Relationship between displacement of the masseter muscle during biting and masseter muscle quality and bite force in healthy elderly persons.

Abstract

Although age-related changes in muscle quality influence muscle strength, the relationship between masseter muscle (MM) quality and maximum biting force (MBF) has never been studied. The aims of the study were to verify the relationship among MM quality, MBF, and the displacement of the MM while biting forcefully (MMD) and to clarify the age-related decline in MBF in healthy elderly persons. Seventy-four healthy community-dwelling individuals (mean age, >65years) from Tokyo metropolis were recruited. The thickness (index of muscle quantity), echo intensity (index of muscle quality) and displacement of the MM while biting forcefully (MMT, MMEI and MMD, respectively) were measured by ultrasonography. MBF was measured using a pressure-sensitive sheet. Independent predictors of MBF and MMD were determined using multivariate linear regression analyses adjusted for age, sex and the number of present teeth. MBF was significantly correlated with the number of teeth (β=0.577, P<.001) and MMD (β=0.302, P=.015), but not with MMT (β=0.019, P=.868) or MMEI (β=0.054 P=.703). MMD was significantly correlated with MMEI (β=-0.606, P<.001), but not with MMT (β=0.048, P=.681) or the number of teeth (β=0.065, P=.613). MMEI was associated with MMD, an index of MBF, regardless of tooth number. The age-related quality change in the MM might cause a decrease in its contraction, resulting in age-related decline in MBF.