Objective: The aim of this study was to compare the differences of the mandibular posterior anatomic limit (MPAL) distances stratified by vertical patterns in skeletal Class III malocclusions using cone-beam computed tomography (CBCT).
Methods: CBCT images of 48 skeletal Class III patients (mean age, 22.8 ± 3.1 years), stratified by the vertical pattern (hypodivergent, normodivergent, and hyperdivergent) groups of 16 were analyzed. While parallel to posterior occlusal line, the shortest linear distances from the distal root of mandibular second molar to the inner cortex of mandibular body were measured at depths of 4, 6, 8 mm (D4,6,8mm) from cementoenamel junction. The MPAL distances were compared between the hypodivergent, normodivergent, and hyperdivergent pattern groups and their correlations were analyzed.
Results: There was no significant difference between the mean ages, gender distribution, asymmetry, or crowding of three groups. MPAL distance was significantly longer in males (3.8 ± 2.6 mm) than females (1.8 ± 1.2 mm) at the 8-mm root level. At all root levels, the MPAL distance was significantly different in the hypodivergent and hyperdivergent (p<0.001), as well as between the normodivergent and hyperdivergent group (p<0.01). The MPAL distances were the shortest in the hyperdivergent group. SN-GoGn angle is highly correlated with the MPAL distance at all root levels (p<0.01).
Conclusions: The MPAL distances were shortest in patients with hyperdivergent patterns and had a decreasing tendency as the SN-GoGn angle increased. The MPAL distances were significantly shorter at the 8-mm root level, the most critical root level, which was about 3.16 mm.

Keywords: Class III treatment, CT, Distalization, Alveolar bone housing