Predictability of soft tissue profile changes following bimaxillary surgery in skeletal class III Chinese patients

The aim of this study was to evaluate the accuracy of soft tissue profile predictions generated by a recently developed computer program (Computer-Assisted Simulation System for Orthognathic Surgery [CASSOS] 2001, SoftEnable Technology, Ltd, Hong Kong) in Chinese skeletal Class III patients treated with bimaxillary surgery.

Presurgical and posttreatment lateral cephalograms of 35 Chinese patients who had combined 1-piece Le Fort I and bilateral sagittal split osteotomies were digitized using the CASSOS 2001 program, and a cranial base superimposition was performed. The hard tissue movements were simulated on the presurgical cephalogram until good superimposition of the hard tissues on the presurgical and posttreatment cephalograms was achieved. A customized cephalometric analysis consisting of 32 linear measurements was used to analyze the differences in the soft tissue profile between the actual posttreatment results and the computer-generated predictions.

Comparison of the predicted and actual changes found that 16 of the 32 soft tissue measurements were significantly different ( P <.05). Most of the significant prediction errors were observed in the upper and lower lip region. The software tended to underestimate the vertical position of both the upper and lower lip and overestimate the horizontal position of the lower lip. However, the mean differences were relatively small, with the greatest mean difference being 2 mm in the vertical position of stomium inferius. The CASSOS 2001 program produced a clinically useful prediction of soft tissue profile changes following bimaxillary surgery in skeletal Class III Chinese patients.