Age-related differences in maximum voluntary lip-closing force and ability to control lip-closing force

Deterioration of lip function in the elderly is a form of oral hypofunction. It is important to understand age-related changes in lip function to improve oral health. This study aimed to quantitatively compare the maximum lip-closing force (LCF) and the ability to control LCF during voluntary lip-pursing movements between elderly and young adults and clarify the influence of aging on both measurements.

Using a multidirectional LCF measurement system, we measured six-directional maximum LCFs (upper, upper right, lower right, lower, lower left, upper right) of 20 healthy elderly men (69.6 ± 4.2 years) and 20 healthy young men (25.1 ± 3.8 years). The ability to control the LCF in each direction was assessed based on the accuracy rate. The directional LCF and the ability to control LCF were compared between the elderly and young adults.

The maximum directional LCF in the elderly adults was significantly smaller than that in the young adults in three directions from the lower lip; moreover, the accuracy rate of the elderly adults was significantly lower than that of young adults in five of the six directions.

Our findings suggest that the influence of aging on the accuracy of LCF may be different from that on muscle strength. Hypofunction of the lips due to aging may result not only from decreased muscle strength but also from reduced LCF accuracy.