The Role of Implant Coronal Surface Properties on Early Adhesion of Streptococcus Oralis—An In Vitro Comparative Study

Dental implant coronal surfaces designed with the primary goal of maintaining crestal bone levels may also promote bacterial adhesion, leading to soft tissue inflammation and peri-implant bone loss. Achieving an optimal surface roughness that minimizes bacterial adhesion while preserving crestal bone is crucial. It is hypothesized that a specific threshold surface roughness value may exist below which, and above which, initial bacterial adhesion does not statistically change. This study evaluated 12 commercially available and 2 custom-designed implant surfaces for their physicochemical properties and initial bacterial adhesion, as represented by Streptococcus oralis (S. oralis) the dominant initial colonizer of the successive waves of bacterial consortia that result in plaque and biofilm formation. Implants were immersed in a S. oralis suspension for 4 h, after which microbial viability was assessed. Marked differences were observed in surface roughness, chemical composition, and wettability, and S. oralis adhesion. Surfaces with Sa > 1 μm had significantly more adherent bacteria after 4 h compared to those with Sa < 1 μm, despite complexity. Adding nanotopography to dual-acid etched surfaces further reduced bacterial adhesion compared to surfaces without these features. The role of chemical composition and wettability was less influential than roughness. In conclusion, there is a cut-off threshold roughness around Sa = 1 μm, above which the adhesion of bacteria increases significantly to a plateau level; while below which, bacterial adhesion is equivalent to a machined surface despite the surface texture of the implant collar.