Soft to hard tissue ratios after bimaxillary orthognathic surgery in class III patients

Abstract

ABSTRACT Objective: The aim of this study was to assess the changes of facial soft tissue profile and determine the soft to hard tissue ratios, and develop a new mathematical formulation between hard and soft tissues for two dimensional simulation systems in Class III patients. Methods: Twenty skeletal Class III patients were included in this study. Preoperative (T0) and posttreatment (T1) cephalometric variables were assessed on lateral cephalograms. Method error was determined by redigitizing 10 patients’ measurements 3 weeks after initial digitization. Presurgical and postsurgical cephalometric measurements were compared with dependent two-sample t-test and statistical significance set at P < .05. Results: Our material was homogeneous in terms of gender and maxillary and mandibular movement. In the maxilla the soft to hard tissue ratios were as follows; 23% for the tip of the nose, 45% for Sn, 70% for A*, and 60% for Ls. Sagitally, the soft to hard tissue ratios for mandible were; Li 77%, B* 101%, Pog* 83%, 81% for Gn*, and 95% for Me*point. According to the results, it was found that the soft tissue B point (B*) moved equally with the mandible (101%), and the tip of the nose (Pn) is the soft tissue point that was least affected by the movement of the underlying skeletal structure (0.23%). Conclusion: The significant improvement in facial profiles of skeletal Class III orthognathic surgery patients after maxillary advancement and mandibular setback surgery is primarily related to the backward movement of the mandible. The correlation between soft and hard tissues in the mandible is higher than in the maxilla. As a result of our study, new formulations and soft to hard tissue ratios were developed for 2D prediction methods.