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

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.

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.

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.

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.