teeth restored with FGDP, titanium and cast posts. Surprisingly, the failure mode evaluation results exhibited significant differences between the groups. Most typically, fracture of the sample in all groups occurred initially at the crown margin on the palatal side where loading was applied. The fracture line then progressed towards the buccal surface of the root, above, below or at the simulated bone level. If the fracture terminates above or at the simulated bone level, this fracture mode was considered to be


design of ZrO2

158 Insights into Various Aspects of Oral Health

natural tissue.

Ceramic dental restorations are designed to restore both function and esthetics of the compromised teeth. However, these materials showed somewhat poor flexural strength, particularly when exposed to fatigue loading in wet environments [88–90]. Consequently, this can result in severe discomfort to patients and can reduce the durability for ceramic prostheses due to their flexural fracture [91–93]. Furthermore, in metal-ceramic restorations, there are mismatches in the mechanical properties between the veneering porcelain and underlying metal core. The Young's modulus of the veneering porcelain is 60–80 GPa, while that of the metal core is in the range of 80–230 GPa [94]. Moreover, there are mismatches in the thermal properties between the veneering porcelain and metal core, where thermal expansion coefficient for metal core is usually higher than that of veneering porcelain (**Figure 7**). These significant mismatches between both materials properties result in stresses concentration at the metal-ceramic interfaces which may cause interface cracking and consequently lead to restoration failure [95, 96].

In spite of the continuous improvement in dental prostheses such as using a strong zirconia or alumina core to support the esthetic porcelain veneer, ceramic prostheses are still susceptible to failure at a rate of about 1–3% each year [97]. Also, ceramics prostheses have a dense, high purity crystalline structure at the cementation surface that cannot be adhesively bonded to tooth dentin support [98]. Although some authors recommended particles abrasion as surface roughening treatment to improve the bond of ceramic-resin-based cements utilizing mechanical interlocking, particles abrasion further causes surface defects or microcracks which could result in deterioration of flexural strength of ceramic prostheses on the long-term service [99–105]. Furthermore, the white opaque appearance of the zirconia cores

**Figure 7.** Schematic of the conventional sharp restoration and the new graded approach.

necessitates placing a thick layer of porcelain veneer with stepwise change in translucency to cover zirconia core thereby achieving better esthetic results [106]. In addition, dental crowns generate over \$2 billion in revenues each year, with 20% of crowns being all ceramic units. Aging populations will drive the demand for all types of dental restorations even higher [107]. Moreover, occlusal contacts induce deformation and cracking of dental crowns leading to structure failure [108].

For the above reasons, it is highly advisable to develop ceramic prostheses that are more resistant to cracking under occlusal contact in recent decade for long term service and success [109, 110]. Composite ceramics have been designed in an effort to improve strength and toughness while enhancing functionality. For many years, simple laminate materials have been developed, where a number of materials with different properties are bonded into a layered structure [111]. Even though these composites combine varying properties, the abrupt interfaces between the two materials often reserve residual stresses [10, 112] and perhaps delaminate under load [113].

#### *3.2.2. Dental crown based on functionally graded concept*

Natural teeth are composed of layered structures, dentin and enamel, that are bonded by a functionally graded dentin-enamel junction (DEJ) layer that is about 10–100 micrometers thick [114, 115]. The DEJ acts as a bridge between the hard brittle enamel (E~70 GPa) and the softer durable dentin layer (E~20 GPa), allowing a smooth Young modulus transition between the two structures [115] as shown in **Figure 8**. He and Swain [35] investigated the nanoindentation mechanical behavior of the inner and outer regions of human enamel. They reported that inner enamel has lower stiffness and hardness but higher creep and stress redistribution abilities than their outer counterpart. They attributed this observation to the gradual compositional change throughout

**Figure 8.** Elastic modulus distribution in natural DEJ [10].

the enamel from the outer region near the occlusal surface to the inner region near DEJ. They suggested that enamel can be regarded as a functionally graded natural bio-composite.

Inspired by the microstructure and mechanical properties of natural teeth, synthetic functionally graded materials were proposed to mimic the DEJ. Recently, functionally graded dental prostheses inspired by the DEJ structures and the linear gradation in Young's modulus of the DEJ have been recommended, as an alternative technique, aiming to enhance the overall performance of metal-ceramic and all-ceramic dental restorative systems. This technique permits the production of a material with very different characteristics within the same material at various interfaces [4].

Francis et al. [115] introduced a procedure to create a DEJ-like interface and enamel coating involved depositing slurries of oxide or glass powder by a draw-down blade method, drying at then higher temperature heating. They used alumina-glass or alumina-polymer composite to mimic the dentin and a calcium phosphate-based coating to mimic the enamel. Bonding between the two materials was accomplished by a eutectic melt in the CaO-Al2 O3 -SiO2 system. The interpenetration in this DEJ-like interface originates from a solidified melt phase penetrating into the dentin. Huang et al. [10] added a FGM layer forming an enamel-like dental ceramic layer. FE simulations of the structure showed that the addition of FGM adhesive layer could significantly reduce the stress concentrations in the sub-surface of ceramic. This increases the resistance of the structure to radial cracking. This suggests the possibility of building synthetic bio-inspired functionally graded dental multilayers that have comparable or better durability than those of natural teeth. Consequently, also showed similar reductions in stress concentrations in simulations using a bio-inspired functionally graded material layer have been shown also by Niu et al. [14]. Their experimental study demonstrated the processing of such functionally graded multi-layers and the increased critical loads in dental multilayer structures with FGM structures.

Rahbar and Soboyejo [13] used computational and experimental effort to develop crack-resistant multilayered crowns that are inspired by the functionally graded DEJ structure. The calculated stress distributions revealed that the highest stress was concentrated at the ceramic outer layer of crown which then was reduced significantly toward the DEJ with the use of bioinspired functionally graded architecture. In addition, promotion of improvements in the critical crack size was reported because of these bioinspired functionally graded layers. Du et al. [116] also found that the bioinspired functionally graded layers were also shown to promote improvements in the critical crack size. Suresh [117] established that controlled gradients in mechanical properties offer unprecedented opportunities for the design of surfaces with resistance to contact deformation and damage that cannot be realized in conventional homogeneous materials.

Graded dental crowns have been shown to display improved features relative to conventional ones, namely higher resistance to contact and sliding [118, 119]; higher adhesion of porcelain to the substructure (metal or ceramic) [120–122]; improved esthetical properties and improved behavior under fatigue conditions [122]. FGM design can address another important point related to diminishing the thermal residual stresses which persist at the metal-ceramic interface after firing of porcelain throughout its cooling cycles. Such stresses

**Figure 8.** Elastic modulus distribution in natural DEJ [10].

to structure failure [108].

160 Insights into Various Aspects of Oral Health

under load [113].

*3.2.2. Dental crown based on functionally graded concept*

necessitates placing a thick layer of porcelain veneer with stepwise change in translucency to cover zirconia core thereby achieving better esthetic results [106]. In addition, dental crowns generate over \$2 billion in revenues each year, with 20% of crowns being all ceramic units. Aging populations will drive the demand for all types of dental restorations even higher [107]. Moreover, occlusal contacts induce deformation and cracking of dental crowns leading

For the above reasons, it is highly advisable to develop ceramic prostheses that are more resistant to cracking under occlusal contact in recent decade for long term service and success [109, 110]. Composite ceramics have been designed in an effort to improve strength and toughness while enhancing functionality. For many years, simple laminate materials have been developed, where a number of materials with different properties are bonded into a layered structure [111]. Even though these composites combine varying properties, the abrupt interfaces between the two materials often reserve residual stresses [10, 112] and perhaps delaminate

Natural teeth are composed of layered structures, dentin and enamel, that are bonded by a functionally graded dentin-enamel junction (DEJ) layer that is about 10–100 micrometers thick [114, 115]. The DEJ acts as a bridge between the hard brittle enamel (E~70 GPa) and the softer durable dentin layer (E~20 GPa), allowing a smooth Young modulus transition between the two structures [115] as shown in **Figure 8**. He and Swain [35] investigated the nanoindentation mechanical behavior of the inner and outer regions of human enamel. They reported that inner enamel has lower stiffness and hardness but higher creep and stress redistribution abilities than their outer counterpart. They attributed this observation to the gradual compositional change throughout are additionally exaggerated due to the presence of a prominent mismatch between the metal and porcelain thermal expansion behavior. Basing on the remnant thermal residual stress level in the crown and along with those originating from occlusal functional loads, a disastrous restoration failure can follow. It was revealed that FGMs reduce dramatically the remnants of thermal stresses raised at the metals and ceramics interface in other fields of applications [123]. Some studies demonstrated that when the contact surface of alumina or silicon nitride was infiltrated with aluminosilicate or oxynitride glass, respectively, they noticed that the graded glass/ceramic surfaces produced in this manner offered much better resistance to contact damage with and without a sliding action than either constituent ceramic or glass [124, 125].

A number of the studies investigated the effects of increasing elasticity as a function of depth from the surface on the resistance to contact damage. They established that mass fracture and failure of veneer may be considerably diminished by specific gradual inclination of the modulus of elasticity through the veneer material thickness. These graded layers show a noticeable increased resistance to fatigue sliding-contact and flexural damage regarding veneered and monolithic core ceramics. This is due to the reduction of the tensile stresses intensity as a result of this gradient and, at the same time, transfers these stresses from the surface layer toward the interior, away from the source of failure-inducing surface defects [126–133] as shown in **Figure 9**.

**Figure 9.** Morphology of the graded zone. (A) Schematic of graded structure, (B) Section view of graded zone of glassinfiltrated yttria stabilized zirconia [126].

## **4. Conclusions and future perspectives**

The development and selection of biocompatible, long-lasting, direct-filling tooth restoratives and indirectly prosthetic materials capable of withstand the aggressive environment of the oral cavity, have been a challenge for practitioners of dentistry since the beginning of dental practice. In order to replace the mechanical function of tooth from a restorative perspective, it is not only important to study its localized tissue properties but also its bulk structural behavior. Therefore, this chapter highlights functionally graded dental implant and restorations inspired from nature. The bioinspired functionally graded structure can be seen as the precursor to recent studies. This is a remarkable example of nature's ability to engineer functionally graded dental prostheses. These dental prostheses mimic the biological and mechanical behavior of natural bone and tooth. These prostheses could potentially lead to superior long-term clinical performance for dental prostheses.

Work in this area is promising and provides a basis for exciting improvements in dental implant and restorations for patients. However, the body of research to date has still not clearly identified the optimal graduation for the most effective biomechanical and biological properties and their behaviors. Therefore, further studies are necessary to evaluate the potential of advanced manufacturing methods to optimize the graduation structure of dental prostheses. The present chapter opens a new avenue for recent researches aimed at further development of new direct filling tooth restoratives and indirect prosthetic materials for improving their clinical durability.

## **Author details**

Elham M. Senan1 and Ahmed A. Madfa1,2\*

\*Address all correspondence to: ahmed\_um\_2011@yahoo.com

1 Restorative and Prosthodontic Department, College of Dentistry, University of Science and Technology, Sana'a, Yemen

2 Department of Conservative Dentistry, Faculty of Dentistry, Thamar University, Dhamar, Yemen

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**Figure 9.** Morphology of the graded zone. (A) Schematic of graded structure, (B) Section view of graded zone of glass-

are additionally exaggerated due to the presence of a prominent mismatch between the metal and porcelain thermal expansion behavior. Basing on the remnant thermal residual stress level in the crown and along with those originating from occlusal functional loads, a disastrous restoration failure can follow. It was revealed that FGMs reduce dramatically the remnants of thermal stresses raised at the metals and ceramics interface in other fields of applications [123]. Some studies demonstrated that when the contact surface of alumina or silicon nitride was infiltrated with aluminosilicate or oxynitride glass, respectively, they noticed that the graded glass/ceramic surfaces produced in this manner offered much better resistance to contact damage with and without a sliding action than either constituent

A number of the studies investigated the effects of increasing elasticity as a function of depth from the surface on the resistance to contact damage. They established that mass fracture and failure of veneer may be considerably diminished by specific gradual inclination of the modulus of elasticity through the veneer material thickness. These graded layers show a noticeable increased resistance to fatigue sliding-contact and flexural damage regarding veneered and monolithic core ceramics. This is due to the reduction of the tensile stresses intensity as a result of this gradient and, at the same time, transfers these stresses from the surface layer toward the interior, away from the source of failure-inducing surface defects [126–133] as

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162 Insights into Various Aspects of Oral Health

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**Provisional chapter**

## **Assessment of All-Ceramic Dental Restorations Behavior by Development of Simulation-Based Experimental Methods Behavior by Development of Simulation-Based Experimental Methods**

**Assessment of All-Ceramic Dental Restorations** 

DOI: 10.5772/intechopen.69162

Liliana Porojan, Florin Topală and Sorin Porojan

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69162

Liliana Porojan, Florin Topală and

#### **Abstract**

Sorin Porojan

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New dental materials are often introduced into the market and especially in the current practice, without a basic understanding of their clinical performance because long‐term controlled clinical trials are required, which are both time consuming and expensive. Ceramic materials are known for their relatively high fracture resistance and improved aesthetics, but brittleness remains a concern. The stressed areas of the materials are key factors for the failure analysis, and numerical simulations may play an important role in the understanding of the behavior of all‐ceramic restorations. Simulation‐based medicine and the development of complex computer models of biological structures are becoming ubiquitous for advancing biomedical engineering and clinical research. The studies have to be focused on the analysis of all‐ceramic restorations failures, investigating several parameters involved in the tooth structure–restoration complex, in order to improve clin‐ ical performances. The experiments have to be conducted and interpreted reported to the brittle behavior of ceramic systems. Varied simulation methods are promising to assess the biomechanical behavior of all‐ceramic systems, and first principal stress criterion is an alternative for ceramic materials investigations. The development of well‐designed experiments could be useful to help to predict the clinical behavior of these new all‐ ceramic restorative techniques and materials.

**Keywords:** all‐ceramic restorations, design parameters, simulation methods, stress, biomechanical behavior

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **1. Introduction**

Ceramic materials and their technologies applied in dental field are in continuous develop‐ ment, but the clinical performance of all‐ceramic restorations has to be improved due to the brittle nature of these materials.

As a consequence of brittle behavior, crack initiations and propagations in the materials can result in compromise of the restorations during functions and will be reflected in a poor clinical performance. In order to minimize clinical failures, restorations should be fabricated with con‐ sideration of their constituent material properties. Ceramic materials are known for their rela‐ tively high fracture resistance and improved aesthetics, but brittleness remains a concern [1]. The stressed areas of the materials are key factors for the failure analysis, and numerical simulations may play an important role in the understanding of the behavior of all‐ceramic restorations.

New materials are often introduced into the market and especially in the current practice, without a basic understanding of their clinical performance because long‐term controlled clinical trials are required, which are both time consuming and expensive. Simulation‐based medicine and the development of complex computer models of biological structures are becoming ubiquitous for advancing biomedical engineering and clinical research [2–4].

In order to improve clinical performances of new all‐ceramic restorations, studies have to be focused on the analysis of their failures, investigating different parameters involved in the tooth‐restoration complex. Some of these parameters, like framework design, depend on the manufacturing technique and can be easily modified, influencing the failure rates and frac‐ ture modes of the restorations. How different designs may influence the fracture load and the mode of fracture of all‐ceramic restorations is a topic of interest.

Finite element analysis (FEA) is a simulation method, widely used to understand and predict biomechanical phenomena in different areas of interest. Because modeling and simulation in dental field are complex, they involve skilled developers. With the advances in modeling and simulation, the clinical simulation becomes more real. FEA is a powerful and flexible compu‐ tational tool to model dental structures and devices simulate the occlusal loading conditions and predict the stress and strain distribution. Establishing guidelines for model development and simulation, particularly for complex structures and different materials, pose a challenge in the field of dental technology.

Further studies are required to assess the durability of such restorations by different experi‐ mental methods before clinical use [5–7].

## **2. Digital design for all‐ceramic crowns**

The use of computer‐aided design/computer‐aided manufacturing (CAD/CAM) technology has grown in the last 30 years with the development of data acquisition technologies and computing technology. This led to improved quality restorations in terms of both resistance and adaptation to preparation and accuracy of occlusal morphology.

The evolution of these technologies has led to the widespread use of materials with superior mechanical and esthetic properties, like zirconia ceramics, which has the advantage that it can be used for almost any type of fixed prosthetic restoration.

**1. Introduction**

brittle nature of these materials.

174 Insights into Various Aspects of Oral Health

in the field of dental technology.

mental methods before clinical use [5–7].

**2. Digital design for all‐ceramic crowns**

and adaptation to preparation and accuracy of occlusal morphology.

Ceramic materials and their technologies applied in dental field are in continuous develop‐ ment, but the clinical performance of all‐ceramic restorations has to be improved due to the

As a consequence of brittle behavior, crack initiations and propagations in the materials can result in compromise of the restorations during functions and will be reflected in a poor clinical performance. In order to minimize clinical failures, restorations should be fabricated with con‐ sideration of their constituent material properties. Ceramic materials are known for their rela‐ tively high fracture resistance and improved aesthetics, but brittleness remains a concern [1]. The stressed areas of the materials are key factors for the failure analysis, and numerical simulations may play an important role in the understanding of the behavior of all‐ceramic restorations.

New materials are often introduced into the market and especially in the current practice, without a basic understanding of their clinical performance because long‐term controlled clinical trials are required, which are both time consuming and expensive. Simulation‐based medicine and the development of complex computer models of biological structures are becoming ubiquitous for advancing biomedical engineering and clinical research [2–4].

In order to improve clinical performances of new all‐ceramic restorations, studies have to be focused on the analysis of their failures, investigating different parameters involved in the tooth‐restoration complex. Some of these parameters, like framework design, depend on the manufacturing technique and can be easily modified, influencing the failure rates and frac‐ ture modes of the restorations. How different designs may influence the fracture load and the

Finite element analysis (FEA) is a simulation method, widely used to understand and predict biomechanical phenomena in different areas of interest. Because modeling and simulation in dental field are complex, they involve skilled developers. With the advances in modeling and simulation, the clinical simulation becomes more real. FEA is a powerful and flexible compu‐ tational tool to model dental structures and devices simulate the occlusal loading conditions and predict the stress and strain distribution. Establishing guidelines for model development and simulation, particularly for complex structures and different materials, pose a challenge

Further studies are required to assess the durability of such restorations by different experi‐

The use of computer‐aided design/computer‐aided manufacturing (CAD/CAM) technology has grown in the last 30 years with the development of data acquisition technologies and computing technology. This led to improved quality restorations in terms of both resistance

mode of fracture of all‐ceramic restorations is a topic of interest.

It has been shown that resistance to fracture of ceramic restorations is not influenced only by the mechanical properties of the used material but also by the design of the preparations and the proper thickness of the restoration [8].

Traditionally, zirconia frameworks were fabricated at 0.5 mm thickness. Introduction of new types of zirconia served to reduce their thickness to 0.3 mm, allowing more conservative prep‐ arations [9]. Recommended finishing lines for these restorations are shoulder with rounded internal angles and slight chamfer, as a minimally invasive preparation designs, acceptable from both mechanical and periodontal reasons [8]. A point of interest is the effect of zirconia copings design on the resistance to load in posterior area, in order to prevent "chipping." In current practice, the framework is obtained by milling even thickness copies, rather than using a scientific‐based design [2]. The main reason for zirconia restoration failures is veneer‐ ing ceramic fracture and chipping. These are caused by an inappropriate framework design, which cannot provide a proper support and thickness for porcelain veneer layer [10–12].

The following example suggests various designs for the framework of zirconia‐ceramic molar crowns [13]. For the experiments, a maxillary right first molar prepared for all‐ceramic crown was used. The tooth was prepared leaving a chamfer finishing line; with anatomical occlusal reduction, a 6° occlusal convergence angle and the palatal surface of the functional cusp were reduced in two planes.

The master die, the antagonist stone cast, and bite‐registration were scanned using the Cercon Eye scanner (Degudent, Hanau, Germany) (**Figure 1**).

Scanned data were computed, and frameworks for all‐ceramic crowns were designed using Cercon Art 3.2 software (Degudent, Hanau, Germany). Three different framework designs were chosen: first, a 0.6‐mm‐thick framework was prepared, second, a cutback design was prepared as same as that for metal‐ceramic crowns, in order to obtain a uniform, adequate thickness for the veneering porcelain, and third, a buccal reduction from the anatomic frame‐ work, for esthetic purposes (**Figures 2**–**4**).

All steps indicated from the manufacturer have been completed for each type of framework design. Cercon Art allows obtaining different designs for lateral single crowns frameworks due to the continuous improvements of the software. Hence, the design of the framework and the future veneer can be controlled.

Cercon Art soft allows also the possibility to scan the bite‐registration and therefore an improved digital design of the framework (**Figures 5** and **6**), concerning the control of the veneer thickness in case of the cutback design and also of the contacts with the antagonists in case of a buccal veneering.

In case of the uniform framework thickness, the veneer design can be also digitized and have an overview of the finished restoration. Beginning from the final morphology of the restora‐ tion, the cutback design provides a uniform thickness of the veneer and a digital control of the

**Figure 1.** Scanned preparation, adjacent teeth, antagonists, and occlusion.

**Figure 2.** Uniform thickness of zirconia framework and digital control of the veneer design.

Assessment of All-Ceramic Dental Restorations Behavior by Development of Simulation-Based... http://dx.doi.org/10.5772/intechopen.69162 177

**Figure 3.** Uniform thickness of veneering ceramic when the framework is obtained with cutback design.

**Figure 1.** Scanned preparation, adjacent teeth, antagonists, and occlusion.

176 Insights into Various Aspects of Oral Health

**Figure 2.** Uniform thickness of zirconia framework and digital control of the veneer design.

**Figure 4.** Full anatomic contour of the zirconia framework, with buccal reduction of the veneer.

**Figure 5.** Zirconia anatomical framework design.

**Figure 6.** Zirconia anatomical framework design after optimization of the contact points with the adjacent teeth and antagonists.

framework thickness. The vestibular veneer became possible also due bite registration, allow‐ ing accurate and individualized modeling of the occlusal morphology. A facility of the soft is to have diagnostic tools, regarding thicknesses and distances, which allow a better control of the design (**Figure 7**).

Literature concerning the clinical performance of all‐ceramic systems is inconclusive regard‐ ing the relative performance of different materials and physical configurations. Proper studies investigated modified designs and showed the benefits of additional porcelain support com‐ pared with a standard design by improving the reliability of all‐ceramic crown systems [14]. Clinical studies on zirconia fixed partial dentures with anatomic framework design showed promising survival rates [15].

Improper framework designs cause an inadequate substrate for the veneering material and also its inadequate thickness. The improvement of the framework design, by creating an appropriate support, allows a proper thickness of the veneer proved to reduce the chip‐ ping rates [16]. The cutback design of the zirconia framework for all‐ceramic crowns is thus a promising way to reduce veneer chipping failures [10].

The design of the substructure, especially the zirconia frameworks, provided different sup‐ port of the veneering. Veneering porcelain with improved strength and fracture toughness may be one aspect to reduce chipping effects, but only with the change in the design of the supporting substructure, the number of chipping should be effectively reduced [17].

**Figure 7.** Diagnostic tools of the soft regarding thicknesses and distances.

**Figure 6.** Zirconia anatomical framework design after optimization of the contact points with the adjacent teeth and

antagonists.

**Figure 5.** Zirconia anatomical framework design.

178 Insights into Various Aspects of Oral Health

Various influencing factors have been reported, such as the support and thickness of the veneer, the morphology of the circular finishing line, the adhesive forces between substruc‐ ture and veneering, the mismatch of coefficients of thermal expansion, or the firing protocol during the veneering process [17–20].

Optimization of the zirconia substructure design has been proven as a considerable factor in reducing chipping failures, and coping modifications are still a topic of current investigations [14, 21].

Experiments using finite element analysis may help to predict the fracture behavior of specific material combinations, but failure types and patterns are notably influenced by clinical vari‐ ables, such as an individual crown design with its occlusal variations, the patients chewing behavior, and functioning in an oral environment [22, 23].

## **3. Simulation methods applied in all‐ceramic bilayered crowns**

For restoring teeth with single crowns, yttria‐stabilized zirconia cores veneered with dental porcelains are highly esthetic alternatives to conventional metal‐ceramic crowns. Zirconia ceramics can be processed only with computer‐aided design/computer‐aided manufacturing technologies, and its properties were proven under in vitro and in vivo conditions over the past years [24–27].

The application of full‐contour zirconia restorations is currently discussed as alternative to commonly veneered restorations [27–29].

By applying veneering materials, esthetically superior results can be achieved, but these materials have mechanical properties inferior to those of the frameworks. Because the veneer‐ ing glass ceramic is the weakest part in this system, clinically observed failures are mainly restricted to the veneer layer [30].

Failure of all‐ceramic dental restorations is predominately caused by cohesive fractures of the glass ceramic veneering material [31].

Failure rates were reported due to this "chipping" called failure mode. Some investigations showed an influence of the firing process of the glass ceramic veneering and the difference in the coefficients of thermal expansion [32–34].

Another important factor influencing the chipping behavior of veneered zirconia restorations is the framework design. An anatomical shape of the framework results in a low and nearly constant veneering thickness. This design is considered to prevent chipping in contrast to a thin framework with a thick and irregularly shaped veneering [35, 17].

Mechanical stresses that occur during mastication can also be strongly affected by the frame‐ work design [36].

Laboratory tests such as finite element analysis may help to predict fracture behavior of spe‐ cific material combinations. It was demonstrated that failure types and patterns are mainly influenced by clinically determined reasons, such as preparation design, internal and mar‐ ginal fit, cement thickness, and also technological reasons, like the individual crowns design with occlusal morphology and therefore different effects on stress distribution. Simulations imitating clinical situations during fatigue and thermal variations may help to study the behavior of the restorations under clinically approximated conditions. Failures resulted after simulation should be combined with clinically observed failures. Fractographic methods pro‐ vide additional information to describe ceramic failures [26].

FEA can be used to evaluate the effect of core design on stress distribution in all‐ceramic crowns [37]. A maxillary first premolar tooth was used as primary 3D model. The design of the prepared tooth was according to the clinical rules listed as follows: occlusal 2 mm reduction, 0.8 mm deep reduction chamfer margin, 6° convergence angle. The nonparametric modeling software (Blender 2.57b) was used to obtain the tooth shape. The collected data were used to construct three dimensional models using Rhinoceros (McNeel North America) Nonuniform Rational B‐Splines (NURBS) modeling program (**Figure 8**).

A digital model of the bilayer crown was designed to occupy the space between the origi‐ nal tooth form and the prepared tooth form. Two different framework designs were con‐ structed: model 1—a coping with a constant framework thickness of 0.6 mm and model 2—an anatomically modified shaped cusp‐supporting framework with a constant veneering thickness (**Figure 9**). The geometric models were imported in the finite element analysis software Ansys and meshed using curvature‐based mesh software. Finite element calcula‐ tions were carried out.

**Figure 8.** 3D model of the premolar.

Various influencing factors have been reported, such as the support and thickness of the veneer, the morphology of the circular finishing line, the adhesive forces between substruc‐ ture and veneering, the mismatch of coefficients of thermal expansion, or the firing protocol

Optimization of the zirconia substructure design has been proven as a considerable factor in reducing chipping failures, and coping modifications are still a topic of current investigations

Experiments using finite element analysis may help to predict the fracture behavior of specific material combinations, but failure types and patterns are notably influenced by clinical vari‐ ables, such as an individual crown design with its occlusal variations, the patients chewing

For restoring teeth with single crowns, yttria‐stabilized zirconia cores veneered with dental porcelains are highly esthetic alternatives to conventional metal‐ceramic crowns. Zirconia ceramics can be processed only with computer‐aided design/computer‐aided manufacturing technologies, and its properties were proven under in vitro and in vivo conditions over the

The application of full‐contour zirconia restorations is currently discussed as alternative to

By applying veneering materials, esthetically superior results can be achieved, but these materials have mechanical properties inferior to those of the frameworks. Because the veneer‐ ing glass ceramic is the weakest part in this system, clinically observed failures are mainly

Failure of all‐ceramic dental restorations is predominately caused by cohesive fractures of the

Failure rates were reported due to this "chipping" called failure mode. Some investigations showed an influence of the firing process of the glass ceramic veneering and the difference in

Another important factor influencing the chipping behavior of veneered zirconia restorations is the framework design. An anatomical shape of the framework results in a low and nearly constant veneering thickness. This design is considered to prevent chipping in contrast to a

Mechanical stresses that occur during mastication can also be strongly affected by the frame‐

Laboratory tests such as finite element analysis may help to predict fracture behavior of spe‐ cific material combinations. It was demonstrated that failure types and patterns are mainly

thin framework with a thick and irregularly shaped veneering [35, 17].

**3. Simulation methods applied in all‐ceramic bilayered crowns**

during the veneering process [17–20].

180 Insights into Various Aspects of Oral Health

behavior, and functioning in an oral environment [22, 23].

[14, 21].

past years [24–27].

work design [36].

commonly veneered restorations [27–29].

restricted to the veneer layer [30].

glass ceramic veneering material [31].

the coefficients of thermal expansion [32–34].

**Figure 9.** Tooth preparations and overlying restorations.

For the structural simulations, the Young's modulus and Poisson's ratio were entered into the computer soft: Young's modulus (GPa): 18 for dentin, 64 for veneering ceramics, and 205 for zirconia; Poisson's ratio 0.27 for dentin, 0.21 for veneering ceramics, and 0.31 for zirconia. Five loading areas were defined on the occlusal surface, each with a diameter of 0.5 mm. A total force of 600 N was applied as pressure load normal to the surface in each point. The bottom of the teeth models was constrained in all directions, for all simulations.

A static structural analysis was performed, in order to generate stress distribution for all designs taken into the study. Maximal equivalent stresses were recorded in the tooth struc‐ tures and in the restorations for all preparation types (**Figures 10** and **11**).

For all cases, the stress values were higher in the veneers. Regarding the distribution, in the veneers, stresses were located around the contact areas with the antagonists. In the frame‐ works, maximal equivalent stress values were higher for the cutback design, but for interpre‐ tation, they have to be correlated with the thicknesses of the frameworks. The outer geometry of all‐ceramic restorations is strongly defined by anatomical and physiological circumstances, and therefore, the thickness is variable.

However, a modification of the framework design does not affect the outer shape and thick‐ ness of the restoration which means that a thicker framework automatically results in a thin‐ ner veneering and vice versa.

Therefore, the models were created with constant outer shape, where the framework thick‐ ness was chosen to be either constant or anatomically optimized [38].

Different studies indicated core and veneer designs that minimize tensile loading of porce‐ lain. They investigated the effect of differential coping designs on the stress distribution of all‐ ceramic crowns under varying loads. The hypothesis of whether a customized coping design could reduce the stress on veneers is partially accepted [39].

Mechanical testing of anatomic core design modification revealed a significant increase in the reliability of the coping design and resulted in reduced chip sizes in the veneer porcelain [40].

**Figure 10.** Von Mises equivalent stress distribution in model 1.

**Figure 11.** Von Mises equivalent stress distribution in model 2.

Based on the results, chipping seems to be a phenomenon, which is not limited to zirconia restorations, but to the design of the substructure. The chipping failures of all‐ceramic zir‐ conia crowns can be significantly reduced in number and surface by fabricating optimized zirconia substructures. These have to provide occlusal support and similar layer thickness for the veneering porcelain [17].

For the structural simulations, the Young's modulus and Poisson's ratio were entered into the computer soft: Young's modulus (GPa): 18 for dentin, 64 for veneering ceramics, and 205 for zirconia; Poisson's ratio 0.27 for dentin, 0.21 for veneering ceramics, and 0.31 for zirconia. Five loading areas were defined on the occlusal surface, each with a diameter of 0.5 mm. A total force of 600 N was applied as pressure load normal to the surface in each point. The bottom of

A static structural analysis was performed, in order to generate stress distribution for all designs taken into the study. Maximal equivalent stresses were recorded in the tooth struc‐

For all cases, the stress values were higher in the veneers. Regarding the distribution, in the veneers, stresses were located around the contact areas with the antagonists. In the frame‐ works, maximal equivalent stress values were higher for the cutback design, but for interpre‐ tation, they have to be correlated with the thicknesses of the frameworks. The outer geometry of all‐ceramic restorations is strongly defined by anatomical and physiological circumstances,

However, a modification of the framework design does not affect the outer shape and thick‐ ness of the restoration which means that a thicker framework automatically results in a thin‐

Therefore, the models were created with constant outer shape, where the framework thick‐

Different studies indicated core and veneer designs that minimize tensile loading of porce‐ lain. They investigated the effect of differential coping designs on the stress distribution of all‐ ceramic crowns under varying loads. The hypothesis of whether a customized coping design

Mechanical testing of anatomic core design modification revealed a significant increase in the reliability of the coping design and resulted in reduced chip sizes in the veneer porcelain [40].

the teeth models was constrained in all directions, for all simulations.

tures and in the restorations for all preparation types (**Figures 10** and **11**).

ness was chosen to be either constant or anatomically optimized [38].

could reduce the stress on veneers is partially accepted [39].

**Figure 10.** Von Mises equivalent stress distribution in model 1.

**Figure 11.** Von Mises equivalent stress distribution in model 2.

and therefore, the thickness is variable.

ner veneering and vice versa.

182 Insights into Various Aspects of Oral Health

The results showed that not only the substructure design but also the application technique and type of veneering material influenced the chipping behavior of zirconia molar crowns [41].

Some authors investigated the influence of framework design and framework material on the stress distribution in a single tooth restoration, also under different mastication scenarios using the finite element method. The results presented here show that a cusp‐supporting framework design can significantly decrease maximum tensile stresses in the veneering mate‐ rial of single crowns. Therefore, it can be expected that such a design could decrease the risk of chipping in all‐ceramic restorations in vivo [38].

Use of controlled veneer application techniques, such as the press technique, as well as mini‐ mizing stress during the firing conditions may constitute one possibility to reduce cracking and chipping failures. However, only in combination with an anatomically reduced substruc‐ ture design and a constant layer of the veneering porcelain, the number and dimension of failures (chippings, cracks) are likely to be effectively reduced [41].

## **4. Simulation methods applied in monolithic ceramic crowns**

Zirconia is considered a proper material for posterior teeth restoration, because of the excel‐ lent esthetic quality, biocompatibility, and mechanical properties. Thus, zirconia is getting attention to replace existing ceramic systems. Processing of zirconia is closely linked to the development of CAD/CAM systems [42–44]. CAD/CAM technology has been increasingly used to fabricate dental crowns in recent years. It resulted in new restorative materials that would otherwise have been infeasible to use in the dental market, like Yttria‐Stabilized Tetragonal Zirconia Polycrystals (Y‐TZP). Recently, the introduction of new computerized milling technologies and new zirconia made it possible to manufacture full‐contour zirconia crowns with higher strength [45–47]. Several manufacturers have improved the aesthetics of the zirconia materials mainly by reducing the opacity of the material and by addition of color‐ ing pigments. It might also be assumed that, by omitting the veneering, a more solid frame‐ work can be made and a conservative preparation similar to full‐cast metal‐alloy restorations can be performed [48].

Monolithic crowns offer advantages compared to bilayered crowns like reduced production time and related improved cost effectiveness. Because crown preparation involves traumati‐ zation to the vital tooth, eliminating the veneering material in monolithic crowns allows to achieve minimally invasive preparations and subsequent restorations [49–51].

Finite element analysis is a specific method for stress analyses. Since it was developed, it has been a popular option to analyze stresses in engineering field. In dentistry, FEA has been introduced to study stress distributions in the teeth structures and all kind of restorations [52–54]. Even computer‐controlled techniques are used in producing dental crowns in order to improve the accuracy during the manufacturing process, not enough studies have been conducted on stresses in esthetic monolithic crowns regarding the load values. Therefore, it is advisable to compare the stresses in anatomic contour zirconia crown to that of glass ceramic crown regarding the load values, from biomechanical point of view [55]. For the experimental analyses, first upper molars were chosen in order to simulate the biomechanical behavior of the teeth restored with complete esthetic monolithic crowns made of yttria‐stabilized tetrago‐ nal zirconia polycrystals and glass ceramic. The prepared dies were designed with a chamfer finishing line and an 6° occlusal convergence angle of the axial walls.

Geometric models of monolithic crowns were designed to occupy the space between the origi‐ nal obtained tooth form and the modeled prepared tooth form. At first, a nonparametric mod‐ eling software (Blender 2.57b) was used to obtain the 3D tooth shapes. The collected data were used to construct 3D models using Rhinoceros modeling program (McNeel North America) (Nonuniform Rational B‐Splines). These were imported in the FEA software ANSYS; meshed and finite element calculations were carried out. In order to simulate stress distribution and calculate stress values, the Young's modulus and Poisson's ratio were introduced: Young's modulus (GPa) 18 for dentin, 64 for glass ceramic, and 205 for zirconia and Poisson's ratio 0.27 for dentin, 0.21 for glass ceramic, and 0.31 for zirconia. Five loading areas were defined on the occlusal surface, in order to simulate physiological mastication behavior. Each defined loading area had a diameter of 0.5 mm. A total force between 200 N, respective 800 N was allo‐ cated to these areas as pressure load normal to the surface in each point. For all simulations, the bottom of the abutment teeth models was constrained in all directions. A static structural analysis was performed using the computer‐aided engineering software, to calculate stress values and highlight stress distribution. First principal stresses were recorded in the tooth structures and in the restorations for all load values and all geometries. Stresses were calcu‐ lated in the crowns for both materials and in the teeth structures, under different load values (**Figures 12** and **13**).

Between the materials, the highest stresses were recorded in glass ceramic, followed by zirco‐ nia. In the dentin, the lowest stresses were recorded for the teeth restored with glass ceramic, followed by zirconia. Compared to the tensile strength of the materials, 745 MPa for zirconia,

**Figure 12.** First principal stress distribution in the zirconia crowns and subjacent dentin (for 200 N load).

Assessment of All-Ceramic Dental Restorations Behavior by Development of Simulation-Based... http://dx.doi.org/10.5772/intechopen.69162 185

**Figure 13.** First principal stress distribution in the glass ceramic crowns and subjacent dentin (for 200 N load).

and 48.8 MPa for glass ceramic, the maximal principal stresses in the crowns exceed them for 600 N and 800 N load for zirconia crowns, respective for 400 N, 600 N, and 800 N load for glass ceramic crowns. The maximal principal stresses in the crowns do not exceed the strength of the materials in case of 200 N load for both studied materials. For glass ceramic at a load of 400 N, maximal principal stresses exceed the tensile strength value of the material.

Regarding stress distribution in the crowns, high stresses are concentrated around the con‐ tact areas with the antagonists, and they are larger for the zirconia crowns. In the dentin for molars, high stresses were distributed around the shoulder, and under the preparation line for all type of restorations.

The material is important to withstand increased loads which occur during functions. Reported loads during normal function in vivo vary considerably. It is not stated how these loads should be replicated in vitro. Some authors use lower loads, 100–200 N, others use loads in the range of 500–800 N [56].

According to the literature data [57] that the tensile strengths of dentin ranged from 44.4 to 97.8 MPa, no harmful effects occur in hard teeth structures, because in all cases, first principal stresses in dentin are much lower.

When compared with some reported clinical failure rates, it can be stated that the theoretical predictions showed relevant quantitative values for some materials. Even though there are some differences in assumptions between clinical and theoretical models, they can be justified and an even more accurate prediction tool for single crowns may be developed by incorporat‐ ing better mechanical models in the future [58].

## **5. Conclusions and perspectives**

introduced to study stress distributions in the teeth structures and all kind of restorations [52–54]. Even computer‐controlled techniques are used in producing dental crowns in order to improve the accuracy during the manufacturing process, not enough studies have been conducted on stresses in esthetic monolithic crowns regarding the load values. Therefore, it is advisable to compare the stresses in anatomic contour zirconia crown to that of glass ceramic crown regarding the load values, from biomechanical point of view [55]. For the experimental analyses, first upper molars were chosen in order to simulate the biomechanical behavior of the teeth restored with complete esthetic monolithic crowns made of yttria‐stabilized tetrago‐ nal zirconia polycrystals and glass ceramic. The prepared dies were designed with a chamfer

Geometric models of monolithic crowns were designed to occupy the space between the origi‐ nal obtained tooth form and the modeled prepared tooth form. At first, a nonparametric mod‐ eling software (Blender 2.57b) was used to obtain the 3D tooth shapes. The collected data were used to construct 3D models using Rhinoceros modeling program (McNeel North America) (Nonuniform Rational B‐Splines). These were imported in the FEA software ANSYS; meshed and finite element calculations were carried out. In order to simulate stress distribution and calculate stress values, the Young's modulus and Poisson's ratio were introduced: Young's modulus (GPa) 18 for dentin, 64 for glass ceramic, and 205 for zirconia and Poisson's ratio 0.27 for dentin, 0.21 for glass ceramic, and 0.31 for zirconia. Five loading areas were defined on the occlusal surface, in order to simulate physiological mastication behavior. Each defined loading area had a diameter of 0.5 mm. A total force between 200 N, respective 800 N was allo‐ cated to these areas as pressure load normal to the surface in each point. For all simulations, the bottom of the abutment teeth models was constrained in all directions. A static structural analysis was performed using the computer‐aided engineering software, to calculate stress values and highlight stress distribution. First principal stresses were recorded in the tooth structures and in the restorations for all load values and all geometries. Stresses were calcu‐ lated in the crowns for both materials and in the teeth structures, under different load values

Between the materials, the highest stresses were recorded in glass ceramic, followed by zirco‐ nia. In the dentin, the lowest stresses were recorded for the teeth restored with glass ceramic, followed by zirconia. Compared to the tensile strength of the materials, 745 MPa for zirconia,

**Figure 12.** First principal stress distribution in the zirconia crowns and subjacent dentin (for 200 N load).

finishing line and an 6° occlusal convergence angle of the axial walls.

(**Figures 12** and **13**).

184 Insights into Various Aspects of Oral Health

In current practice, frameworks of all‐ceramic restorations are obtained by milling even thick‐ ness copies, rather than using a scientific‐based design. The recent possibility of the softs of the CAD/CAM systems to scan the bite‐registration allows achieving an improved digital design for the framework, through the control of the final veneer thickness in case of cutback design and of the contacts with the antagonists in case of buccal veneering.

The effect of zirconia copings design on the resistance to load in posterior crowns in order to prevent "chipping" is very important. Finite element analyses provide a biomechanical explanation of the clinical behavior of different all‐ceramic bilayer crowns. A cusp‐supporting design reduces maximum stresses in the framework, but these have to be correlated also with the thickness of the framework.

The biomechanical behavior of ceramic monolithic crowns for the posterior areas can be assessed using finite element analyses. The material is important to withstand increased loads which occur during functions.

Stress values and distribution results can provide design guidelines for new and varied esthetic crowns, in order to withstand functional loads in the posterior areas. The develop‐ ment of well‐designed experiments could be useful to help to predict clinical survival of these new all‐ceramic restorative techniques and materials. The experiments have to be conducted and interpreted reported to the brittle behavior of ceramic systems. Varied simulation meth‐ ods are promising to assess the biomechanical behavior of all‐ceramic systems and first prin‐ cipal stress criterion is an alternative for ceramic materials investigations.

## **Acknowledgements**

This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation CNCS‐UEFISCDI, project number PN‐II‐RU‐TE‐2014‐4‐0476.

## **Author details**

Liliana Porojan<sup>1</sup> \*, Florin Topală<sup>2</sup> and Sorin Porojan<sup>3</sup>

\*Address all correspondence to: lilianasandu@gmail.com

1 Department of Dental Prostheses Technology, School of Dentistry, "V. Babes" University of Medicine and Pharmacy, Timisoara, Romania

2 Department of Dental Prosthodontics, School of Dentistry, "V. Babes" University of Medi‐ cine and Pharmacy, Timisoara, Romania

3 Department of Oral Rehabilitation, School of Dentistry, "V. Babes" University of Medicine and Pharmacy, Timisoara, Romania

## **References**

[1] Zhang Y, Mai Z, Barani A, Bush M, Lawn B. Fracture‐resistant monolithic dental crowns. Dental Materials Journal. 2016;**32**(3):442‐449. DOI: 10.1016/j.dental.2015.12.010

[2] Kokubo Y, Tsumita M, Kano T, Fukushima S. The influence of zirconia coping designs on the fracture load of all‐ceramic molar crowns. Dental Materials Journal. 2011;**30**(3):281‐ 285. DOI: 10.4012/dmj.2010‐130

The effect of zirconia copings design on the resistance to load in posterior crowns in order to prevent "chipping" is very important. Finite element analyses provide a biomechanical explanation of the clinical behavior of different all‐ceramic bilayer crowns. A cusp‐supporting design reduces maximum stresses in the framework, but these have to be correlated also with

The biomechanical behavior of ceramic monolithic crowns for the posterior areas can be assessed using finite element analyses. The material is important to withstand increased loads

Stress values and distribution results can provide design guidelines for new and varied esthetic crowns, in order to withstand functional loads in the posterior areas. The develop‐ ment of well‐designed experiments could be useful to help to predict clinical survival of these new all‐ceramic restorative techniques and materials. The experiments have to be conducted and interpreted reported to the brittle behavior of ceramic systems. Varied simulation meth‐ ods are promising to assess the biomechanical behavior of all‐ceramic systems and first prin‐

This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation CNCS‐UEFISCDI, project number PN‐II‐RU‐TE‐2014‐4‐0476.

1 Department of Dental Prostheses Technology, School of Dentistry, "V. Babes" University of

2 Department of Dental Prosthodontics, School of Dentistry, "V. Babes" University of Medi‐

3 Department of Oral Rehabilitation, School of Dentistry, "V. Babes" University of Medicine

[1] Zhang Y, Mai Z, Barani A, Bush M, Lawn B. Fracture‐resistant monolithic dental crowns. Dental Materials Journal. 2016;**32**(3):442‐449. DOI: 10.1016/j.dental.2015.12.010

and Sorin Porojan<sup>3</sup>

cipal stress criterion is an alternative for ceramic materials investigations.

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186 Insights into Various Aspects of Oral Health

which occur during functions.

**Acknowledgements**

**Author details**

Liliana Porojan<sup>1</sup>

**References**

\*, Florin Topală<sup>2</sup>

Medicine and Pharmacy, Timisoara, Romania

cine and Pharmacy, Timisoara, Romania

and Pharmacy, Timisoara, Romania

\*Address all correspondence to: lilianasandu@gmail.com


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**Research Guidelines on Oral Health Promotion**

**Provisional chapter**

## **Oral Health Promotion: Evidences and Strategies**

**Oral Health Promotion: Evidences and Strategies**

DOI: 10.5772/intechopen.69330

Vikram R. Niranjan, Vikas Kathuria, Venkatraman J and Arpana Salve Venkatraman J and Arpana Salve Additional information is available at the end of the chapter

Vikram R. Niranjan, Vikas Kathuria,

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69330

#### **Abstract**

Oral health promotion is for upliftment of oral health of community rather than an indi‐ vidual and has long‐term impact. Since Ottawa Charter for health promotion is imple‐ mented, significant advancements have happened in oral health promotion. Under comprehensive health programs, India has been running oral health promotion pro‐ grams, and these evidences are shared here. Such examples are apt learning and exe‐ cution to any part of world having similarities. The chapter put forward the strategic view points to consider further oral health promotion aspects and based on the needs. The authors have gathered various examples from national programs implemented in India. The authors discuss how these programs are linked to the Oral health promo‐ tion concept. For example, National tobacco control program which currently running across many states in India, how the banning on tobacco products near school premises helped to reduce the incidence is discussed. The worldwide literature and evidences of oral health promotion strategies are explained. The evidences and strategies mentioned can be significant for another region of world. Unless published, many programs remain hidden and are loss of valuable evidences to oral health science.

**Keywords:** oral health, oral health promotion, fluorosis, school health, dental health

## **1. Introduction**

The twentieth century was noteworthy in dentistry for many epidemiologic advances that occurred in the study of oral diseases and conditions. These combined efforts of optimum personal, social, biological, behavioral and environmental factors contributed to better oral health. Hence, oral health promotion is a planned effort to build public policies, create sup‐ portive environments, strengthen community action, develop personal skills or reorient

health services pertaining to influence above factors. Following are enlisted examples of effec‐ tive oral health promotion:


Ottawa Charter principles form a sound base for oral health promotion. This suggest that individuals alone are not at risk but the entire population, which needs to be involved in directing action towards the causes of ill health. Importantly, three principles, that is, partner‐ ship, participation and protection, are taken into consideration while planning a public health program or intervention. Empowerment than compelling is the key for successful Oral health promotion while achieving good oral health [2].

The purpose of this article is threefold. First, it reviews the relevance of need of oral health promotion particularly through the public health surveillance of oral disease burden. Second, it puts forward the evidences from the various examples of oral health promotion programs integrated into general health promotion carried across the India. Finally, the authors briefly discuss the strategies for expanding frame of oral health promotion.

## **2. Oral health promotion through Ottawa Charter**

Health promotion programs achieve success through actions that influence the social, physi‐ cal, economic and political determinants of health. Health promotion irrefutably acknowl‐ edges the broader health determinants and focuses on risk reduction via sensitive policies and actions. Ideally, promotion of health in a day‐to‐day life setting having people live, work, learn and play is credible for efficacious and cost‐effective way of improving oral health and indeed the quality of life. Imperatively, actions that address the determinants of health should not be progressed in isolation. Research evidences suggests that isolated activities can have limited impact, particularly over the long term. For this reason, we suggest using the logic model based on Ottawa Charter to develop a comprehensive oral health promotion program, involving a range of interventions.

The Ottawa Charter was developed by the World Health Organization<sup>1</sup> (WHO) as a frame‐ work for constructing health promotion programs that address the wider determinants of health. The charter suggests that programs be built around the following five action areas:


<sup>1</sup> WHO = World Health Organization.


health services pertaining to influence above factors. Following are enlisted examples of effec‐

Ottawa Charter principles form a sound base for oral health promotion. This suggest that individuals alone are not at risk but the entire population, which needs to be involved in directing action towards the causes of ill health. Importantly, three principles, that is, partner‐ ship, participation and protection, are taken into consideration while planning a public health program or intervention. Empowerment than compelling is the key for successful Oral health

The purpose of this article is threefold. First, it reviews the relevance of need of oral health promotion particularly through the public health surveillance of oral disease burden. Second, it puts forward the evidences from the various examples of oral health promotion programs integrated into general health promotion carried across the India. Finally, the authors briefly

Health promotion programs achieve success through actions that influence the social, physi‐ cal, economic and political determinants of health. Health promotion irrefutably acknowl‐ edges the broader health determinants and focuses on risk reduction via sensitive policies and actions. Ideally, promotion of health in a day‐to‐day life setting having people live, work, learn and play is credible for efficacious and cost‐effective way of improving oral health and indeed the quality of life. Imperatively, actions that address the determinants of health should not be progressed in isolation. Research evidences suggests that isolated activities can have limited impact, particularly over the long term. For this reason, we suggest using the logic model based on Ottawa Charter to develop a comprehensive oral health promotion program,

work for constructing health promotion programs that address the wider determinants of health. The charter suggests that programs be built around the following five action areas:

(WHO) as a frame‐

tive oral health promotion:

196 Insights into Various Aspects of Oral Health

• Promotion of healthy eating

• Training of relevant oral hygiene methods

• Promotion of topical fluoride application [1].

promotion while achieving good oral health [2].

involving a range of interventions.

• Building healthy public policy

WHO = World Health Organization.

1

• Creating supportive environments

discuss the strategies for expanding frame of oral health promotion.

The Ottawa Charter was developed by the World Health Organization<sup>1</sup>

**2. Oral health promotion through Ottawa Charter**

• Access to preventive oral health services at the earliest

• Reorientating health services [2].

## **3. Need for oral health promotion**

The remarkable improvements in oral health over the past half century reflect the strong sci‐ ence base for prevention of oral diseases that has been developed and applied in the commu‐ nity, in clinical practice and in the home. Yet, despite the remarkable achievements in recent decades, millions of people worldwide have been excluded from the benefits of socioeco‐ nomic development and the scientific advances that have improved health care and quality of life. Social and cultural determinants comprising poverty, lack of education, unsupportive traditions, cultures and beliefs increase the relative risk of oral disease and conditions. For instance, lack of safe water and sanitary facilities are the environmental risk factors for both oral and general health. While, access to high sugar containing foods and unhealthy dietary habits may lead to higher risk of dental caries in certain communities. Improvement in avail‐ ability, accessibility and feasibility of oral health services can definitely cure and control oral diseases. However, strong evidences suggest that limiting the risks to disease is best possible when health services are primary care and prevention oriented. Clinically, oral health status is measured in terms of causal factors, that is, tobacco, sugar, micro‐flora, which have negative impact on quality of life. Emphasizing the risk behavior modifications, such as curbing use of tobacco and alcohol; restraining sugar intake in terms of quantity, intake frequency and nature; proper oral hygiene practices, is equally important incongruent to social and cultural determinants [3].

The Global Burden of Disease (GBD) 2010 Study produced comparable estimates of the bur‐ den of 291 diseases and injuries in 1990, 2005 and 2010. Pertaining to oral health, dental caries, aggressive periodontitis and tooth loss are considered as global burden, which compared from 1990 to 2010. Criteria used were disability adjusted life‐years (DALYs) and years lived with disability (YLDs) metrics to quantify burden. These oral diseases/conditions encroached 3.9 bil‐ lion. Among all, prevalence of dental caries in permanent teeth was among the highest preva‐ lent condition evaluated for the entire GBD 2010 study (global prevalence of 35% for all ages combined). Among the top 100 ranking as causes of DALYs, oral diseases also secured a ranking after some serious diseases. Oral diseases altogether affected 15 million DALYs globally with the breakdown as 1.9% of all YLDs; 0.6% of all DALYs. Statistical calculations imply that could be average health loss of 224 years *per* 100,000 populations. While there was reduction observed for other diseases from 1990 to 2010, DALYs due to oral conditions increased by 20.8%. This was due to population overgrowth and aging. DALYs due to aggressive periodontitis and den‐ tal caries increased, however due to extensive tooth loss has decreased. While DALYs differed by age groups and regions, those not by genders. The report revealed the challenging scenario of diversified oral health needs across the globe, with alarming needs in developing countries. Further, the burden of oral diseases has unevenly risen in the past 20 years.

As the noted prevalence of oral diseases is very high and has association with disability, it accounted for a substantial number of DALYs. Dental caries without any treatment was the most prevalent condition among all 291 conditions. Moreover, the disability weight in con‐ nection with extensive tooth loss (0.073) was marginally neared to those reported for moder‐ ate heart failure (0.068) and moderate consequences of stroke (0.074). Oral diseases received ranking of 31st, 34th and 35th of health outcomes causing YLDs in the category of non‐fatal outcomes. Compared to other non‐communicable diseases/conditions, such as maternal con‐ ditions, hypertensive heart disease, schizophrenia, hemoglobinopathies and hemolytic ane‐ mias, oral diseases/conditions were ranked higher. While oral conditions scored high index for more YLDs than 25 of 28 categories of cancer, shows its significance in terms of affecting individuals equal to lethal diseases. The other organ cancers, such as stomach, liver and tra‐ chea, and bronchus and lung cancers ranked higher than oral diseases [4].

The global burden of oral conditions is shifting from extensive tooth loss toward aggressive periodontitis and untreated dental caries. Tooth loss is a final common pathway when pre‐ ventive or conservative treatments to alleviate pain fail or are unavailable. The social, eco‐ nomic, political and cultural determinants of health are significant, and it may be argued that better health can be achieved by reducing poverty. Poverty, poor education and inequality not only result in poor oral health but also affect the way in which people think about their oral health. In spite of excellent oral health care, oral diseases are prevalent. This suggests that improving healthcare services merely will not address the issue, oral health promotion is mandatory. Hence, health policymakers should be made aware of these evidences and directs themselves to restructure the policy framework. Health promotion policy acknowl‐ edges complimentary measures such as legislation, fiscal measures, taxation and organiza‐ tional change altogether. These are best example of a coordinated effort towards creating supportive environments and strengthening community action. Ottawa Charter implemen‐ tation for health promotion through establishing concrete and effective community actions in setting priorities, making decisions, planning strategies leads to achieve better health. Communities facilitate themselves with self‐help, social support, participation and owner‐ ship for development and empowerment. They are the best possible existing human and material resources of community and for community.

Oral health promotion through sensitive health policies and actions which already exist in some parts of world can address the global burden of oral diseases, essentially to improve oral health and quality of life.

## **4. Evidences: country examples from India**

Identifying a significant health issue on the basis of prevalence, incidence, severity, cost, or impact on quality of life is preliminary step to design prevention programs. A combina‐ tion of community, professional and individual strategies is the cost‐effective and creative methods for oral disease prevention. Incorporating public, practitioners and policymakers into strategic development of oral disease prevention and health promotion intervention is necessary. They should be liable to create a healthy setting, limit risk factors, inform target groups, generate knowledge and thus improve behaviors. This section includes a discussion of knowledge and practices of the public and healthcare providers regarding the oral health promotion. The purpose of this discussion is not to outline specific health promotion strate‐ gies to enhance knowledge and practices but to indicate the opportunities and needs for both broad‐based and targeted health promotion programs and activities.

#### **4.1. Oral health promotion in health promoting schools (HPS)**

As the noted prevalence of oral diseases is very high and has association with disability, it accounted for a substantial number of DALYs. Dental caries without any treatment was the most prevalent condition among all 291 conditions. Moreover, the disability weight in con‐ nection with extensive tooth loss (0.073) was marginally neared to those reported for moder‐ ate heart failure (0.068) and moderate consequences of stroke (0.074). Oral diseases received ranking of 31st, 34th and 35th of health outcomes causing YLDs in the category of non‐fatal outcomes. Compared to other non‐communicable diseases/conditions, such as maternal con‐ ditions, hypertensive heart disease, schizophrenia, hemoglobinopathies and hemolytic ane‐ mias, oral diseases/conditions were ranked higher. While oral conditions scored high index for more YLDs than 25 of 28 categories of cancer, shows its significance in terms of affecting individuals equal to lethal diseases. The other organ cancers, such as stomach, liver and tra‐

The global burden of oral conditions is shifting from extensive tooth loss toward aggressive periodontitis and untreated dental caries. Tooth loss is a final common pathway when pre‐ ventive or conservative treatments to alleviate pain fail or are unavailable. The social, eco‐ nomic, political and cultural determinants of health are significant, and it may be argued that better health can be achieved by reducing poverty. Poverty, poor education and inequality not only result in poor oral health but also affect the way in which people think about their oral health. In spite of excellent oral health care, oral diseases are prevalent. This suggests that improving healthcare services merely will not address the issue, oral health promotion is mandatory. Hence, health policymakers should be made aware of these evidences and directs themselves to restructure the policy framework. Health promotion policy acknowl‐ edges complimentary measures such as legislation, fiscal measures, taxation and organiza‐ tional change altogether. These are best example of a coordinated effort towards creating supportive environments and strengthening community action. Ottawa Charter implemen‐ tation for health promotion through establishing concrete and effective community actions in setting priorities, making decisions, planning strategies leads to achieve better health. Communities facilitate themselves with self‐help, social support, participation and owner‐ ship for development and empowerment. They are the best possible existing human and

Oral health promotion through sensitive health policies and actions which already exist in some parts of world can address the global burden of oral diseases, essentially to improve

Identifying a significant health issue on the basis of prevalence, incidence, severity, cost, or impact on quality of life is preliminary step to design prevention programs. A combina‐ tion of community, professional and individual strategies is the cost‐effective and creative methods for oral disease prevention. Incorporating public, practitioners and policymakers into strategic development of oral disease prevention and health promotion intervention is necessary. They should be liable to create a healthy setting, limit risk factors, inform target

chea, and bronchus and lung cancers ranked higher than oral diseases [4].

material resources of community and for community.

**4. Evidences: country examples from India**

oral health and quality of life.

198 Insights into Various Aspects of Oral Health

Oral health education has been considered as one of the fundamentals in oral health pro‐ motion [5, 6]. With education, a child receives training and encouragement especially to stimulate development of skills, aptitude formation and creation of values, which lead to act positively in relation to his oral health and other people's oral health on a daily basis. High caries risk, change in dentition, ability to change bad habits and facilities to learn make oral health promotion for children a priority. The importance of oral health education programs in schools is significantly reported predominantly in the form of positive learning and behavior in children [5–11].

One‐fifth of the world's population is adolescent, defined by WHO as a person between 10 and 19 years of age. The oral health promotion programs should primarily focus on this age group who become easy victims of excessive consumption of sweets, sugary beverages, tobacco and alcohol. Commonly, their main association is with home, school and community organizations. These three along with oral health professionals can form an effective alliance to control risks to oral diseases and form oral health promotion programs for young people [12]. Prevalence of dental caries and gingivitis is high in human populations throughout the world, and over 80% of schoolchildren are affected in some parts of the world. Dental erosion due to excessive car‐ bonated beverages consumption is on rise, which was earlier noticed only among the late adult‐ hood. Enamel defects due to malnourishments, dental trauma due to negligence and safety barriers are some of the increasing evidences in children. Moreover, youth became the easy targets of tobacco‐containing products. Eventually and unknowingly, early start of tobacco consumption manifolds risks of oral precancerous lesions and cancer in life ahead [8, 10, 13].

Strong arguments for oral health promotion through schools include the following:


The need to set up oral health promotion programs in schools is evident, and it can easily be integrated into general health promotion, school curricula and activities. One of the proposed examples has been shown in **Figure 1** [13].

Using the structures and systems already in place as a competent setting for the installation of vital facilities such as safe water and sanitation can instigate oral health promotion in schools. The HPS strategies are effective, leading to potential long‐term cost savings. For instance, Each key components of an HPS, that is, *healthy school environment, school health education, school heath services, nutrition and food services, physical exercise and leisure activities, mental health and well‐being, health promotion for staff and community relationships and collaboration*, incorporate equal opportunities oral health promotion as well as general health promotion. While oral health issue is specifically addressed, it can be admixed in general health promotion strategy. It is well illustrated in following examples of school health policies as shown in **Table 1** [13].

**Figure 1.** Integration of oral health in health‐promoting schools: an example from Denmark.


• Schools can provide a platform for the provision of oral health care, that is, preventive and

• Common risk factor approach‐based oral health promotion policies in schools can lead to

The need to set up oral health promotion programs in schools is evident, and it can easily be integrated into general health promotion, school curricula and activities. One of the proposed

Using the structures and systems already in place as a competent setting for the installation of vital facilities such as safe water and sanitation can instigate oral health promotion in schools. The HPS strategies are effective, leading to potential long‐term cost savings. For instance, Each key components of an HPS, that is, *healthy school environment, school health education, school heath services, nutrition and food services, physical exercise and leisure activities, mental health and well‐being, health promotion for staff and community relationships and collaboration*, incorporate equal opportunities oral health promotion as well as general health promotion. While oral health issue is specifically addressed, it can be admixed in general health promotion strategy. It is well illustrated in following examples of school health policies as shown in **Table 1** [13].

improvement in oral health and reduce oral health inequality [10, 16].

**Figure 1.** Integration of oral health in health‐promoting schools: an example from Denmark.

curative services [14–18].

200 Insights into Various Aspects of Oral Health

examples has been shown in **Figure 1** [13].


**Table 1.** Examples of oral health‐related school health policies to be promoted in HPS.

There is an association of socio‐economic, geographic factors and type of schools with school based health promoting activities. On an average, students attending private schools belong to more advantaged backgrounds than their counterparts in public schools. Privately managed schools achieve greater efficiency or academic value‐added than publicly‐managed schools [18]. According to one study, ten out of eleven participated countries (including India) had the large socio‐economic gap between private and public school pupils except Chile [19]. Moreover, students going to city/town schools generally belonged to more privileged back‐ grounds than their counterparts in village schools. All the school headmasters in this study reported that primary school student's absenteeism rate decreased when the students received support in the form of school uniforms, textbooks, meals and various financial assistance schemes. For example, urban schools tend to have greater resources than those in rural. Also, students in private schools had higher levels of positive behavior than those in public schools, and these results were statistically significant for most countries [19]. Public and private school differ from each other in many ways as better amenities in school, extra‐curricular activities, outdoor and indoor sports, etc. The private school allots more fees from students for such activities/facilities. Consequently, children from upper and high middle socioeconomic status prefer private schools, while children with low socioeconomic strata attend public schools [20]. Students gain more attention when the student to teacher ratio is higher. Bruneforth et al. [19] also reported inferior pupil‐teacher ratios in village schools than in city/town schools in India. The children who do not have adult supervision after school are more vulnerable to indulge them into health hazarding habits like smoking, drugs and substance abuse and behavioral problems. The schools providing self care activities after school were found more effective in reducing the prevalence of smoking among ninth‐grade students in Los Angeles and San Diego Counties [21]. Smoking and chewing tobacco are systematically associated with socioeconomic markers [20].

#### **4.2. Healthy food at school: Mid Day Meal Scheme of India**

The whole school approach with availability of healthy food in school canteen, tuck shops, instructing parents for healthy food and school staff involved in planning for food and cur‐ riculum has amplified student's knowledge. However, it has not led to change in behavior [22, 23].

Providing healthy food in schools can meet the nutritional requirement of students and also guide the parents to deal with healthy diet chart for their children. In UK, campaigns like the ones conducted by famous chef, Jamie Oliver, are one example of actions in this area.

In India, Mid Day Meal Scheme in school started in 1925 from a single city, Madras (now Chennai) and now spread to all States. From April 1st, 2008, the program covers all children studying in Government, Local Body and Government‐aided primary and upper primary schools across the country. The Mid Day Meal Scheme is the world's largest school feed‐ ing program reaching out to 0.84 billion primary students and 0.33 billion upper primary Students, in total about 1.2 billion children in over 9.50 ten thousands schools across the coun‐ try during 2009–2010 [24].

Unhealthy eating habits and sedentary lifestyles are closely bound not only to various socio‐ economic indicators such as the parent's education levels, financial resources and profes‐ sional situations, but also to living in economically deprived areas. This suggests significant contributions of gender, age and religion belief to the eating habit. Therefore, Schools should introduce healthy food policy and activity after consulting with school authority, nutrition expert and parents so as to maintain good eating habits among students [25].

#### **4.3. National tobacco control program of India**

There is an association of socio‐economic, geographic factors and type of schools with school based health promoting activities. On an average, students attending private schools belong to more advantaged backgrounds than their counterparts in public schools. Privately managed schools achieve greater efficiency or academic value‐added than publicly‐managed schools [18]. According to one study, ten out of eleven participated countries (including India) had the large socio‐economic gap between private and public school pupils except Chile [19]. Moreover, students going to city/town schools generally belonged to more privileged back‐ grounds than their counterparts in village schools. All the school headmasters in this study reported that primary school student's absenteeism rate decreased when the students received support in the form of school uniforms, textbooks, meals and various financial assistance schemes. For example, urban schools tend to have greater resources than those in rural. Also, students in private schools had higher levels of positive behavior than those in public schools, and these results were statistically significant for most countries [19]. Public and private school differ from each other in many ways as better amenities in school, extra‐curricular activities, outdoor and indoor sports, etc. The private school allots more fees from students for such activities/facilities. Consequently, children from upper and high middle socioeconomic status prefer private schools, while children with low socioeconomic strata attend public schools [20]. Students gain more attention when the student to teacher ratio is higher. Bruneforth et al. [19] also reported inferior pupil‐teacher ratios in village schools than in city/town schools in India. The children who do not have adult supervision after school are more vulnerable to indulge them into health hazarding habits like smoking, drugs and substance abuse and behavioral problems. The schools providing self care activities after school were found more effective in reducing the prevalence of smoking among ninth‐grade students in Los Angeles and San Diego Counties [21]. Smoking and chewing tobacco are systematically associated

• Working closely with central or local oral health service providers

• Monitoring of oral health‐related complaints and absenteeism.

• Role of teachers in oral health surveillance, screening and basic treatment,

• Commitment to provide safe facilities for training in sport and leisure

• Exercise and physical education are a compulsory part of the school

**Areas Cause Health promoting school measures** Areas Cause Health promoting school measures

*Oral health service*

for example, ART

• Training for school staff

*Physical exercise*

activities

curriculum

**Table 1.** Examples of oral health‐related school health policies to be promoted in HPS.

• Dealing with dental emergencies

Lack of knowledge, habits, social environment

202 Insights into Various Aspects of Oral Health

General and oral health

with socioeconomic markers [20].

Tobacco consumption either in smoke form or smokeless form has deleterious effect general and oral health. Tobacco abuse is the leading preventable cause of death and disease so far. Long list of diseases caused by tobacco abuse includes different cancers – lung cancer, oral can‐ cer, cardiovascular disease, stroke and chronic lung disease. Pertaining to oral health, it causes aggressive periodontitis, tooth loss, wound healing complications and mainly pre‐cancerous or cancerous lesion leading to disfigurement of face. Risk of oral cancer is 10‐fold in smokers than no‐smokers and 11‐fold risk in smokeless tobacco users than non‐users. One can expect a normal life expectancy with early acknowledgement of tobacco health hazards and culminat‐ ing tobacco use especially below 35 years. Prevention is the prime key factors, and at initial stage, most of the adverse effects of tobacco are reversible. This fact can be used to motivate tobacco using people to curb the use of tobacco [26].

India is the second largest consumer and producer of tobacco. India accounts for 10% of the world tobacco area and 9% of the production. 30% of cancer deaths, majority of cardiovas‐ cular and lung disorders; 40% of tuberculosis and other related diseases are attributed to tobacco consumption. Over 80% of oral cancers are caused due to tobacco use. As per the WHO Global Report on "Tobacco Attributable Mortality" 2012, 7% of all deaths (for ages 30 and over) in India are attributable to tobacco. Ministry of Health and Family Welfare (MoHFW), Government of India inaugurated *The National Tobacco Control Program (NTCP)* in 2007–2008, as included in 11th five year plan. The program includes objectives as:

	- Effective primordial and primary level prevention strategies are planned under the *National Tobacco Control Program (NTCP)*.

The prime areas under the NTCP as targets are:


Indian government implemented Cigarette and Other Tobacco Products Act (COTPA; addressing tobacco use in public places, tobacco advertising and sale and packaging regulations) since 2003 with comprehensive action in 2005 following the Framework Convention of Tobacco Control (FCTC). Following laws through the lobbying of anti‐tobacco advocates were successfully estab‐ lished by Indian judiciary.


The achievements of this national program are examples of apt implementation. Increase in taxation had led to a reduction in self‐reported tobacco sales and consumption at the short‐term end‐point. The GATS data (2009) indicate that 54.7 and 62.9% are aware of health warnings on cigarette and smokeless tobacco packaging, respectively. Trials of school‐based education interventions demonstrated a positive impact on knowledge, advocacy skills and tobacco use. Teaching about the risks of tobacco use for health professional trainees appeared more widespread, but may have reduced slightly post‐FCTC. Community‐based education interventions and education interventions for adult tobacco users appeared ben‐ eficial. Moreover, the secondary outcomes of tobacco control programs observed as cleaner streets and air quality, preservation of forests, increased performance at school/work, reduction in fire hazards, healthy mother and infants and indeed a better quality of life. Tobacco‐use outcomes could be improved by school/community‐based and adult education interventions and cessation assistance that are facilitated by training for health professionals and schoolteachers [28].

#### **4.4. National fluorosis prevention program**

(MoHFW), Government of India inaugurated *The National Tobacco Control Program (NTCP)* in

• Nationwide awareness regarding tobacco use harms and following tobacco control laws.

○ Effective primordial and primary level prevention strategies are planned under the

• Training of trainers, that is, health and social workers, NGOs, school teachers and enforce‐

Indian government implemented Cigarette and Other Tobacco Products Act (COTPA; addressing tobacco use in public places, tobacco advertising and sale and packaging regulations) since 2003 with comprehensive action in 2005 following the Framework Convention of Tobacco Control (FCTC). Following laws through the lobbying of anti‐tobacco advocates were successfully estab‐

• *Section 5: Prohibition of direct and indirect advertisement, promotion and sponsorship of cigarette* 

• *Section 6a: Prohibition of sale of cigarette and other tobacco products to a person below the age of* 

• *Section 6b: Prohibition of sale of tobacco products within a radius of 100 yards of educational* 

• *Section 7: Mandatory depiction of statutory warnings (including pictorial warnings) on tobacco* 

The achievements of this national program are examples of apt implementation. Increase in taxation had led to a reduction in self‐reported tobacco sales and consumption at the short‐term end‐point. The GATS data (2009) indicate that 54.7 and 62.9% are aware of health warnings on cigarette and smokeless tobacco packaging, respectively. Trials of school‐based education interventions demonstrated a positive impact on knowledge, advocacy skills and tobacco use. Teaching about the risks of tobacco use for health professional trainees

• *Section 7(5): Display of tar and nicotine contents on tobacco packs* [27].

2007–2008, as included in 11th five year plan. The program includes objectives as:

• Necessary actions for strong implementation of the Tobacco Control Laws.

*National Tobacco Control Program (NTCP)*.

• Information, Education and Communication (IEC) activities.

• Medicinal treatment facility for cessation at district level.

The prime areas under the NTCP as targets are:

ment officers.

204 Insights into Various Aspects of Oral Health

• School Programs.

lished by Indian judiciary.

*and other tobacco products.*

*18 years.*

*packs.)*

*institutions.*

• Monitoring tobacco control laws.

• Co‐ordination at village level activities.

• *Section 4: Prohibition of smoking in public places.*

Fluoride is an essential mineral for human health. It widely exists in natural water and in foods such as tea, fish and beer. The twentieth century documented association among reduced level of dental caries with communal fluoridated water consumption. Soon, fluo‐ ride has become an effective preventive measure for dental caries. Easy incorporation into toothpaste has improved oral health in some parts of world, particularly in developing countries [26].

However, the other part of world suffers from excessive fluoride in natural environment. Fluorosis, a public health problem, is caused by excess intake of fluoride through drinking water/food products/industrial emission over a long period. Moderate‐level chronic exposure (above 1.5 mg/liter of water–the WHO guideline value for fluoride in water) is more common. Acute high‐level exposure to fluoride is rare and usually due to accidental contamination of drinking‐water or due to fires or explosions. It results in major health disorders like dental fluorosis, skeletal fluorosis and non‐skeletal fluorosis. The late stages of skeletal and dental fluorosis are permanent and irreversible in nature and are detrimental to the health of an individual and the community, which in turn has adverse effects on growth, development & economy of the country. There is no treatment for severe cases of skeletal fluorosis, only efforts can be made towards reducing the disability which has occurred. However, the dis‐ ease is easily preventable if diagnosed early and steps are taken to prevent intake of excess fluorosis through provision of safe drinking water, promote nutrition and avoid foods with high fluoride content.

Fluorosis is worldwide in distribution and endemic at least in 25 countries. It has been reported from fluoride belts: one that stretches from Syria through Jordan, Egypt, Libya, Algeria, Sudan and Kenya, and another that stretches from Turkey through Iraq, Iran, Afghanistan, India, northern Thailand and China. There are similar belts in the Americas and Japan. In India, fluorosis is mainly due to excessive fluoride in water except in parts of Gujarat and Uttar Pradesh where industrial fluorosis is also seen. The desirable limit of fluoride as per Bureau of Indian Standards (BIS) is 1 ppm (parts per million or 1 mg per liter). High levels of Fluoride were reported in 230 districts of 20 States of India (after bifurcation of Andhra Pradesh in 2014). The population at risk as per population in habitations with high fluoride is 11.7 million as on 1.4.2014. Rajasthan, Gujarat and Andhra Pradesh are worst affected states. Punjab, Haryana, Madhya Pradesh and Maharashtra are moderately affected states, while Tamil Nadu, West Bengal, Uttar Pradesh, Bihar and Assam are mildly affected states.

Understanding the clinical manifestations of fluorosis

	- Gastrointestinal symptoms: Abdominal pain, excessive saliva, nausea and vomiting are seen after acute high‐level exposure to fluoride.
	- Neurological manifestation: Nervousness and depression, tingling sensation in fingers and toes, excessive thirst and tendency to urinate.
	- Muscular manifestations: Muscle weakness and stiffness, pain in the muscle and loss of muscle power, inability to carry out normal routine activities.
	- Allergic manifestation: Skin rashes, perivascular inflammation—pinkish red or bluish red spot, round or oval shape on the skin that fade and clear up within 7–10 days.
	- Effects on fetus: Fluoride can also damage a fetus, if the mother consumes water/food with high concentrations of fluoride during pregnancy/breast feeding. Abortions, still births and children with birth defects are common in endemic areas.
	- Low hemoglobin levels: Fluoride accumulates on the erythrocyte (red blood cells) mem‐ brane, which in turn looses calcium content. The membrane which is deficient in calcium content is pliable and is thrown into folds. The shape of erythrocytes is changed. Such RBCs are called echinocytes and found in circulation. The echinocytes undergo phago‐ cytosis (eaten‐up by macrophages) and are eliminated from circulation. This would lead to low hemoglobin levels in patients chronically ill due to fluoride toxicity.
	- Kidney manifestations: Low volume, dark yellow to red color of urine is seen.
	- Calcification of ligaments and blood vessel: Forms unique feature of the disease helps in differential diagnosis.

With an aim to prevent and control fluorosis cases, Government of India initiated the National Program for Prevention and Control of Fluorosis (NPPCF) as a new health initiative in 2008–09. During the 11th Plan, 100 districts from 17 States were identified for program imple‐ mentation. During the 12th 5‐Year Plan period, it is proposed to add another 95 districts for prevention and control of fluorosis. In the 12th Plan, the program has been brought under the Non‐Communicable Disease Flexi‐pool of National Health Mission (NHM).

#### *4.4.1. Goal and objectives*

Understanding the clinical manifestations of fluorosis

206 Insights into Various Aspects of Oral Health

• *Dental fluorosis*: It is categorized into mild, moderate and severe dental fluorosis depending on the extent of staining and pitting on the teeth. In severe dental fluorosis, unaesthetic & brittle enamel is found. Vitamins A and D deficiency or a low protein‐energy diet are also linked to enamel defects. Ingestion of fluoride after 6 years of age will not cause dental fluorosis. The teeth could be chalky white and may have white, yellow, brown or black spots or streaks on the enamel surface. Discoloration is away from the gums and bilaterally symmetrical.

• *Skeletal fluorosis*: The early symptoms of skeletal fluorosis include stiffness and pain in the joints. In severe cases, the bone structure may change and ligaments may calcify, with resulting impairment of muscles and pain. Constriction of vertebral canal and intervertebral foramen

○ Gastrointestinal symptoms: Abdominal pain, excessive saliva, nausea and vomiting are

○ Neurological manifestation: Nervousness and depression, tingling sensation in fingers

○ Muscular manifestations: Muscle weakness and stiffness, pain in the muscle and loss of

○ Allergic manifestation: Skin rashes, perivascular inflammation—pinkish red or bluish red spot, round or oval shape on the skin that fade and clear up within 7–10 days.

○ Effects on fetus: Fluoride can also damage a fetus, if the mother consumes water/food with high concentrations of fluoride during pregnancy/breast feeding. Abortions, still

○ Low hemoglobin levels: Fluoride accumulates on the erythrocyte (red blood cells) mem‐ brane, which in turn looses calcium content. The membrane which is deficient in calcium content is pliable and is thrown into folds. The shape of erythrocytes is changed. Such RBCs are called echinocytes and found in circulation. The echinocytes undergo phago‐ cytosis (eaten‐up by macrophages) and are eliminated from circulation. This would lead

○ Calcification of ligaments and blood vessel: Forms unique feature of the disease helps in

With an aim to prevent and control fluorosis cases, Government of India initiated the National Program for Prevention and Control of Fluorosis (NPPCF) as a new health initiative in 2008–09. During the 11th Plan, 100 districts from 17 States were identified for program imple‐ mentation. During the 12th 5‐Year Plan period, it is proposed to add another 95 districts for prevention and control of fluorosis. In the 12th Plan, the program has been brought under the

exerts pressure on nerves, blood vessels leading to paralysis and pain.

muscle power, inability to carry out normal routine activities.

births and children with birth defects are common in endemic areas.

to low hemoglobin levels in patients chronically ill due to fluoride toxicity. ○ Kidney manifestations: Low volume, dark yellow to red color of urine is seen.

Non‐Communicable Disease Flexi‐pool of National Health Mission (NHM).

• *Nonskeletal fluorosis/Effects of fluorosis on soft tissues/systems***:**

seen after acute high‐level exposure to fluoride.

and toes, excessive thirst and tendency to urinate.

differential diagnosis.


#### *4.4.2. Strategy*


#### *4.4.3. Expected outcome*

The expected outcome of the National Program for Prevention & Control of Fluorosis in the districts will be:


Likewise, fluoride is double edge sword, that is, its deficiency and excess both affect the oral health. Hence, science based on effectiveness, safety and benefits should be implemented at different needs at different part of the world.

## **5. Strategies for oral health promotion**

#### **5.1. Generation of strategies based on evidences**

WHO aim at building healthy populations involving all communities by combating every possible illness. The organization has recommended strategic framework which focuses and guide on oral health promotion activities/programs.


Program goals are broad statements on the overall purpose of a program. For instance, "to eliminate racial disparities in oral cancer survival rates," "to improve the oral health of nurs‐ ing home residents" or " to improve the oral health of country's children under 5 years. Program objectives are more specific statements of desired endpoints of program.

Objectives of oral health programs should meet SMART criteria:

*Specific*—they should describe an observable action, behavior or achievement.

*Measurable*—they are systems, methods or procedures to track to record the action upon which objective is focused.

*Achievable*—the objective is realistic, based on current environment and resources.

*Relevant*—the objective is important to the program and is under the control of program.

*Time based*—there are clearly defined deadlines for achieving the objective [3].

Designing an oral health promotion program: step by step can be studied as shown in **Figure 2** [1]:

Best practices in oral health promotion and prevention can take various forms, be it education, health promotion, integrating oral health promotion into general health promotion programs, policy changes which promote better oral health, the provision of care services, or programs specifically designed at addressing oral health inequalities. It is interesting to learn how oral

**Figure 2.** A step‐by‐step design of an oral health promotion program (based on Ministry of Health, New Zealand, 2006).

health promotion and practices are implemented in through various interventions applying the Ottawa Charter guidelines.

#### *5.1.1. Building healthy public policy*

Likewise, fluoride is double edge sword, that is, its deficiency and excess both affect the oral health. Hence, science based on effectiveness, safety and benefits should be implemented at

WHO aim at building healthy populations involving all communities by combating every possible illness. The organization has recommended strategic framework which focuses and

• *Reduction in oral disease/condition burden and disability, especially in poor and marginalized* 

• *Promoting healthy lifestyles and reducing risk factors to oral health that arise from environmental,* 

• *Developing oral health systems that equitably improve oral health outcomes, respond to people's* 

• *Framing policies in oral health, based on integration of oral health into national and community health programs, and promoting oral health as an effective dimension for development policy of* 

Program goals are broad statements on the overall purpose of a program. For instance, "to eliminate racial disparities in oral cancer survival rates," "to improve the oral health of nurs‐ ing home residents" or " to improve the oral health of country's children under 5 years.

*Measurable*—they are systems, methods or procedures to track to record the action upon

Designing an oral health promotion program: step by step can be studied as shown in

Best practices in oral health promotion and prevention can take various forms, be it education, health promotion, integrating oral health promotion into general health promotion programs, policy changes which promote better oral health, the provision of care services, or programs specifically designed at addressing oral health inequalities. It is interesting to learn how oral

Program objectives are more specific statements of desired endpoints of program.

*Achievable*—the objective is realistic, based on current environment and resources.

*Time based*—there are clearly defined deadlines for achieving the objective [3].

*Relevant*—the objective is important to the program and is under the control of program.

*Specific*—they should describe an observable action, behavior or achievement.

Objectives of oral health programs should meet SMART criteria:

different needs at different part of the world.

208 Insights into Various Aspects of Oral Health

**5. Strategies for oral health promotion**

**5.1. Generation of strategies based on evidences**

guide on oral health promotion activities/programs.

*economic, social and behavioral causes.*

*legitimate demands and are financially fair.*

*populations.*

*society* [7].

which objective is focused.

**Figure 2** [1]:

Establishing healthy policies is integral in improving oral health. Based on the needs, evi‐ dences and situation analysis, National Government, health ministry, local governments, organizations, communities, schools, primary healthcare settings and local stakeholders forms or reforms the healthy policy. Health promotion advocates hold key responsibility to convey appropriate health needs of the population.

Examples of interventions that build healthy public policy


#### *5.1.2. Creating supportive environments*

Making the healthy choice easy choice is the aim of health promotion. This can be achieved by creating supportive social, physical, biological and cultural environments. These determi‐ nants of health directly and indirectly affect the oral health with or without general health consequences. Hence, the needs of local population should be considered in order to design and implementation of health promotion actions. Health promotion practitioners play a lead role in creating supportive environments along with public health units, government agen‐ cies, health organizations, NGOs, professional Dental Association, industry organizations and print and digital media.

Interventions that harness creating healthy supportive environments for oral health


#### *5.1.3. Strengthening community action*

Communities are a powerful force for achieving actions for any health promotion program where the key success factors are: *partnership, participation and engagement*. Encompassing all the communities for united efforts to understand their own oral health needs and ascer‐ tain to improve the oral health outcomes of their community. These health promotion programs may differ with age, society, culture and environment. Among the five actions themes of Ottawa Charter, community action is unique as concentrate on how particular health actions to be carried out. It eventually may turn out to be effective examples to be followed. Important factor for communities to have equitable access to resources to support the control they must have over their own health and development. Hence, strengthening community action is about providing and facilitating access to sufficient and appropriate resources.

Examples of interventions that strengthen community action for oral health


#### *5.1.4. Developing personal skills*

*5.1.2. Creating supportive environments*

210 Insights into Various Aspects of Oral Health

and print and digital media.

oral health promotion.

*5.1.3. Strengthening community action*

avail.

resources.

water supply.

activities.

chocolates.

Making the healthy choice easy choice is the aim of health promotion. This can be achieved by creating supportive social, physical, biological and cultural environments. These determi‐ nants of health directly and indirectly affect the oral health with or without general health consequences. Hence, the needs of local population should be considered in order to design and implementation of health promotion actions. Health promotion practitioners play a lead role in creating supportive environments along with public health units, government agen‐ cies, health organizations, NGOs, professional Dental Association, industry organizations

Interventions that harness creating healthy supportive environments for oral health

• Media coverage of healthy food choices which enhance oral health.

• Promoting safe water supply at all the public events.

• Oral health awareness and promotion through social marketing campaigns.

Examples of interventions that strengthen community action for oral health

• Provision of fluoridated toothpastes at subsidized cost that low income group can also

• Reforming supermarket's marketing policies for instance replacing sugary products like

• Encouragement for usage of smoke‐free environment advertisements and sponsorship for

Communities are a powerful force for achieving actions for any health promotion program where the key success factors are: *partnership, participation and engagement*. Encompassing all the communities for united efforts to understand their own oral health needs and ascer‐ tain to improve the oral health outcomes of their community. These health promotion programs may differ with age, society, culture and environment. Among the five actions themes of Ottawa Charter, community action is unique as concentrate on how particular health actions to be carried out. It eventually may turn out to be effective examples to be followed. Important factor for communities to have equitable access to resources to support the control they must have over their own health and development. Hence, strengthening community action is about providing and facilitating access to sufficient and appropriate

• Engaging the community to support water fluoridation/de‐fluoridation and encourage safe

• Engaging communities to participate in school oral health programs through leadership

Personal skills can help individual to take control of his own health. Empowering people with appropriate knowledge and skills to improve and maintain their oral health is essen‐ tial. Oral health literacy is the way that provides information, education and skills for oral health improvement. Such things help increases the resources available to people to exercise more control over their own health and environments. Health promotion programs needs to be updated that go collateral with changing environment and culture. Hence, continuum for health education, particularly for oral health, throughout life is necessary. Here, comes the role of oral health professionals who forms the bridge between health promotion advo‐ cates and health promotion program communities. At community level or at individual level, they create support system to ingress healthy personal skills to improve and maintain oral health. Oral health professionals fulfill this role of trainer by providing information, resources and training.

Interventions that help developing personal skills


#### *5.1.5. Reorientating health services*

Health services carry the burden of all diseases by providing three tier cares. With advancing burden of new diseases and population explosion challenges, reorientation of health services is inevitable. The global burden of oral diseases had led to integrate oral health into general health. Indeed, it is giving a new direction for oral health services and recognizing that oral health is not merely a biomedical process. Health services should be reformed such that they not only treat the diseases but also find suitable solutions for health promotion. Strengthening of health services to analyze needs, to understand the socioeconomic determinants of health of the population is required. Such reformation which reduces oral health inequalities and improves oral health‐related quality of life is all about reorienting health services. While prime focus is on primary healthcare services, prevention, allocation, access and cost‐benefi‐ cial health services are obligatory to achieve this.

Interventions for reorientating health services


Oral health should be an important agenda on the country's health policy. The above inter‐ national policy examples envision the challenges and opportunities for better identification, prioritization and integration of oral health services. Collaborative planning and organiza‐ tion may accelerate the process to arrest the global burden of oral diseases and pioneer the oral health promotion. Relevant international developments suggest that some other health promotion frameworks exists that are parallel to Ottawa Charter framework. Although their principles are same, the implementation may differ according to the needs and socio‐cultural environment of the region. One can develop or reform a different model based on above evi‐ dences for oral health promotion programs at their region.

#### **5.2. Country examples for oral health promotion program**

Investment in simple preventive programs is cost‐effective for prevention of oral diseases and promotion of good oral health which is already proven in Europe. Twenty eight examples of good practice are presented from across Europe as shown in **Figure 3**. These cover all areas of oral health promotion across the life course and include programs aimed at pregnant moth‐ ers, children and adolescents, the elderly and disadvantaged groups. To solve the problem of poor oral health in other parts of world a thorough evaluation of existing successful poli‐ cies and programs, identification of evidence‐based interventions can be learned from these programs.

These programs outline a number of successful initiatives that can help prevent oral diseases, which reduce the social burden and in turn reduce existing inequalities. This is done with various measures, for instance: prevention programs in communities; lim‐ iting social, economic, cultural and environmental risk factors for non‐communicable diseases, oral hygiene promotion, oral health literacy and an appropriate access to oral health care [30].

**Figure 3.** Examples of good practices in oral health promotion programs existing across the Europe.

## **6. Conclusion**

Interventions for reorientating health services

212 Insights into Various Aspects of Oral Health

components of oral health promotion.

healthcare professionals and community [1].

dences for oral health promotion programs at their region.

**5.2. Country examples for oral health promotion program**

primary healthcare professionals.

centers.

programs.

health care [30].

• Establishing community‐led oral healthcare providers.

curative burden from Government is reduced.

• Extensive collaboration with NGOs and social services for oral health promotion, so the

• Linking general health services and children oral health care under primary health

• Training the trainers, that is, training all health professionals about preventive and social

• Facilitating and building knowledge for diagnosing early caries detection programs by

• Provision of professional fluoride lack and excess treatment facilities delivered by primary

Oral health should be an important agenda on the country's health policy. The above inter‐ national policy examples envision the challenges and opportunities for better identification, prioritization and integration of oral health services. Collaborative planning and organiza‐ tion may accelerate the process to arrest the global burden of oral diseases and pioneer the oral health promotion. Relevant international developments suggest that some other health promotion frameworks exists that are parallel to Ottawa Charter framework. Although their principles are same, the implementation may differ according to the needs and socio‐cultural environment of the region. One can develop or reform a different model based on above evi‐

Investment in simple preventive programs is cost‐effective for prevention of oral diseases and promotion of good oral health which is already proven in Europe. Twenty eight examples of good practice are presented from across Europe as shown in **Figure 3**. These cover all areas of oral health promotion across the life course and include programs aimed at pregnant moth‐ ers, children and adolescents, the elderly and disadvantaged groups. To solve the problem of poor oral health in other parts of world a thorough evaluation of existing successful poli‐ cies and programs, identification of evidence‐based interventions can be learned from these

These programs outline a number of successful initiatives that can help prevent oral diseases, which reduce the social burden and in turn reduce existing inequalities. This is done with various measures, for instance: prevention programs in communities; lim‐ iting social, economic, cultural and environmental risk factors for non‐communicable diseases, oral hygiene promotion, oral health literacy and an appropriate access to oral

• Health care led healthy policies supporting access to oral health care.

Gradient shift to rural population to urban area, issues of migrants, urbanization, socio, cul‐ tural and environmental changes alienate health promotion. Isolated intervention may not be successful at such circumstances. Oral health promotion actions with different approaches can only improve. Health for all is certainly efficient way than the target specific behaviors. It is evident that an effective and sustainable intervention combines health, society and individ‐ ual through organization, policy and laws to create healthy living conditions which promotes better quality lifestyle.

WHO is considered as an accountable and reliable organization which provide necessary technical and policy support. Their evidence based guidance enable countries to integrate oral health promotion programs into the general health promotion. The organization has different expertise at Collaboration Centers across globe that is resourceful for oral health promotion guidance. However, most of the developed and developing countries utilize own resources and develop their own action program for health promotion. It is based upon local expe‐ riences and strengths, active communities to contribute participation facilitate community empowerment by creating sustainable supporting environment. WHO has given a vision to oral health promotion programs, that is, "think globally—act locally." To conclude the chap‐ ter, an oral health promotion program should focus on following aspects:


Oral health promotion is one practice that involves strategic planning, integrative activi‐ ties, evidence‐based concepts, evaluation, policy making and other related multifactor. Knowledge generation for oral health promotion through evidence‐based concepts is the goal of this chapter.

## **Abbreviations**


## **Author details**

expertise at Collaboration Centers across globe that is resourceful for oral health promotion guidance. However, most of the developed and developing countries utilize own resources and develop their own action program for health promotion. It is based upon local expe‐ riences and strengths, active communities to contribute participation facilitate community empowerment by creating sustainable supporting environment. WHO has given a vision to oral health promotion programs, that is, "think globally—act locally." To conclude the chap‐

• Recognition of health determinants, capacity building for designing and implementing in‐

• Community led and based oral health promotion programs, having equal opportunity for

• Planning, monitoring and evaluation strategies to be implemented strictly for national oral

• Methods and methodological development to analyze the processes and outcomes of na‐

• Collaboration with strong of networks and alliances that strengthen local, national and international activities for oral health promotion. Every experience, whether success or failure should be counted and shared to acknowledge the cost‐effective and cost‐beneficial

Oral health promotion is one practice that involves strategic planning, integrative activi‐ ties, evidence‐based concepts, evaluation, policy making and other related multifactor. Knowledge generation for oral health promotion through evidence‐based concepts is the goal

ter, an oral health promotion program should focus on following aspects:

terventions to promote oral health.

214 Insights into Various Aspects of Oral Health

marginalized segments of population.

health promotion activities/programs.

of this chapter.

**Abbreviations**

tional oral health promotion interventions.

WHO World Health Organization GBD Global burden of disease DALYs Disability adjusted life‐years YLDs Years lived with disability HPS Health promoting school

NTCP National tobacco control program MoHFW Ministry of Health and Family Welfare COTPA Cigarette and Other Tobacco Products Act

GATS Global Adult Tobacco Survey

NGOs Non‐government organizations

NPPCF National Program for Prevention and Control of Fluorosis

experience that yield to improve oral health quality of life.

Vikram R. Niranjan<sup>1</sup> \*, Vikas Kathuria<sup>2</sup> , Venkatraman J3 and Arpana Salve4

Address all correspondence to: drvikramn@gmail.com

1 Queen Mary University of London, UK and S.D. Dental College, Parbhani, India

2 Consultant Dentist, Hadi Hospital, Jabriya, Kuwait

3 Department of Pathology, Mahatma Gandhi Medical college and Research Institute, Puducherry, India

4 Senior Registrar, Skin & VD Department, Government Medical College & Hospital, Aurangabad, India

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## *Edited by Jane Francis Manakil*

Chronic inflammation such as seen in periodontitis and its bidirectional influence on the systemic health has been of increased interest for a decade. In this text book, we have explored the biological and genetic pathways by which periodontal diseases may influence these disease processes and vice versa. Occlusal rehabilitation using the MEAW technique for the effective treatment of class II deep bite malocclusion and the timely management of cleft lip and palate to benefit the holistic welfare of the patient are presented here. The book addresses the development of bioinspired functionally graded dental restorative materials and also a simulation method that can improve clinical durability and enhance the functional capability of the dentition and indirect prostheses. In conclusion, various pathways for the promotion of oral health with evidence-based concepts are considered.

Photo by LIgorko / iStock

Insights into Various Aspects of Oral Health

Insights into Various

Aspects of Oral Health

*Edited by Jane Francis Manakil*