[Computerised three-dimensional surgical simulator. Introduction and precision analysis of a new system].

Computed tomography (CT)-based anatomic three-dimensional (3D) models have become important tools in oral maxillofacial surgery. There are three problems involved in the precise transfer of the experience gained and the results of simulation surgery to the patient: (1) 3D models have no precise reference points; (2) it is difficult to measure translations three-dimensionally; and (3) exact transfer to the patient intraoperatively is impossible. We have introduced a new system which solves these problems. In the first step 3D dental arches are replaced by plaster models, using an occlusal device with three radioopaque hemispheres as reference. A computerised electromagnetic tracker makes 3D measurements possible during simulated surgery, and a newly developed transfer system with a neurosurgical head frame to provide stable anchorage is used for positioning during surgery. We present our experience with this system in 15 orthognathic patients undergoing bimaxillary surgery. With the 3D computerised simulation surgery and model operation transfer system (3D-COSMOS) the dental arches can be replaced with a mean accuracy of 0.03 mm. The 3D translations of jaw segments can be measured precisely (0.11 mm) and simultaneously at the osteotomy line and the teeth. The new jaw position is transferred mechanically with a precision of 0.05 mm. Operation time is prolonged only by 15 min.