Kazuhiro Yamada

Background The relationship between the maximum lip‐closing force (LCF) and malocclusion has long been studied. Recently, a method to measure the ability to control directional LCF from eight directions (upper, lower, right, left and the four directions in between) during lip pursing was established. Objective It is considered important to evaluate the ability to control directional LCF. The aim of this study was to investigate the ability of skeletal class III patients to control directional LCF. Methods Fifteen skeletal class III patients (mandibular prognathism group) and 15 people with normal occlusion (normal occlusion group) were recruited. The maximum LCF and the accuracy rate (the ratio of the matched time in which the participant was able to keep the LCF in the target range over a total time of 6 s) were measured. Results The maximum LCF was not significantly different between the mandibular prognathism group and the normal occlusion group. The accuracy rate in the mandibular prognathism group was significantly lower in all six directions than that in the individual normal occlusion group. Conclusion As the accuracy rate in all six directions was significantly lower in the mandibular prognathism group than that in the normal occlusion group, occlusion and craniofacial morphology might influence lip function.