Relationship between Balance of Upper and Lower Lip-Closing Forces during Pursing-like Lip-Closing and Lateral Craniofacial Morphology

The aim of this study was to clarify the relationship between the balance of upper-and lower-lip-closing forces (LCF) during pursing-like lip-closing and lateral craniofacial morphology.Sixty-two females with malocclusion were subjected to lateral cephalography and divided into 3 groups (skeletal Classes I, II and III) by the value of ANB.The LCF was measured using a multidirectional LCF measurement system, which could assess eight directional LCF during pursing-like lip-closing.Statistical analysis by the comparison of values among the groups was performed by the Kruskal-Wallis test, and correlation coefficients were tested by Pearson's product-moment correlation.Significance was set at P < 0.05.Total upper LCF, which was the sum of upper, right and left upper directional LCF, in Class II was significantly greater than that in Class I.The balance index of upper and lower LCF in group II was significantly higher than that in group III.There were weak positive correlations between upper LCF and FMA, and the balance index of upper and lower LCF and ANB or convexity, whereas there was a negative correlation between FMIA and the balance index of upper and lower LCF.These findings support the concept of dental compensation for anterior-posterior malposition of the maxillary and mandibular regions by inclination of the incisors.