Effects of varying anteroposterior craniodentofacial morphologies on three-dimensional smile variables.

Background/purpose: Research regarding clinical facial assessment has increasingly shifted toward three-dimensional (3D) methods. This cross-sectional study examined the associations between 3D smile variables and two anteroposterior craniodentofacial morphologies (overjet [OJ] and point-A-nasion-point-B angle [ANB]) and quantified facial soft tissue displacement during the transition from rest to posed smiles. Materials and methods: This study included 119 participants aged 18-30 years. They were divided into three OJ groups (0-4 mm, >4 mm, and <0 mm) and three ANB groups (0°-4°, >4°, and <0°). 3D facial images were taken at rest and during smiling. Subsequently, landmark positions were analyzed. Linear, angular, and proportional measurements were obtained, and landmark displacements were measured. Results: Of the 257 3D soft tissue variables considered, 41 differed significantly among the 3 OJ groups, and 46 differed significantly among the 3 ANB groups during smiling. The intercommissural width measured during smiling in ANB group 1 was more significant than that in the other two groups. Labiomental angles were larger in ANB group 3 at rest and during smiling, whereas the angle at rest was smaller in OJ group 2. Lower lip movements in OJ group 3 and ANB group 3 were more restricted than those in groups 1 and 2. Conclusion: OJ and ANB primarily affect soft tissue landmarks during smiling. A large OJ may lead to a deep labiomental sulcus, whereas a negative ANB may result in a flattened sulcus. Reverse OJ and Class III skeletal malocclusion affect the lower lip by restricting its movement.