Diabetes mellitus and periodontal disease are among the most frequently occurring conditions that have a substantial effect on the global health economy. The literature regarding medical professionals’ knowledge of the bidirectional link between diabetes mellitus and periodontal disease has not been analyzed systematically. The review aimed to investigate the knowledge and understanding of physicians and specialists regarding the two-way relationship between diabetes mellitus and periodontal disease and their approach to referring their patients for a dental consultation. An electronic search of PubMed and Google Scholar databases was conducted to review the studies that assessed knowledge and understanding of medical professionals regarding the relationship between diabetes mellitus and periodontal disease. Data from 13 included studies involved 4,027 participants: 3,256 primary care physicians and 771 medical specialists. Just over 50% of the medical professionals had an understanding of oral health and/or periodontal disease. Over one-third of medical professionals were ignorant of the relationship between oral health and diabetes mellitus. Only 30% reported ever referring their patients for an oral health assessment. Another key finding of the investigation was the absence of interprofessional collaborative care between medical and dental professionals while managing patients with diabetes mellitus. Medical professionals with an integrated knowledge of elementary oral health education and training could play a central role in the timely diagnosis and management of periodontal disease in patients living with diabetes mellitus.