Influence of Incisor Inclination on Alveolar Bone Remodelling in Mandible During Presurgical Orthodontic Decompensation in Class III Patients.

Objective: This study aims to investigate the correlation between alveolar bone loss and IMPA (Incisor Mandibular Plane Angle) in individuals with skeletal Class III malocclusion during pre-surgical orthodontic decompensation (POD).

Materials and methods: This retrospective cohort study evaluated 90 Class III patients, grouped by initial IMPA into Low-IMPA group (IMPA ≤ 78.5°), Moderate-IMPA group (78.5 < IMPA ≤ 85.7) and High-IMPA group (IMPA > 85.7), and by IMPA change into Small-change group (change ≤ 3.7°), Moderate-change group (3.7 < change ≤ 8.17°) and Large-change group (change > 8.17°). Cone-beam computed tomography (CBCT) measured alveolar bone area (ABA), vertical bone level (VBL), mid-root horizontal thickness (mHBT) and apical horizontal thickness (aHBT). Mandibular regional superimpositions were used to measure horizontal and vertical movements of the incisal edge and root.

Results: Before POD, mHBT, aHBT and ABA were highest in the High-IMPA group and lowest in the Low-IMPA group, while VBL was highest in the Low-IMPA group and lowest in the High-IMPA group. After POD, significant changes were observed only on the lingual side, with the same pattern. Labial aHBT and ABA changes followed Large-change group > Moderate-change group > Small-change group, whereas lingual aHBT and ABA changes followed the opposite pattern.

Conclusion: Higher initial IMPA correlated with better alveolar bone condition before POD and better lingual bone condition after POD. Greater IMPA change during POD was linked to increased labial bone thickness and area, but reduced lingual bone thickness and area. The horizontal backward movement of the root apex was the primary factor driving these changes.