Imaging Analysis And The Application Of Three-dimensional Digital Technology In Reduction Gonioplasty

ObjectiveEvaluate the effects of bone regeneration on facial width and the soft-tissue response of reduction gonioplasty. Get long-term observation of the masseter after reduction gonioplasty. Establish a standardized protocol for VSP and 3D surgical templates-assisted mandible contour surgery and evaluate the accuracy of the protocol. Explore the feasibility to perform robotic-assisted reduction gonioplasty to achieve easier, more accurate and safer reduction gonioplasty.Methods1. We retrospectively reviewed patients who underwent reduction gonioplasty from 2009 to 2013. A high-speed rotary cutting bur without a water coolant was routinely used from the new gonial point to the inferior mandibular rim under the second premolar, while the elongated the osteotomy line (mandibular-chin body osteotomy) was performed with a reciprocating saw. Forty-nine patients with preoperative, immediate postoperative, and 12-month postoperative frontal cephalograms were included in our study. Mandible and soft tissue profiles were measured on cephalograms.2. The Plastic Surgery Hospital database was retrospectively reviewed for patients who underwent reduction gonioplasty. Fifty-six patients with both preoperative and 4 years postoperative three-dimensional computed tomography (3DCT) were included. The changes in the volume and morphology of the masseter muscle after reduction gonioplasty were assessed quantitatively. The 3DCT data were analyzed using Mimics 10.01 software.3. In this study, we enrolled 20 patients for mandible contour surgery prospectively. VSP were performed based on 3D CT data. Surgical templates were 3D-printed based on preoperative VSP. The accuracy of the method was analyzed by 3D comparison of VSP and post-op results.4. We performed 3 experimental reduction gonioplasty on cadaver head with the Da Vinci Surgical Robot. PZE osteotome (Synthes Piezoelectric System) was attached with the Da Vinci work arm to perform osteotomy. The CT scans of the head was done the day before the experimental surgery. Visual surgical plans for facial contour surgeries were created based on 3D CT data. The surgical design was superimposed onto the mandible during the operation.Result1. Bone regeneration in high-speed rotary cutting bur ostectomy region was -0.79±1.76 mm (1cm above Go-Go),-0.75±1.46 mm (Go-Go, bigonial line),-0.77±2.10 mm(1cm below Go-Go), while 0.07±1.79 mm (2cm below Go-Go) in ostectomy region performed by reciprocating saw. The soft-tissue response ratios were 76.72 ± 30.70% (Go-Go),108.8 ± 54.11%(1cm below Go-Go), and 155.9 ± 66.82%(2cm below Go-Go).2. All patients were satisfied with the outcome. No complications happened. There were significant differences between the preoperative and 4 years postoperative volume and morphology.3. All patients had symmetric, natural osteotomy lines, and satisfactory facial ratios in a single-stage operation. The average relative error of VSP and post-op result on the skull was 0.41 ±0.13 mm. The average new left gonial error(Go’-L Error) was 0.43±0.77mm. The average new right gonial error(Go’-R Error) was 0.45±0.69mm.The Average Pg error was 0.79±1.21mm. Patients were very satisfied with the esthetic results. Surgeons were very satisfied with the performance of surgical templates to facilitate the operation.4. Excellent visualization and easy manipulation was achieved. Accurate operation navigation was achieved. PZE osteotome attached with the Da Vinci work arm was able to perform reduction gonioplasty osteotomy.Conclusion1. Bone regeneration does not lead to an increase in facial width after reduction gonioplasty with our technique, and the use of a high-speed rotary cutting bur without a water coolant decreases bone regeneration. The soft-tissue response ratio is higher in the anterior mandible and the outcome of reduction gonioplasty is a sharper lower face with a full cheek. Reduction gonioplasty is an effective and predictable lower face reshaping surgery.2. After reduction gonioplasty, the masseter muscle atrophied(reduced by 20.98% ± 8.75%), especially the lower part of the masseter muscle(reduced by 53.18% ±12.50% below plane C) in the long-term follow-up. Most patients with prominent mandibular angles should be treated with reduction gonioplasty without approaching the masseter muscle.3. Our standardized protocol of VSP and 3D printed surgical templates result in accurate, safe, and predictable single-stage mandible contour surgery.4. Our cadaver experiment served as a proof of concept investigation, it demonstrated the feasibility of accurate and safe robotic trasoral reduction gonioplsaty with current Da Vinci Surgical System. This method is promising in achieving highly accurate, consistent, and safe pre-programmed transoral reduction gonioplasty and lower the technical difficulties of the surgery.