Trifocal distraction osteogenesis for segmental mandibular defect: a technical innovation

Current status of transport-disc-distraction osteogenesis for mandibular reconstruction

Surgical intervention including composite mandibulectomy is the mainstay of treatment for extrication of disease in patients with neoplasms involving the mandible. The associated morbidities and reduction in quality of life after reconstruction of the mandibular defect are dependent on the quality of the reconstruction. Therefore, alternative treatments, such as distraction osteogenesis, could be a viable option to improve patient outcome. The goal of this technology is to restore bony continuity through the use of in-situ bone in an attempt to create an anatomically correct regenerate that is better than bone grafting or revascularised free-tissue transfer. Distraction osteogenesis involves a three-step process in which bone adjacent to the defect is osteotomised and gradually opened (distracted) with the aid of a mechanical device, followed by formation of new bone with subsequent consolidation. Previous work has shown encouraging results regarding the translation of distraction osteogenesis technology from an animal model to human application, with particular success in the unradiated setting. The major challenge surrounding the use of this technology in head and neck oncological reconstruction will be the effect of radiotherapy on the regenerate bone in patients who have previously received or will need radiotherapy as part of their treatment. Although distraction osteogenesis provides an attractive alternative for reconstruction of mandibular defects, large studies of human populations are needed to further assess the use of this technology and its role in the treatment framework for mandibular neoplasms.

New internal transport distraction device for reconstructing segmental defects of the mandible

We have developed a new internal distraction device for the transport of bone, which comprises a bridging reconstruction plate, a bracket with miniplates for fixing the transport disc, a traction mechanism, and traction wire. The entire device except for part of the traction mechanism is placed internally. Activation of the traction mechanism slides the bracket on the rail of the reconstruction plate with the traction wire, which carries the transport disc along the rail. The traction mechanism can be removed after the period of distraction, leaving only the other components during consolidation.

Effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on bone consolidation on distraction osteogenesis: a preliminary study in rabbit mandibles

AIM

To examine the effectiveness of administering recombinant human bone morphogenetic protein-2 (rhBMP-2) in distraction osteogenesis.

MATERIAL AND METHODS

Twenty-one mature male Japanese white rabbits underwent unilateral mandibular osteotomy. After 5 days, the osteotomized mandibles were distracted 1mm/day for 10 days. On the first day (groups A-1 [n=4] and A-2 [n=4]) or on the last day (group B [n=5]) of distraction, rhBMP-2 mixed with collagen gel was injected into the distraction zone. In control groups (groups C-1 [n=4] and C-2 [n=4]), the mandibles were distracted without rhBMP-2 injection. At the end of the distraction period (groups A-1 and C-1) and after 2 weeks of consolidation (groups A-2, B, and C-2), the distracted mandibles were harvested and examined with soft radiographs, peripheral quantitative computed tomography (pQCT), and microscopy.

RESULTS

Radioopacity was more marked in the distraction zone of the groups with rhBMP-2 than in control groups. The mineral density of the cortical bone (BMD) was higher in groups B and A-2 than in group C-2. Histologically, bone formation was more advanced in groups A-2 and B than in group C-2. The cortical BMD was higher in group A-1 than in group C-1. Histologically, bone formation was more advanced in groups A-2 and B than in group C-2.

CONCLUSION

These results suggest that rhBMP-2 promotes bone formation in distraction osteogenesis.

Reconstruction of mandibular symphyseal defects by trifocal distraction osteogenesis: an experimental study in Rhesus

Mandibular symphyseal defects caused by tumor surgery, trauma, or congenital misshape can produce maxillofacial deformity and functional handicap. Recently, the technique of distraction osteogenesis has become a valuable reconstructive method for craniofacial bone defects. Four adult rhesus monkeys were used in this study. The anterior mandibulectomy (ranged from canine to canine) was performed, and bilateral transport segments (ranged from first premolar to first molar) were created. Custom-made multiplanar distractors were applied for the reconstruction of the monkeys' artificial mandibular symphyseal defects by trifocal distraction osteogenesis. After a delay period of 7 days, the bilateral transport discs were distracted forward and inward simultaneously. Serial X-ray and three-dimensional CT films were taken within the experimental period. Two monkeys were sacrificed at 8 and 16 weeks, respectively, after the completion of distraction. The distracted calluses and united areas between bilateral transport discs were harvested and processed for histological examination. The mandibular symphyseal defects in all animals were repaired successfully and the anterior mandibular contours were similar to the normal ones. Perfect bone regeneration in the distraction gaps was found, and fibro-bony union between the bilateral transport segments was observed in the midline region at 16 weeks after the end of distraction. The success of distraction osteogenesis for repair of mandibular symphseal defects in monkeys by this distractor may provide an alternative method to reconstruct the anterior part of mandible.

Distraction osteogenesis in the irradiated mandible. A case report

BACKGROUND

Distraction osteogenesis has been suggested as a relatively simple method of mandibular reconstruction following ablative head and neck surgery. Some authors report good results in irradiated patients while other authors report limitations with this group of patients.

PATIENT

In a 72-year-old male an attempt was made to reconstruct the irradiated mandible using distraction osteogenesis.

RESULTS

Distraction osteogenesis only resulted in an enlarged soft tissue envelope, while there was no evidence of bone formation in the distraction gap.

CONCLUSION

Based on this experience and a search of the literature, it is hypothesized that distraction osteogenesis is only a reliable reconstructive method in irradiated patients if the cumulative dose to the mandibular bone at the distraction site does not exceed a certain maximum still to be defined.

Bone Regeneration in Cranial Defects Previously Treated with Radiation

OBJECTIVES/HYPOTHESIS

Bone reconstruction in the head and neck region is frequently performed in the context of previous radiation treatment. Thus, the effectiveness of tissue engineering approaches for regenerating bone in radiated defects needs to be determined before considering application to patients. Incomplete healing is described when using osteoinductive protein therapy alone for bone defects previously treated with radiation. We hypothesized that a different approach using ex vivo gene therapy can heal these severely compromised defects.

STUDY DESIGN

Animal study using Fisher rats.

METHODS

Two weeks before surgery, rats received either no radiation or a 12 Gray radiation dose to the calvarium. Syngeneic dermal fibroblasts were transduced ex vivo using an adenoviral vector containing the cDNA for bone morphogenetic protein (BMP)-7. Critical-sized calvarial defects were created, and either a transduced cell-seeded scaffold or an autologous bone graft was placed into the defect. Nonradiated defects were harvested 4 weeks later for both groups. Radiated defects treated with bone grafts were harvested at 4 weeks, and those treated with gene therapy were harvested either at 4 or 8 weeks. Gross inspection and histology were used to evaluate wound healing.

RESULTS

None of the bone grafts had gross or histologic evidence of healing at the wound margins. The nonradiated gene therapy treated defects revealed gross and histologic near-100% bone regeneration by 4 weeks after surgery. By gross inspection, the radiated defects had soft tissue admixed with islands of bone at both 4 and 8 weeks. The histologic appearance revealed areas of dense bone in a nonconfluent pattern admixed with adjacent cells having the morphologic appearance of hypertrophic chondrocytes, suggesting continued endochondral ossification.

CONCLUSIONS

Preoperative radiation significantly impairs the ability of BMP-7 ex vivo gene therapy to heal rat critical-sized cranial defects. This finding has significant implications for translating this tissue engineering approach to patients with cancer-related segmental bone defects.

Vector Control in Transportation Osteogenesis

PURPOSE

To evaluate the ability to control vectors in the technique of transportation osteogenesis using 4 principles.

PATIENTS AND METHODS

Sixteen defects measuring approximately 30-180 mm were retrospectively evaluated. Vector control was attempted using a single or combination of the following principles: multiple linear vectors, exaggerated linear distraction ("sausage effect"), braced guided distraction, and reorientation osteotomies. Observations were made regarding the ability to create the desired vectors. Angular deviation from desired vectors was determined and recorded numerically by evaluating either submental vertex or occlusal radiographs, stereolithographic models, or digital radiographs. Radiographic evaluation of symmetry alone was not used to determine the desired vector because a more laterally displaced segment was desirable to maintain favorable facial balance when soft tissue deficiency was pronounced. A subjective evaluation scale was developed to supplement the numerical values.

RESULTS

Vector control primarily required the use of 2 or more principles. The most common combination was that of exaggerated linear distraction and reorientation osteotomy.

CONCLUSION

The use of multiple linear vectors, exaggerated linear distraction ("sausage effect"), reorientation osteotomies, and braced guided distraction greatly assisted the operator in achieving the goal of symmetrical reconstruction. Transportation osteogenesis may be considered an effective tool in the box to reconstruct patients. In cases in which vector control is achieved, the advantages of diminishing the volume of bone graft required or achieving final bony reconstruction can outweigh the disadvantages of the technique.

Internal Distraction Osteogenesis With a Unidirectional Device for Reconstruction of Mandibular Segmental Defects

PURPOSE

To present the authors' clinical experience with unidirectional internal distraction devices to reconstruct mandibular defects.

PATIENTS AND METHODS

Five patients have been treated with mandibular distraction osteogenesis to reconstruct different acquired segmental defects. These mandibular defects (35 to 80 mm in length) were reconstructed by means of internal distraction devices with a transcutaneous activator. All the patients underwent complete resection of the affected bone and immediate placement of the distraction device on the remaining mandible.

RESULTS

The results' analysis was based on clinical observation, postoperative radiographs, histopathologic findings and 3-dimensional computed tomographic scans. Successful distraction osteogenesis was achieved in 3 cases. In 1 case, extensive intraoral exposure of the device was observed, resulting in a failure of the procedure. One patient died of distant metastases 4 months after the resective surgery.

CONCLUSION

Because of the limited number of cases, this study is preliminary. However, considering the good experimental and clinical results, this new technique offers an alternative for patients with segmental mandibular defects in which, because of local or general reasons, a more aggressive procedure should be avoided.

Experimental study of mechanical analysis in mandibular lengthening

In distraction osteogenesis, the assessment of new bone formation and the decision of when to remove the distraction device are very important from clinical viewpoint. The purpose of this study was to measure bone stiffness using a strain gauge during and after mandibular lengthening, and to compare the results with those from radiographic and histological examinations. Twelve adult mongrel dogs served as the experimental subjects. An external distraction device was connected to the mandible, and distraction was started 7 days after operation and continued for 10 consecutive days. The animals underwent strain gauge measurement and radiographic examination of the mandible at the completion of distraction and every 2 weeks until the end of the consolidation period. The animals were then sacrificed at 2, 4, 6, 8, 10, and 12 weeks after completion of the distraction for histologic examinations. There was correlation between the amount of decrease in strain, increase in ratio of radiopacity, and newly formed bone in the distracted area.

Use of a plate-guided distraction device for transport distraction osteogenesis of the mandible

BACKGROUND

Transport distraction osteogenesis has been used to reconstruct continuity defects by regenerating bone and soft tissues. A challenge has been to maintain the correct vector during the distraction process. A new type of distraction device was recently developed that uses a standard reconstruction plate to "guide" the transported segment of the bone. This plate-guided distractor device (PGD) intimately follows the shape of the plate, thus allowing for 3-dimensional vector control during the distraction process.

PATIENTS AND METHODS

Four patients underwent transport distraction osteogenesis for reconstruction of segmental mandibular defects ranging in size from 4 to 7 cm. The age of the patients ranged from 27 to 62 years. Two patients had been treated with radiotherapy as part of treatment for oral malignancy. A standard locking reconstruction plate was placed to bridge the continuity gap. An osteotomy was performed to create a bone transport segment. The PGD was secured to both the reconstruction plate and the transport bone. After a latency period of 7 days, the device was activated at a rate of 1 mm/d. The distraction process continued until the transport segment reached the opposing bone or sufficient bone and soft tissue were reconstructed for oral rehabilitation.

RESULTS

All patients achieved hard and soft tissue formation. Two patients had premature consolidation of the distraction regenerate but had sufficient tissue for rehabilitation.

CONCLUSION

A PGD can be used to regenerate missing hard and soft tissues. An advantage of this technique is that it uses a reconstruction plate that is routinely placed to bridge mandibular continuity defects. This device allows for ultimate vector control by intimately following a carefully adapted plate.

Reconstruction of segmental mandibular defects by distraction osteogenesis for mandibular reconstruction

BACKGROUND

Distraction osteogenesis is an established technique for the lengthening of long bones and correction of selected craniofacial deformities. Regenerate osteoid bone matrix formed during the distraction phase is malleable and can recreate the three-dimensional form of native bones. Animal experiments and early clinical experience have confirmed that distraction osteogenesis can be used for the reconstruction of segmental bony defects. Herein we discuss the principles of distraction osteogenesis in reference to reconstruction of segmental bony defects and report its clinical application of the mandible continuity defects.

PATIENTS AND METHODS

Four patients (age, 7-83 years) with critical segmental mandibular defects (range, 3.5 cm-6.5 cm), resulting from ablative oncologic head and neck surgery underwent primary mandibular reconstruction by transport distraction osteogenesis. Two defects were at the angle and body region, one at the body, and the other at the parasymphysis and body region. Synthes Titanium Multi-vector and Leibinger Multi-guide distractors in bifocal (n = 2) and trifocal (n = 2) architecture were used after the stabilization of the segmental continuity defect using a defect-bridging mandibular reconstruction plate. Osteodistraction was carried out at a rate of 1 mm per day, with once or twice a day rhythm, after a 1-week latency period. The consolidation period was equal to the period of distraction.

RESULTS

All patients tolerated the distraction procedure. Satisfactory bone formation was observed in two patients, and partial bone formation was seen in one patient. Treatment failure was encountered in one patient who had a second oral cavity primary tumor observed during the consolidation period, requiring interruption of the treatment sequence.

CONCLUSIONS

Mandibular reconstruction with distraction osteogenesis is a potentially useful technique in selected patients with segmental mandibular continuity defects after ablative head and neck cancer surgery.

Simultaneous orbital expansion and intraoral distraction osteogenesis of upper and lower jaws in a patient with hemifacial microsomia

BACKGROUND

Correction of a micro-orbit, caused by clinical anophthalmia is a very challenging task. In hemifacial microsomia a micro-orbit may be combined with hypoplasia of the malar and the ascending mandibular ramus.

MATERIAL

A 5-year-old patient with hemifacial microsomia is described. Hypoplasia of the malar bone and the tilted occlusal plane were corrected by means of intraoral distraction osteogenesis in the upper jaw following precise simulation surgery on a 3D-model. At the same time, the ascending mandibular ramus was lengthened with a second distraction device and a spherical tissue expander was inserted into the hypoplastic orbit.

RESULTS

The malar as well as upper and lower jaws were lengthened and positioned symmetrically. The orbital cavity was expanded to 79% of that of the healthy side. Following removal of the distraction devices, the expander was exchanged for a larger one and orbital expansion was continued until overcorrection of the orbit up to 118 percent was achieved.

CONCLUSION

Orbital expansion is a minimally invasive method of enlarging the volume of the eye socket three-dimensionally. Intraorally activated buried distraction devices enable "growth" of the jaws making bone transplants avoidable in many cases. By combining both methods, complex malformations can be corrected simultaneously in children.

The effects of irradiation and hyperbaric oxygen on bone formation during rabbit mandibular distraction

[18F-]fluoride positron-emission tomography (PET) was used to assess bone formation during mandibular distraction osteogenesis. There were three study groups: irradiation, irradiation+hyperbaric oxygen and control. The two experimental groups received a tumoricidal dose of irradiation to the mandible, and one group was also given hyperbaric oxygen (2.5 ATA (atmospheres absolute) for 90 min) 18 times preoperatively. Control animals received neither irradiation nor oxygen. A unilateral osteotomy was made and, after a period of latency, bone distraction was started, continued for 2 weeks, and the distraction generated was then allowed to consolidate for 4 weeks. The first PET study was performed at the end of distraction and the second at the end of consolidation. At the end of distraction, the metabolic activity of bone in the distracted area was significantly higher in the controls than in either experimental group; differences between the experimental groups were not statistically significant. By the end of consolidation, activity in the control group had diminished to the same as in the two experimental groups, in which no significant change had occurred. Radioactivity was still significantly higher at second imaging on the distracted than non-distracted side in the control and irradiation+hyperbaric oxygen groups, but not in the group that was only irradiated. The results indicate that previous irradiation disturbs bone formation during mandibular distraction osteogenesis. Hyperbaric oxygen was not able to prevent the suppression of osteogenesis caused by radiotherapy but it might improve bone formation by prolonging high osteogenic activity.

Osteodistraction of a previously irradiated mandible with or without adjunctive hyperbaric oxygenation: an experimental study in rabbits

The purpose of this study was to analyse the effects of irradiation and hyperbaric oxygenation (HBO) on mandibular osteodistraction (OD). Eighteen rabbits were divided into three groups: 1. Irradiation (R), 2. Irradiation+HBO (R-HO), and 3. Control group (C). Animals of groups R and R-HO received in the mandible irradiation 22.4 Gy in four 5.6 Gy fractions (equivalent to 50 Gy/25 fractions). In addition, group R-HO was given HBO at 2.5 ATA for 90 min per day 18 times preoperatively. Unilateral osteotomy was made 1 month after completion of radiotherapy. After a 1 week latency period bone distraction was started at rate of 1 mm per day, continued for 2 weeks, and left to consolidate for 4 weeks. Amount of new bone was measured histomorphometrically from midsagittal sections. Area of new bone was equal in all groups. Bone was more mature and bone spicules better organized in group C than in groups R and R-HO. Cartilaginous cells were found in distracted bone in all groups but larger chondroid islands were evident only in group R. It seems that despite delayed bone formation, OD can be performed after radiotherapy. HBO had a beneficial effect on bone quality of a previously irradiated mandible.

Transport distraction osteogenesis: a new method to heal adult calvarial defects

Popularized by Gavril Ilizarov in the 1960s, monofocal distraction osteogenesis has become a well-established method of endogenous bone engineering. This revolutionary surgical technique has significantly augmented the available reconstructive orthopedic and craniomaxillofacial procedures. Bifocal distraction osteogenesis, or bone transportation, is a modification of monofocal distraction that involves moving a free segment of living bone to fill an intercalary bone defect. Bifocal distraction has been applied successfully to reconstruct complex mandibular and long bone defects. Because traumatic or postsurgical calvarial defects do not spontaneously heal in humans older than 18 to 24 months of age, we hypothesized that bifocal distraction osteogenesis could be applied to the skull to close critical size calvarial defects. Critical size (15 x 15 mm) calvarial defects were created in eight New Zealand White rabbits. Next, a 15-mm x 10-mm calvarial box osteotomy was created just anterior to the skull defect. This osteotomy created a free bone segment that could be transported. A custom-made transport distraction device was fixed into place and the skin incision was closed. After a 4-day latency period, the distraction device was activated (0.5 mm once daily for 30 days) in seven animals; the distraction device in one animal was not activated and served as a control. All animals underwent 30 days of consolidation and were then killed. Radiographs and computed tomographic scans were performed at the following time points: end of latency period (postoperative day 4), mid-distraction (postoperative day 19), and end of consolidation period (postoperative day 64). Gross and histologic analysis was performed to evaluate the quality of the bony regenerate. The control animal healed with a fibrous union. Complete closure of the skull defects was observed in five of seven rabbits at the end of the consolidation period. One animal was removed from the study because of an early loosening of the distraction device, and one was removed because of device failure. Of the remaining five animals that completed the distraction protocol, radiographs and computerized tomographic scans showed successful ossification in all five rabbits at the end of the consolidation period. This study suggests that transport distraction osteogenesis is a promising technique that may be applied to a variety of commonly encountered craniofacial problems such as nonhealing calvarial defects.

Experimental mandibular regeneration by distraction osteogenesis with submerged devices: preliminary results of a canine model

The authors describe a new technique for reconstruction of mandibular body defects. The feasibility of distraction osteogenesis with submerged (internal) devices for reconstruction of segmental mandibular defects is investigated in an experiment with five adult dogs. A segmental mandibulectomy was performed on the horizontal ramus. The bony defect was regenerated using distraction osteogenesis (bone transport) at a rate of 1 mm daily. The animals were killed after the consolidation period. Complete bone regeneration of the surgically created gap was successful in three of five dogs. Two animals failed to create new bone. In these two cases, the screws did not offer proper stability to the bony fragments, and this caused a lack of ossification. This experimental study demonstrates the possibility to use internal distraction devices to reconstruct segmental mandibular defects in a canine model. Internal devices show enormous advantages in comparison with the external ones. This method with no donor-site morbidity may become a very useful option in human mandibular reconstruction.

Distraction osteogenesis for reconstruction after mandibular segmental resection

Distraction osteogenesis with the shortening and lengthening method is a well-established procedure for repairing extremities. We used this technique for reconstruction after mandibular segmental resection. A 74-year-old woman underwent distraction osteogenesis with an intraoral device, initially shortening the mandible after a 20-mm-long segmental resection, followed by lengthening at a rate of 0.8 mm per day for 21 days. Eight weeks after the distraction, the device was removed and a dental implant was placed at the site of distraction. Radiographic observation showed new bone formation, and the implant was completely osseointegrated. Although the follow-up period is relatively short, the clinical course was uneventful. Distraction osteogenesis with the shortening and lengthening method seems to be a feasible option for reconstruction after segmental resection of the mandible.

Closure of vertical alveolar bone defects with guided horizontal distraction osteogenesis: an experimental study in pigs and first clinical results

PURPOSE

To evaluate the option of treating alveolar clefts by guided distraction osteogenesis instead of applying osteoplasty with autologous bone grafts from iliac crest, rib or fibula.

MATERIAL AND METHODS

At first, 30 land-bred pigs were operated upon. Treatment of each animal included creating bony defects measuring 2, 4 or 8 mm in the maxilla, anterior to the canine region and up to the nasal periosteum. In 15 of the 30 animals, a new horizontal segment distractor was tested. The device was placed in situ prior to creating an alveolar segment posterior to the defect. This segment was then transported gradually by distraction, thus crossing and closing the defect. At the end of the distraction and stabilization periods the newly formed bony tissue was examined.

RESULTS

The critical size of defects was found to be larger than 4 mm. In five of six animals with a horizontal defect of 8 mm, complete ossification of the defect had occurred following distraction osteogenesis. This technique was then applied to five patients successfully.

CONCLUSION

It was shown that distraction osteogenesis is a valid alternative for treating alveolar clefts.

Segmental mandibular reconstruction by microincremental automatic distraction osteogenesis: an animal study

We investigated the reconstruction of a surgically created critical size mandibular defect in sheep using a newly developed automatic distraction device. The device has an implantable component, which is fixed to the mandible to allow the transfer of the transport disc across the created defect, and an external component which is mounted on the activation pump and secured away from the site of bone distraction. Compression of the bellows in the external component causes fluid to be forced through the connecting tube into the distraction component. Distraction at a rate of 1 mm over 24 h was achieved in six sheep. New bone generated at the site of the created defects both anterior (compression side) and posterior (tension side) to the transport disc and had similar radiodensity to the adjacent mandibular bone eight weeks after the completion of distraction.

Craniofacial distraction osteogenesis: a review of the literature: Part 1: clinical studies

A review of the literature dealing with distraction osteogenesis (DO) of the craniofacial skeleton, provided by a PUBMED search (National Library of Medicine, NCBI; revised 3 April 2000) from 1966 to December 1999 was conducted. Key words used in the search were distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, craniofacial and maxillofacial. This search revealed 285 articles. One hundred and nine articles were clinically orientated and were analysed in detail in this study. The type of distraction, indications, age, type of surgery, distraction rates and rhythms, latency and contention periods, amount of lengthening, follow-up period, relapse, complications and the nature of the distraction device were analysed. This review revealed that 828 patients underwent DO of the craniofacial skeleton; 579 underwent mandibular DO, 129 maxillary DO, 24 simultaneous mandibular and maxillary DO and 96 midfacial and/or cranial DO. Craniofacial DO has proven to be a major advance for the treatment of numerous congenital and acquired craniofacial deformities. Treatment protocols and success criteria for craniofacial DO are suggested on the basis of these results. There is still, however, a lack of sufficient data, especially on follow-up and relapse, so that treatment strategies have to be validated by long-term studies in the future.

The fate of developing teeth in mandibular lengthening by distraction: an experimental study

PURPOSE

The purpose of this study was to observe developing teeth in a lengthened mandible after distraction.

MATERIAL

Ten mongrel dogs with deciduous dentitions were used.

METHODS

A corticotomy was carefully made around a tooth bud and the external distractor (Orthofix M-100) was connected. After a 5-day latent period, distraction was started at a rate of 0.75 mm per day for 10 consecutive days. Then, the lower jaw was stabilized by an external fixation to allow ossification. While the operation was performed on the left side (Distraction group), the contralateral side was studied for comparison (Control). In addition, a corticotomy, artificial fracture and external fixation were carried out to confirm the influence of the operation (Fracture group). Then macroscopic, radiographic and histological evaluations were carried out.

RESULTS

In the Distraction group, the space between the wall of the dental follicle and the crown expanded as distraction began. The end of the calcified root became wider and irregular during the distraction period, and finally, the apex closed. In the Fracture group, the teeth erupted although slight alterations of the root shape were observed in association with the operation period.

CONCLUSION

The root became irregular, but the teeth erupted within the distraction area.

Mandibular lengthening by distraction osteogenesis in children--a one-year follow-up study

OBJECTIVE

The present study was undertaken to document whether mandibular length could be increased by distraction osteogenesis in children and what happens to the mandibular position 1 year after the distraction.

METHODS

Five patients with hemifacial microsomia (four unilateral, one bilateral) had distraction osteogenesis performed to lengthen the mandible. All patients had cephalometric and panoramic radiographs obtained before and 3, 6, and 12 months after the distraction osteogenesis.

RESULTS

The total mandibular length (Co-Gn) on the affected side was increased by 11.2 mm after the distraction and remained stable during a 1-year observation period. However, the increased mandibular length tended to move the chin downward (8 mm) more than forward (2 mm) during the same period.

CONCLUSIONS

Distraction osteogensis can be used to lengthen the hypoplastic mandible. However, most of the increased mandibular length moved the chin downward more than forward.

Seven years clinical experience with mandibular distraction in children

Mandibular distraction was performed on 14 children, between September 1991 and December 1997. Their average age was 6.9 years, ranging from 1.5 to 13.5 years. All patients had severe hypoplastic mandibles with retromandibulism. Seven of the children (50%) had respiratory distress due to obstruction of the upper airway before distraction. This resolved in every case. Five patients underwent unilateral and nine bilateral distraction. A total of 23 distractors were used, 15 were applied extraorally and 8 endorally. The average latency time after operation was 2.8 days, but for the past 2 years, distraction was started beginning with the operation. The distraction was increased twice daily for an average of 5.5 weeks, by 0.4 or 0.5 mm each time, depending on the distractor. Computed tomography and ultrasound were used to follow the ossification process in the distraction gap and to measure the lengthening achieved. Subsequent retention time averaged 2.4 weeks. The mandibles were elongated by up to 18 mm (average 9.3 mm) and the respiratory distress symptoms resolved in all patients. Several minor complications which are reported occurred. Six patients were followed up for periods between 3 and 7 years. During this time further growth of the distracted mandibles was recorded.