Dynamic change in the thickness of the masseter muscle between contraction and relaxation is associated with the masticatory function in older adults: a cross-sectional study

Abstract

Decreased masticatory function contributes to malnutrition in the elderly. The purpose of our study was to explore whether the masseter muscle is involved in masticatory function in older adults and to help determine if the masticatory function of the elderly can be improved by exercising the masseter muscle. Random sampling was adopted in our research, and a total of 413 older adults from 9 nursing homes in China were recruited from March 10 to June 12, 2022. The thickness and echo intensity of their masseter muscles were assessed using ultrasound. Masticatory function was measured using a color-changing chewing gum, and the change of α* before and after chewing (Δα*) was defined as masticatory function. If Δα* <14.2 in males or <10.8 in females was masticatory dysfunction. Their number of molar occlusal supports (MOSN), comorbidity, oral diadochokinesis (ODK), maximum tongue pressure (MTP), and calf circumference (CC) were evaluated. Multiple linear regression analysis was performed to identify the factors independently associated with the masticatory function. Of the 413 older adults, 179 (43.3%) had masticatory dysfunction. The average thickness of the masseter muscle between contraction and relaxation was 1.3 mm (range, 0.7-2.0 mm). The thickness of the masseter muscle and ODK decreased with age, while the echo intensity of the masseter muscle increased. The results of the multiple linear regression analysis showed that dynamic change in the thickness of the masseter muscle between contraction and relaxation (β=0.085; P=0.049), MTP (β=0.147; P=0.001) and MOSN (β=0.349; P<0.001), brushing teeth ≥2 times/day (β=-0.187; P<0.001), and CC (β=0.135; P=0.002) were independent factors affecting masticatory function. We found that masticatory dysfunction was prevalent among older adults in nursing homes in Southwest China, and the dynamic change in the thickness of the masseter muscle between contraction and relaxation was positively correlated with masticatory function. This result suggests that we can improve the masticatory function of the elderly by increasing the thickness of the masseter muscle between contraction and relaxation (e.g., by exercising the masseter).