Accurate positioning of the mandibular proximal segments in reconstructive and orthognathic surgery. The role of the virtual planning and CAD–CAM technology

Abstract

The correction of developmental and acquired facial deformities demands an accurate surgical plan. In some cases, however, traditional methods of planning may fail due to inherent limitations, as the incapability of predicting 3D movements with 2D predictive tracings. Considering this, a virtual surgical simulation technique was created and has been used successfully in complex cases requiring orthognathic surgery or mandibular reconstruction, allowing precise repositioning of the mandibular proximal segment. We present the case of a 45 years old Caucasian female with asymmetry who was treated using the described method. The patient history included shortening of the mandibular perimeter due to a body fracture. Using CAD–CAM softwares and a standardized sequence of movements, Le Fort I and bilateral sagittal split osteotomy were planned to achieve optimal symmetry. However, the best outcome was reached when a body osteotomy over the malunited fracture was performed and the mandibular advancement simulated, creating a 12.5 mm continuity defect in the mandible. In order to reproduce the same movement during the surgery, a first guide was designed to orient the drilling and cutting and a second one to assure correct positioning of both distal and proximal segments as it was screwed against the mandible using the same holes drilled with the first guide. The surgery was performed uneventfully. Superimposition of the 3D-simulation and postoperative 3D-CT scan showed high level of accuracy, assessed by a distance color map (disparity inferior to 1.5 mm). The precision of this technique is related to computer-aided manufactured guides for drilling, cutting and positioning, in addition to the occlusion-based guides designed with the current virtual planning methods. The technique is particularly useful when grafting in extensive mandibular continuity defects through the intraoral approach seems challenging due to the difficulty in positioning and fixing the proximal segments in their desired positions.