A lip seal study of Japanese children with malocclusion.

The purpose of this study was to clarify the relationship between lip seal and malocclusion in Japanese children. Fifty-three patients aged 7 to 14 years (mean 10.24 +/- 1.93) were selected randomly, and compared with 20 subjects with normal occlusion aged 7 to 14 years (mean 10.50 +/- 2.56). The subjects were divided into a good lip seal group and poor lip seal group by observing the distance between the upper and lower lip at rest. The variables that were analyzed for morphological evaluation included model analysis and cephalometric analysis. Noted for functional evaluation were tongue position, the size of the tonsils and adenoids and the oral muscle force measured by button pulling. In the evaluation of the degree of lip seal, there was no statistical difference between subjects with malocclusion and those with normal occlusion. Within the group with malocclusions, however, there were significant differences in overbite (p < 0.01), overjet (p < 0.01), and oral muscle force by button pulling (p < 0.05) between the good lip seal and poor lip seal groups. These results suggest that there is a need not only to correct malocclusion but also to be aware of lip sealing so that it may be improved in Japanese children.