Osteoblastic activity and neoangiogenesis in distracted bone of irradiated rabbit mandible with or without hyperbaric oxygen treatment

The effects of irradiation and hyperbaric oxygenation (HBO) on osteoblastic activity and angiogenesis in rabbit mandibular distraction (DO) were evaluated. Three groups were studied. The mandible of two groups received a 22.4Gy dose of irradiation. One of the irradiated groups was also given HBO, 18 times at 2.5ATA for 90min per day preoperatively. The third group was given neither radiotherapy nor HBO. Mandibular lengthening was performed unilaterally. Osteoblastic activity was assessed ex vivo by [18F]fluoride digital autoradiography. Neovascularization of distracted bone was evaluated histomorphometrically. Osteoblastic activity was higher in non-irradiated than irradiated animals. In non-irradiated rabbits, the activity was evenly distributed over the distraction area. In the irradiated groups, the activity was greater in the central third of the lengthened bone than the peripheral thirds. HBO changed the osteogenic pattern towards that of non-irradiated bone. In the non-irradiated group the number of blood vessels was 1.7-fold as compared to irradiated rabbits without HBO (P=0.0012), and the fewest number of vessels was found in irradiated rabbits without HBO. Blood vessels were more numerous in the central region than in peripheral regions in non-irradiated animals and irradiated animals with HBO, but not in irradiated rabbits without HBO therapy. It is concluded that radiotherapy disturbs distraction bone formation and neovascularization related to DO. HBO increases osteoblastic activity, but not to the level of non-irradiated bone. Angiogenic response is markedly increased by HBO.     

The effect of irradiation and hyperbaric oxygenation (HBO) on extracellular matrix of the condylar cartilage after mandibular distraction osteogenesis in the rabbit

The effects of irradiation and hyperbaric oxygenation (HBO) on the extracellular matrix of condylar cartilage after mandibular distraction were evaluated. Unilateral distraction was performed on 19 rabbits. Five study groups were included: control, low- and high-dose irradiation, and low- and high-dose irradiation groups with HBO. Additionally, four temporomandibular joints (TMJ) were used as control material. The high-dose irradiated animals were given in the TMJ 22.4 Gy/4 fractions irradiation (equivalent to 50 Gy/25 fractions). Low-dose irradiation group received a 2.2 Gy dosage. Two groups were also given preoperatively HBO 18 x 2.5ATA x 90 min. After a two-week distraction period (14 mm lengthening) and four-week consolidation period the TMJs were removed. Proteoglycan (PG) distribution of the extracellular matrix was evaluated using safranin O staining and collagen I and II using immunohistochemistry. The organization of fibrillar network was studied by polarized light microscopy. On the operated side of the control group and on the unoperated side in all, except for high-dose irradiated group, PG distribution and fibrillar network were normal appearing. In the irradiated groups, with or without HBO, the cartilaginous layer was partially or totally devoid of PG and the network structure was severely damaged. In conclusion, irradiation in conjunction with the pressure applied by distraction causes severe damage to extracellular matrix of condylar cartilage.     

Osteoblastic activity of the rabbit temporomandibular joint during distraction osteogenesis assessed by [18F]fluoride positron emission tomography

The purpose of the study was to evaluate the effects of irradiation and hyperbaric oxygenation (HBO) on osteoblastic activity of the temporomandibular joint (TMJ) region during mandibular distraction osteogenesis. Unilateral distraction was performed on 19 rabbits, which were divided into five groups. One group served as a control group, while the others received either high- or low-dose irradiation in the TMJ region before surgery. Some of the animals were also given HBO 18 times at 2.5 ATA x 90 min preoperatively. Osteogenesis was assessed by [18F]fluoride positron emission tomography at the end of the distraction. Osteoblastic activity was higher on the distracted side in all groups, except in the high-dose irradiated group without preceding HBO. HBO increased osteogenesis on both sides after radiotherapy. It is concluded that increased osteoblastic activity reflects increased pressure on the TMJ region of the distracted side, resulting from lengthening. It seems that more remodeling is required after irradiation than without preceding radiotherapy. After radiotherapy, HBO increased osteoblastic activity.     

Distraction osteogenesis in irradiated rabbit mandibles with adjunctive hyperbaric oxygen therapy.

PURPOSE: The purpose of this study was to evaluate the effect of hyperbaric oxygen therapy on bone regeneration during distraction of irradiated rabbit mandibles. MATERIALS AND METHODS: Twenty New Zealand white rabbits were randomly sub-divided into 4 groups. Group 1 served as control, group 2 received preoperative radiation therapy, group 3 received pre- and postoperative hyperbaric oxygen (HBO) therapy, and group 4 received preoperative radiation therapy and pre- and postoperative HBO therapy. All rabbits underwent a corticotomy of the left body of the mandible after placement of a distraction device. Distraction, at a rate of 1 mm/day and a rhythm of 1 turn/day, began after a 3-day latency period for 14 days. Thirty days after completion of the distraction protocol, the animals were euthanized, and histomorphometric and radiographic data of the distraction segments were obtained. RESULTS: Histomorphometric analysis of new bone fill was greatest in the non-irradiated groups compared to groups receiving radiation therapy, regardless of HBO therapy (P = .03). Pre-corticotomy bone density measurements showed a significant increase in bone density over time (P = .0007). This resulted in a significant relationship between HBO therapy, radiation therapy, and time (P = .0050). CONCLUSIONS: The results of the study support the use of HBO therapy during distraction osteogenesis. Any additional therapeutic benefit of HBO therapy in irradiated bone would require additional investigation.     

Changes in parathyroid hormone-related protein and 3-dimensional trabecular bone structure of the mandibular condyle following mandibular distraction osteogenesis in growing rats.

PURPOSE: Distraction osteogenesis (DO) is commonly performed for mandibular reconstruction during the growth period. We tested the hypothesis that parathyroid hormone-related protein (PTHrP) in mandibular condylar cartilage and underlying trabecular bone in growing individuals undergo changes in response to distraction forces. MATERIALS AND METHODS: Forty-eight 6-week-old male Sprague-Dawley rats were used. Animals underwent unilateral mandibular distraction using a distractor that we devised, and unoperated animals were evaluated as controls. DO procedure was performed: 3 days' latency period, 0.4 mm/day rate, total 4.0 mm. Changes in cartilage morphology, PTHrP activity, and 3-dimensional trabecular bone structure changes measured by micro-computed tomography were examined at 0, 2, 4, and 6 weeks of consolidation. RESULTS: A marked irregularity was noted in the superior portion of the distracted side's condylar cartilage that resolved after distraction ceased. PTHrP was more strongly expressed in the hypertrophic layer of condylar cartilage on the distracted side than in controls, up to 6 weeks after the end of distraction. Subchondral trabecular bone volume, percent bone volume, and trabecular number in the superior and posterior regions of the condyle decreased significantly by 2 weeks after distraction. These parameters returned to normal in the posterior condyle, but not in the superior part of the condyle by 6 weeks following distraction. CONCLUSION: These results suggest that unilateral mandibular distraction in growing rats causes temporary morphologic alterations of trabecular bone structure on the distracted side accompanied by increased production of PTHrP in the mandibular condyle.     

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.     

Microscopic changes in the condyle and disc in response to distraction osteogenesis of the minipig mandible.

PURPOSE: Unilateral mandibular distraction osteogenesis (DO) has been shown to cause gross changes in the mandibular condyle and articular disc. The purpose of this study was to correlate histologic findings with these gross changes in a minipig distraction model. MATERIALS AND METHODS: Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0-day latency and rates of 1, 2, or 4 mm/day for a 12-mm gap. After the minipigs were killed (at 0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested, decalcified, prepared for standard paraffin embedding, and evaluated to determine changes in 1) morphology and thickness of the articular cartilage and subchondral bone and 2) morphology of the disc. RESULTS: In control animals, there were no degenerative changes in the articular cartilage and underlying condylar bone; there were no significant differences in the mean articular cartilage thickness. The temporomandibular joint discs were normal. In experimental animals, distracted condyles showed increasing degenerative changes and mean articular cartilage thickness as the DO rate increased. The discs were thinner. These changes were present, but to a lesser degree, in the contralateral condyles. After 90 days, degenerative changes in the condyles and discs were reduced, after remodeling, except in the 4 mm/day DO group. CONCLUSIONS: Histologic changes in the condyles and temporomandibular joint discs in response to mandibular DO correlated with previously reported gross changes. These changes were greater at higher distraction rates and remodeling back to normal occurred in mandibular condyles distracted at 1 mm/day.     

Comparing calvarial transport distraction with and without radiation and fat grafting

The purpose of this study is to: a) assess transport distraction to reconstruct cranial defects in radiated and non-radiated fields b) examine adipose grafting's effect on the bony regenerate and overlying wound, and c) elucidate sources of bone formation during transport distraction osteogenesis.Twenty-three male New Zealand white rabbits (3 months; 3.5 kg) were used, 10 non-irradiated and 13 irradiated (17 treatment, 6 control) with a one-time fraction of 35 Gy. A 16 × 16 mm defect was abutted by a 10 × 16 mm transport disc 5 weeks after irradiation, and 11 animals were fat grafted at the distraction site. Latency (1 day), distraction (1.5 mm/day), and consolidation (4 weeks) followed. Fluorochromes were injected subcutaneously and microCT, fluorescence, and histology assessed.In distracted animals without fat grafting, bone density measured 701.87 mgHA/ccm and 2271.95 mgHA/ccm in irradiated and non-irradiated animals. In distracted animals with fat grafting, bone density measured 703.23 mgHA/ccm and 2254.27 mgHA/ccm in irradiated and non-irradiated animals. Fluorescence revealed ossification emanating from the dura, periosteum, and transport segment with decreased formation in irradiated animals.Transport distraction is possible for cranial reconstruction in irradiated fields but short-term osseous fill is significantly diminished. Adipose grafting enhances wound healing in previously irradiated fields but does not enhance ossification.     

牵张成骨延长一侧下颌骨对颞下颌关节的影响

目的：研究牵张成骨（DO）延长一侧下颌骨对双侧颞下颌关节（TMJ）的影响。方法：用DO技术将8只山羊的一侧下颌骨延长10mm，在牵张完成后第8和16周分别处死4只动物，取双侧关节作组织学和扫描电镜研究。结果：下颌一侧DO术后双侧髁状突发生适应性改建，髁突表面超微结构正常。结论：在适当的牵张条件下延长一侧下颌骨不会对TMJ造成病理性损害。     

Changes in growth and morphology of the condyle following mandibular distraction in minipigs: overloading or underloading?

OBJECTIVE: Loading of temporomandibular tissues during mandibular distraction may cause changes in condylar growth and cartilage thickness. This study examines the effects of distraction on the condyle in a large animal model by explicitly measuring growth and in vivo loading. DESIGN: Unilateral mandibular distraction was carried out on 20 growing minipigs divided into three groups. One group underwent distraction but not consolidation, whereas the other two groups were allowed a period of consolidation of either 1 or 2 weeks. Animals received fluorochrome and 5-bromo-2'-deoxyuridine (BrdU) labelling and masticatory strain was measured from the condylar neck. Condylar strain was also recorded in an age-matched sample of eight animals that received no distraction surgery. Immunohistochemical procedures were used to identify dividing prechondroblasts and histological analysis was used to measure mineral apposition rate, count dividing cells, and measure the thickness of condylar cartilage. RESULTS: Strain magnitude, particularly compressive strain, was much larger on the non-distraction side compared to the distraction side condyle. Compared to normal loading levels, the distraction side condyle was underloaded whereas the condyle on the intact side was overloaded. Mineral apposition and cartilage thickness were greater on the distraction side condyle compared to the opposite side. Differences between the sides were most pronounced in the group with no consolidation and became progressively reduced with consolidation time. CONCLUSIONS: Increased mineralisation and cartilage thickness on the distraction side condyle are associated with reduced, not increased loading, perhaps because of disruption of the distraction side masseter muscle.     

Changes in the condyle and disc in response to distraction osteogenesis of the minipig mandible.

PURPOSE: Distraction osteogenesis (DO) is a commonly used technique for mandibular lengthening, but changes in the temporomandibular joint have not been well documented. The purpose of this study was to evaluate the effect of DO, at varying rates, on the mandibular condyle and articular disc. MATERIALS AND METHODS: Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0 day latency and rates of 1, 2, or 4 mm/d for a 12-mm gap. After the animals were killed (0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested and evaluated to determine changes in 1) condylar form and size, 2) condylar surface, and 3) the articular disc. RESULTS: Articular surfaces of the condyles in control animals were smooth, with no irregularities or erosions. In animals undergoing distraction, ipsilateral condyles showed increasing changes in morphology and AP dimension, and surface contour irregularities as the DO rate increased. These changes were present, but to a lesser degree, in the contralateral condyles. Articular discs of both ipsilateral and contralateral sides showed variable thinning at the medial aspect at end DO. After 90 days, changes in the condyles and discs were reduced by remodeling except in the 4 mm/d DO groups. CONCLUSIONS: Results of this preliminary study indicate that gross changes occur in condyles and discs after unilateral mandibular DO. These changes are more severe at faster distraction rates (4 mm/d) and tend to resolve during neutral fixation when a rate of 1 mm/d is used.     

兔下颌骨放疗后牵张成骨动物模型的建立

目的探讨建立兔下颌骨放疗后牵张成骨动物模型的可行性。方法24只成年新西兰大白兔随机分为放疗组和未放疗组,每组12只。放疗组采用60Co放疗机照射兔下颌骨,5.4Gy/次,隔日1次,共5次。3个月后在2组兔下颌骨的双侧截骨处安装牵张器,经5d延迟期后开始牵张,速率为1mm/d,0.5mm/次,每日2次,连续7d,共延长下颌骨7mm。固定期的第0、4、6周摄下颌骨侧位X线片。固定期的第4、6周分别取出下颌骨行组织学观察。结果兔对放疗和牵张成骨术耐受良好,未见放疗引起的不良反应。X线片有新骨形成,未见死骨;组织学观察见放疗组较未放疗组有更多软骨形成。结论兔是一种用于建立放射损伤区牵张成骨模型的良好动物。     

A histomorphometric study of bone reactions to titanium implants in irradiated bone and the effect of hyperbaric oxygen treatment.

The present study was undertaken to histomorphometrically analyze early peri-implant bone tissue reactions that occur after radiotherapy and to determine whether hyperbaric oxygen therapy (HBO) affects bone tissue at the microscopic level by altering bone morphology. Twelve rabbits received a single dose (15 Gy) of cobalt60 radiation to one hind leg and the other hind leg served as a control. Titanium screws were placed into the femur and tibia directly after irradiation. Six animals received HBO during the first 4 postoperative weeks. After 8 weeks of follow-up, bone specimens containing the screws were prepared for histomorphometry. Bone-metal contact and the amount of bone in the thread areas and in the mirror areas were measured in a blinded manner. Periosteal bone formation and bone remodeling decreased after irradiation; also after HBO treatment. Hyperbaric oxygen therapy improved bone formation in nonirradiated bone and to some extent also in the irradiated bone. Bone maturation was improved in the HBO animals after irradiation. It was concluded that irradiation reduces the capacity for osseointegration of titanium implants. Hyperbaric oxygen treatment may improve bone formation and especially has positive effects on bone maturation after irradiation.     

Histological evaluation of condylar hyperplasia model of rabbit following distraction osteogenesis of the condylar neck

Summary Condylar hyperplasia is the excessive unilateral growth of mandibular leading to facial asymmetry, occlusal disturbance, joint pain and dysfunction. The aim of this study is to evaluate the histological presence of temporomandibular joint in model of condylar hyperplasia by lengthening unilateral condylar neck of distraction osteogenesis. An extra oral distractor was employed to achieve unilateral condylar neck distraction (1·0 mm daily for 7 days). The experimental condylar necks were elongated by 7 mm compared to the contralateral. Eleven adult white rabbits were used. Eight rabbits were, respectively, sacrificed after the post‐distraction period (4 or 8 weeks). All animals were evaluated clinically and histomorphometrically. The condyles radiologically showed remodelling, flattening and sclerosis. In 4‐week group, thinning of the cartilage was evident, and the trabeculae were long, not multiply connected. A thin, dense fibrous layer covered all over the surface of cartilage. In 8‐week group, the cartilaginous layer was similar to thickness of the normal cartilage, but still thinner than control. However, the fibrous layers covering condyle manifested slight degenerative changes, and even depressions and erosions were seen in the cartilage and subchondral bone. The trabeculae showed denser and multiply connected. In 8‐week group, the cartilaginous thickness of surgical condyles was significantly thinner than the contralateral. This study indicates that unilateral distraction of condylar neck loads the condyles asymmetrically. Asymmetrical loads affect more on the surgical condyles than the contralateral, and after 8 weeks of the post‐distraction, condyle could recover from asymmetrical loads in some degree.     

牵引成骨结合组织工程化软骨重建山羊髁突缺损的实验研究

目的：利用牵引成骨结合组织工程化软骨重建山羊髁突缺损。方法：12只山羊随机分为两组：实验组在下颌切迹下方作截骨线,切除一侧髁突及其颈部,左右随机。再于下颌支后缘形成转移盘,在转移盘的远中植入软骨细胞支架复合物。对照组在转移盘的远中仅植入支架。分别于牵引结束4、8、12周大体及组织学观察山羊髁突的形成情况。结果：牵引结束后4周,实验组山羊髁突已具备良好的外形,髁突表面覆盖软骨组织：对照组山羊新形成之髁突外形虽与正常髁突相似但表面无软骨层。12周时,实验组山羊髁突外形与正常髁突相似,表面仍有软骨层覆盖：而对照组山羊新形成的髁突外形虽与正常髁突相似,但表面仍无软骨层覆盖。结论：利用牵引成骨结合组织工程化软骨的方法不仅可以从外形上重建山羊髁突,而且在解剖结构上与正常髁突相似,为髁突正常功能的行使提供了良好的解剖学基础。     

Changes in the temporomandibular joint after mandibular lengthening with different rates of distraction

This study assessed the changes in the condyle after mandibular lengthening with 2 different rates of distraction (1 mm/day and 2 mm/day). Unilateral mandibular distraction was performed in 8 young adult goats. The animals were sacrificed 8 weeks after the completion of distraction, and the temporomandibular joint (TMJ) specimens were harvested and processed for histologic examination and histomorphometric analysis. Adaptive changes in the condyle were observed in the goats distracted at a rate of 1 mm/day, whereas degenerative alterations were found in those distracted at a rate of 2 mm/day. This study suggests that the TMJ is able to withstand the impact of distraction at a rate of 1 mm/day, but more rapid distraction may induce degeneration in the condylar cartilage.     

兔下颌骨牵张成骨中NO及NOS的变化规律及意义

目的:检测兔下颌骨牵张成骨各期血清NO及NOS的浓度变化规律,初步探讨其在牵张成骨的作用。方法:日本大耳白兔24只,随机分为6组,每组4只,随机选取一侧下颌牙槽嵴行牵张成骨术。分别处死空白对照组、牵张后1 d、1周、2周、4周、6周各组兔子,抽取耳缘静脉血2 mL,提取血清,至于-70℃冰箱保存,统一检测牵张不同时期NO含量及NOS的活性,并对局部牵张区行X线和组织学观察。结果:X线显示牵张成骨过程局部成骨区逐渐钙化,组织学显示牵张区骨小梁逐渐成熟;除6周组,其余实验各组的NO含量及NOS活性较对照组增多(P<0.01)。结论:血清NO及NOS含量的增加,提示其在牵张成骨过程中起一定作用。     

Microstructural and strength evaluation of regenerate tissue during the consolidation period after vertical mandibular ramus distraction

Mandibular ramus height restoration by distraction osteogenesis (DO) is a key procedure in mandibular hypoplasia reconstruction. The objective of this study was to evaluate short-term skeletal changes in the regenerated bone after vertical mandibular ramus DO using a buried distraction device. Eight subadult beagle dogs underwent bilateral vertical mandibular ramus DO. After a 7-day latency period, distraction was performed at a rate of 0.5 mm twice a day for 12 days. Four dogs were killed at 1 month and four dogs at 2 months after the end of distraction. One intact beagle was included as an unoperated control. After sacrifice, micro computed tomography (muCT) and mechanical testing of distracted sites were used to measure bone volume (BV), total volume (TV), and mechanical peak load strength, respectively. The muCT images showed wide variation in the response, with some animals demonstrating considerable bone formation and reconstitution of the canal for the inferior alveolar nerve. Quantitatively, BV was no more than 67% and BV/TV was less than 25% of the intact control, and strength was approximately 33% of the intact control value. The 1 and 2 month values were similar. These results suggest that internal distractors can successfully reconstitute bone but that the regenerated tissue did not regain structural and mechanical characteristics of native bone within the 2 month study period.     

Effect of distraction rate and consolidation period on bone density following mandibular osteodistraction in rats

The high cost of large animal protocols has limited the study of distraction osteogenesis (DO) in the craniofacial region. This study was designed to characterise a rat model for DO with regard to distraction rate and consolidation period. Unilateral mandibular distraction was performed on 129 male Sprague-Dawley rats using an osteotomy from the sigmoid notch to the inferior border of mandible. After a 3-day latency, 12 groups of 8-9 rats underwent distraction for 5 days at four different rates (0, 0.2, 0.4, 0.6mm per day), with three different post-osteotomy sacrifice times (10, 24, and 38 days) and four final predicted distraction lengths (0, 1, 2, and 3mm). Another four groups of rats (N=8 per group) were sacrificed 6 days post-osteotomy, resulting in distraction for 3 days with a predicted distraction length of 0, 0.6, 1.2, 1.8mm. Changes in mandibular morphology were measured from radiographs of disarticluated hemimandibles. The bone density of the regenerate and control sites was measured using microdensitometry calibrated with an epoxy stepwedge. Distraction linearly increased mandibular length, distraction gap width and the area of the distraction gap (P<0.00005). Mandibular length increased by 0.394 mm per distraction rate. Gap width and area increased by 0.67 and 5.8mm(2) per distraction rate, respectively. The increase in length represents only 39.4% of what was predicted, suggesting that compensatory alteration in condylar or mandibular morphology may have occurred. This speculation was further supported by the finding that mandibular length, measured without the condylar landmark, was 53.8% of predicted. During DO and early consolidation, the measures of bone density in the regenerates decreased compared to control for all groups. Thereafter, bone density in the regenerates generally increased in all groups until day 24 (P<0.01), obtaining levels that were comparable to the unoperated side. At both rostral and caudal sites adjacent to the osteotomies, measures of bone density were enhanced over control in all groups, with the rostral site also showing significant increases over time in the sham and the highest distraction groups (P<0.008 and P<0.014). We conclude that this rat model for mandibular distraction osteogenesis provides bone density changes that are consistent with those reported using larger animal protocols.     

Experimental study of mineralization in mandibular bone distraction with irradiation during the consolidation phase

INTRODUCTION: This study aimed at assessing the effect of radiotherapy on regenerated bone mineralization and consolidation obtained by mandibular bone distraction. The planned application was a new immediate mandibular reconstruction technique in defects following surgery for oral cavity tumours requiring postoperative radiotherapy. MATERIAL AND METHODS: Ten sheep underwent bilateral mandibular bone distraction (control group). A second group of 6 sheep (study group) had bilateral mandibular bone distraction followed by irradiation on the 21st postoperative day. The animals were sacrificed on the 60th postoperative day. Radiographic and histomorphometric studies were performed. RESULTS: In the control group, 9 distraction sites out of 20 were consolidated. In the irradiated group, 9 out of 12 were consolidated. Histomorphometric analysis did not demonstrate any statistically significant difference between the osseous and cartilaginous samples, the trabecular thickness of the new bone, or the osteoid surface of basal bone in the control and test groups (p=0.126, 0.247, 0.792, 0.082). However, the osteoid surface of the regenerated bone in the test group was statistically smaller (p=0.017) than in the control group. CONCLUSION: In this experiment, radiotherapy did not hinder bone mineralization or consolidation following distraction of mandibular bone receiving irradiation on the 21st postoperative day. Bone distraction could be proposed for the repair of mandibular defects following surgery for oral tumours which require early postoperative radiotherapy.