A Three-Item Oral Function Impairment Score Is Associated with White Matter, but Not Gray Matter, Volume Ratio in Older Adults: A Cross-Sectional Study

Background/Objectives: Declining oral function is associated with adverse health outcomes in older adults; however, its relationship with underlying brain structure remains unclear. We examined whether a three-item oral function impairment score (OFIS), based on the number of present teeth, tongue pressure, and oral diadochokinesis (ODK), was associated with white matter (WM) and gray matter (GM) volume ratios in community-dwelling older adults. Methods: This cross-sectional study used data from the 2017 Hirosaki Dementia cohort. The primary analysis included 912 participants after excluding those with missing data or a history of neurological conditions; a sensitivity analysis included participants with neurological conditions (n = 947). One point was assigned for <20 present teeth, tongue pressure <30 kPa, and reduced ODK, yielding an OFIS ranging from 0 to 3, with higher scores indicating impairment across a greater number of oral function domains. WM and GM volume ratios were calculated as tissue volume divided by total intracranial volume. Associations with OFIS were evaluated using multivariable linear regression adjusted for demographic, lifestyle, and vascular/metabolic factors. Results: A higher OFIS was associated with a lower WM volume ratio after multivariable adjustment (B = −0.282; 95% CI, −0.402 to −0.161; p < 0.001). No significant association was observed between the OFIS and GM volume ratio after adjustment (B = 0.066; 95% CI, −0.064 to 0.196; p = 0.319). The association with WM remained consistent in the sensitivity analysis. In separate covariate-adjusted secondary models, each OFIS component was associated with the WM volume ratio. Conclusions: In this cross-sectional study, greater impairment across the three assessed oral function domains was associated with a lower cerebral WM volume ratio, but not GM volume ratio, in community-dwelling older adults.