**Harmonized standard ISO 10993:2003**

Further cytotoxicity and other biocompatibility aspects are summarised according to the outline in the harmonized standard ISO 10993:2003. An experimental orthopaedic Caaluminate-based material was the test material. This material is judged as mildly cytotoxic during the initial curing, and as non-cytotoxic as cured material. See Table below.


Table 8. Cytotoxicity testing of an orthopaedic Ca-aluminate based material

A sensitization test (ISO 10993-10), Guinea Pig Maximization Test was performed with the orthopaedic Ca-aluminate material during curing. No sensitizing potential was obtained. Additional irritation and delayed hypersensitivity testing according to ISO 10993-10:2002 was conducted with both polar and non-polar extract from cured material, and the results showed no discrepancies after intracutaneous injections in the rabbit compared to the blank injections. The acute systemic toxicity study according to ISO 10993-11 was performed with both polar and non-polar extracts from cured Ca-aluminate material (Xeraspine), and the results showed no signs of acute systemic toxicity. Sub-acute, sub-chronic and/or chronic toxicity studies according to ISO 10993-11 were not conducted explicitly, since data from the two implantation studies in rabbit (see below) were judged to support that no long term toxicity is expressed. From the implantation studies histopathological organ and tissue data is available, and no adverse effects were reported.

Additionally, in an *in vivo* genotoxicity assay, the mice micronucleus test of bone marrow was used. The extract (The experimental Ca-aluminate material during curing and cured material) was administered intraperitoneally twice. The results showed no clastogenic effect. Three *in vivo* implantation studies based on ISO 10993-6 have been performed. Two studies in rabbit (femur) and one in sheep (vertebrae). *In vivo* implantation studies are judged as the most relevant studies for documentation of safety of a product. In the rabbit implantation

The standard for cellular biocompatibility in *in vitro* testing has been stated in the International Organization for Standardization (ISO) standards documents. The standard allows for the contact testing of solid dental materials for cytotoxicity with cell lines. Due to several disadvantages of direct contact testing, indirect testing methods have been developed and compared to the direct testing assays (Tang et al 2002). Introduction of a standard cell culture device, i.e. cell culture insert or transwell, provided an opportunity for such cytotoxicity screening of dental materials with indirect contact between material specimens and cell culture monolayer. It is believed that such a testing system more closely mimics the *in vivo* exposure pattern by providing the test of the material in both its solid and dissolved phases at the same time. It has been shown that this testing system has produced the most stable results as compared to other testing systems, such as direct contact test. In a complementary cytotoxicity test using the pulp derived cell response, the experimental CA-

Further cytotoxicity and other biocompatibility aspects are summarised according to the outline in the harmonized standard ISO 10993:2003. An experimental orthopaedic Caaluminate-based material was the test material. This material is judged as mildly cytotoxic

Type of test Method Cytotoxicity (scale 0-4 or 100-0%

A sensitization test (ISO 10993-10), Guinea Pig Maximization Test was performed with the orthopaedic Ca-aluminate material during curing. No sensitizing potential was obtained. Additional irritation and delayed hypersensitivity testing according to ISO 10993-10:2002 was conducted with both polar and non-polar extract from cured material, and the results showed no discrepancies after intracutaneous injections in the rabbit compared to the blank injections. The acute systemic toxicity study according to ISO 10993-11 was performed with both polar and non-polar extracts from cured Ca-aluminate material (Xeraspine), and the results showed no signs of acute systemic toxicity. Sub-acute, sub-chronic and/or chronic toxicity studies according to ISO 10993-11 were not conducted explicitly, since data from the two implantation studies in rabbit (see below) were judged to support that no long term toxicity is expressed. From the implantation studies histopathological organ and tissue data

Additionally, in an *in vivo* genotoxicity assay, the mice micronucleus test of bone marrow was used. The extract (The experimental Ca-aluminate material during curing and cured material) was administered intraperitoneally twice. The results showed no clastogenic effect. Three *in vivo* implantation studies based on ISO 10993-6 have been performed. Two studies in rabbit (femur) and one in sheep (vertebrae). *In vivo* implantation studies are judged as the most relevant studies for documentation of safety of a product. In the rabbit implantation

during the initial curing, and as non-cytotoxic as cured material. See Table below.

During curing, undiluted ISO 10993-5, § 8.2 2 (mild) During curing, diluted ISO 10993-5, § 8.2 0-1 (none-slight) During curing XTT-test 60 % (slight) During curing, diluted XTT-test > 70 % (none) Cured, undiluted ISO 10993-5, § 8.2 0 (none) Cured, diluted diluted XTT-test > 70% (none)

Table 8. Cytotoxicity testing of an orthopaedic Ca-aluminate based material

material showed no sign of toxicity (Schmalz 2002).

is available, and no adverse effects were reported.

**Harmonized standard ISO 10993:2003** 

studies Ca-aluminate material was compared to the PMMA-material CMW 1, and in the sheep study Ca-aluminate material was compared to the PMMA-material Vertebroplastic, and to the Bis-GMA material CortossTM. The results are summarized in Table 9.


Table 9. Implantation studies in femur rabbit, and in vertebrae sheep, details in (Hermansson et al 2008)

The 6 months femur study in rabbits included a 12 months subgroup. The amount of aluminium in blood and selected organs was analysed. The main target organs of the animals (kidney, lung, liver) were histopathologically investigated. Granulomatous inflammation in the cavity, pigmented macrophages and new bone formation were the treatment-related observations at 6- and12-months examination. No difference between Caaluminate material and PMMA was detected. There were no signs of aluminium accumulation in the analysed tissues.

In the 12-week study, the histopathology of vertebrae obtained one week after surgery showed the most severe inflammatory reaction to the surgery in the *sham* operated vertebrae. The bone marrow in the vertebrae filled with Ca-aluminate was not reported to be infiltrated by any inflammatory cells. In vertebrae obtained 12 weeks after surgery no inflammatory reactions were reported, and no obvious differences were observed in the pathological reactions to the surgery (sham) or the filler materials. Overview of the histological contact zone to the Ca-aluminate based material is shown in Figure 4.

The analysis of serum samples showed low concentrations of aluminum in comparison to what is normal in humans. Since the concentration of aluminum did not increase after surgery and in some instances was lower after surgery than in the 0-samples, one may regard these concentrations as within the normal variation.

Fig. 4. Histology image of an experimental Ca-aluminate material (black) in close contact with sheep vertebral bone.

Nanostructural Chemically Bonded Ca-Aluminate Based Bioceramics 59

system and water during setting and hydration, the presence of Ca-ions and hydroxyl ions,

5Ca*2+* + *3*PO*43-* + OH*-*  Ca*5*(PO*4*)*3*OH This reaction occurs upon the biomaterial surface/periphery towards tissue. The apatite is

Apatite crystal

Katoite is formed as a main phase, and is kept as katoite in the bulk material according to the mechanism 1 above. However, in long-time contact with body liquid containing phosphate ions the katoite is transformed at the interface tobody tissue into the at neutral

(OH)4 + 2 Ca2+ + HPO4

When apatite is formed at the interface according to any of the reaction mechanisms 2-4 above, at the periphery of the bulk biomaterial, the biological integration may start. Bone ingrowth towards the apatite allows the new bone structure to come in integrated contact with the biomaterial. This is an established fact for apatite interfaces. For the CA-system the ingrowth is discussed below, 4.4. The transition from tissue to the biomaterial is smooth and

Fig. 6. Integration of CA in tissue – a model using albino adult New Zealand White rabbits

(OH) + 2 Al(OH)3 + 5 H2O

2- + 2 H2PO4


*-* + OH*-* PO*42-* + H*2*O,

the hydrogen phosphate ions are neutralised according to

whereafter the apatite-formation reaction occurs

HPO*42-* + H*2* PO*<sup>4</sup>*

precipitated as nano-size crystals (Hermansson et al, 2006). See figure 5.

Fig. 5. Nano-size apatite formation in the the contact zone to hard tissue

(PO4)3 .

pH even more stable apatite and gibbsite phases according to

(Al(OH)4)2 .

Ca5 .

Ca3 .

intricate.

(Hermansson et al, 2008).

Repeated haemocompatibility studies have been performed to evaluate possible reactions in whole human blood as a result of contact with Ca-aluminate materials (Axen et al 2004). Test items were an experimental Ca-aluminate based material and Xeraspine, Vertebroplastic and Norian (Calcium Phosphate Cement, Synthes Inc). A Chandler loop model was used in which circulating human blood was in contact with the test materials for up to 4 hours. For comparison, loops free from test materials were used. Platelet count (PLT), thrombin-antithrombin (TAT) complex, complement factors C3a and C5b-9 (TCC), and TNF-α were assayed. The degree of haemolysis was assessed by the Drabkin method. Norian (a calcium phosphate based material) invariably induced extensive clotting already after 60 minutes, verified macroscopically and also by significantly reduced PLT in comparison to the Control loops, whereas there was no significant reduction in PLT in the loops with Ca-alumiante material or Vertebroplastic, respectively, neither at 60 nor at 240 minutes. The Ca-aluminate material did not induce haemolysis to a greater extent than any of the other materials tested. TCC was activated to a certain degree by the biomaterial, comparable to what is commonly observed for artificial materials. TNF-α generation, indicative of activation of white blood cells, was not enhanced by either Vertobroplastic or the Ca-aluminate material.

Based on all above mentioned data and generated toxicity data, it is considered that there is no reason to expect that the Ca-aluminate biomaterials when used in accordance with the intended clinical use will create any adverse effects. The Ca-aluminate based materials fulfill the requirements of the harmonized standard ISO 10993:2003.

3.1.1.1 Complementary reactions of Ca-aluminate in presence of body liquid.

Complementary reactions occur when the Ca-aluminate is in contact with tissue containing body liquid. Several mechanisms have been identified, which control how the Ca-aluminate material is integrated onto tissue. These mechanisms affect the integration differently depending on what type of tissue the biomaterial is in contact with, and in what state (unhydrated or hydrated) the CA is introduced. These mechanisms are summarized as follows and described in more details elsewhere (Hermansson, 2009);


When phosphate ions or water soluble phosphate compounds are present in the biomaterial (powder or liquid) an apatite formation occurs according to the reaction

$$\text{\color{red}{5}Ca^{2+} + \text{\color{red}{3}PO\_4^{3-} + OH^-} \rightarrow \text{Ca}\_5(PO\_4)\_3OH}$$

This complementary reaction to the main reaction occurs due to the presence of Ca-ions and a basic (OH-) environment created by the Ca-aluminate material. The solubility product of apatite is very small [Ks = 10-58], so apatite is easily precipitated. Body liquid contains among others the following ions HPO42- and H2PO4 -. In contact with the Ca-aluminate system and water during setting and hydration, the presence of Ca-ions and hydroxyl ions, the hydrogen phosphate ions are neutralised according to

$$\cdot \text{HPO}\_{4^{2-}} + \cdot \text{H}\_2\text{PO}\_4^- + \text{OH}^- \rightarrow \text{PO}\_4^{2-} + \text{H}\_2\text{O}\_2^-$$

whereafter the apatite-formation reaction occurs

58 Biomaterials – Physics and Chemistry

Repeated haemocompatibility studies have been performed to evaluate possible reactions in whole human blood as a result of contact with Ca-aluminate materials (Axen et al 2004). Test items were an experimental Ca-aluminate based material and Xeraspine, Vertebroplastic and Norian (Calcium Phosphate Cement, Synthes Inc). A Chandler loop model was used in which circulating human blood was in contact with the test materials for up to 4 hours. For comparison, loops free from test materials were used. Platelet count (PLT), thrombin-antithrombin (TAT) complex, complement factors C3a and C5b-9 (TCC), and TNF-α were assayed. The degree of haemolysis was assessed by the Drabkin method. Norian (a calcium phosphate based material) invariably induced extensive clotting already after 60 minutes, verified macroscopically and also by significantly reduced PLT in comparison to the Control loops, whereas there was no significant reduction in PLT in the loops with Ca-alumiante material or Vertebroplastic, respectively, neither at 60 nor at 240 minutes. The Ca-aluminate material did not induce haemolysis to a greater extent than any of the other materials tested. TCC was activated to a certain degree by the biomaterial, comparable to what is commonly observed for artificial materials. TNF-α generation, indicative of activation of white blood cells, was not enhanced by either Vertobroplastic or

Based on all above mentioned data and generated toxicity data, it is considered that there is no reason to expect that the Ca-aluminate biomaterials when used in accordance with the intended clinical use will create any adverse effects. The Ca-aluminate based materials fulfill

Complementary reactions occur when the Ca-aluminate is in contact with tissue containing body liquid. Several mechanisms have been identified, which control how the Ca-aluminate material is integrated onto tissue. These mechanisms affect the integration differently depending on what type of tissue the biomaterial is in contact with, and in what state (unhydrated or hydrated) the CA is introduced. These mechanisms are summarized as follows

Mechanism 2: Apatite formation in presence of phosphate ions in the

Mechanism 3: Apatite formation in the contact zone in presence of body liquid Mechanism 4: Transformation of hydrated Ca-aluminate into apatite and

Mechanism 5: Biological induced integration and ingrowth, i.e. bone formation

Mechanism 6: Point-welding due to mass increase when in contact with body

When phosphate ions or water soluble phosphate compounds are present in the biomaterial

5Ca*2+* + *3*PO*43-* + OH*-*  Ca*5*(PO*4*)*3*OH This complementary reaction to the main reaction occurs due to the presence of Ca-ions and a basic (OH-) environment created by the Ca-aluminate material. The solubility product of apatite is very small [Ks = 10-58], so apatite is easily precipitated. Body liquid contains among others the following ions HPO42- and H2PO4-. In contact with the Ca-aluminate

the requirements of the harmonized standard ISO 10993:2003.

and described in more details elsewhere (Hermansson, 2009);

gibbsite

liquid.

biomaterial

at the contact zone

(powder or liquid) an apatite formation occurs according to the reaction

3.1.1.1 Complementary reactions of Ca-aluminate in presence of body liquid.

Mechanism 1: Main reaction, the hydration step of CAC (Eq. 1 above)

the Ca-aluminate material.

$$\text{\color{red}{5}Ca^{2+} + \text{\color{red}{3}PO\_4^{3-} + OH^-} \rightarrow \text{Ca}\_5(PO\_4)\_3OH^-}$$

This reaction occurs upon the biomaterial surface/periphery towards tissue. The apatite is precipitated as nano-size crystals (Hermansson et al, 2006). See figure 5.

Fig. 5. Nano-size apatite formation in the the contact zone to hard tissue

Katoite is formed as a main phase, and is kept as katoite in the bulk material according to the mechanism 1 above. However, in long-time contact with body liquid containing phosphate ions the katoite is transformed at the interface tobody tissue into the at neutral pH even more stable apatite and gibbsite phases according to

$$\begin{aligned} \text{Ca}\_3 \cdot (\text{Al(OH)}\_4)\_2 \cdot (\text{OH})\_4 &+ 2\text{Ca}^{2+} + \text{HPO}\_4^{2-} + 2\text{ H}\_2\text{PO}\_4^- \rightarrow \\\\ \text{Ca}\_5 \cdot (\text{PO}\_4)\_3 \cdot (\text{OH}) + 2\text{ Al(OH)}\_3 &+ 5\text{ H}\_2\text{O} \end{aligned}$$

When apatite is formed at the interface according to any of the reaction mechanisms 2-4 above, at the periphery of the bulk biomaterial, the biological integration may start. Bone ingrowth towards the apatite allows the new bone structure to come in integrated contact with the biomaterial. This is an established fact for apatite interfaces. For the CA-system the ingrowth is discussed below, 4.4. The transition from tissue to the biomaterial is smooth and intricate.

Fig. 6. Integration of CA in tissue – a model using albino adult New Zealand White rabbits (Hermansson et al, 2008).

Nanostructural Chemically Bonded Ca-Aluminate Based Bioceramics 61

The bacteriostatic and antibacterial properties are primarily related to the development of the nanostructure and the nano-size porosity during hydration of the Ca-aluminate system. The initial low pH ( < 8) of the system in the case of the presence of a polycarboxylic acid for cross-linking, is such not a hindrance for the antibacterial properties. The requirements of the microstructure of Ca-aluminate and/or Ca-silicate based biomaterials to achieve antibacterial properties are related to the general nanostructure obtained; A nanoparticle/crystal size of hydrates in the interval 15-40 nm, a nanoporosity size of 1-4 nm

The above mentioned requirements will guarantee that the nanostructure will be free of large pores meaning no escape of bacteria within the original liquid, paste or dental void, during the hydration. The nanocrystals will participate on all walls, within the liquid, and on all inert particles and on bacteria within the original volume. The formation of nanocrystals will continue to all the void is filled. The bacteria will be totally encapsulated and will be chemically dissolved. Also the number of nanopores will be extremely which will have the possibility of catching and fasten bacteria to the hydrate surface – an analogue to how certain peptides may function as antibacterial material due to a structure with

Alternative dental materials and implant materials based on bioceramics are found within all the classical ceramic families: traditional ceramics, special ceramics, glasses, glassceramics, coatings and chemically bonded ceramics (CBC) (Ravaglioli and Krajewski, 1992). The CBC-group, also known as inorganic cements, is based on materials in the system CaO-Al2O3-P2O5-SiO2, where phosphates, aluminates, and silicates are found. Depending on in vivo chemical and biological stability, the CBC biomaterials can be divided into three groups: stable, slowly resorbable and resorbable. The choice for dental and stable materials is the Ca-aluminate based materials (Hermansson et al 2008). Slowly resorbable materials are found within Ca-silicates and Ca-phosphates, and fast resorbing materials among Casulphates and some Ca-phosphates. The stable biomaterials are suitable for dental applications, long-term load-bearing implants, and osteoporosis-related applications. For trauma and treatment of younger patients, the preferred biomaterial is the slowly resorbable materials, which can be replaced by new bone tissue (Nilsson, 2002). In this section are summarised some of the possible new applications using the strong chemically bonded ceramics based on Ca-aluminate. The presentation is devided in three application areas;

The following product areas have been identified based on experimental material data, preclinical studies, pilot studies and on-going clinical studies (Jefferies et al, 2009). The application areas are; Dental cement, endodontic products (orthograde and retrograde), sealants, restoratives, and pastes for augmentation and dental implant coatings. For lowviscosity and early hardening of the CA, a complementary glass ionomer can preferrably be used. Clinical use of the materials is foreseen within the next coming years. The use of CA within odontology is based on the following features; early/rapid anchoring, high strength, long-term stability, no shrinkage, combined bonding and bulk material, biocompatibility and in situ apatite formation ability (nanocrystals formed in the contact zone between

and the number of pores per square micrometer of at least 500, preferably > 1000.

nanosize hole within the structure.

dental, orthopaedics and drug delivery.

material and tissue).

**4. Materials and biomaterials application** 

The actual contact zone developed depends on a combination of the above discussed mechanisms and the tissue. The latter varies from a cellular-free high content apatite tissue in the case of a dental enamel, via dentine to a bone structure with cellular and body liquid contact. Also the material can be in contact with other implant materials as dental crowns, dental screws or coatings on implants. In the tables 10 and 11 are summarized in which applications and specific tissues the demonstrated mechanisms are predominant.


Table 10. Type of tissue and possible mechanisms.


Table 11. Applications and possible mechanisms.

#### **Nanostructure and nano-porosity used in certain applications**

The nanostructure including nanoporosity developed in the Ca-aluminate biomaterial system when near complete hydration occurs, yields some unique properties related to how bacteriostatic and antibacterial properties may develop in the biomaterial. The nanoporosity can also be used to control release of drugs incorporated the biomaterial. The background to this is that even if the total porosity is low, all porosity is open, thus allowing transport of molecules in the nanoporosity channels. The nanostructure used in thin film coatings will also be touched upon.

#### **Antibacterial aspects**

The surprising finding in studies recently performed (Doxa patent application 2010) shows that the bacteriostatic and antibacterial properties of the Ca-aluminate biomaterial are not primarily related to pH or specific ions and ion concentration or reducing agents, but to the hydration procedure and the microstructure obtained. This also to some extent is an answer why highly biocompatible and even bioactive biomaterials can combine apparently contradictory features such as biocompatibility, bioactivity and apatite formation and environmental friendliness with bacteriostatic and antibacterial properties.

The actual contact zone developed depends on a combination of the above discussed mechanisms and the tissue. The latter varies from a cellular-free high content apatite tissue in the case of a dental enamel, via dentine to a bone structure with cellular and body liquid contact. Also the material can be in contact with other implant materials as dental crowns, dental screws or coatings on implants. In the tables 10 and 11 are summarized in which

Tissue Mech 1 Mech 2 Mech 3 Mech 4 Mech 5 Mech 6

Bone x x X x x x

Application Mech 1 Mech 2 Mech 3 Mech 4 Mech 5 Mech 6

x (x)

x

x

(x)

The nanostructure including nanoporosity developed in the Ca-aluminate biomaterial system when near complete hydration occurs, yields some unique properties related to how bacteriostatic and antibacterial properties may develop in the biomaterial. The nanoporosity can also be used to control release of drugs incorporated the biomaterial. The background to this is that even if the total porosity is low, all porosity is open, thus allowing transport of molecules in the nanoporosity channels. The nanostructure used in thin film

The surprising finding in studies recently performed (Doxa patent application 2010) shows that the bacteriostatic and antibacterial properties of the Ca-aluminate biomaterial are not primarily related to pH or specific ions and ion concentration or reducing agents, but to the hydration procedure and the microstructure obtained. This also to some extent is an answer why highly biocompatible and even bioactive biomaterials can combine apparently contradictory features such as biocompatibility, bioactivity and apatite formation and

environmental friendliness with bacteriostatic and antibacterial properties.

X x x

x X x x x

x X x (x)

x X x x

applications and specific tissues the demonstrated mechanisms are predominant.

Dentine x x X x (x)

x x

x x

x x

x x

**Nanostructure and nano-porosity used in certain applications** 

Enamel x x

Table 10. Type of tissue and possible mechanisms.

Table 11. Applications and possible mechanisms.

Cementation a. towards tissue b. towards implant

Dental fillings a. towards enamel b. towards dentine

Endo fillings a. orthograde

b. retrograde incl bone

towards implant gap filling

Coatings and augmentation

coatings will also be touched upon.

**Antibacterial aspects** 

The bacteriostatic and antibacterial properties are primarily related to the development of the nanostructure and the nano-size porosity during hydration of the Ca-aluminate system. The initial low pH ( < 8) of the system in the case of the presence of a polycarboxylic acid for cross-linking, is such not a hindrance for the antibacterial properties. The requirements of the microstructure of Ca-aluminate and/or Ca-silicate based biomaterials to achieve antibacterial properties are related to the general nanostructure obtained; A nanoparticle/crystal size of hydrates in the interval 15-40 nm, a nanoporosity size of 1-4 nm and the number of pores per square micrometer of at least 500, preferably > 1000. The above mentioned requirements will guarantee that the nanostructure will be free of large pores meaning no escape of bacteria within the original liquid, paste or dental void, during the hydration. The nanocrystals will participate on all walls, within the liquid, and on all inert particles and on bacteria within the original volume. The formation of

nanocrystals will continue to all the void is filled. The bacteria will be totally encapsulated and will be chemically dissolved. Also the number of nanopores will be extremely which will have the possibility of catching and fasten bacteria to the hydrate surface – an analogue to how certain peptides may function as antibacterial material due to a structure with nanosize hole within the structure.

#### **4. Materials and biomaterials application**

Alternative dental materials and implant materials based on bioceramics are found within all the classical ceramic families: traditional ceramics, special ceramics, glasses, glassceramics, coatings and chemically bonded ceramics (CBC) (Ravaglioli and Krajewski, 1992). The CBC-group, also known as inorganic cements, is based on materials in the system CaO-Al2O3-P2O5-SiO2, where phosphates, aluminates, and silicates are found. Depending on in vivo chemical and biological stability, the CBC biomaterials can be divided into three groups: stable, slowly resorbable and resorbable. The choice for dental and stable materials is the Ca-aluminate based materials (Hermansson et al 2008). Slowly resorbable materials are found within Ca-silicates and Ca-phosphates, and fast resorbing materials among Casulphates and some Ca-phosphates. The stable biomaterials are suitable for dental applications, long-term load-bearing implants, and osteoporosis-related applications. For trauma and treatment of younger patients, the preferred biomaterial is the slowly resorbable materials, which can be replaced by new bone tissue (Nilsson, 2002). In this section are summarised some of the possible new applications using the strong chemically bonded ceramics based on Ca-aluminate. The presentation is devided in three application areas; dental, orthopaedics and drug delivery.

The following product areas have been identified based on experimental material data, preclinical studies, pilot studies and on-going clinical studies (Jefferies et al, 2009). The application areas are; Dental cement, endodontic products (orthograde and retrograde), sealants, restoratives, and pastes for augmentation and dental implant coatings. For lowviscosity and early hardening of the CA, a complementary glass ionomer can preferrably be used. Clinical use of the materials is foreseen within the next coming years. The use of CA within odontology is based on the following features; early/rapid anchoring, high strength, long-term stability, no shrinkage, combined bonding and bulk material, biocompatibility and in situ apatite formation ability (nanocrystals formed in the contact zone between material and tissue).

Nanostructural Chemically Bonded Ca-Aluminate Based Bioceramics 63




Below are presented in more details the state–of-the-art for different possible applications of

Long-term success after cementation of indirect restorations depends on retention as well as maintenance of the integrity of the marginal seal. Sealing properties of great importance deal with microleakage resistance, the retention developed between the dental cement and the environment, compressive strength and acid resistance. Data presented below support the Ca-aluminate-system as highly relevant for dental cement materials. Integration with tooth tissue is a powerful feature and the foundation of the Ca-aluminate technology platform. Secondary caries occurs not only after filling procedures but also after other restorative procedures such as the cementation of crowns and bridges. The consequence of the difference in the mechanism of action between Ca-aluminate products and conventional products is illustrated by the study presented in details in (Pameijer et al , 2008, 2009), illustrated in Figure 2 below. It shows that the micro leakage, measured by dye penetration after thermo cycling, of a leading dental cement (Ketac Cem®, 3M) was significantly higher, both before and after thermo cycling compared to Ceramir C&B, a Ca-aluminate based product recently approved by FDA. This has also recently been verified using techniques for studying actual bacterial leakage. The above described nanostructural precipitation upon tissue walls, biomaterials and within the original Ca-aluminate paste is the main reason for

General properties of the CAPH-system used as dental cement have been presented (Pameijer et al, 2008), see Fig. 7 and Table 12 below. General features of all the dental cement

**Mean Micro Leakage** 

No Thermo cycling After thermo cycling

XeraCem™ Ketac Cem

Fig. 7. Micro leakage leakage of a Ca-aluminate based material (blue) and Ketac Cem (red).



this, in addition to a high acid corrosion resistance.

0 0,2 0,4 0,6 0,8 1 1,2 1,4

**mm**

classes available are presented as a summary in Table 13 below.


Ca-aluminate based materials.

**4.1.1 Dental cement** 

#### **4.1 Dental applications**

The existing dental materials are mainly based on amalgam, resin composites or glass ionomers. Amalgam, originating from the Tang dynasty in China, was introduced in the early 19th century as the first commercial dental material. It is anchored in the tooth cavity by undercuts in the bottom of the cavity to provide mechanical retention of the metal. Although it has excellent mechanical characteristics it is falling out of favor in most dental markets because of health and environmental concerns. One exception is the US in which amalgam still has a redlatively large market share.

The second generation material is the resin composites, first introduced in the late 1950s. These are attached to the tooth using powerful bonding agents that glue them to the tooth structure. After technical problems over several decades, these materials today have developed to a level where they work quite well and provide excellent aesthetic results. Despite the improvements, resin composites have some drawbacks related to shrinkage, extra bonding, irritant components, a risk of post-operative sensitivity, and technique sensitivity in that they require dry field treatment in the inherently moist oral cavity. The key problem, due to shrinkage or possible degradation of the material and the bonding, is the margin between the filler material and tooth, which often fails over time leading to invasion of bacteria and secondary caries. Secondary caries is a leading cause of restorative failure and one of the biggest challenges in dentistry today. As a significant number of dental restorations today are replacement of old, failed tooth fillings, it is clear that tackling this problem is a major market need (Mjör, 2000). Secondary caries occurs not only after filling procedures but also following other restorative procedures such as the cementation of crowns and bridges.

Glass ionomers were first introduced in 1972 and today are an established category for certain restorations and cementations. Their main weakness is the relatively low strength and low resistance to abrasion and wear. Various developments have tried to address this, and in the early 1990s resin-modified ionomers were introduced. They have significantly higher flexural and tensile strength and lower modulus of elasticity and are therefore more fracture-resistant. However, in addition to the problems of resin composites highlighted above, wear resistance and strength properties are still inferior to those of the resin composites.

The nature of the mechanisms utilized by Ca-aluminate materials (especially Mechanism 1 above) when integrating and adhering to tooth tissue and other materials makes these materials compatible with a range of other dental materials, including resin composite, metal, porcelain, zirconia, glass ionomers and gutta-percha. This expands the range of indications for Ca-aluminate based products from not only those involving tooth tissue, e.g. cavity restorations, but also to a range of other indications that involve both tooth tissue and other dental materials. Examples include dental cementation, base and liner and core buildup and endodontic sealer /filler materials, which involve contact with materials such as porcelain, oxides and polymers and metals, and coatings on dental implants such as titanium or zirconia-based materials.

The use of the Ca-alumiante materials may be a first step towards a paradigm shift for dental applications. The features are summarized below.

Nanostructural integration


Below are presented in more details the state–of-the-art for different possible applications of Ca-aluminate based materials.

#### **4.1.1 Dental cement**

62 Biomaterials – Physics and Chemistry

The existing dental materials are mainly based on amalgam, resin composites or glass ionomers. Amalgam, originating from the Tang dynasty in China, was introduced in the early 19th century as the first commercial dental material. It is anchored in the tooth cavity by undercuts in the bottom of the cavity to provide mechanical retention of the metal. Although it has excellent mechanical characteristics it is falling out of favor in most dental markets because of health and environmental concerns. One exception is the US in which

The second generation material is the resin composites, first introduced in the late 1950s. These are attached to the tooth using powerful bonding agents that glue them to the tooth structure. After technical problems over several decades, these materials today have developed to a level where they work quite well and provide excellent aesthetic results. Despite the improvements, resin composites have some drawbacks related to shrinkage, extra bonding, irritant components, a risk of post-operative sensitivity, and technique sensitivity in that they require dry field treatment in the inherently moist oral cavity. The key problem, due to shrinkage or possible degradation of the material and the bonding, is the margin between the filler material and tooth, which often fails over time leading to invasion of bacteria and secondary caries. Secondary caries is a leading cause of restorative failure and one of the biggest challenges in dentistry today. As a significant number of dental restorations today are replacement of old, failed tooth fillings, it is clear that tackling this problem is a major market need (Mjör, 2000). Secondary caries occurs not only after filling procedures but also following other restorative procedures such as the cementation of

Glass ionomers were first introduced in 1972 and today are an established category for certain restorations and cementations. Their main weakness is the relatively low strength and low resistance to abrasion and wear. Various developments have tried to address this, and in the early 1990s resin-modified ionomers were introduced. They have significantly higher flexural and tensile strength and lower modulus of elasticity and are therefore more fracture-resistant. However, in addition to the problems of resin composites highlighted above, wear resistance and strength properties are still inferior to those of the resin

The nature of the mechanisms utilized by Ca-aluminate materials (especially Mechanism 1 above) when integrating and adhering to tooth tissue and other materials makes these materials compatible with a range of other dental materials, including resin composite, metal, porcelain, zirconia, glass ionomers and gutta-percha. This expands the range of indications for Ca-aluminate based products from not only those involving tooth tissue, e.g. cavity restorations, but also to a range of other indications that involve both tooth tissue and other dental materials. Examples include dental cementation, base and liner and core buildup and endodontic sealer /filler materials, which involve contact with materials such as porcelain, oxides and polymers and metals, and coatings on dental implants such as

The use of the Ca-alumiante materials may be a first step towards a paradigm shift for

**4.1 Dental applications** 

crowns and bridges.

composites.

titanium or zirconia-based materials.

Nanostructural integration


dental applications. The features are summarized below.


amalgam still has a redlatively large market share.

Long-term success after cementation of indirect restorations depends on retention as well as maintenance of the integrity of the marginal seal. Sealing properties of great importance deal with microleakage resistance, the retention developed between the dental cement and the environment, compressive strength and acid resistance. Data presented below support the Ca-aluminate-system as highly relevant for dental cement materials. Integration with tooth tissue is a powerful feature and the foundation of the Ca-aluminate technology platform. Secondary caries occurs not only after filling procedures but also after other restorative procedures such as the cementation of crowns and bridges. The consequence of the difference in the mechanism of action between Ca-aluminate products and conventional products is illustrated by the study presented in details in (Pameijer et al , 2008, 2009), illustrated in Figure 2 below. It shows that the micro leakage, measured by dye penetration after thermo cycling, of a leading dental cement (Ketac Cem®, 3M) was significantly higher, both before and after thermo cycling compared to Ceramir C&B, a Ca-aluminate based product recently approved by FDA. This has also recently been verified using techniques for studying actual bacterial leakage. The above described nanostructural precipitation upon tissue walls, biomaterials and within the original Ca-aluminate paste is the main reason for this, in addition to a high acid corrosion resistance.

General properties of the CAPH-system used as dental cement have been presented (Pameijer et al, 2008), see Fig. 7 and Table 12 below. General features of all the dental cement classes available are presented as a summary in Table 13 below.

Fig. 7. Micro leakage leakage of a Ca-aluminate based material (blue) and Ketac Cem (red).

Nanostructural Chemically Bonded Ca-Aluminate Based Bioceramics 65

A clinical 2-year study comprising 35 cemented crowns was conducted at Kornberg School of Dentistry, Temple University, and follow-up data and feedback from participating

 Fig. 8. Cemented ceramic crown (left), and HRTEM of the nanostructure of Ca-aluminate hydrates, hydrates formed in the interval 10-30 nm(right), bar = 10 nm (Hermansson et al,

In a review of the biocompatibility of dental materials used in contemporary endodontic therapy (Haumann and Love, 2003) amalgam was compared with gutta-percha, zinc oxideeugenol (ZOE), polymers, glass ionomer cements (GICs), composite resins and mineral trioxide aggregate (MTA). A review (Niederman, 2003) of clinical trials of *in vivo* retrograde obturation materials summarized the findings. GIC's appeared to have the same clinical success as amalgam, and orthograde filling with gutta-percha and sealer was more effective than amalgam retrograde filling. Retrograde fillings with composite and Gluma, EBA cement or gold leaf were more effective than amalgam retrograde fillings. However, none of the clinical trials reviewed in included MTA. In a 12 week microleakage study, the MTA performance was questioned compared to that of both amalgam and a composite (Alamo et

The Ca-aluminate-based material discussed in this paper belongs to the same material group as MTA, the chemically bonded ceramics. MTA is a calcium silicate (CS) based cement having bismuth oxide as filler material for improved radio-opacity, whereas the Caaluminate material consists of Ca-aluminate phases CA and CA2 with zirconia as filler material. MTA is claimed to prevent microleakage, to be biocompatible, to regenerate original tissues when placed in contact with the dental pulp or periradicular tissues, and to be antibacterial. The product profile of MTA describes the material as a water-based product, which makes moisture contamination a non-issue (Dentsply 2003). The CA-cement materials are more acid resistant than the CS-based materials, and in general show higher mechanical strength than the CS materials. A two-year and a five-year retrospective clinical study of Ca-aluminate based material have been conducted (Pameijer et al, 2004, Kraft et al, 2009). The study involved patients with diagnosis of either chronic per apical osteitis, chronic per apical destruction, or trauma. Surgery microscope was used in all cases. For orthograde therapy the material was mixed with solvent into appropriate consistency and put into a syringe, injected and condensed with coarse gutta-percha points. Machine burs were employed for root canal resection. For the retrograde root fillings, the conventional surgery procedure was performed. The apex was detected with surgery microscope and rinsed and prepared with an ultrasonic device. Crushed water-filled CA-tablets were then inserted and condensed with dental instruments. The patients' teeth were examined with X-

dentists were excellent with no failures at all reported (Jefferies et al 2009).

2010)

al, 1999).

**4.1.2 Endodontics** 


Table 12. Selected properties, Test methods according to SO 9917-1


Table 13. Overview of dental luting cements (Hermansson et al, 2010)

Material aspects 4-12 in Table 13 are also relevant for all other Ca-aluminate based dental applications.

A clinical 2-year study comprising 35 cemented crowns was conducted at Kornberg School of Dentistry, Temple University, and follow-up data and feedback from participating dentists were excellent with no failures at all reported (Jefferies et al 2009).

Fig. 8. Cemented ceramic crown (left), and HRTEM of the nanostructure of Ca-aluminate hydrates, hydrates formed in the interval 10-30 nm(right), bar = 10 nm (Hermansson et al, 2010)
