Anterior and Posterior Occlusal Plane Inclinations Differ Between Class II and Class III Mixed Dentitions-A Retrospective Cross-Sectional Study of a Morphological Characteristic.

Background: To investigate if the sagittal inclinations of anterior occlusal plane (AOP) and posterior occlusal plane (POP) differ between skeletal classes II and III in the mixed dentition period. Methods: Retrospective analysis of cross-sectional lateral cephalometric radiograph data of 61 children with skeletal class II and 60 children with skeletal class III (average age 8.4 ± 1.5 years). We measured the inclinations of AOP and POP to the Frankfort horizontal (FH) and the sella-nasion line (SN). Angles FH-AOP, FH-POP, SN-AOP, and SN-POP were compared between both groups using model-based ANOVA F tests and quantile regressions. Results: The differences in means between the groups came to 1.3° ± 5.1 (FH-AOP), 1.8° ± 4.6 (FH-POP), 2.6° ± 5.3 (SN-AOP), and 5.5° ± 4.4 (SN-POP). In the ANOVA, angles SN-AOP, FH-POP, and SN-POP differed significantly between the groups (p = 0.041, p = 0.006, p < 0.001, respectively). Quantile regressions showed significant between-group differences for FH-AOP (lower quartile, p = 0.012), FH-POP (upper quartile, p = 0.006), SN-AOP (median, p = 0.004; upper quartile, p = 0.011), and SN-POP (all 3 quartiles, p < 0.001). Conclusions: Distinct occlusal plane inclinations of mixed dentitions represent diagnostic traits. Longitudinal and interventional data are needed if therapeutic flattening of mixed dentition AOP or POP is beneficial in treating skeletal class II, same as their steepening in skeletal class III. Our clinical hypothesis suggests alterations by approximately 3° (AOP) and 6° (POP) but requires further study and confirmation.