Three-dimensional analysis of maxillary alveolar bone and point A remodeling after premolar-extraction decompensation in patients with skeletal Class III malocclusion.

INTRODUCTION This study evaluated the remodeling patterns of point A (subspinale) and the maxillary alveolar bone after premolar-extraction decompensation in patients with skeletal Class III malocclusion.

Methods

Cone-beam computed tomography data from 40 patients with skeletal Class III malocclusion were collected before and after presurgical decompensation (pre-DC and post-DC). A 3-dimensional cephalometric analysis was used to evaluate dentoskeletal changes. Surface-based registration and voxel-based analysis were used to assess anterior maxillary displacement. The root length, alveolar bone height, and thickness were measured for the maxillary anterior teeth. Pearson correlation was used to analyze the associations between point A and other parameters.

Results

SNA, FH-NA, U1-SN, and U1-NA decreased by 1.22°, 0.99°, 9.43°, and 7.06° (P < 0.001). All landmarks moved posteriorly (P < 0.001): point A by 1.07 mm, superior prosthion by 3.87 mm, maxillary central incisor incisal midpoint by 5.28 mm, and root apex by 2.26 mm. Bodily movement of the anterior teeth accounted for an average of 41% of the retraction, and tipping accounted for 59%. Point A retraction was weakly positively correlated with SNA (r = 0.336), FH-NA (r = 0.312), and the proportion of bodily retraction (r = 0.288) and weakly negatively correlated with U1-SN (r = -0.306), U1-NA (r = -0.354), and the proportion of tipping retraction (r = -0.288). However, Bonferroni correction substantially reduced the significance of these correlations. The maxillary anterior teeth showed partial root resorption (mean, 1.11-1.97 mm); the palatal alveolar bone thinned significantly in the cervical and middle thirds, whereas labial bone volume increased apically.

Conclusions

Decompensation typically displaces maxillary teeth, alveolar bone, and point A posteriorly in patients with skeletal Class III malocclusion, frequently accompanied by palatal alveolar bone resorption. Hard-soft tissue remodeling resulting from changes in tooth position and point A should be incorporated into initial treatment planning to individualize the mode and amount of maxillary incisor retraction, which is critical for patients with Class III malocclusion who are ineligible for bimaxillary surgery or who require only mandibular surgery.