The Microbiome as a Mediator Between Biocompatibility and Inflammation in the Soft Periodontal and Peri-Implant Tissues of the Diabetic Patient: A Systematic Review

Background: Patients with diabetes mellitus exhibit increased susceptibility to peri-implant inflammation and implant failure due to systemic metabolic dysfunction, impaired immunity, and delayed tissue healing. The oral microbiome is increasingly recognized as a key intermediary in these pathogenic processes. Aims: This review aims to systematically evaluate the available literature examining the relationships among the oral microbiome, biomaterial biocompatibility, and inflammatory changes in peri-prosthetic tissues in insulin-dependent diabetic patients. Methods: A systematic search of PubMed and Scopus databases identified studies published between January 2000 and July 2025. Eligible studies (25 in total) included clinical, histological, microbiological, or immunohistochemical investigations involving diabetic patients rehabilitated with dental implants or prostheses. Study selection and reporting followed PRISMA 2020 guidelines. Results: Diabetic cohorts showed consistent microbial alterations, including a higher relative abundance of periopathogenic species (P. gingivalis, T. forsythia, and F. nucleatum), lower microbial diversity, and greater biofilm-forming potential. Histological analyses frequently described increased inflammatory infiltrates, higher cytokine expression, and reduced soft-tissue integration. Biomaterial surface characteristics were also associated with differences in microbial adhesion, while hyperglycemia was linked to microbial and host-response patterns suggestive of greater pathogenicity and inflammation. Collectively, these findings suggest that diabetes-associated dysbiosis may be associated with increased peri-implant inflammatory changes and altered peri-implant homeostasis. Conclusions: The oral microbiome may be involved in inflammatory activity and biocompatibility at the tissue–implant interface in diabetic patients. A better understanding of host–microbe–material interactions may support risk assessment and help inform future personalized management strategies, such as targeted antimicrobial approaches, probiotic modulation, and biomaterial surface optimization, although these implications should be interpreted cautiously given the predominantly observational and heterogeneous nature of the available evidence.