Evaluation of Nasolabial Angle in Skeletal Class Iii Malocclusion Patients

Objective: To evaluate the nasolabial angle changes between closed lip position at centric occlusion and relaxed lip position at which the bite is open so that the lips do not touch and to elucidate the significance of the relaxed lip position for dentofacial diagnosis. Methods: To determine whether the nasolabial angle at closed lip position were different from that at relaxed lip position, a paired t-test was used. To elucidate skeletal and dental variables which are correlated with nasolabial angle changes between two lip positions, Pearson correlation analysis was used. Using the cluster analysis, the subjects were divided into three groups according to the pattern of nasolabial angle change : Group1 (27 persons, -8°Æ ~1°Æ), Group 2 (30 persons, 2°Æ ~ 17°Æ), and Group 3 (3 persons, over 18°Æ). And one-way analysis of variance(ANOVA) was used to compare the dentofacial characteristics among groups. Results: In skeletal Class III malocclusion adult patients, there were significant differences in the nasolabial angle changes between closed lip position and relaxed lip position. The changes in the nasolabial angle were greater in the patients with the following conditions: more hypodivergent pattern, greater antero-posterior dysplasia, greater dental compensation of the lower incisor, more protrusive and shorter upper lip. Conclusion: The results showed that the pattern of the nasolabial angle change between closed lip position and relaxed lip position varies according to dentofacial characteristics of skeletal Class III malocclusion patients. Thus, relaxed lip position should be taken into account when diagnostic records are obtained and analyzed to accurately evaluate the facial soft tissues and predict facial esthetics after surgical-orthodontic treatment.