Within the limitations of an in vitro study, our results indicate that surface roughness as well as wettability may influence the adhesion properties of bacteria on implant surfaces. Furthermore, the predominant factor for adhesion depends on the bacterial species itself. Zirconia implant material did not show any lower bacterial colonization potential than titanium. The influence of substratum material, surface texture, and wettability of implant surfaces on microbial adhesion does not exactly follow universal rules and differs between bacterial species. Additionally, arithmetical mean roughness values R _a (measured by stylus profilometer) are inadequate for describing surface roughness in respect to its potential influence on microbial adhesion. Future studies may use more sophisticated techniques such as confocal microscopy, wide-angle confocal microscopy or laser scanning microscopy in order to gain precise three-dimensional topographical values and to evaluate their influence on microbial adhesion.