How Much Inter-Arch Discrepancy Occurs During Orthognathic Surgery?

BACKGROUND

Orthognathic surgery depends on the accurate transfer of virtual surgical planning to the operative field. Although surgical splints play an important role in this process, information about intraoperative adaptation error is limited.

PURPOSE: The purpose of this study was to define and quantify interarch discrepancy during splint-guided orthognathic surgery and to evaluate whether its magnitude differs according to facial symmetry and surgical sequence.

STUDY DESIGN, SETTING, SAMPLE: A retrospective cohort study was conducted at Seoul National University Dental Hospital. Patients with skeletal Class III malocclusion who underwent bimaxillary or mandible-only surgery (January 2017-February 2025) were included. Patients with craniofacial syndromes, cleft lip or palate, previous orthognathic surgery, segmental osteotomies, or incomplete imaging records were excluded.

PREDICTOR VARIABLES: Predictor variables included facial symmetry (symmetric vs asymmetric) and surgical sequence (maxilla-first, mandible-first, and mandible-only).

MAIN OUTCOME VARIABLE: The primary outcome was the interarch discrepancy, evaluated as both the signed 3-dimensional vector components (X, Y, and Z) and the root mean square (RMS) magnitude.

COVARIATES: Covariates included age, sex, and absolute planned transverse mandibular movement.

ANALYSES: Signed axis deviations were tested against zero, and RMS magnitudes were compared between groups using Welch's t-test and Welch's analysis of variance, as appropriate. Multiple linear regression was used to evaluate independent associations, and a P value of < .05 was considered statistically significant.

RESULTS

The study included 119 subjects (44 females [37.0%], mean age 22.16 ± 3.84 years); 40 (33.6%) were classified as asymmetric. Surgical sequence included 54 (45.4%) maxilla-first, 54 (45.4%) mandible-first, and 11 (9.2%) mandible-only. Across the entire cohort, the signed Y-axis deviation showed a statistically significant inferior deviation at all 3 regions: anterior -1.07 ± 1.00 mm, left posterior -0.50 ± 0.64 mm, and right posterior -0.54 ± 0.67 mm (all P < .001). The overall RMS discrepancy was 1.23 ± 0.61 mm. In group comparisons and multivariable regression, no clinical variables, including facial symmetry and surgical sequence, were statistically significantly associated with the overall RMS discrepancy.

CONCLUSIONS AND RELEVANCE: Interarch discrepancy showed a statistically significant inferior displacement across regions, although its overall magnitude was modest.