Do Surgical Intervention Type and Baseline Condylar Position Affect Spatial Dimension Changes of the Temporomandibular Joint in the Surgical Correction of Skeletal Class II Deformities?

Background: One of the key features of orthognathic surgery is altering temporomandibular joint (TMJ) condylar positions.

Purpose: This multivariate study aimed to identify surgical interventions and patient factors significantly associated with changes in TMJ spatial dimensions after the surgical correction of skeletal Class II deformities.

Study Design, Setting, Sample: This is a retrospective cohort study including patients who had undergone an isolated bilateral sagittal split ramus osteotomy (BSSO) or a bimaxillary osteotomy (BMO) for mandibular advancement and a control sample of patients treated with the removal of odontogenic cysts in the mandibular posterior region. Excluded were those who presented with specific radiographic signs of TMJ osteoarthrosis, severe facial asymmetry, or deformity secondary to trauma.

Predictor/exposure/independent Variable: The primary predictors were condylar position at baseline (anterior, concentric, and posterior), time points (T0, preoperatively; T1, immediately after surgery; and T2, 1-year follow-up), and surgical intervention type (BSSO, BMO, and control group).

Main Outcome Variables: The primary outcomes were changes in posterior spatial dimension (PSD), superior spatial dimension, and medial spatial dimension assessed by cone-beam computed tomography preoperatively, immediately after surgery, and at 1-year follow-up.

Covariates: Covariates included sex, age, and amount of mandibular advancement.

Analyses: Estimations of independent effects of primary predictors on outcome variables were made by applying generalized estimation equation models. The value of statistical significance was P < .05.

Results: The study sample included 88 participants. The BSSO samples included 39 patients, and the BMO group included 22 patients; the control group comprised 27 subjects. The average age was 31.2 years; the majority were female (61.4%). Adjusted generalized estimation equation models yielded a significant time interaction between BSSO and spatial dimensions over time (PSD, P < .001). Key predictors of spatial dimension changes were the baseline posterior (PSD, P < .001) and the central condylar position (PSD, P < .001).

Conclusion And Relevance: This controlled study, for the first time, provides scientific evidence on the effects of surgical intervention type and baseline condylar position on spatial dimension changes in the TMJ. It shows a more favorable outcome in long-term spatial dimension changes for patients treated by a BMO procedure.