Abstract
One-step transport disc distraction osteogenesis (TDDO) is an effective method for the restoration of mandibular defects. This study aimed to investigate the feasibility of double-step TDDO in the reconstruction of unilateral mandibular segmental defects after tumour resection using internal distraction devices. Six patients with unilateral mandibular segmental defects were reconstructed successfully with this technique. In the double-step TDDO procedure, the mandibular body was lengthened first and then the mandibular ramus was restored. The distraction movement was set at a rate of 0.4 mm twice per day. Dental rehabilitation followed distractor removal. The maximal amount of lengthening was 55 mm in the mandibular body and 42 mm in the mandibular ramus. The average amount of lengthening was 52 mm in the mandibular body and 34 mm in the mandibular ramus. The aesthetic and functional results were excellent in all patients. The implants were integrated successfully and dental restoration was satisfactory. In this study, double-step TDDO is a reliable method for reconstruction of mandibular defects after tumour resection, especially for large mandibular defects. This technique is an ideal method for dental rehabilitation, despite the long overall treatment time.
Large mandibular defects resulting from benign or malignant tumour ablation inevitably cause difficulties in speech, mastication, swallowing and aesthetics. Owing to the unique anatomy and complex function of the mandible, the deformity causes serious and complicated problems in functional and aesthetic aspects . Non-vascularized bone grafts (NVBG) and vascularized bone grafts (VBG) have been used successfully to restore the mandible defect, but high rates of complication limited their applications . It is necessary to develop a new and effective alternative for mandibular reconstruction.
Distraction osteogenesis was introduced by Ilizarov in 1957. It has been widely applied by orthopaedic surgeon over the past 40 years to lengthen the long bones of the extremities . Transport disc distraction osteogenesis (TDDO) is based on the principles of distraction osteogenesis, the difference being the transported fragment in the final joining of the free sides. By means of distraction, the transport disc was moved in the desired direction rationally and new bone was regenerated inside the gap. McCarthy et al. reported the first clinical case of mandibular lengthening by gradual distraction . Recently, excellent results have been obtained in mandibular reconstruction with distraction osteogenesis .
One-step TDDO has some limitations, for example it cannot handle large mandibular defects involving body, angle, and part or whole ramus. The total length of the mandibular defect is limited by means of the use of this device, because most internal devices have the maximum length. On the other hand, the angle shape is difficult to restore.
In this article, the unilateral mandibular defects involving body, angle, and the ramus were reconstructed with two-step TDDO following mandibulectomy. In the distraction procedure, the first distraction was carried out horizontally and mandibular body was lengthened. The second distraction aimed to reconstruct the residual defect of mandibular ramus.
The three-dimensional (3D) computerized scan of the craniofacial skeleton and the virtual operation were carried out by the computer-assisted surgery unit before surgery. After all distractors had been removed, dental implants were inserted under local anaesthesia. The authors attempted to evaluate the effectiveness of this technique in the reconstruction of large mandibular defects. In addition, the superiority, disadvantages, indications, and limitations of this technique are described in this report.
Materials and methods
6 patients underwent mandibular reconstruction. The patients were informed in detail about the advantages and disadvantages of double-step TDDO and traditional bone grafting (VBG and NVBG) preoperatively. The patients had a sound understanding before making a choice. Only those who preferred double-step TDDO were selected. These patients had been treated by the same therapy group.
The classification of the mandibular defects is that proposed by Urken’s report ( Table 1 ). The method of double-step TDDO was used to reconstruct the unilateral mandibular segmental defects of these patients. The mandibular body was lengthened first, then the residual defect of the mandibular ramus was restored. According to the study protocol, photographs and cephalograms (lateral and poster-anterior) were obtained at four times: before and after operation, at the time of removing the device, and 6 months thereafter. Panoramic radiographs were also obtained monthly after the surgical procedure.
| Cases | Sex | Age | Diagnosis | Tumour size (cm 3 ) | Mandibular defect * |
|---|---|---|---|---|---|
| 1 | Male | 22 | Ameloblastoma | 8 × 10 × 4 | Body + ramus + condyle |
| 2 | Female | 18 | Ossifying fibroma | 6 × 6 × 3 | Body + ramus |
| 3 | Male | 25 | Ameloblastoma | 6 × 5 × 2 | Body + part of ramus |
| 4 | Female | 20 | Ameloblastoma | 5 × 7 × 4 | Part of body + ramus |
| 5 | Female | 33 | Ondontogenic keratocyst | 10 × 8 × 3 | Body + ramus + condyle |
| 6 | Female | 19 | Central haemangioma | 5 × 5 × 4 | Part of body + ramus of jaws |
After diagnosis, the individual surgical plan was formulated. Before the operation, preoperative CT scanning was performed in all patients ( Figs. 1 and 2 ). Digital data were transferred to a workstation where the preoperative structure of the craniomaxillary bones was realized virtually. Virtual mandibulectomy was carried out according to the individual surgical plan. The mandibular defect was then virtually reconstructed by the computer-assisted surgery unit. The final results were transformed into an individual solid model using a digital model manufacture machine. The individual mandibular model and distractor were built according to the preoperative data for each patient. Distraction osteogenesis was simulated on stereolithographic models of patients before the operation. After discussion, the authors were confident to give treatments to the patients.
The operation included the following steps. In step 1, all patients had previously undergone a 3D computerized scan of the craniofacial skeleton, which was used as the basis of the planning process. The scan data were imported into Med Graphics workstation (a surgical navigation system) where the preoperative structure of the craniomaxillary bones was virtually realized. In step 2, virtual mandibulectomy (cut diseased side) was carried out according to the individual surgical plan by the computer-assisted surgery unit. The surgeon chose the location of the osteotomy and performed the cut virtually. The distractor vector defined the location of the screw and the osteotomy line. The optimal distractor was suggested from the system according to the mandibular defect. The system automatically determined the position where the distractor would be placed and the placement of the screws. The mandibular defect was virtually reconstructed through reflecting the healthy mandibular area of the opposite side using a mirror technique. The final results were transformed into an individual solid model using a digital model manufacture machine.
In step 3, mock surgery was performed on the stereolithographic models before the operation on the patients was carried out. The osteotomy and distraction processes were simulated. A surgical template was designed to fit the contour of the mandible. In step 4, to execute the planned process successfully it was necessary to transfer information regarding the distractor plan and screw positions from the model to the patient. A file containing the computer data was sent to Medical Appliance Company (Ningbo Cibei Medical Treatment appliance Company, Limited) to fabricate individual distractors and the surgical template.
In step 5, the mandibular body was scheduled for lengthening first, followed by the residual defect of the mandibular ramus. The above steps were repeated after the reconstruction of the mandibular body to restore the residual defect of the mandibular ramus. After the distractors were removed, the dental implants were inserted under local anaesthesia.
Operation and distraction protocol
A submandibular approach was used to provide good access. Mandibulectomy (cutting the diseased side) was carried out according to the individual surgical plan ( Fig. 3 ). An osteotomy in the residual region of the mandible was performed proximal to the defect to obtain a transport disc. The distraction device was installed under the direction of the surgical template.
The transport bone fragment was fixed to the movable part of the distraction device ( Fig. 4 ). The distraction activator placed percutaneously, direct closure of the submandibular approach was performed.
After a 5-day latency period, posterior distraction proceeded at a rate of 0.4 mm twice per day. The healthy side underwent intermaxillary fixation to avoid skeletal discrepancies and development of severe malocclusion during distraction. Intermaxillary fixation was started immediately after the operation and generally lasted 15 days after the horizontal distraction. Panoramic radiographs were obtained monthly after the surgical procedure. The distraction position of the transport disc and the new bone generation were observed. The process of distraction was stopped when the length of the new bone was similar to the healthy side. The period of distraction varied depending on the initial size of the defect. The consolidation phase generally took 14 weeks to obtain adequate height for the new bone ( Figs. 5 and 6 ). During this phase, the apparatus remained in place and functioned as an external fixator. At the end of the consolidation period, adequate new bone was generated and the strength of the new bone could endure the second surgical procedure and distraction.
The second surgical procedure and distraction were carried out to reconstruct the mandibular ramus. The surgical procedures were similar to the first operation. Before the second surgical procedure, the first distraction device was removed. A new transport disc was obtained from the posterior border of the newly generated mandibular body. The second distraction device was placed ( Figs. 7, 8 and 9 ). After a 5-day latency period, vertical distraction was initiated at a rate of 0.4 mm twice per day. The intermaxillary fixation lasted from immediately after the operation to the entire procedure of vertical distraction movement. The period of fixation depended on the individual situation of each patient and their CT and X-ray examinations ( Figs. 10 and 11 ). The transport disc was distracted regularly towards the temporal bone or the docking site. The activation period was completed after the total length of the new bone reached the length of the healthy side.
