The aim of this job is to evaluate a method to predict the chin alterations throughout the predictive tracings and model surgery in bimaxillary surgeries, without genioplasty procedures. Twenty-seven patients who underwent bimaxillary surgery during an 18-month period were included in this study. The antero-posterior chin position was traced from the postoperative cephalogram and predictive tracing onto the original tracing. Comparison between the planned chin position in the cephalometric tracing and actual position was made using the paired t -test when data distribution was symmetric or Wilcoxon’s signed-rank test when data distribution was non-symmetric. Association between planned surgical movements and post-surgical changes was investigated with Pearson’s correlation. Statistical significance was set at p < 0.05. The mean difference in chin position from predictive tracings to final position was −0.72 mm (SD: 1.72 mm) and the mean difference from model surgery to final position of the chin was −1.11 mm (SD: 2.08 mm). There was no statistically significant difference between the predicted values of chin position change and the real change in the cephalometric tracings ( p = 0.536). Neither it was observed a statistically significant difference between the values of chin position change in model surgery and the real change in the cephalometric tracings ( p = 0.621). The changes in the final position of the chin presented a strong and statistically significant correlation with the planned position in model surgery ( r 2 = 0.85; p < 0.001) and predictive tracings ( r 2 = 0.91; p < 0.001). The results of this study suggest that is possible to predict the final position of the chin during bimaxillary surgeries. The changes in the final position of the chin presented a strong and statistically significant correlation with the planned position in model surgery.
Predictability of chin position after bimaxillary surgery
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