In Vitro Effects of Streptococcus oralis Biofilm on Peri-Implant Soft Tissue Cells

Abstract

Human gingival epithelial cells (HGEps) and fibroblasts (HGFs) are the main cell types in peri-implant soft tissue. HGEps are constantly exposed to bacteria, but HGFs are protected by connective tissue as long as the mucosa-implant seal is intact. <i>Streptococcus oralis</i> is one of the commensal bacteria, is highly abundant at healthy implant sites, and might modulate soft tissue cells-as has been described for other streptococci. We have therefore investigated the effects of the <i>S. oralis</i> biofilm on HGEps and HGFs. HGEps or HGFs were grown separately on titanium disks and responded to challenge with <i>S. oralis</i> biofilm. HGFs were severely damaged after 4 h, exhibiting transcriptional inflammatory and stress responses. In contrast, challenge with <i>S. oralis</i> only induced a mild transcriptional inflammatory response in HGEps, without cellular damage. HGFs were more susceptible to the <i>S. oralis</i> biofilm than HGEps. The pro-inflammatory interleukin 6 (IL-6) was attenuated in HGFs, as was interleukin 8 (CXCL8) in HGEps. This indicates that <i>S. oralis</i> can actively protect tissue. In conclusion, commensal biofilms can promote homeostatic tissue protection, but only if the implant-mucosa interface is intact and HGFs are not directly exposed.