A reversed approach for simultaneous mandibular symphyseal split osteotomy and genioplasty.

Performing a mandibular symphyseal split and genioplasty simultaneously and accurately is a technical challenge for the surgeon. The aim of this study was to validate a reversed approach for simultaneous symphyseal split and genioplasty. A cutting guide and a repositioning guide were designed and printed three-dimensionally in titanium. The symphyseal split and genioplasty were performed successfully. The accuracy of the technique appears to be appropriate for clinical application.

Fluctuating asymmetry of the normal facial skeleton.

The purpose of this study was to produce reliable estimations of fluctuating facial asymmetry in a normal population. Fifty-four computed tomography (CT) facial models of average-looking and symmetrical Chinese subjects with a class I occlusion were used in this study. Eleven midline landmarks and 12 pairs of bilateral landmarks were digitized. The repeatability of the landmark digitization was first evaluated. A Procrustes analysis was then used to measure the fluctuating asymmetry of each CT model, after all of the models had been scaled to the average face size of the study sample. A principal component analysis was finally used to establish the direction of the fluctuating asymmetries. The results showed that there was excellent absolute agreement among the three repeated measurements. The mean fluctuating asymmetry of the average-size face varied at each anthropometric landmark site, ranging from 1.0mm to 2.8mm. At the 95% upper limit, the asymmetries ranged from 2.2mm to 5.7mm. Most of the asymmetry of the midline structures was mediolateral, while the asymmetry of the bilateral landmarks was more equally distributed. These values are for the average face. People with larger faces will have higher values, while subjects with smaller faces will have lower values.

A new approach of splint-less orthognathic surgery using a personalized orthognathic surgical guide system: A preliminary study.

The purpose of this study was to evaluate a personalized orthognathic surgical guide (POSG) system for bimaxillary surgery without the use of surgical splint. Ten patients with dentofacial deformities were enrolled. Surgeries were planned with the computer-aided surgical simulation method. The POSG system was designed for both maxillary and mandibular surgery. Each consisted of cutting guides and three-dimensionally (3D) printed custom titanium plates to guide the osteotomy and repositioning the bony segments without the use of the surgical splints. Finally, the outcome evaluation was completed by comparing planned outcomes with postoperative outcomes. All operations were successfully completed using the POSG system. The largest root-mean-square deviations were 0.74mm and 1.93° for the maxillary dental arch, 1.10mm and 2.82° for the mandibular arch, 0.83mm and 2.59° for the mandibular body, and 0.98mm and 2.45° for the proximal segments. The results of the study indicated that our POSG system is capable of accurately and effectively transferring the surgical plan without the use of surgical splint. A significant advantage is that the repositioning of the bony segments is independent to the mandibular autorotation, thus eliminates the potential problems associated with the surgical splint.

A new design of CAD/CAM surgical template system for two-piece narrowing genioplasty.

The purpose of this study was to develop and validate a new chin template system for a two-piece narrowing genioplasty. Nine patients with wide chin deformities were enrolled. Surgeries were planned with the computer-aided surgical simulation (CASS) planning method. Surgical splints and chin templates were designed in a computer and fabricated using a three-dimensional printing technique. The chin template system included a cutting guide and a repositioning guide for a two-piece narrowing genioplasty. These guides were also designed to avoid the mental foramen area and inferior alveolar nerve loops during the osteotomy, for nerve protection. After surgery, the outcome evaluation was completed by first superimposing the postoperative computed tomography model onto the planned model, and then measuring the differences between the planned and actual outcomes. All surgeries were completed successfully using the chin template system. No inferior alveolar nerve damage was seen in this study. With the use of the chin templates, the largest linear root mean square deviation (RMSD) between the planned and the postoperative chin segments was 0.7mm and the largest angular RMSD was 4.5°. The results showed that the chin template system provides a reliable method of transfer for two-piece osseous narrowing genioplasty planning.

The surgery-first approach in orthognathic surgery: a retrospective study of 50 cases.

The surgery-first approach (SFA), without presurgical orthodontic treatment, has become favoured in the treatment of dentomaxillofacial deformities. This approach has been applied in our institution since 2012. The purpose of this study was to report our experience with the SFA for skeletal malocclusion. Fifty patients with skeletal malocclusions were enrolled in this study (11 bimaxillary protrusion, 27 skeletal class III malocclusion, and 12 facial asymmetry). After orthognathic-orthodontic consultation, suitability for SFA was determined and a treatment plan drawn up. Patients then underwent orthognathic surgery, which included Le Fort I maxillary osteotomy, bilateral sagittal split ramus osteotomy, subapical osteotomy, and genioplasty. Postoperative orthodontic treatment was started after a healing period of 2 weeks. The mean postoperative orthodontic treatment duration was 14.9 months, which is shorter than that of traditional joint orthognathic-orthodontic treatment. In the bimaxillary protrusion group, this was about 19 months, which was longer than for the other groups. After joint orthognathic-orthodontic treatment, a good facial profile and ideal occlusion were achieved. With the advantages of earlier improvements in patient facial aesthetics and dental function, the reduction in difficulty and treatment duration of orthodontic management, and increasing patient acceptance, SFA is regarded as an ideal and valuable alternative for this potentially complicated procedure.

Computer-assisted surgical planning and intraoperative navigation in the treatment of condylar osteochondroma.

Mandibular condylar osteochondroma (OC) results in asymmetric prognathism with facial morphology and functional disturbances. The aim of this study was to explore the feasibility of computer-assisted surgical planning combined with intraoperative navigation in the treatment of condylar OC. Five patients with mandibular condylar OC were enrolled in this study. Surgical planning and simulation was performed based on a computed tomography reconstruction model using SurgiCase software. Under the guidance of navigation, a condylar OC resection and conservative condylectomy was carried out via intraoral approach. Simultaneous orthognathic surgery was used to correct the facial asymmetry and malocclusion. All patients healed uneventfully. No facial nerve injury or salivary fistula occurred. Facial symmetry and morphology were greatly improved and stable occlusion was obtained in all cases. Good matching between preoperative planning and postoperative results was achieved. Patients showed no signs of recurrence or temporomandibular joint ankylosis during follow-up of 12-30 months. Computer-assisted surgical planning and intraoperative navigation is a valuable option in the treatment of mandibular condylar OC.

Point-based superimposition of a digital dental model on to a three-dimensional computed tomographic skull: an accuracy study in vitro.

We investigated the accuracy of point-based superimposition of a digital dental model on to a 3-dimensional computed tomographic (CT) skull with intact dentition. The physical model was scanned by CT to give a virtual skull model, and a plaster dental model was taken and laser-scanned to give a digital dental model. Three different background investigators were recruited and calibrated to make the point-based superimposition, and afterwards were asked to repeat 5 superimpositions each. Five bone-to-tooth measurements for the maxilla and 6 for the mandible were selected to indicate the relation of teeth to skull. Repeated measures were made on the physical model to act as a control group, and on the virtual model to act as the test group. The absolute agreement intra-class correlation coefficient (ICC) was used to assess the intra/inter-investigator reliability; Bland-Altman analysis was used to calculate the general differences, limits of agreement, and precision ranges of the estimated limits. Inter/intra-investigator reliability was excellent with ICC varying from 0.986 to 1; Bland-Altman analysis indicated that general difference was 0.01 (0.25)mm, the upper limit of agreement was 0.50mm and the lower limit -0.47 mm, and the precision range for the upper limit was 0.43 mm to 0.57 mm and for the lower limit -0.54 mm to -0.40 mm. Clinically acceptable accuracy can be achieved using a direct point-based method to superimpose a digital dental model on to a 3-dimensional CT skull.

Navigation-guided en bloc resection and defect reconstruction of craniomaxillary bony tumours.

The aim of this study was to evaluate the validity of navigation-guided en bloc tumour resection and defect reconstruction in the treatment of craniomaxillary bony tumours. Three patients with ossifying fibroma and two patients with fibrous dysplasia were enrolled in this study. After preoperative planning and three-dimensional simulation, the osteotomy lines for resection were delineated and the normal anatomic structures for defect reconstruction were ascertained. With the guidance of an Accu-Navi navigation system, an en bloc tumour resection and simultaneous defect rehabilitation were performed. The system provided continuously updated information on the position and movement of surgical instruments in the operating field in relation to the preoperative imaging data set. The system error measured by the computer did not exceed 1mm. The osteotomy lines and reconstruction contour were checked by postoperative computed tomography, and good matching with the preoperative planning was achieved. Patients showed no signs of tumour recurrence or prosthesis infection during follow-up (range 12-35 months). Image-guided navigation makes radical bone tumour resection more reliable by implementing preoperative planning, showing the determined safety margins, preserving vital structures and guiding reconstruction.

Endoscope-assisted conservative condylectomy in the treatment of condylar osteochondroma through an intraoral approach.

Mandibular condylar osteochondroma (OC) can result in morphological and functional disturbances, including facial asymmetry and temporomandibular joint (TMJ) dysfunction. The aim of this study was to explore the feasibility of endoscope-assisted tumour resection and conservative condylectomy via an intraoral approach. Seven patients with condylar OC were enrolled in this study. Endoscope-assisted tumour resection and conservative condylectomy were achieved intraorally, and no conventional extraoral incision was needed. Direct vision of the magnified and illuminated operative field was realized with the assistance of an endoscope. No facial nerve injury or salivary fistula occurred in any patient. Stable occlusion was realized through postoperative orthodontic treatment. The patients showed no signs of tumour recurrence or TMJ ankylosis during follow-up (range 18-43 months). Endoscope-assisted condylar OC resection and conservative condylectomy via intraoral approach offers great advantages with no significant complications compared with conventional extraoral incisions. The endoscope provides us with a valuable treatment option for this potentially complicated procedure.

Computer-assisted three-dimensional surgical planing and simulation. 3D soft tissue planning and prediction.

The purpose of this paper is to report a new technique for three-dimensional facial soft-tissue-change prediction after simulated orthognathic surgical planning. A scheme for soft tissue deformation, "Computer-assisted three-dimensional virtual reality soft tissue planning and prediction for orthognathic surgery (CASP)", is presented. The surgical planning was based on three-dimensional reconstructed CT visualization. Soft tissue changes were predicted by two newly devised algorithms: Surface Normal-based Model Deformation Algorithm and Ray Projection-based Model Deformation Algorithm. A three-dimensional color facial texture-mapping technique was also used for generating the color photo-realistic facial model. As a final result, a predicted and simulated patient's color facial model can be visualized from arbitrary viewing points.

Three-dimensional virtual reality surgical planning and simulation workbench for orthognathic surgery.

A new integrated computer system, the 3-dimensional (3D) virtual reality surgical planning and simulation workbench for orthognathic surgery (VRSP), is presented. Five major functions are implemented in this system: post-processing and reconstruction of computed tomographic (CT) data, transformation of 3D unique coordinate system geometry, generation of 3D color facial soft tissue models, virtual surgical planning and simulation, and presurgical prediction of soft tissue changes. The basic mensuration functions, such as linear and spatial measurements, are also included. The surgical planning and simulation are based on 3D CT reconstructions, whereas soft tissue prediction is based on an individualized, texture-mapped, color facial soft tissue model. The surgeon "enters" the virtual operatory with virtual reality equipment, "holds" a virtual scalpel, and "operates" on a virtual patient to accomplish actual surgical planning, simulation of the surgical procedure, and prediction of soft tissue changes before surgery. As a final result, a quantitative osteotomy-simulated bone model and predicted color facial model with photorealistic quality can be visualized from any arbitrary viewing point in a personal computer system. This system can be installed in any hospital for daily use.