Computer-assisted Pre- and Postoperative Evaluation of Surgically Assisted Rapid Maxillary Expansion

Objective: Computer-assisted methods were used to evaluate different variants of surgically assisted rapid maxillary expansion (SARME) in terms of bone repositioning, new bone formation in the osteotomy gap, and bone quality before and after surgery. Materials and Methods: Twenty-nine patients (18 male, 11 female) with a mean age of 29 years (16 to 44 years) were included in the study. Surgically assisted rapid maxillary expansion with Le Fort I osteotomy was performed in all patients studied. High-resolution computed tomography (CT) was carried out directly before and 6 to 8 weeks after surgery. After registration of the preoperative CT data on the postoperative data, 3D models were constructed and superimposed. New bone formation in the osteotomy gap was visualized by means of a visualization procedure developed specifically for this purpose. Bone quality was analyzed by dividing the models into different anatomical segments. A qualitative comparison of the data was accomplished using a direct volume rendering procedure with a special transfer function. A quantitative comparison was carried out based on the pre- and postoperative histograms of each region. Results: Maxillary widening was confirmed in all patients by computer-assisted analysis. Four patients exhibited significant maxillary asymmetry after surgery. New bone formation within the osteotomy gap was irregular along the osteotomy lines but often symmetrical on both sides. The more symmetrical the osteotomy, the more symmetrical the new bone formation proved to be. In all but two cases, the postoperative qualitative and quantitative analyses showed a significant decrease in Hounsfield units, particularly in the vestibular bone. Conclusion: The differences in new bone formation in the osteotomy gap suggest that the type of surgical technique and distractor used influence the outcome. Our results indicate that SAME results in a decrease in bone quality, particularly in the vestibular bone. Computer-assisted analysis clearly results in an information gain. Keywords: surgically-assisted rapid maxillary expansion, maxilla, distractor, bone quality, new bone formation, medical visualization, 3D reconstruction, direct volume rendering, transfer function