Hongtao Shang

Accurate reconstruction of discontinuous mandible using a reverse engineering/computer-aided design/rapid prototyping technique: a preliminary clinical study.

PURPOSE To improve the reconstructive surgical outcome of a discontinuous mandibular defect, we used reverse engineering (RE), computer-aided design (CAD), and rapid prototyping (RP) technique to fabricate customized mandibular trays to precisely restore the mandibular defects. Autogenous bone grafting was also used to restore the bony continuity for occlusion rehabilitation. PATIENTS AND METHODS Six patients who had undergone block resection of the mandible underwent reconstruction using a custom titanium tray combining autogenous iliac grafts. The custom titanium tray was made using a RE/CAD/RP technique. A virtual 3-dimensional model was obtained by spiral computed tomography scanning. The opposite side of the mandible was mirrored to cover the defect area to restore excellent facial symmetry. A bone grafting tray was designed from the mirrored image and manufactured using RP processing and casting. The mandibular defects were restored using the trays in combination of autologous iliac grafting. An implant denture was made for 1 of the 6 patients at 24 weeks postoperatively for occlusion rehabilitation. RESULTS The trays fabricated using this technique fit well in all 6 patients. The reconstructive procedures were easy and time saving. Satisfactory facial symmetry was restored. No severe complications occurred in the 5 patients without occlusion rehabilitation during a mean 50-month follow-up period. The reconstruction in the patient with occlusion lasted for only 1 year and failed eventually because of bone resorption and infection. CONCLUSIONS Mandibular reconstruction was facilitated using the RE/CAD/RP technique. Satisfactory esthetic results were achieved. However, the rigidity of the cast tray could cause severe stress shielding to the grafts, which could lead to disuse atrophy. Therefore, some modification is needed for functional reconstruction.

CAD/CAM surface templates as an alternative to the intermediate wafer in orthognathic surgery

OBJECTIVE A new simple technique using a pair of surface templates fabricated by CAD/CAM technique as an alternative to the use of intermediate surgical wafer is presented. STUDY DESIGN A patient with transverse maxillary cant and maxillary midline deviation was scanned using computed tomography (CT) to create a 3D model of the maxillofacial bone. Eight virtual cylindrical markers were placed on the selected locations of maxilla. Subsequently, the locations of these cylinders were expressed as drill holes in the preosteotomy templates. The maxillary segment was separated and repositioned in the computer according to preoperative plans. Postosteotomy surface templates were then designed and resin templates were fabricated by a rapid prototyping machine. After investing and casting, metal templates were fabricated. At the beginning of operation, surgical fixation holes on the maxilla were drilled with the preosteotomy templates. Once maxillary osteotomy and segmentation were finished, screws were placed through the holes in the postosteotomy templates into the predrilled holes on the bone correspondingly, and maxillary segments were fixed with the titanium plates. RESULTS After the postosteotomy templates were positioned and fixed, the maxillary segment was placed to the desired position. Maxillary transverse cant and midline deviation were corrected as the preoperative plan and simulation. CONCLUSION The use of the surface templates before and after osteotomy as an alternative to intermediate wafer in orthognathic surgery can minimize labor and errors contained in the traditional way, reducing preoperative work as well as a reduction in operation time.

Modified internal mandibular distraction osteogenesis in the treatment of micrognathia secondary to temporomandibular joint ankylosis: 4-Year follow-up of a case

Micrognathia and obstructive sleep apnoea syndrome (OSAS) are problems subsequent to temporomandibular joint ankylosis (TMJa) in growing patients. For patients with micrognathia and OSAS secondary to TMJa, it is important to restore proper mandibular form and dimension, achieve occlusal stability and recover satisfactory joint movement. We report a 4-year follow-up of a patient with micrognathia and OSAS secondary to bilateral TMJa. The treatment of this patient involved (1) a modified internal mandibular distraction osteogenesis without altering the pre-existing occlusion; (2) TMJ arthroplasty in which the dislocated disc was found and repositioned and the shape of the glenoid fossa and articular head was formed without removing bone in vertical dimension; (3) passive mouth-opening exercise with an individualized occlusal pad postoperatively for one month; and (4) orthodontic treatment for the occlusal disturbance and active mouth-opening exercise for one year. After the treatment the micrognathia was corrected; the oropharyngeal airway was increased significantly; mouth-opening increased to 40mm intraoperatively was maintained at 36.66mm 4 years after surgery. Satisfactory occlusion was achieved after orthodontic treatment. Through the 4-year follow-up, no signs of reankylosis were found. In conclusion, this new clinical protocol is a safe, effective and quick way to treat micrognathia and OSAS secondary to TMJa.

Correction of hemifacial microsomia with the help of mirror imaging and a rapid prototyping technique: case report

A 23-year-old man presented with an 8-year history of unilateral hemifacial microsomia. A three-dimensional model of the maxillofacial bones was generated after acquisition of helical computed tomographic data. A customised implant model was designed by projecting a mirror image of the healthy mandible on to the three-dimensional model. A resin model of the implant was then made using a rapid prototyping machine. A polymeric biomaterial was sculpted according to the model and implanted into the affected side of the mandible to restore his facial symmetry. The hemifacial microsomia was corrected and a symmetrical facial contour obtained. No complications developed during the 6-year follow-up.

Reconstruction of curved mandibular angle defects using a new internal transport distraction device: an experiment in goats.

A new internal distraction device, comprising a square-bodied bow, a transport plate, a traction mechanism, and two stabilisers, was developed to allow transportation of bone around an arc. Eight adult goats were studied. A curved mandibulectomy 3cm long was made on the mandibular angle. The distractor was implanted to restore the defect. The bone was distracted at a rate of 1mm per day after a 5-day latent period. Distraction lasted 25 to 32 days. Curvilinear distraction was successful in six of the eight goats. After consolidation periods of four or eight weeks, smooth curved bone masses were restored in the distracted areas. Radiographically, there was considerable bone density in the distraction area and opaque columns streamed in the direction of distraction. Histological examination showed membranous bony regeneration in the restored bone. These results suggest that restoration of curved bone defects using the new internal transport distraction device was feasible in goats.

Reconstruction of Mandibular Defects Using a Custom-Made Titanium Tray in Combination With Autologous Cancellous Bone

PURPOSE To esthetically and functionally restore a 40-mm canine mandibular discontinuity defect using a custom-made titanium bone-grafting tray packed with autologous iliac bone. MATERIALS AND METHODS Individualized titanium bone-grafting trays were made using a reverse engineering, computer-aided design, and rapid prototyping technique. A 40-mm discontinuity defect in the right mandibular body was created in 10 hybrid dogs. The defect was restored immediately using the tray that was densely packed with autologous cancellous iliac particles and covered with trimmed iliac chips. Sequential radionuclide bone imaging was performed postoperatively at 2, 4, 8, 12, and 24 weeks. The ratio of activity between the grafted mandible and the contralateral native mandible on each transaxial slice was calculated. The mean activity ratio was analyzed at each time point to evaluate the bone metabolism and reconstitution of the grafts. The subjects were sacrificed at 4, 12, and 24 weeks after grafting. The specimens were evaluated by postmortem gross dissection, biomechanical testing, 3-dimensional microcomputed tomographic scanning, and histologic examination. RESULTS All the subjects tolerated the grafting operation well. Over an observation period of 24 weeks, tray extrusion occurred in 3 of the 10 subjects. Bony continuities were reconstructed in 9 of the 10 subjects. Radionuclide bone imaging revealed that the tracer uptake increased in the grafted mandible, and the radionuclide ratio between the graft and the native mandible decreased with time. Gross evaluation, microcomputed tomographic examination, biomechanical testing, and histologic examination demonstrated corticalization of the grafts. CONCLUSIONS The use of a customized technique using reverse engineering, computer-aided design, and rapid prototyping tray containing autologous cancellous bone is a potentially powerful grafting technique for the reconstruction of mandibular discontinuity defects.

Prototyped flexible grafting tray for reconstruction of mandibular defects.

In our previous studies, prototyped individual bone-grafting trays have been used to restore discontinuous mandibular defects. However, the attempts have shown that the trays have shielded the graft from stress, which caused considerable resorption of bone. To eliminate the shielding, we designed a flexible tray. Finite element analysis was used to compare the distribution of strain on the bone grafts that were placed in flexible and conventional trays. The analogue computation suggested that most of the strain on the graft in the flexible tray resulted in a beneficial mechanical environment, while in the conventional tray more than half of graft was in the lowest class of strain (disuse - <50 μstrains). Animal experiments were conducted on hybrid dogs, and the prototype flexible tray was used to carry particles of autologous cancellous iliac bone to reconstruct a 40 mm defect in the mandibular body. Sequential radionuclide bone imaging was used to monitor the bone metabolism. Animals were killed at 4, 12 and 24 weeks, and specimens processed for quantitative histological examination. The data from the flexible trays were compared with those from the conventional trays, as in our previous study. The results showed that bone metabolism was more active in the flexible tray than in the conventional tray during the early stages. There was increased bony adaptation in the flexible tray. These results indicate that the flexible tray can efficiently eliminate the shielding from stress, and allow more occlusive force to be conducted on to the bone graft, which results in better remodelling of the graft.

A novel method for transferring press during curvilinear distraction

rifocal1,2 and multiplanar1 distraction have been used, but either provides real curvilinear distraction. Rather, they ivide an arch into two intersecting lines, approximating only he original shape of the maxillofacial bone. An arced guide-plate combined with a slide has been used uccessfully, but its ability to transfer pressure and the strucure it can support are limited. The length and curvature of ew bone required in maxillofacial reconstruction mean that t cannot be used for obvious curvilinear distraction in three imensions.3 Recently, wires have been used as traction cables to ransfer the force during curvilinear distraction.4,5 Howver, increased resistance may cause cables to break late in istraction.4 The challenge remains to find an effective way o transfer pressure during curvilinear distraction.

Biomechanical analysis of a curvilinear distractor device for correcting mandibular symphyseal defects.

PURPOSE The local mechanical environment is a determinant of successful transport disc distraction osteogenesis. This study assessed the biomechanics of a curvilinear distractor device for correcting mandibular symphyseal defects. MATERIALS AND METHODS The finite element method was used to analyze an intact mandible, mandibular distractor bodies with different rail thicknesses (4, 6, 8, and 10 mm), and mandibular distractor bodies with rails and auxiliary lingual brackets. RESULTS Rail thickness was positively correlated with maximum von Mises stress in the distractor and negatively correlated with maximum displacement of the mandibular distractor bodies. The maximum von Mises stress occurred at the junction of the rails and fixed arms. It also exceeded the yield strength of the titanium material. Compared with the maximum displacement of the intact mandible, that of the mandibular distractor bodies was visibly increased. CONCLUSION An auxiliary lingual bracket can effectively decrease stress in such devices and displacement of mandibular distractor bodies. Rail fixation alone cannot achieve stability for distraction osteogenesis. Using an auxiliary lingual bracket effectively prevents distractor breakage and exposure.

Segmental curvilinear distraction osteogenesis.

Curvilinear distraction is currently under investigation to reconstruct curved maxillofacial bone defects. However, previous studies have revealed the discrepancy between the contour of the regenerated bone in the distraction gap and the curvilinear pathway of the transport disc. We hypothesize that the discrepancy is because of the conflict of the distraction vector and the strain vector during the consolidation. In curvilinear distraction osteogenesis, the distraction vector varies, while the strain vector during the consolidation phase is fixed-linear, from the beginning to the end of the distraction pathway. Here we bring forward a solution of segmental curvilinear distraction osteogenesis to divide the curvilinear distraction into several segments, with respective consolidation for each distraction gap. If this hypothesis is verified, the segmental distraction curvilinear distraction will benefit the reconstruction of complicated long-range maxillofacial bone defects.