There are practical and cost-effective opportunities for the prevention and early intervention of periodontal disease, a common oral condition. Depression and anxiety represent major global mental health challenges, and they are characterized by high prevalence rates and an elevated suicide risk. Their clinical management is complicated by extended treatment timelines and substantial healthcare costs. Accumulating evidence demonstrates a statistically significant bidirectional association between periodontal disease and depression/anxiety disorders. However, established clinical pathways integrating these conditions remain lacking. This review presents a comprehensive analysis of current research examining the relationship between periodontal disease and mood disorders, specifically depression and anxiety. This study explored the bidirectional mechanisms within the microbiota-oral-brain axis, which includes both periodontal disease inducing neuroinflammation through pro-inflammatory factors, such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) activating the TLR-4/NF-κB signaling pathway, and depression and anxiety leading to “glucocorticoid resistance” through hypothalamic-pituitary-adrenal (HPA) axis dysregulation, thus causing dual immune dysfunction that exacerbates periodontal tissue destruction, as well as the mechanisms by which biological, psychological, and social factors contribute to the bidirectional association between periodontal disease and depression/anxiety. We propose implementing bidirectional referral protocols between dental and psychiatric services in clinical practice, incorporating mental health screening tools, such as Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder-7(GAD-7), for patients with moderate-to-severe periodontal disease, and incorporating periodontal examination into routine assessment during psychiatric services. This multidisciplinary approach aims to break the vicious circle between these conditions and provide clinicians with pragmatic intervention strategies.