Association between Oral Function and Dementia from Epidemiological Studies

As the global population ages, dementia has emerged as a prominent concern in terms of long-term care. Crosssectional studies have shown that individuals affected by dementia have poor oral health. Although longitudinal studies have demonstrated the association of oral health with the onset of dementia and cognitive decline before 2012, these studies were limited and presented inconsistent findings; for example, the association between tooth loss and the onset of dementia and cognitive decline was inconsistent among them. In 2014, a review performed by the authors identified several relevant original articles that found an association between the number of teeth in an individual and the incidence of dementia and cognitive decline. A literature search performed in May 2023 found seven systematic reviews, of which five were meta-analyses, that investigated and substantially supported this association. However, critiques from a life course perspective have been raised, contending that the association between the number of teeth and cognitive function in the older population simply refl ects the disparities between children with normal cognitive function and those with impaired cognitive function at an older age. To generate robust evidence capable of withstanding such criticisms, further epidemiological research that incorporates causal inference and fosters collaboration among epidemiological, clinical, and fundamental research groups is highly desirable.