On the influence of Streptococcus salivarius on the wear response of dental implants An in vitro study

This study aims to understand microorganisms' effect and relevance of aseptic conditions on wear performance of dental materials. Tribocouple zirconia/titanium was submitted to tribological tests in the presence of Streptococcus salivarius biofilm, the most abundant bacteria in the oral cavity. Reciprocating ball-on-plate tests were carried out at 37°C, pH 7, 2 N, and 1 Hz, during 2 h, using Ti6Al4V balls as pins and Y-TZP plates. Simultaneous OCP readings assessed corrosion tendency. Tested lubricants were artificial saliva, artificial saliva plus glucose, and artificial saliva plus glucose and S. salivarius. Wear volume and worn surfaces were analyzed after test. S. salivarius proliferation was enhanced in artificial saliva plus glucose. When a highly populated biofilm was present at the zirconia/titanium interface, titanium wear decreased by ~60% compared to artificial saliva and artificial saliva plus with glucose, respectively, with 0.0060 and 0.0053 mm³ loss. Wear was not observed in zirconia under any tested condition. Presence of S. salivarius also decreased corrosion activity during wear. Lowest free OCP value reached during sliding was −260 mV in artificial saliva, −246 mV in artificial saliva plus glucose, and −196 mV in artificial saliva plus glucose and bacteria. This decreased to −147 mV when a highly-populated S. salivarius biofilm was present at the interface. Overall, obtained results show that the presence of S. salivarius clearly changes the corrosion-wear performance of the tested dental materials, confirming that it must be recognized, and that asepsis level and conditions during wear test of dental materials must be clearly established and controlled to ensure reproducible results and supported conclusions.