The Effects of Different Bimaxillary Orthognathic Surgery Sequencing on the Temporomandibular Joint Space of Skeletal Class II Malocclusion Patients.

Abstract

Background: Changes in the temporomandibular joint (TMJ) space are known consequences of bimaxillary surgery, and the surgery sequence may influence postoperative TMJ space or risk of relapse.

Purpose: The purpose of this study was to measure the association of bimaxillary surgery sequence and changes in the TMJ space over time in patients with skeletal Class II malocclusion.

Study design, setting, and sample: A retrospective cohort study involving patients with skeletal Class II malocclusion who underwent bimaxillary orthognathic surgery was conducted at the Hospital of Stomatology, Wuhan University from 2018 to 2021. Patients without complete cone beam computed tomography were excluded.

Predictor variable: The predictor variable was sequence of bimaxillary orthognathic surgery, grouped as mandible-first and maxilla-first.

Main outcome variables: The main outcome variables were radiographic linear measurements and changes in the anterior joint space, posterior joint space (PJS), and superior joint space (SJS) at 3 time points: preoperative, 1 week postoperative, and 6-12 months postoperative.

Covariates: The evaluated covariates included sex, age, mandibular advancement.

Analyses: Repeated-measures analysis of variance was used to assess changes in joint space over time and side, with surgical sequence as a between-subjects factor. Additional analyses included independent t-tests and canonical correlation. (P ≤ .05).

Results: The sample comprised 48 subjects (96 joints), with a mean age of 29.2 (8.5) years; 11 (23%) were male. At 1 week postsurgery, the Maxilla-First group showed a significantly greater radiographic increase in SJS than the Mandible-First group (mean difference: 1.3 mm; 95% CI: 0.7-2.0; P = .0005). At the same time point, all 3 joint spaces (SJS, anterior joint space, and PJS) increased significantly in both groups (P < .05). By 6-12 months postoperatively, surgery sequence showed a negative effect on TMJ space changes, as SJS and PJS significantly decreased in the maxilla-first group (mean differences: 1.9 and 1.1 mm; 95% CIs: 1.2-2.5 and 0.3-1.8; P = .0001 and .005, respectively).

Conclusions and relevance: TMJ space changes in skeletal Class II malocclusion varied over time and were associated with the order of surgery sequence, with smaller changes observed in the mandibular-first group.