Computer-assisted orthognathic surgery: Consequences of a clinical evaluation

Abstract

Purpose and method: Computer-assisted systems, as any medical technology, have to go through several steps within an endless loop before becoming routine. The first step is the conception of a prototype, the second is its adaptation to the clinical modalities (via animals or cadavers studies), the third is the clinical validation and the last one is the ergonomics optimization preceding the industrialization. The aim of this work is to present the evolution of a computer-assisted system built for orthognathic surgery i.e. for the surgery of the maxilla and more specifically for repositioning the mandibular condyle after sagittal split osteotomies. The system was based on three-dimensional optical localization of infrared emitting diodes. Eleven patients (“empirical group”) underwent condylar repositioning using the empirical repositioning method (standard technique) and were considered controls. In ten patients (“active group”) the computer-assisted system was used to replace the condyle bearing fragment in its sagittal preoperative position; in these cases the condylar torque wasn't controlled. In the third group of ten patients (“graft group”), the computer-assisted system was used to replace the condyle in all three directions; very often it was necessary, in this group, to fill the osteotomy gap by a bone graft. The clinical evaluation was based on four major criteria: the quality of postoperative dental occlusion, the stability of skeletal position on successive teleradiographies, the occurrence of temporo-mandibular dysfunction (TMJD), and the preservation of mandibular motion. Clinical assessment was made at 1,3, 6 and 12 months of follow-up. Results: Forty-five percent of the “empirical group” patients do not have the expected postoperative occlusion, five patients showed evidence of clinical relapse at one year, forty-five percent worsened their TMJD status, and they recovered only 63.37% of their mandibular motion amplitudes at 6 months. All the patients of the “active group”had the expected occlusion, only one patient exhibited a mild relapse and TMJD symptoms, and the average mandibular motion recovery was only 62.65% at 6 months. All the patients of the “graft group” had a good occlusion and no relapse or TMJD. Their percentage of mandibular motion recovery was 77.58%. Conclusion: Those results confirm the utility of a condyle repositioning system. They also prove the accuracy of this computer-assisted method. This lead to an improvement of the system using a smaller localizer and a simple PC directly commanded by the surgeon with a foot-switch, without any technical support. The surgical ancillary is also simplified to reduce the time needed for the setting up of the sensors. The simplified system became a CE marked product and it is now routinely used for every orthognathic procedure in our department.