From gums to moods: Exploring the impact of the oral microbiota on depression

Depression is a complex and heterogeneous disorder that results from a combination of genetic vulnerability, environmental stressors, and dysregulated biological processes. While systemic inflammation and gut dysbiosis have been extensively investigated in the context of depression, the role of the oral microbiome has only recently begun to emerge. The oral microbiome is a highly diverse and dynamic ecosystem, comprising bacteria, fungi, viruses, and archaea, which coexist in a delicate balance with the host's immune system. This microbial community plays a fundamental role in maintaining not only oral health, but also systemic homeostasis. Emerging evidence suggests that disruptions in this balance, or oral dysbiosis, may contribute to a range of systemic inflammatory conditions, including psychiatric disorders such as depression. Factors comprising periodontal disease, dental infections, and poor oral hygiene can lead to an imbalance in oral microbial composition, promoting immune system activation, chronic inflammation and microbial translocation, which are increasingly recognised mechanisms involved in the pathophysiology of depression. This review delves into the emerging evidence linking oral dysbiosis to depression, elucidating the underlying biological mechanisms and their clinical implications. By bridging the gap between oral health and mental well-being, it underscores the importance of a multidisciplinary approach in addressing depression—one that extends beyond conventional psychiatric treatments to include oral health interventions as a viable component of comprehensive care strategies.