The study investigated in vitro the effect of Porphyromonas gingivalis and its cysteine proteases (gingipains) on epithelial cell adhesion to titanium-zirconium alloy surfaces. Titanium-zirconium discs with a standard machined (M) or chemically modified hydrophilic surface (modM) were coated with lamin-5 and incubated with telomerase-inactivated gingival keratinocytes (TIGK). Three P. gingivalis strains or gingipains were either added simultaneously with TIGK or after TIGK cells were already attached to the disks. Adhered TIGK cells were counted at 24 h. All P. gingivalis strains clearly inhibited adhesion of TIGK cells to M and modM surfaces. Compared with bacteria/gingipain-free TIGK cell cultures, the number of attached TIGK cells was reduced by about 80% and 60% when P. gingivalis was added simultaneously or after TIGK cells were already attached to the disks (each p < 0.01), respectively. Counts of attached cells were similarly reduced when only gingipains were used. Adhesion molecules of TIGK cells, in particular E-cadherin, were cleaved by P. gingivalis. In conclusion, P. gingivalis and gingipains interfere with the adhesion of epithelial cells to titanium-zirconium alloy surfaces by cleaving adhesion molecules, while a chemically modified hydrophilic titanium-zirconium alloy surface did not yield any protection. (c) 2019 Wiley Periodicals, Inc. J Biomed Mater Res B Part B, 2019.