**The Role of Hydrophilic Sandblasted Titanium and Laser Microgrooved Zirconia Surfaces in Dental Implant Treatment**

Aleksa Markovic

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62702

#### **Abstract**

Dental implant surface modifications affect surface roughness, chemistry, topography, and consequently influence biological bone response. Current surface treatments are directed toward increased hydrophilicity and wettability of dental surfaces that allow earlier implant loading due to accelerated osseointegration. This is clinically reflected in increased implant stability and mainteined crestal bone level. Further modification includes microgrooving of zirconia implants by femtosecond laser ablation. Favorable initial results encourage further clinical assessment of this microgrooved zirconia implants.

**Keywords:** Dental implant surface, Femtosecond laser, Hydrophilicity, Titanium, Zir‐ conia

**1. Introduction**

Dental implant surfaces can be modified using several additive and subtractive techniques. Additive techniques involve impregnation and coating. In contrast to impregnation, when chemical agent is integrated into the core material (e.g., fluoride ions incorporated to titanium surface or calcium phosphate crystals within TiO2 layer), the coating is addition of an agent of various thicknesses superficially on the surface of core material [1].

The subtractive techniques imply removal of the layer of core material or plastic deformation of the superficial surface. This is achieved through mechanical or chemical treatments. Mechanical methods used for surface alteration are grinding, blasting, and machining. Sand,

hydroxyapatite, TiO2, and Al2O3 particles are usually used for grit blasting. Grit blasting is always followed by an acid etching to remove the residual blasting particles as well as to smooth out sharp peaks and to provide roughness that would promote protein adhesion during early healing [1, 2]. Acid etching is a chemical method of surface modification that usually implies hydrofluoric, nitric, or sulfuric acid or their combinations [3].

Current modification of dental implant surfaces is based on the use of lasers. Their main applications are laser-assisted coatings and laser texturing. Laser pulses are used to evaporate the target materials which later condense on the substrate forming a thin coating. Their further role is in dental implant surface texturing in order to form three-dimensional structures on micrometer or submicrometer scales. Several laser sources such as Nd:YAG, CO2, Excimer, and diode lasers have been examinated for surface modifications [4].

Lasers are particularly useful for dental implants with complex surface geometry or for those made of material difficult to be removed. Dental implant surface modification by laser is a noncontact, clean and fast process with high precision [4]. Lasers overcome drawbacks of conventional mechanical and chemical surface modification techniques such as unreliable control of achieved roughness or inability of surface texturing. However, laser processing might be associated with microcracks and heat-affected zones [4, 5].

#### **1.1. Surface topography**

Scientific evidence from in vitro studies indicates that micro-topography of dental implant surfaces affects cellular behavior, mainly, proliferation, cell differentiation, and cell adhesion as well as the production of growth factors [6]. Microgrooves at implant surfaces direct cell spreading and cell alignment and define the orientation of ECM proteins. This directional movement of bone cells known as "contact guidance" contributes to bone–implant interlock‐ ing and thus provides favorable conditions for further healing events [7]. Microtextured sur‐ faces suppress fibroblast spreading and growth preventing fibrous encapsulation of dental implants. Important parameters of surface roughness are average height deviation (Sa) and developed surface area ratio (Sdr) that indicates surface enlargement if a surface is flattened out. According to Sa values determined by optical interferometry, implant surfaces are con‐ sidered as smooth with an Sa value of 0.5 μm; minimally rough surfaces with an Sa of 0.5–1 μm, moderately rough surfaces with Sa 1–2 μm, and rough surfaces with an Sa of 42 μm. Moderately rough surfaces with Sa 1.5 μm and Sdr of 50% promote the strongest bone re‐ sponse [2]. To mimick the architecture of natural bone that consists of nanosized hydroxia‐ patit and organic protein collagen, dental implant surfaces with nano-features have been introduced. Although initial data are promising, the effect of surface nanoroughness on bio‐ logical response is still uncertain [3].

Surface topography is usually examined by scanning electron microscopy (SEM), light interferometry (LIF), and atomic force microscopy (AFM), whereas X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and energy dispersive X-ray spectro‐ scopy (EDX) provide information related to surface chemical composition [3, 8].

SEM is the gold standard for characterization of dental implant topography at the micrometer level. For the characterization of nanotopography of dental implant surfaces, field emission-SEM with higher resolution is required [3].

LIF is an efficient optical tool for quantitative analysis of implant surfaces. This technique uses reflecting light as an optical stylus allowing easy access to even unapproachable parts of the implant flunks. Despite its high resolution in height direction, LIF is suitable for characteriza‐ tion of dental implant surfaces at a micrometer scale, because of limited spatial resolution [8].

AFM can be used to assess dental implant surface topography at nano-level. An atomic force microscope consists of a tip mounted on a cantilever. When tip scans a dental surface, interatomic forces between the tip and the sample surface displace the tip which results in the cantilever bending. Consequently, specialized software produces topographical image of the surface with atomic resolution based on data from detector regarding the laser beam reflected from the cantiliver. This tool has resolution at molecular level, but its usage is unreliable for certain level of surface roughness because their microtopography significantly interferes with the vertical piezoelectric AFM scanning probe [3, 8].

XPS also known as electron spectroscopy for chemical analysis (ESCA) determines what elements (except hydrogen and helium) and in which chemical state and quantity are present within the top 1–12 nm of the implant surface. This tool also provides information related to possible contamination on the surface or in the bulk of the sample as well as those related to the presence and thickness of layers of different materials within the top 12 nm of the implant surface. XPS spectra are obtained by irradiating a dental implant surface with a beam of Xrays and measuring the kinetic energy and number of electrons emitted from the top of the surface [3, 8].

AES provides quantitative elemental and chemical state analysis of dental implant surfaces with lateral spatial resolution of only 8 nm. Approximate depth resolution of AES is 5 nm. However, ion-sputtering used with Auger spectroscopy allows depth chemical profiling up to 100 nm, which is suitable for the characterization of coatings on implant surfaces or impregnation within a TiO2 layer [3]. For the AES analysis, implant surface is excited with a finely focused electron beam while an electron energy analyzer measures the energy of Auger electrons emitted from the surface. Based on the kinetic energy and intensity of an Auger peak, elements from the implant surfaces are identified.

EDX is used for the elemental analysis or chemical characterization of a dental implant surface. It is based on the unique set of peaks on X-ray emission spectrum of each element. Coupled to SEM, EDX determine the elemental composition of structures observed with SEM down to the nanoscale [3].

### **1.2. Surface wettability**

hydroxyapatite, TiO2, and Al2O3 particles are usually used for grit blasting. Grit blasting is always followed by an acid etching to remove the residual blasting particles as well as to smooth out sharp peaks and to provide roughness that would promote protein adhesion during early healing [1, 2]. Acid etching is a chemical method of surface modification that

Current modification of dental implant surfaces is based on the use of lasers. Their main applications are laser-assisted coatings and laser texturing. Laser pulses are used to evaporate the target materials which later condense on the substrate forming a thin coating. Their further role is in dental implant surface texturing in order to form three-dimensional structures on micrometer or submicrometer scales. Several laser sources such as Nd:YAG, CO2, Excimer,

Lasers are particularly useful for dental implants with complex surface geometry or for those made of material difficult to be removed. Dental implant surface modification by laser is a noncontact, clean and fast process with high precision [4]. Lasers overcome drawbacks of conventional mechanical and chemical surface modification techniques such as unreliable control of achieved roughness or inability of surface texturing. However, laser processing

Scientific evidence from in vitro studies indicates that micro-topography of dental implant surfaces affects cellular behavior, mainly, proliferation, cell differentiation, and cell adhesion as well as the production of growth factors [6]. Microgrooves at implant surfaces direct cell spreading and cell alignment and define the orientation of ECM proteins. This directional movement of bone cells known as "contact guidance" contributes to bone–implant interlock‐ ing and thus provides favorable conditions for further healing events [7]. Microtextured sur‐ faces suppress fibroblast spreading and growth preventing fibrous encapsulation of dental implants. Important parameters of surface roughness are average height deviation (Sa) and developed surface area ratio (Sdr) that indicates surface enlargement if a surface is flattened out. According to Sa values determined by optical interferometry, implant surfaces are con‐ sidered as smooth with an Sa value of 0.5 μm; minimally rough surfaces with an Sa of 0.5–1 μm, moderately rough surfaces with Sa 1–2 μm, and rough surfaces with an Sa of 42 μm. Moderately rough surfaces with Sa 1.5 μm and Sdr of 50% promote the strongest bone re‐ sponse [2]. To mimick the architecture of natural bone that consists of nanosized hydroxia‐ patit and organic protein collagen, dental implant surfaces with nano-features have been introduced. Although initial data are promising, the effect of surface nanoroughness on bio‐

Surface topography is usually examined by scanning electron microscopy (SEM), light interferometry (LIF), and atomic force microscopy (AFM), whereas X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and energy dispersive X-ray spectro‐

scopy (EDX) provide information related to surface chemical composition [3, 8].

usually implies hydrofluoric, nitric, or sulfuric acid or their combinations [3].

and diode lasers have been examinated for surface modifications [4].

might be associated with microcracks and heat-affected zones [4, 5].

**1.1. Surface topography**

130 Dental Implantology and Biomaterial

logical response is still uncertain [3].

Important characteristic of dental implant surfaces is surface energy that dertermines wetta‐ bility of surfaces. It is measured by liquid–solid contact angle (CA) which is an angle between the tangent line to a liquid drop's surface at the three-phase boundary, and the horizontal solid's surface [9]. There are two methods commonly used to assess CA of dental implant surfaces: the sessile drop technique where CA of the droplet deposited by a syringe onto the sample surface is measured directly by goniometer or image analysis software and the second, tensiometry (Wilhelmy method) that indirectly measure CA according to the force exerted on the sample surface by the liquid, while sample surface attached to a force meter is vertically dipped into a pool of the probe liquid [10].

The CA ranges from 0° to 180° where CA lower than 90° designate surfaces as hydrophilic and CA very close to 0° as superhydrophilic. Dental implant surfaces with CA above 90° are considered hydrophobic, and those with CA above 150° are superhydrophobic [9]. Currently available dental implants are mainly hydrophobic [11]. Although optimal degree of wettability is not known, there is abundant scientific evidence that hydrophilic surfaces enhances early stages of osseointegration compared to hydrophobic ones [12–14].

Hydrophilicity of dental implant surfaces determines adhesion of proteins on the surface of placed implant, interaction of hard and soft tissue cells with implant surface, and consequently the rate of osseointegration [9]. Hydrophilic surfaces promotes superior adsorption and functional orientation of proteins from blood and interstitial fluids. Composition of the proteins adhered to the implant surface affects cell adhesion, morphology, and migration [15]. Hydrophilic dental implants favor osteoblastic differentiation of mesenchymal stem cells [16], enhance osteoblast maturation [17], produce an anti-inflammatory microenvironment [18], and increase the quantity and quality of mineralization [19]. These molecular and cellular events provide accelerated osseointegration of hydrophilic dental implants in contrast to hydrophobic which has been verified histomorphometricaly as increased bone-to-implantcontact (BIC) at very early point in healing [12–14].

Advantages of hydrophilic surfaces recognized in in vitro and in vivo studies on dental osseointegration have directed contemporary modifications of dental implant surfaces toward to greater hydrophilicity. Today, several methods of hydrophilizing dental implant surfaces are available including radio frequency glow discharge treatment, atmospheric pressure plasma, surface coating with crystalline TiO2, and irradiation by UV-A as well as Ti surface with native oxide hydrophilized using higher energy UV-C rays [9]. Also, changes in dental implant surface roughness and chemistry affect hydrophilicity, which complicates the analysis of the independent effect of each of these surface characteristics on clinical behavior of available dental implants.

#### **1.3. Clinical outcome of dental implant surfaces**

Osseointegration of dental implants is clinically reflected in implant stability. Primary implant stability is a mechanical issue determined by bone quantity and quality, surgical technique, and implant macro-design, whereas secondary implant stability as a biological phenomenon indicates bone apposition and remodeling processes and it is influenced by conditions of implant surface [20, 21]. Contemporary implant surfaces accelerate osseointegration and provide conditions for early or even immediate implant loading if sufficient implant stability is achieved. Therefore, non-invasive, objective and quantitative tool for the assessment and monitoring of implant stability in clinical conditions is of great importance.

Resonance frequency analysis (RFA) is a wireless system for the measurement of implant stability that includes a metal rod (a peg) screwed into the implant body and stimulated by magnetic pulses from a handheld computer. The result of a measurement is expressed as the implant stability quotient (ISQ) ranging from 1 (lowest stability) to 100 (highest stability) (**Figure 1**). ISQ values higher than 47 indicate stable implant [22]. The recommendations for immediate and early loading of single-implant crowns are ISQ 60–65 [23]. Implants with high ISQ values during the follow-up are successfully osseointegrated, whilst low and decreasing ISQ values may be a warning sign of ongoing implant failure [20, 21].

**Figure 1.** Resonance frequency analysis measurement using Ostell Mentor® device.

surfaces: the sessile drop technique where CA of the droplet deposited by a syringe onto the sample surface is measured directly by goniometer or image analysis software and the second, tensiometry (Wilhelmy method) that indirectly measure CA according to the force exerted on the sample surface by the liquid, while sample surface attached to a force meter is vertically

The CA ranges from 0° to 180° where CA lower than 90° designate surfaces as hydrophilic and CA very close to 0° as superhydrophilic. Dental implant surfaces with CA above 90° are considered hydrophobic, and those with CA above 150° are superhydrophobic [9]. Currently available dental implants are mainly hydrophobic [11]. Although optimal degree of wettability is not known, there is abundant scientific evidence that hydrophilic surfaces enhances early

Hydrophilicity of dental implant surfaces determines adhesion of proteins on the surface of placed implant, interaction of hard and soft tissue cells with implant surface, and consequently the rate of osseointegration [9]. Hydrophilic surfaces promotes superior adsorption and functional orientation of proteins from blood and interstitial fluids. Composition of the proteins adhered to the implant surface affects cell adhesion, morphology, and migration [15]. Hydrophilic dental implants favor osteoblastic differentiation of mesenchymal stem cells [16], enhance osteoblast maturation [17], produce an anti-inflammatory microenvironment [18], and increase the quantity and quality of mineralization [19]. These molecular and cellular events provide accelerated osseointegration of hydrophilic dental implants in contrast to hydrophobic which has been verified histomorphometricaly as increased bone-to-implant-

Advantages of hydrophilic surfaces recognized in in vitro and in vivo studies on dental osseointegration have directed contemporary modifications of dental implant surfaces toward to greater hydrophilicity. Today, several methods of hydrophilizing dental implant surfaces are available including radio frequency glow discharge treatment, atmospheric pressure plasma, surface coating with crystalline TiO2, and irradiation by UV-A as well as Ti surface with native oxide hydrophilized using higher energy UV-C rays [9]. Also, changes in dental implant surface roughness and chemistry affect hydrophilicity, which complicates the analysis of the independent effect of each of these surface characteristics on clinical behavior of available

Osseointegration of dental implants is clinically reflected in implant stability. Primary implant stability is a mechanical issue determined by bone quantity and quality, surgical technique, and implant macro-design, whereas secondary implant stability as a biological phenomenon indicates bone apposition and remodeling processes and it is influenced by conditions of implant surface [20, 21]. Contemporary implant surfaces accelerate osseointegration and provide conditions for early or even immediate implant loading if sufficient implant stability is achieved. Therefore, non-invasive, objective and quantitative tool for the assessment and

monitoring of implant stability in clinical conditions is of great importance.

dipped into a pool of the probe liquid [10].

132 Dental Implantology and Biomaterial

stages of osseointegration compared to hydrophobic ones [12–14].

contact (BIC) at very early point in healing [12–14].

**1.3. Clinical outcome of dental implant surfaces**

dental implants.

RFA is not suitable for the measurement of stability of one-piece dental implants and in such indication the use of the Periotest is recommended. The Periotest produces percussion of the implant and provides a stability number ranging from −8 to + 50, with the lower the Periotest value (PTV), the higher the stability (**Figure 2**) [24]. In the literature, different ranges of PTVs

**Figure 2.** Measurement of implant stability of one-piece dental implants using Periotest.

for successfully osseointegrated dental implants have been reported (−9 to +9; −5 to +5; −7 to 0; −4 to −2; −4 to +2) [24–27].

Another important clinical parameter that reflects condition at implant–bone interface is change in crestal bone level. It is recommended to follow this parameter on retroalveolar radiographs obtained via long cone technique. This technique uses film holder that allows repeatability of tube orientation (**Figure 3**). Image analysis software is used for precise measurement of digitized radiographs following their calibration (**Figure 4**). Implant is considered successful with an crestal bone loss of 1.5 mm following 1 year of loading and subsequent loss of 0.2 per year [28].

**Figure 3.** Obtaining radiographs using long cone technique. A plastic ring, connected to the film holder provided con‐ trol of tube orientation.

**Figure 4.** Image analysis software for crestal bone loss measurement.
