Comparison of Different 3D Surface Registration-Based Methods to Assess Facial Asymmetry

Facial asymmetry is gaining an increasing diagnostic interest in many clinical contexts. Several three-dimensional surface-based methods have been proposed for its assessment; however, they might provide non-equivalent data. Since there is a lack of comparative studies in these terms, this study aims to compare three methods for assessing the asymmetry of the face and facial thirds, thus addressing whether the potential differences can be considered clinically acceptable or not. Two 'maxillofacial' methods based on the trigeminal nerve distribution and one 'orthodontic' method based on reference horizontal planes were used to identify the facial thirds on 3D facial models of 80 Italian healthy adults to calculate the asymmetry of the face, and the upper, middle, and lower thirds of the face differently selected by each method. As a measure of asymmetry, the Root Mean Square value was calculated through a mirroring surface-based registration. Intra- and inter-operator reliability was verified for each method. Differences and interchangeability between the methods were tested, respectively, by two-way repeated measures ANOVA (Analysis of Variance) and Bland-Altman and Similarity Percentage model analysis. Additionally, the time required to perform each method was assessed. All methods demonstrated excellent intra- and inter-operator reliability. While the ANOVA analysis found significant differences ( < 0.001) for the majority of facial Regions of Interest between each method, the Bland-Altman analysis revealed that the differences were clinically acceptable (