: There is emerging evidence that several oral diseases and conditions can be associated with DM. Dental caries, hyposalivation, fungal diseases and endodontics lesions may represent potential oral complications that can be aggravated by chronic hyperglycemia. Individuals with DM have a low perception of oral diseases which can lead to clinically important oral and systemic complications. This review aims to provide data on the most common oral signs and symptoms related to DM and to explore the mechanisms that might explain associations between DM and oral diseases in order to clarify the risks posed by poor oral health in DM. Since the linkage between oral diseases and DM is part of multifactorial aspects related to chronic hyperglycemic status and several common conditions affecting the whole body, both require rigorous self-control from patients and attention from medical and dental professionals.