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Implant and abutment material

Ever since the ground-breaking studies of Branemark, titanium has been the material of choice in oral implantology, which is due to its excellent biocompatibility and osseointegration. As a result of these positive features, only little attention has been drawn on developing alternative implant materials with lower susceptibility to adhere biofilms on their surface. Only in the recent years, several manufacturers introduced implants made from zirconia, titanium/zirconia alloys, or polyether ether ketone on the market, yet—particularly with regard to biofilm formation on their surface—data on the performance of implants made from different materials featuring a surface roughness optimized for osseointegration and minimal biofilm formation are scarce. The implant abutment plays a very crucial role in prosthetic dentistry, and due to its exposure to the oral cavity, its surface might be even more relevant for the formation of biofilms than the implant surface. Thus, studies on biofilm formation on implant surfaces have focused on the implant abutment rather than the implant body. In the recent years, the steadily increasing demand for esthetic restorations has—apart from titanium as the classical material for the fabrication of implant abutments (Fig. 5.5)— led to the fabrication of implant abutments from zirconia (Fig. 5.6) or polyether ether ketone; provisional abutments can also be fabricated from polymethyl methacrylate.

Several clinical studies analyzed the formation of biofilms on different materials that can be employed for the fabrication of implant abutments. Though data gathered in laboratory studies are frequently contradictory, the conventional wisdom from the clinical studies performed is that surface parameters such as surface roughness, surface topography, or surface free energy overrule the impact of the surface chemistry. However, on a supragingival level, conflicting data have been published regarding differences in biofilm formation on the surface of titanium and zirconia. For instance, Scarano et al. (2004) investigated the area covered by biofilms on specimens that had been exposed to the oral cavity for 24 h, reporting that 19.3% of the available titanium surface but only 12.1% of the available zirconia surface was covered by bacteria. Using a similar supragingival set up with intraoral splints and the DNA checkerboard hybridization, other researchers identified higher number of bacteria adhering to cast

Standardized implant abutment made from titanium

Figure 5.5 Standardized implant abutment made from titanium.

Individually prepared implant abutment made from zirconia

Figure 5.6 Individually prepared implant abutment made from zirconia.

titanium in relation to machined titanium and zirconia (Do Nascimento et al., 2014). In contrast, Rasperini et al. (1998) could not identify significant differences in biofilm formation on the surface of titanium and an experimental zirconia abutment material after 24 h, seven days and 14 days of supragingival biofilm formation. Employing a similar experimental setup, Yamane et al. (2013) investigated supragingival biofilm formation on the surface of potential abutment materials such as titanium, gold-platinum alloy, zirconia, alumina, and hydroxyapatite, and identified significantly fewer adherent bacteria on the gold-platinum alloy than on the other materials. On a subgingival level, clinical studies comparing biofilm formation on the surface of titanium and zirconia identified only very few significant differences. Van Brakel et al. investigated the prevalence and quantity of seven bacterial species relevant for periodontal inflammation on titanium and zirconia abutments using a split-mouth design and the real-time PCR technique for microbial analysis. In addition to similar surface roughness, no significant differences in the prevalence and counts of the bacterial species were identified between the two abutment materials (Van Brakel et al., 2011); similar results have been published by the same group in a later clinical study that investigated titanium and zirconia abutments in a split-mouth design, identifying no significant differences in terms of clinical performance and microbiological parameters (Van Brakel et al., 2014). Comparing the microbiological and clinical performance of a ceramic abutment (Ra 0.06 qm) with a titanium abutment (Ra 0.2 qm), no significant differences in microbial counts and microbial diversity were identified by the Bollen group (1996); similar results have been published by other groups (Salihoglu et al., 2011). The results of these studies indicate that—from a microbiological point of view and biofilm perspective—neither titanium nor zirconia can be favored for application in implant abutments.

In the last years, some promising modifications of titanium implant surfaces have been invented, and some groups analyzed the impact of these modified surfaces on biofilm formation. For instance, Scarano et al. (2003) reported that supragingival biofilm formation on the surface of titanium was significantly higher than on the surface of titanium nitride. In several clinical studies on a supragingival level, GroBner-Schreiber et al. (2004, 2009) investigated biofilm formation on the surface of titanium nitride (TiN)-coated glass, zirconium nitride (ZrN)-coated glass, and titanium as well as unmodified reference surfaces for 24 h and 60 h, observing that fewer microorganisms adhered to the surface of TiN- and ZrN-coated specimens than on unmodified controls; moreover, the authors highlighted that the metabolic activity of the bacteria adherent to the surface of the TiN- and ZrN-coated materials was lower than for those on unmodified titanium (GroBner-Schreiber et al., 2004), while the quality of the microbial community was not substantially impacted (GroBner-Schreiber et al., 2009). However, with regard to the latter aspect, the same group performed a clinical study in a single patient, investigating biofilm formation on the surface of ZrN-coated glass, ZrN-coated polished titanium, and polished titanium at two time points after 24 h and 14 days, observing that the microbial composition of the biofilms on ZrN-coated polished titanium was significantly different from biofilms adherent to polished titanium (Rehman et al., 2012). These observations suggest that both quantitative and qualitative aspects of biofilm formation may be influenced by using modified titanium surface, yet underline that further extensive research is necessary before commercially available modified implant materials can be introduced.

To date, only very limited scientific evidence is available regarding biofilm formation on abutments made from polyether ether ketone (PEEK). A laboratory study investigating the formation of biofilms on the surface of titanium, zirconia, and PEEK showed almost similar biofilm formation on the various materials (Hahnel et al., 2015). These findings are supported by the results of a clinical study analyzing the bacterial colonization of healing abutments made from PEEK and titanium, where no significant differences between PEEK and titanium could be identified. However, the data of this study need to be interpreted with caution, as only small samples of the biofilm adherent to the surfaces have been analyzed by employing the real-time PCR technique (Volpe et al., 2008).

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