The Oral–Gut Microbiome Connection in Patients with Periodontitis: A Systematic Review

Background and Objectives: This study aims to evaluate the recent literature on the oral–gut connection in the context of periodontal disease, emphasizing the significance of systemic risk associated with chronic inflammation. This review explores whether chronic inflammation resulting from periodontal disease can induce systemic conditions through alterations in the gut microbiome and whether periodontal treatment may contribute to overall health improvement. Materials and Methods: A systematic database search was performed using pre-established search strategies. Searches were conducted in three databases between 1 and 20 October 2025. A total of 578 articles were screened for eligibility based on inclusion and exclusion criteria. Two authors agreed on the selection process used. The methodological quality of the included studies was assessed using the Newcastle–Ottawa scale and the Risk of Bias 2 Tool. Results: Eleven studies were considered eligible for inclusion in the review. The gut microbiome is similar to the oral microbiome in patients with periodontitis. Gut microbial shifts may drive systemic inflammation and metabolic dysfunction. Tooth loss and gum disease are linked to alterations in the gut bacteria, potentially compromising the intestinal barrier permeability. In contrast, the presence of natural teeth may prevent oral–gut bacterial transmission. Changes in the gut microbiota are correlated with improvements in periodontal status after non-surgical periodontal therapy. Conclusions: The evidence presented in this review supports an association between periodontitis, oral–gut microbial alterations, and systemic inflammatory conditions. However, most available studies are observational, limiting causal inference. Targeted modulation of the gut microbiome may represent a promising area for future research, but its clinical applicability remains inconclusive.