Association between number of teeth and functional tooth units and prevalence of mild cognitive impairment in Japan: Baseline data from the Aidai Cohort Study

Background Epidemiological studies have suggested a possible association between tooth loss and dementia, yet evidence regarding mild cognitive impairment (MCI) remains limited. Objective We examined the association between the number of remaining teeth and functional tooth units (FTUs) and the prevalence of MCI. Methods A total of 8697 adults aged 20–95 years (3786 men and 4911 women) were included. Dental status was assessed visually, excluding third molars. MCI was defined as a score of less than 26 on the Japanese version of the Montreal Cognitive Assessment. Participants were categorized into five groups based on the FTUs of natural teeth (n-FTUs) and total FTUs: n-FTUs ≥10; n-FTUs 6–9 and total FTUs ≥10; n-FTUs 6–9 and total FTUs <10; n-FTUs <6 and total FTUs ≥10; and n-FTUs <6 and total FTUs <10. Results The prevalence of MCI was 35.5%. A reduced number of teeth was significantly associated with the higher prevalence of MCI ( p for trend <0.0001). Compared with having n-FTUs ≥10, having n-FTUs <6 and total FTUs ≥10, and having n-FTUs <6 and total FTUs <10 were independently associated with a higher prevalence of MCI. There was no association between having 6–9 n-FTUs, regardless of total FTUs, and the prevalence of MCI. Conclusions Even when occlusal function is maintained through prosthodontic restorations, a reduced number of natural teeth is independently associated with MCI, underscoring the importance of preserving natural dentition for maintaining cognitive health.