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Dental implants materials and surface treatments

Shariq Najeeb1, Maria Mali2, Syed Azeem Ul Yaqin3, Muhammad Sohail Zafar4, Zohaib Khurshid3, Abdullah Alwadaani3 and Jukka P. Matinlinna5 1 National Center for Proteomics, Karachi University, Pakistan, 2Department of Orthodontics, Islamic International Dental College & Hospital, Riphah International University, Islamabad, Pakistan, 3Department of Prosthodontics and Dental Implantology, College of Dentistry, King Faisal University, Al-Ahsa, Saudi Arabia, 4Department of Restorative Dentistry, College of Dentistry, Taibah University, Almadinah Almunawwarah, Saudi Arabia, 5Dental Materials Science, Applied Oral Sciences, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, Sai Ying Pun, Hong Kong SAR, P.R. China

Chapter Outline 21.1 21.2 21.3 21.4 21.5 21.6

Introduction 581 Osseointegration: cellular and biomaterial aspects 583 Biomaterial properties and implant surface characteristics Biomechanical properties of dental implants 584 Surface properties 585 Type of dental implant material 586 21.6.1 Alveolar bone properties 587 21.6.2 Influence of oral health and systemic disease on implant survival

21.7 Modification of the dental implants

584

587

588

21.7.1 Modification of titanium implants 588

21.8 Functionally graded/hierarchical dental implant surfaces 590 21.9 Modification of the polyetheretherketone dental implants 590 21.10 Modification of zirconia implants 592 21.11 Conclusion 592 References 592

21.1

Introduction

In general, a dental implant is a synthetic medical device that is surgically placed directly into the alveolar bone and supports a prosthodontic or an orthodontic appliance (Adell, 1981). Ideally, there needs to be a direct physical, chemical, and biological interface between the human tissues and the implant material (Le Gue´hennec et al., 2007). There are two main components of a dental implant: the abutment and Advanced Dental Biomaterials. DOI: https://doi.org/10.1016/B978-0-08-102476-8.00021-9 Copyright © 2019 Elsevier Ltd. All rights reserved.

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Figure 21.1 A titanium screw in the dog mandible. The implant is osseointegrated and the soft tissue integration is present. The abutment connects the implants with the crown, which is made of metal in this experimental setting. Source: Adapted from Gruber, R., Bosshardt, D.D., 2014. Dental implantology and implants —tissue interface. In: Stem Cell Biology and Tissue Engineering in Dental Sciences. Academic Press, pp. 735 747. https://doi.org/10.1016/B978-0-12-397157-9.00078-3, with publisher permission (Gruber and Bosshardt, 2014).

the screw (fixture). The abutment is the portion that is visible above the gingiva level and retains or supports a prosthodontic or an orthodontic appliance, while the screw or the root of the implant is submerged in the alveolar bone. As a dental implant is a foreign object, it is imperative for the human hard and soft tissues to “accept” it and form an intimate physical, stable, and functional interface with it (Annunziata and Guida, 2015). The initial goal of implant therapy is to achieve osseointegration, which is the direct stabilized physical and structural interface between the implant and the surrounding bone. A diagram of an osseointegrated implant is shown in Fig. 21.1. Mankind has tried to use various materials as dental implants. Archeological evidence indicates the use of ivory, human teeth, bamboo, and some metal alloys as implants in ancient civilizations. However, it was not until the 1950s that titanium

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was attempted as an implant material when titanium chambers were placed into the soft tissues of rabbit ears at the University of Cambridge (Bra˚nemark and Lindstro¨m, 1963). While studying the process of bone healing at Lund University, Per-Ingvar Bra˚nemark noticed that he was unable to remove the titanium chambers from rabbit femurs. Following research on animal and human subjects, Bra˚nemark developed further the contemporary titanium dental implant. In 1965 he placed the implants in the jaws of human volunteers. He termed this stable physical and biofunctional interface between bone and implant as osseointegration (Bra˚nemark and Lindstro¨m, 1963). There are two possible scenarios when an implant is placed into the alveolar bone. The first possibility is the formation of a connective tissue between the implant and the bone (Smeets et al., 2016). This scenario is unfavorable as it may cause the implant to be loosened and dislodged from the bone, leading to implant failure. The most favorable outcome of dental implant therapy is osseointegration (also called osteointegration) which is the formation of a direct, stable interface between the implant and surrounding bone. Although the most common material used in implant dentistry has been traditionally titanium and its alloys, more recently several other materials have been used as implants (Lang and Matinlinna, 2014). The aim of this chapter is to provide the reader with a comprehensive background on the concept of osseointegration along with implant biomaterials, prosthodontic and clinical aspects of oral implantology. Moreover, factors governing the failure and success rates of implants will be discussed.

21.2

Osseointegration: cellular and biomaterial aspects

Following placement in the alveolar bone, the first tissue that comes into contact with the implant material is blood (Telleman et al., 2010). Just within around 1 minute of implantation, plasma proteins are adsorbed onto the implant surface. Platelets are attracted to, and interact with, the adsorbed proteins. Platelets play a vital role in healing, blood clotting, and thrombus formation. Eventually, other cells migrate to the implant site and interact with the implant surface proteins through membrane receptors. Plasma delivers nutrients (glucose, proteins, amino acids, and cholesterol) and other substances to the surgical site. The interactions of these substances and cells alter the surface properties of the implant. Several cells interact with the dental implant fixture surface following blood clotting. However, mesenchymal stem cells (MSCs) play a determining factor in healing of tissues around the implant. Growth factors released following surgery and during inflammation have been indicated to attract MSCs to the implant surface and adhere to it. In the right environment, MSCs have the potential to differentiate into many different types of cells, including bone-forming cells (osteoblasts), cartilage-forming cells (chondroblasts), and fibroblastic cells. Ideally, MSCs should differentiate into osteoblasts around the portion of the dental implant submerged in

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the alveolar bone, leading to osteointegration. However, if a fibrous capsule forms instead, implant failure occurs. There are a number of factors that affect osseointegration. Local factors include biomaterial properties and implant surface characteristics, the quality of the alveolar bone, periodontal disease, and oral hygiene. Systemic factors include general health, immunity smoking status, genetics, and metabolic disease (Marei and El Backly, 2018; Vin˜a et al., 2014; Zafar et al., 2015).

21.3

Biomaterial properties and implant surface characteristics

As dental implant therapy primarily involves placement of a foreign object (i.e., the artificial implant) in direct contact with a living tissue, the type of the implant material used, and its surface properties play a pivotal role in the success—or failure—of a dental implant. The abutment (root connection) portion of a dental implant may be divided into two areas: the core and the surface. The core is the main bulk of the dental material used in the construction of the implant (Lang and Matinlinna, 2014; Aboushelib and Matinlinna, 2014), while the surface is the portion of the implant in direct contact with living tissue (Guillaume, 2016).

21.4

Biomechanical properties of dental implants

The bone and its related soft tissues are dynamic. They remodel according to the physiomechanical demands throughout life. Most dental implant materials used today are significantly less elastic when compared to human bone. According to Wolff’s Law, the amount of bone remodeling and formation is dependent upon the mechanical load applied to it (Frost, 1994). As evident in Table 21.1, titanium has a significantly higher elastic modulus and tensile strength compared to bone. If a Table 21.1 Comparison of the different hard tissue with dental implants materials with relation to tensile strength and modulus of elasticity. Material

Tensile strength

Modulus of elasticity

References

Enamel Dentine Human cortical bone Titanium PEEK CFR-PEEK

47.5 104 104 121 954 976 80 120

40 83 15 14 102 110 3 4 18

Rees and Jacobsen (1993) Rees and Jacobsen (1993) Rho et al. (1993) Niinomi (1998) Sandler et al. (2002) Sandler et al. (2002)

CFR-PEEK, carbon-reinforced polyetheretherketone; PEEK, polyetheretherketone.

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relatively inelastic material, such as a titanium implant, is placed in the bone, it may prevent the load from being transferred to the surrounding bone. This may lead to bone resorption. This process is known as stress-shielding (Asgharzadeh Shirazi et al., 2017). That said, one of the ideal properties of a dental implant material would be to have physical properties identical to that of alveolar bone. However, it is very difficult to replicate nature in a cost-effective fashion. Hence, research has been conducted to produce various Ti alloys (Lang and Matinlinna, 2014) and dental implant biocomposites that have similar mechanical behavior to bone (Asgharzadeh Shirazi et al., 2017). Commercially pure titanium is the most commonly used dental implant material. Titanium is graded 1 4 according to the purity, that is, oxygen and iron contents. Commercially pure type 4 titanium (grade 4 cpTi) is used to fabricate dental implants. For example, Ti6Al4V is a grade 5 titanium alloy that has a higher fatigue resistance and strength than other grades. Hence, Ti6Al4V is also used as dental implant material. More recently, materials such as reinforced polymeric composites (e.g., glass fiber reinforced composites), ceramics, and silicon nitrate have been studied for potential dental implant applications (Osman and Swain, 2015; Zhang and Matinlinna, 2012). At the implant surface, two factors affect the initial bone formation around the dental implant: surface roughness and hydrophilicity (Eliasa et al., 2012). Other factors, such as the presence of biomimetic molecules and factors in the implant material, may also impact osteointegration (Khurshid et al., 2018; Najeeb et al., 2017b). Surface roughness dramatically increases the surface area of the dental implant (1) to achieve higher initial implant stability by mechanical interlocking and (2) to maximize cell adhesion at the surface to promote bone ingrowth into the surface porosities. Surface roughness can be introduced at three levels: macro, micro, and nano (Khurshid et al., 2015; Najeeb et al., 2016b). Macrolevel surface roughness is the introduction of certain geometrical features to the implant design which are visible to the naked eye or measuring more than 10 µm. A tapered, root-like design and threading are examples of macrolevel surface modifications that improve initial implant fixation (Cook et al., 1982). However, solely opting out to use macrolevel surface treatments increases the chances of ion-leakage. This said, in order to minimize ion-leakage but maximize bone ingrowth, microlevel (1 10 µm) and nanolevel (,1 µm) implant modifications are more appropriate. They may also be concurrently used with certain macrolevel surface treatments (Ryu et al., 2014).

21.5

Surface properties

In general, human tissues comprise up to 60% water. Hence, it is widely understood that it is important for the implant surface to be highly hydrophilic (Ferraris et al., 2015). The hydrophilicity of a material is the measure of its affinity for water. Ideally, the surface of a perfectly hydrophilic material should form a 0 degree angle with a water droplet. However, practically speaking, a material such as a dental

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Table 21.2 Some examples of titanium implant surface modifications and their respective properties. Implant surface

Surface roughness (Ra)

References

Pure titanium Titanium-sprayed plasma Plasma-sprayed apatite Biomimetic calcium

0.22 6 0.01 7.01 6 2.09 1.06 6 0.21 1.83 6 0.64

Mabboux et al. (2004) Bagno and Di Bello (2004) Giavaresi et al. (2003) Le Gue´hennec et al. (2007)

implant is modified to form an angle which is less than 90 degrees with a water droplet (Ferraris et al., 2015; Hong et al., 2013). The more a liquid droplet spreads out over the surface of the implant material, the lower the surface contact angle. Over the last few decades, a significant amount of research has been conducted to improve the hydrophilicity of dental implants (Ferraris et al., 2015; Held et al., 2013; Hong et al., 2013). It has been observed that highly hydrophilic dental implant surfaces not only exhibit closer bone implant contact (Rupp et al., 2014) but they may also activate macrophages to produce antiinflammatory factors (Hotchkiss et al., 2017). Several methods that increase the hydrophilicity of dental implants will be described in this chapter. In addition to having a hydrophilic surface, a dental implant fixture should also possess osseoconductive and/or osseoinductive properties (Le Gue´hennec et al., 2007). A material is said to be osseoinductive when it promotes the undifferentiated mesenchymal cells in a tissue to mature into bone-forming osteoblasts, whereas osseoconductive materials promote bone formation on their surface. A significant amount of research has been conducted to improve the osseoconductive/osseoinductive properties of implant materials to enhance the bone implant interface. Methods include production of nanoporous implant surfaces (Carrado` et al., 2017), laser treatment only (Han et al., 2017), spraying of osseoconductive materials such as hydroxyapatite and fluoroapatite (Mohseni et al., 2014), using a laser-assisted biomimetic coating of calcium phosphate (Nathanael et al., 2018), and functionalized biomimetic coatings with adhesion peptides for dental implants (Roessler et al., 2001). Moreover, even eicosapentaenoic acid has been attempted in vivo (Mustafa et al., 2016) and some silane coatings in vitro (Villard et al., 2015) as potential, beneficial dental implant coatings. Ultraviolet light treatment and some other disinfection methods may also be worth further study and consideration (Han et al., 2017) (Table 21.2).

21.6

Type of dental implant material

As discussed above, grade 4 cpTi and its alloy Ti6Al4V are the most commonly used dental implant material by manufacturers. Apart from titanium, there are several other materials which have been used clinically as dental implants. Carbon fiber reinforced carbon had been studied as a potential dental implant material in

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the 1970 80s (Adams et al., 1978). In addition, E-glass fibers have been attempted and introduced (Zhang and Matinlinna, 2012). However, due to the possible release of fiber debris from the implant into the periimplant tissues, the US Food and Drug Administration consequently did not approve the use of carbon fiber implants in the human body (Petersen, 2016). Nevertheless, ceramics such as zirconia offer a more esthetic alternative to titanium (Cionca et al., 2017). More recently, polymeric reinforced composites, such as polyetheretherketone (PEEK), have been attempted and tested in animals in order to assess their osseointegration with alveolar bone (Najeeb et al., 2016d). In addition, silicon nitride, a ceramic used in spinal reconstruction and maxillofacial rehabilitation, has also been tested as a dental implant material (Webster et al., 2012). Each material does have a different way of interaction with the human tissues. Hence, choosing the right biocompatible material for implant applications is a major factor which plays an absolutely important role in the clinical success of implants.

21.6.1 Alveolar bone properties As proposed by Lekholm and Zarb, human bone can be classified into four types, depending on its density (Al-Ekrish et al., 2018), as follows: 1. 2. 3. 4.

Type I—Primarily compact bone Type II—A core of dense spongy (trabecular) bone surrounded by compact bone Type III—A core of dense spongy bone surrounded by a thin layer of compact bone Type IV—A core of low-density spongy bone surrounded by a thin layer compact bone

Most studies suggest that implants exhibit the optimal survival rate when placed in Type I or Type II bone. On the other hand, although a 5-year study on 1045 dental implants found no difference in the survival rate of Types I, II, and III implants, a failure rate of 35% was observed in implants placed in Type IV bone (Jaffin and Berman, 1991). Nonetheless, a recent systematic review of the latest studies has suggested that implant surface modifications may improve the survival rate of implants placed in osteoporotic animal bones (Ghanem et al., 2017). However, more clinical studies are necessary before conclusive evidence can be ascertained (Dereka et al., 2018). Conventional radiography and computerized tomography can both be used to assess the bone density before implant placement (Norton and Gamble, 2001). In addition, a meticulous periodontal screening and recording protocol should be employed to document the clinical signs and symptoms of periodontal disease before initiation of implant therapy. The reader is encouraged to refer to textbooks focusing on clinical periodontology and implantology to learn more about periodontal and implant disease and the surgical steps involved in implant therapy.

21.6.2 Influence of oral health and systemic disease on implant survival Several systemic diseases have been implicated in dental implant failures. Smoking, age, uncontrolled diabetes, and a history of radiation therapy in the head and neck

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region have been implicated in early implant failures (Dawson and Jasper, 2015). A recently published systematic review by the authors of this chapter has indicated a negative impact of Down syndrome on successful dental implant therapy (Najeeb et al., 2017a).

21.7

Modification of the dental implants

Before dental implants are placed in the alveolar bone, their fixture surfaces are modified. They may be modified by several mechanisms such as plasma spraying, ion dispersion, coatings of bioactive materials (Khurshid et al., 2019; Najeeb et al., 2016c; Zafar et al., 2019; Aivazi et al., 2016; Han et al., 2018), and antimicrobial proteins/peptides (Khurshid et al., 2018, 2017a, 2017b, 2016). The mechanism of modification primarily depends on the type of the core implant material. As stated above, implants can be modified at the following levels: macro, micro, and nano. Most contemporary dental implants are endosseous, screw-type devices (Le Gue´hennec et al., 2007) which are further modified at the surface and/or by introduction of bioactive substances within the core.

21.7.1 Modification of titanium implants 21.7.1.1 Titanium plasma spraying Titanium plasma spraying (TPS) involves injecting titanium powder through a hot plasma torch, as shown in Fig. 21.2. The molten titanium particles fuse and condense at the surface of the implant to produce a rough surface, enhancing the surface area for improved bone deposition and contact. Studies have indicated that the

Figure 21.2 A schematic diagram of the plasma-spraying process. A molten jet of a surfactant is coated onto the implant surface. The molten material solidifies and adheres to the implant surface.

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thickness of the plasma coating is in the range of 40 50 µm and has an average roughness of approximately 7 µm (Buser et al., 1991). However, TPS has a major drawback: residual particles. Not only have titanium particles been found in bone adjacent to TPS implant surfaces (Urban et al., 2000), organs such as liver, spleen, and abdominal lymph nodes have all been observed to contain the metallic particles in patients who have received hip and knee replacements (Urban et al., 2004). Although the long-term effects of metal debris found in organs are unknown, titanium debris may have local and systemic inflammatory or carcinogenic effects (Le Gue´hennec et al., 2007). Hence, more recently, studies have been conducted to produce more stable and bioactive titanium surfaces, which are described in the following subsections.

21.7.1.2 Grit-blasting Grit-blasting (or sometimes called sand-blasting) involves production of a rough implant surface by means of a jet of a particles of an abrasive material under high pressure (Lung and Matinlinna, 2012). Two commonly used abrasives used to gritblast implants are alumina (Al2O3) and titanium dioxide (TiO2). Although gritblasted dental implant surfaces have been observed to exhibit enhanced boneimplant contact in animal subjects, they may, however, exhibit drawbacks. First, it has been generally believed that residual ceramic particles can detach from the implant surface and cause inflammation in the periimplant bone (Esposito et al., 1998; Le Gue´hennec et al., 2007). However, an animal study by Piattelli et al. (2003) has found no significant negative effects of residual alumina particles. Moreover, alumina particles may undermine the otherwise excellent corrosion resistance of titanium (Aparicio et al., 2003). Other materials that have been used to grit-blast titanium implants are titanium oxide (Hotchkiss et al., 2017; Ivanoff et al., n.d.) and resorbable materials such as calcium phosphates (Xuereb et al., 2015). More recently, grit-blasting with alumina has also been combined with treatment with NaOH, followed by heat treatment at 600 C to produce rough implant surfaces (Herrero-Climent et al., 2018).

21.7.1.3 Nanostructured titanium implant surfaces To maximize the surface area for cellular adhesion and protein adsorption, modification of titanium surfaces at the nanometer-scale has been suggested. Laser and lithography can be employed to produce nanometer-sized roughness on titanium implants (Anselme et al., 2002; Zhu et al., 2004). Modern 3D-printing technology may also give some answers. Indeed, in vitro studies on 3D-printed implant surfaces possessing surface roughness in the range of 32 6 4 nm on Ti microparticles and 40 6 4 nm on underlying flat Ti have exhibited the potential to promote osteoblast proliferation (Gulati et al., 2017). Nonetheless, although the production of nano-sized implant modifications has the potential to enhance osseointegration, due to the lack of animal and clinical studies, nanostructured implant surfaces are not yet widely used in routine implant dentistry.

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21.7.1.4 Acid-etching of titanium surfaces Another possible way to roughen titanium implants is acid-etching, which is a process like enamel and dentine etching employed prior to bonding to resin composites. However, titanium implants, being alloys, require much stronger acids to be etched. Hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), and sulfuric acid (H2SO4) have been used to produce rough implant surfaces in the micrometer range (Klokkevold et al., 2001; Zinger et al., 2004). Acid-etched surfaces have been observed to exhibit higher osseointegration when compared to TPS implant surfaces, possibly due to a greater surface area and a higher wettability (Cho and Park, 2003). Moreover, etching by HF incorporates fluoride ions onto the implant, and these make the surface more osseoconductive (Cooper et al., 2006). Recently, fluoride-modified dental implants have been introduced and marketed as OsseoSpeed (Dentsply Sirona).

21.7.1.5 Calcium phosphate coated titanium surfaces Calcium hydroxyapatite (CHAp) is a form of calcium phosphate primarily found in the mineralized component of animal and human hard tissues. In regenerative medicine, CHAp has been used to promote the regeneration and healing of calcified tissue such as bone and teeth (Zhou and Lee, 2011). Similarly, when coated on dental implants, CHAp has been found to enhance bone implant contact and cellular proliferation (Xuereb et al., 2015).

21.8

Functionally graded/hierarchical dental implant surfaces

Some recent research in regenerative periodontology has proposed producing “functionally graded” or “hierarchical” biomaterial surfaces (Qasim et al., 2017). Rather than consisting of just a core with a coated or modified surface, functionally graded materials (FGMs) have multiple layers, with each layer possessing different physical, chemical, and biological properties (Hedia and Fouda, 2013). Functionally graded CHAp coatings on titanium implants have shown promising results in vivo (Watari et al., 1997). Moreover, computer simulation studies have suggested that using FGMs may reduce the adverse effects of dental implants on alveolar bone (Lin et al., 2009). Nevertheless, FGMs have yet to see use in routine clinical practice, owing to the need for more clinical and preclinical research.

21.9

Modification of the polyetheretherketone dental implants

The ability to modify polymeric composites has enabled them to be used in multiple fields in dentistry. For instance, resin composites have been used as

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tooth-colored materials for decades, poly(methylmethacrylate)-based denture materials have proven to be user-friendly and durable prosthodontic materials. Moreover, polymeric impression materials produce excellent surface detail and elastic properties for producing accurate impressions of soft and hard oral tissues. More recently, PEEK, a polymer produced by the step-growth polymerization of bis-phenolate salts by dialkylation, has been suggested for use as a dental implant material (Najeeb et al., 2015). In addition to being tooth-colored, PEEK may also exert less adverse effects on the periodontal structures due to its physical properties being like that of human bone (as shown in Table 21.1). Studies have suggested that PEEK implants exhibit lesser stress-shielding when compared to titanium implants. However, in its unmodified form, the osseointegration and bioactivity exhibited by PEEK is inferior to those demonstrated by titanium implants (Najeeb et al., 2016a). To address this issue, a number of methods have been proposed to modify the properties of PEEK implants in order to enhance their osseointegration. As shown in Fig. 21.3, PEEK may be combined with various bioactive materials via the process of melt-blending. PEEK may be coated by CHAp through plasma spraying, similarly to titanium implants (Fauchais and Vardelle, 2012). However, plasma spraying at high temperatures on a polymer like PEEK may have deleterious effects on the physical properties of not only the core polymer but also the PEEK coating interface (Molitor et al., 2001). Nonthermal processes such as electron-beam (e-beam) deposition, spin-coating, and plasma gas etching treatment may circumvent that problem (Balmer et al., 2018; Dawson and Jasper, 2015; Han et al., 2017; Lung and Matinlinna, 2012; Najeeb et al., 2017a). E-beam coating involves the formation of a thin, nanorough coating of material on a substrate via electron-induced deposition. Spin-coating is carried out by slowly dropping a solution of apatites in organic solvents onto the implant spinning at high speeds. In plasma gas etching, the implant surface is exposed to plasma gases at high pressure to produce nanorough surfaces. That said, probably the most unique aspect of PEEK implants would be their ability to be combined with bioactive materials such as apatite to produce potentially osteoconductive fiber-reinforced dental implants (Yabutsuka et al., 2018). So far, no large-scale clinical trials have demonstrated

Figure 21.3 A schematic diagram of the melt-blending process by which bioactive PEEK composite implants are produced. During the process, the bioactive particles are codispersed with PEEK in molten form in a suitable solvent. When placed in a mold, the bioactive composite can cool down and produce a solid which is then shaped into an implant. PEEK, Polyetheretherketone.

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long-term clinical viability of PEEK biocomposites. Nevertheless, positive results from recent animal studies may bring these implants into wider use in the dental clinics.

21.10

Modification of zirconia implants

The surface treatments employed for zirconia implants (Aboushelib and Matinlinna, 2014) are like those carried out on titanium implants. Acid-etching, lasermodification, and grit-blasting have all been used to enhance the bone implant interface of zirconia implants (Oliva et al., n.d.). However, clinical data regarding the 5-year survival rate of modified zirconia implants is limited. A systematic review (in 2008) of seven animal studies by Wenz et al. (n.d.) failed to state any recommendation regarding the use of zirconia implants in the clinical setting. Although some reviews of clinical studies show a promising outcome of zirconia implants after 60 months, more comparative studies are required to ascertain their performance when compared to titanium (Balmer et al., 2018; Montero et al., 2015; Wenz et al., n.d.).

21.11

Conclusion

The surface of dental implants is a vital factor. It may be improved in various ways but the systemic health of the implant-recipient, surgical procedures, and the oral environmental factors has major impacts on osseointegration. Nonetheless, materials such as PEEK and zirconia may present a viable esthetic alternative to titanium in the near future.

References Aboushelib, M.N., Matinlinna, J.P., 2014. Zirconia in implant dentistry. In: Matinlinna, J.P. (Ed.), Handbook of Oral Biomaterials. Pan Stanford Publishing, Singapore, pp. 459 476. Available from: https://doi.org/10.1201/b15644. Adams, D., Williams, D.F., Hill, J., 1978. Carbon fiber-reinforced carbon as a potential implant material. J. Biomed. Mater. Res. 12, 35 42. Available from: https://doi.org/ 10.1002/jbm.820120104. Adell, R., 1981. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int. J. Oral Surg. Available from: https://doi.org/10.1016/S0300-9785(81)80077-4. Aivazi, M., Hossein Fathi, M., Nejatidanesh, F., Mortazavi, V., HashemiBeni, B., Matinlinna, J.P., et al., 2016. The evaluation of prepared microgroove pattern by femtosecond laser on alumina-zirconia nano-composite for endosseous dental implant application. Lasers Med. Sci. 31, 1837 1843. Available from: https://doi.org/10.1007/s10103-016-2059-8. Al-Ekrish, A., Widmann, G., Alfadda, S., 2018. Revised, computed tomography based Lekholm and Zarb Jawbone quality classification. Int. J. Prosthodont. 31, 342 345. Available from: https://doi.org/10.11607/ijp.5714.

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