The median surface roughness values (R _a ) of each material group (n = 10) tested are shown in Table 1. The differences in R _a between rough, medium, and smooth specimens were statistically significant for ceramic as well as for titanium (p < 0.01 for all comparisons). The roughness values of rough and medium ceramic specimens (1.32 μm/0.49 μm) were significantly lower than those of titanium specimens (2.98 μm/0.83 μm; p < 0.01 for both comparisons). No significant difference was found between the R _a of smooth titanium and smooth ceramic specimens (0.09 μm/0.05 μm; p = 0.983).

The median water contact angles (wettability) of each specimen are given in Table 1. All four hydrophobic surfaces showed significantly higher contact angles than the corresponding hydrophilic surfaces (p < 0.01 for rough ceramic, smooth ceramic, rough titanium, and smooth titanium). Roughness values did not change after hydrophilization or hydrophobization (data not shown).

Examples of the atomic force micrographs are given in Fig. 1a–d (30 μm × 30 μm = 900 μm² scan area), e–h (3 μm × 3 μm = 9 μm² scan area). Considerably higher roughness values could be observed on the sandblasted ceramic and titanium surfaces than on the corresponding polished surfaces. Neither the 900 μm² scan areas nor the corresponding AFM roughness profiles showed any well-defined differences between ceramic and titanium for smooth and rough specimens (Fig. 2a). On closer examination (9 μm² scan areas), small grooves (measuring approximately 0.5 μm in diameter and 0.08 μm in height) could be observed on the smooth ceramic substrata (Fig. 1g), whereas the smooth titanium surfaces seemed to be totally plane (Fig. 1h). Furthermore, the microstructure of rough titanium appeared to be significantly more irregular than the smooth titanium surface and both ceramic surfaces (Fig. 2b).

The relative fluorescence intensities (rfi) for S. epidermidis, indicating the quantity of adhering staphylococci, narrowly varied between 2931 and 2697 relative fluorescence units (rfu) (Fig. 3a). Except for smooth titanium (2931 ± 99 rfu), on which significantly more adhering bacteria were found than on medium titanium (2697 ± 127 rfu; p = 0.002) and rough titanium (2734 ± 145 rfu; p = 0.014), variations in surface roughness did not lead to any differences in adhering S. epidermidis. The differences in staphylococcal adhesion on smooth (2908 ± 74 rfu), medium (2789 ± 143 rfu), and rough (2749 ± 162 rfu) ceramic specimens were not statistically significant (p > 0.05 for all comparisons).