What Is the Accuracy of Bimaxillary Orthognathic Surgery Using Occlusally-Based Guides and Patient-Specific Fixation in Both Jaws? A Cohort Study and Discussion of Surgical Techniques.

PURPOSE: The development of advanced digital orthognathic surgical protocols requires investigation to determine the accuracy of surgical outcomes. This report's purpose is to quantify 3-dimensional linear discrepancies between simulated and actual results for double-jaw orthognathic surgery utilizing occlusally-based guides in conjunction with patient-specific fixation in both jaws. METHODS: This retrospective cohort study assessed the accuracy of double-jaw orthognathic surgery, in all cases performed by 1 surgeon between May 2019 and January 2021, utilizing occlusally-based guides and patient-specific fixation plates in both maxillary and mandibular surgeries. The primary outcome was absolute linear discrepancy between virtually-planned and surgically-achieved maxillary and mandibular position in 3 dimensions. Secondary outcomes were relative (directional) discrepancy, to assess if protocols erred in 1 direction of each surgical axis. Sequencing of bimaxillary surgery, age, and sex were covariates. Absolute and relative linear differences at A-point, B-point, and pogonion were evaluated using t tests. Descriptive statistics were amassed, and results were analyzed to determine if discrepancies differed from a null hypothesis of 2-mm error. RESULTS: Forty-nine patients were enrolled, consisting of 25 males and 24 females with a mean age of 24.8 years. Thirty-five single-piece and 14 multipiece LeFort I osteotomies, 49 bilateral sagittal splits, and 35 genioplasties were studied; there were 22 maxilla-first and 27 mandible-first surgeries. Mean A-point absolute discrepancies of 0.57 (95% confidence interval: 0.41-0.73), 0.37 (0.24-0.50), and 0.45 (0.33-0.57) mm were observed in horizontal, transverse, and vertical planes, respectively. B-point discrepancies were 1.15 (0.79-1.52), 0.62 (0.47-0.78), and 1.14 (0.91-1.38) mm. Pogonion discrepancies were 1.29 (0.86-1.73), 0.85 (0.64-1.06), and 1.24 (1.00-1.49) mm. All P values were <.001. Sequencing of bimaxillary surgery did not alter absolute differences (P = .2 to >.9) with A-point discrepancies consistently smaller than B-point and pogonion discrepancies regardless of sequencing. Mandible-first surgery was associated with posterior directional error; both sequences were associated with superior directional error at B-point and pogonion. CONCLUSION: Bimaxillary orthognathic surgery utilizing a patient-specific protocol in both jaws produces results highly reproducible to planned simulated surgery and accurate below a 2-mm hypothesis, with maxillary discrepancies approaching 0.5 mm and mandibular discrepancies approaching 1 mm.