The Position of the Virtual Hinge Axis in Relation to the Maxilla in Digital Orthognathic Surgery Planning-A k-Means Cluster Analysis.

The aim of this study was to investigate a possible relation between skeletal phenotypes and virtual mounting data in orthognathic surgery patients. A retrospective cohort study including 323 female (26.1 ± 8.7 years) and 191 male (27.9 ± 8.3 years) orthognathic surgery patients was conducted. A k-means cluster analysis was performed on the mounting parameters: the angle α between the upper occlusal plane (uOP) and the axis orbital plane (AOP); the perpendicular distance (AxV) from the uOP to the hinge axis; and the horizontal length (AxH) of the uOP from upper incisor edge to AxV, with subsequent statistical analysis of related cepalometric values. Three clusters of mounting data were identified, representing three skeletal phenotypes: (1) balanced face with marginal skeletal class II or III and α=8∘, AxV = 36 mm and AxH = 99 mm; (2) vertical face with skeletal class II and α=11∘, AxV = 27 mm and AxH = 88 mm; (3) horizontal face with class III and α=2∘, AxV = 36 mm and AxH = 86 mm. The obtained data on the position of the hinge axis can be applied to any digital planning in orthognathic surgery using CBCT or a virtual articulator, provided that the case can be clearly assigned to one of the calculated clusters.