Differences in dento-facial morphology in lip competence and lip incompetence

Clinicians have hypothesized that lip competence is related to dental inclination, overjet, and overbite. Though some studies have been made to clarify this interrelation, a distinctive conclusion has not been reached. Studies have further shown that some subjects with normal occlusion show lip incompetence. Considering this, it could be hypothesized that dento-facial morphology plays a role in the causes of lip incompetence. To establish this it is necessary to distinguish dento-facial morphology factors from occlusal conditions such as overjet or overbite.A number of methods evaluate lip sealing: visual examination, cephalometric radiographs, and others; however these methods make determinations for short periods, and none evaluate the lip competence directly.The purpose of this study is to elucidate a correlation between lip competence and dento-facial morphology using subjects with normal occlusion, excluding overbite and overjet factors, with a sufficiently reproducible and reliable method to evaluate lip sealing.The study shows that individuals with normal occlusion (n = 30) can be divided into 3 groups based on lip sealing ability: a competent, a partially competent, and an incompetent group. Statistical evaluations showed morphologically significant differences between these groups on SNA, ANB, NA-Pog, NPog-A, ANS-Me, N-ANS/ANS-Me, ANS-Me/N-Me, Wits appraisal, L1-MP, NPog-U1, NPog-L1, and FMIA measurements.According to the results, more skeletal class II relationships, longer anterior lower facial height, and a backward positioned Pogonion were observed, in the group with lip incompetence.