The influences of mandible-first versus maxilla-first sequencing on postoperative occlusion

The aim of this study was to evaluate the influences of surgical sequencing on the postoperative occlusion in bimaxillary osteotomies. Patients who underwent bimaxillary surgery without maxillary segmentation, based on a virtual surgical plan were enrolled. The primary outcome variable was occlusal shift, defined as the difference between the surgical accuracy of the mandible and maxilla. The primary predictor variable was the sequence of surgery, with secondary predictors including inferior maxillary repositioning, counterclockwise rotation and gender. 145 patients were enrolled, 68% female, mean age 28 years. Mandible-first procedures resulted in occlusion shift within 0.5 mm of the planned position along all axes, whereas maxilla-first procedures were associated with a 0.5 mm posterior mandibular position (p = 0.05). Inferior maxillary repositioning and gender had larger greater influence on the final occlusion compared to surgical sequencing. Male patients exhibited vertical discrepancies < 0.6 mm, while females showed tendency to develop anterior open bite of 1.4-1.6 mm (p < 0.01). Rotation of the occlusal plane had no significant effect on postoperative occlusion. While both sequencing offers clinically acceptable occlusal accuracy, postoperative occlusal shift is more strongly correlated with vertical repositioning and gender-specific factors than the surgical sequence itself.