Decline of oral functions in old-old adults and their relationship with age and sex: The SONIC study

Background: Many physical functions decline with aging, but it is not known whether oral functions vary according to sex or decline with aging, as it occurs with physical functions. The present study aimed to examine the association of sex, age, and elapsed years with occlusal force and tongue pressure using a generalized linear mixed-effect model (GLMM) over a 3-year period among old-old Japanese adults. Methods: Participants were community-dwelling older adults who participated in a survey (June 2014–March 2017) and a follow-up survey (July 2017–December 2019) after 3 years (n = 951: 70-year group, n = 466; 80-year group, n = 391; 90-year group, n = 94). Dental examinations including the number of teeth, occlusal force, and tongue pressure were conducted, and a GLMM was used to estimate the association of sex, age, and elapsed years with occlusal force and tongue pressure, adjusting for the number of teeth. Results: The GLMM showed that occlusal force was significantly associated with sex (reference; male, non-standardized coefficient: B = −66.9 [female], p < 0.001), age (reference; 70-year group, B = −81.7 [80-year group], p < 0.001, B = −87.2 [90-year group], p < 0.001), and the number of teeth (B = 13.8, p < 0.001), but did not significantly decrease with elapsed years. Tongue pressure was significantly associated with sex (reference; male, B = −0.94 [female], p = 0.034) and age (reference; 70-year group, B = −1.78 [80-year group], p < 0.001, B = −5.47 [90-year group], p < 0.001). Tongue pressure decreased significantly with elapsed years (B = −0.82, p < 0.001). Conclusions: These findings suggest that tongue pressure significantly decreased over time, but occlusal force did not. Tongue-related muscles may be more susceptible to aging than masticatory muscles.