The problems involved in osseous healing of dental implants appear to be largely solved. Biofilm formation on exposed implant and abutment surfaces, however, is a fortiori crucial for the long-term therapeutic success of an implant, because biofilms are the most frequent cause of peri-implantitis and implant loss [3,4,5,6,7]. Consequently, new implant surface modifications with reduced properties to accumulate microorganisms or even with antibacterial properties are of pertinent clinical interest [8, 9]. In general, the physico-chemical surface properties of an implant—influenced by the type of material, its surface morphology, and surface coatings—define the potential to adhere oral microorganisms [4, 10, 11]. In this context, surface roughness and hydrophobicity seem to be the main material-linked factors influencing microbial adhesion and biofilm formation on implant surfaces [12, 13]. Therefore, the main object of the present study was to investigate bacterial adhesion on different titanium and ceramic implant surfaces, to correlate these findings with surface roughness and surface hydrophobicity, and to define the predominant factor for bacterial adhesion for each material group.

In dental implantology, titanium is the most frequently and most successfully used “gold standard” material because of its biocompatibility and excellent mechanical properties. The surface structure of titanium can be modified very easily by sandblasting, acid etching, plasma spraying, etc. to optimize integration into the surrounding bone [14]. Recently, high-strength zirconia implant materials (ZrO₂) have been invented as an alternative to titanium because of their resistance to corrosion and their enhanced esthetics in case of exposure and because dental ceramics are generally regarded as biomaterial with low potential to accumulate biofilms [15,16,17,18]. In fact, very little information is available on the microbial performance of zirconium implant materials. Some recent studies about biofilm formation on implant surfaces have concluded that zirconium oxide may have lower bacterial colonization potential than titanium [4, 18], an effect that is attributed to the specific chemical structure and the resulting electric conductivity of zirconia [4, 10, 19]. In contrast, other studies have not indicated such superiority of zirconia with regard to its microbial performance but have shown that the development of biofilm is not influenced by the type of material surface [9, 10, 20, 21]. The results of the present study are not unambiguous with regard to the influence of the substratum material (titanium vs. zirconia) on bacterial adhesion. We could not find any difference between the bacterial accumulation on titanium and ceramic for S. epidermidis, but the potential to adhere S. sanguinis was significantly higher on ceramic than on titanium. Some authors reported antibacterial effects for titanium, which may be a further explanation for the rather low amounts of adhering bacteria on titanium [22, 23]. Furthermore, titanium is coated by a layer of surface oxide, which physical and mechanical characteristics are more closely related to ceramic than to metal. This phenomenon may explain why similar protein-binding properties on titanium and zirconium oxide have been reported and why zirconia did not show any reduced bacterial adhesion in the present study [20].