Abstract
The objective of this study was to clarify the relationship between lip-closing function, which was evaluated by lip-closing force (LCF) measured by the novel developed multidirectional LCF measurement system, and lip morphology or anterior teeth occlusion in the early stage of permanent anterior teeth occlusion. In 242 primary school children (136 boys, 106 girls, mean age = 10.3 ± 0.3 years), LCFs in eight directions during maximum voluntary pursing-like lip closure tasks, Overjet (OJ), overbite (OB) and a lateral facial snapshot were recorded in three primary schools in Nagano. The presence of the shrinkage of the chin skin at rest (contraction) was evaluated during taking a facial snapshot. From lateral facial snapshots, the ratios of heights of the lips including upper labial, vermillion and lower labial ratios (proportions of part of the lips relative to the total labial height obtained through the planes perpendicular to the Frankfurt plane) were evaluated. Correlation analyses were performed between LCF and these morphological variables. There was a weak correlation between [Upper] {the proportion of directional LCF from upper direction to total LCF (TLCF)} or [Upper + Lower] and OJ in girls and between TLCF and lower labial ratio in both genders. TLCF and DLCF obtained from lower direction in boys with contraction were significantly smaller than those without contraction. We concluded that the focal lip morphology and the characteristic of anterior teeth occlusion are related-factors to LCF.
