A Novel Classification System for Adult Skeletal Class III Malocclusions Based on Maxillary Occlusal Plane Inclinations

To incorporate the maxillary occlusal plane inclinations (MxOP-FH) into the vertical plane classification for skeletal Class III malocclusions. A total of 145 adult patients with skeletal Class III malocclusions (CIII group; 68 males and 77 females; mean age 23.80 y) and 30 individuals with normal occlusion (N group; 14 males and 16 females; mean age 23.96 y) were selected. The mean values of MxOP-FH (6.5 degree for low-angle, 9.7 degree for average-angle, and 11.4 degree for high-angle patients) were recommended as cutoff values to divide 6 subgroups of CIII patients. Pearson correlation analysis examined the relationship between MxOP-FH and 49 key cephalometric variables on their lateral radiographs. One-way analysis of variance and the Tukey-Kramer method compared profile characteristics between the N group and 6 new classifications. The results showed that the high-angle group, with a steeper MxOP, included features of maxilla retrusion and reduced maxillary fullness. Conversely, the high-angle group, with flatter MxOP, displayed significant increases in upper anterior dental height (UADH) and Go-Gn. Besides, the low-angle group, characterized with flatter MxOP, exhibited small values of UADH and nasolabial angle, along with large values of Go-Gn and Ar-Go. This group also showed a high chin-to-lower facial height ratio and excessive chin fullness. In conclusion, for skeletal Class III malocclusions, MxOP-FH angles of 6.5, 9.7, and 11.4 degrees might be helpful to classify 6 new subgroups. Identifying these novel subgroups is crucial in orthodontics, dentofacial orthopedics, and orthognathic diagnosis and treatment planning.