Unilateral Mandibular Distraction Osteogenesis Research Articles

Postoperative Changes in the Upper Airway Following Mandibular Distraction Osteogenesis in Pediatric Hemifacial Microsomia.

Patients with hemifacial microsomia (HFM) may undergo unilateral mandibular distraction osteogenesis (MDO) before skeletal maturity in an effort to improve facial symmetry. Mandibular distraction osteogenesis's effect on airway volumes have been studied in the past, though to our knowledge, none have accounted for the effect of head and neck posture on airway morphology. This study aimed to tackle this shortcoming, using imaging to analyze the upper airway of patients with HFM before and after surgical intervention with MDO. The authors retrospectively reviewed patients with a diagnosis of unilateral HFM whom underwent unilateral MDO with an oblique vector at age 4 to 14 years at a single institution from 2004 to 2019. Patients with pre- and post-MDO three-dimensional computed tomography scans of the upper airway within 12 months of distractor placement and removal, respectively, were included. Head and neck postures were determined by craniocervical, pitch, roll, and yaw angles. Pre- and post-operative pharyngeal airway volumes, pharyngeal surface area, minimum retropalatal cross-sectional areas (RP CSA) and retroglossal (RG) CSA and associated anteroposterior distances were measured using Mimics 22.0 (Materialise; Leuven, Belgium). Comparison was done using Kruskal-Wallis tests and linear mixed-effects models controlling for head and neck postures. Ten patients met inclusion criteria. Mean age at pre-distractor placement computed tomography scan was 99 ± 35 months, and mean duration between pre- and post-surgery scans was 220 ± 90 days. Head and neck posture were found to be significant predictors of all airway dimensions. After controlling for significant factors with fixed effects linear modeling, surface area was found to be significantly smaller in patients after MDO by 189.48 mm2 (F[10.8] = -3.47, P = 0.0053), compared to their preoperative measurements. Surgery was not a significant predictor of changes in airway volume (F[11.6] = 0.52, P = 0.61), minimum RP CSA (F[12.2] = -0.64, P = 0.53), minimum RG CSA (F[12.6] = -1.64, P = 0.13), RP anteroposterior distance (F[14.0] = 0.30, P = 0.77), or RG anteroposterior distance (F[20.0] = -0.04, P = 0.97). Oblique vector MDO in patients with HFM is associated only with statistically significant changes in the surface area of the upper airway, and is not associated with statistically significant changes in dimensions like volume, CSA, or anteroposterior dimension. This is an important finding, as it may guide discussions surrounding risk/benefit ratio for MDO in childhood.

Application of a newly designed mandibular distraction device for navigation surgery in goats

PurposeThis animal study is to investigate the accuracy of navigation-guided mandibular distraction osteogenesis with a special designed distraction device by TBNavis-CMFS navigation system. Materials and methodsFour goats were included in this study. The 3D simulation unilateral mandibular distraction osteogenesis was simulated for 14 mm lengthening in TBNavis-CMFS navigation system. A new designed mandibular distraction device with the detachable adapter for navigation surgery in combination with the specific mandibular dynamic reference frame was applied. Navigation guided distraction osteogenesis was performed on goats and mandible was gradually distracted according to the simulation. Postsurgical 3-D skeletal measurements of presurgical simulations and postsurgical outcomes were compared statistically. ResultsNavigation assisted distraction osteogenesis was successfully performed and the new designed distraction devices worked uneventful. The accuracy of intra-operative registration was within 1 mm. The mandible was lengthened for 14.25 mm in average (13.87–14.36 mm). There were no significant differences between simulation distraction and post-operative 3-D measurements (p > 0.05). ConclusionsA new designed distraction device could be used in navigation guided mandibular distraction osteogenesis on goats with high accuracy by using the TBNavis-CMFS navigation system.

Treatment of mandibular retrognathia with unilateral temporomandibular joint ankylosis and skeletal deformity of the mandibular ramus using unilateral mandibular distraction osteogenesis

This case report describes the surgical orthodontic treatment of severely retrognathic mandible and mandibular deviation in a patient with a medical history of unilateral subcondylar fracture and temporomandibular joint (TMJ) ankylosis. Because of the severe skeletal deformity of the mandibular ramus on the side with the injury, it was impossible to perform the conventional sagittal split ramus osteotomy (SSRO) on the affected side for the correction of mandibular retrognathia. The patient was treated by Le Fort I osteotomy, mandibular distraction on the affected side, and SSRO on the unaffected side, simultaneously. After treatment, acceptable occlusion and facial esthetics were obtained, though retrognathic mandible and facial asymmetry still remained.

Effect of unilateral mandibular distraction osteogenesis on mandibular morphology in rabbits with antigen-induced temporomandibular joint arthritis

Aim was to evaluate effect of unilateral distraction osteogenesis (DO) on mandibular morphology in rabbits with antigen-induced arthritis in the temporomandibular joint (TMJ). Forty 8-week-old rabbits were divided into four groups. In groups A,C, arthritis was induced in the right TMJ. Groups A,B underwent DO. Group D served as control group. Cephalometric analysis of mandibular angle, mandibular ramus height, mandibular collum height, and total posterior mandibular height was done on CT-scans preoperatively (T0), after distraction (T1), and at euthanasia (T2). Two-factor ANOVA evaluated the effect of DO and antigen-induced arthritis. No effect of DO or arthritis was observed on mandibular angle or mandibular collum height. For T0–T1, DO increased mandibular ramus height 12.3% (95% CI 5.2–19.4%) in group B (P=0.001) and total posterior mandibular height 6.2% (95% CI 0.3–12.1%) in group A (P=0.04) and 10.0% (95% CI 4.3–15.7%) in group B (P=0.001). For T1–T2, no significant changes occurred in arthritic rabbits (group A). In conclusion, DO increased total posterior mandibular height in rabbits with arthritis. Postoperatively, no significant effect of DO was observed in rabbits with arthritis. Mandibular DO could be a viable treatment modality in patients with TMJ-arthritis.

Finite Element Analysis of the Effect of Mastication on Endochondral Ossification During the Consolidation Period of Mandibular Distraction Osteogenesis

Masticatory movements have been hypothesized to have a close relationship with the endochondral ossification of mandibular distraction gap tissue. This study investigated whether the local biomechanical environment of the gap tissue contributes to endochondral ossification of new tissue during the early consolidation period of mandibular distraction osteogenesis (DO) in the case of unstable fixation. A 3D finite element model was used to evaluate the compressive hydrostatic pressure stresses and shear stresses of new tissue in the unilateral mandibular DO gap after 4 weeks of consolidation. Four basic clenching conditions—namely clenching in the intercuspal position (ICP), left unilateral molar clenching (L-MOL), right unilateral molar clenching (R-MOL), and incisal clenching (INC)—were investigated. The gap tissue was always subjected to compressive hydrostatic pressure stresses and shear stresses, but the stress value of a specific location varied with clenching conditions. Under ICP, the gap tissue gained the maximum compressive hydrostatic pressure stresses and shear stresses; L-MOL experienced lower compressive hydrostatic pressure stresses and shear stresses, followed by R-MOL, while INC experienced minimum stress. During ICP, L-MOL, and R-MOL conditions, the junction area of lingual and distal surfaces of the gap tissue showed a greater compressive hydrostatic pressure stress, especially the area close to the inferior mandibular border, an area in which endochondral ossification has been observed in vivo during the early phase of consolidation. The results suggest that masticatory movement may contribute to endochondral ossification in the distraction gap in the early phase of consolidation under unstable fixation. During DO, stable fixation is an important factor in ensuring comparability of the results.

Navigation-guided mandibular distraction osteogenesis: a preliminary study

Purpose: This preliminary animal study aim to evaluate the accuracy of navigation assisted distraction osteogenesis (DO) in goat’s mandible by TBNavis-CMFS navigation system. Materials and methods: A total of 6 adult goats were included in this study. After 5 maxillary marking screws implantation and intermaxillary fixation with prefabricated occlusal splint, CT scan with 0.625 mm thickness was performed. The CT data was then transferred to the workstation of TBNavis-CMFS navigation system (Multifunctional Surgical Navigation System, Shanghai, China) to reconstruct a 3D imagine. Simulating distraction osteogenesis was planned in unilateral mandibular body for 10 mm lengthening and three dimensional measurement was carried out for each animal. An imagine-guided navigation surgery was performed for unilateral mandibular distraction osteogenesis based on the pre-operative design. Post-surgical measurement was compared statistically at the time of 3 m post-operatively. Results: The accuracy of intra-operative registration was within 1 mm and mandible was lengthened 10.02 mm in average (9.89–10.12 mm). No significant differences were recognized of pre and post-surgical 3D measurements comparison (P> 0.05). Conclusions: Pre-surgical planning could be transferred to unilateral mandibular distraction osteogenesis surgery with high accuracy by using of TBNavis-CMFS navigation system.

Recruitment of exogenous mesenchymal stem cells in mandibular distraction osteogenesis by the stromal cell-derived factor-1/chemokine receptor-4 pathway in rats

Distraction osteogenesis is widely used in orthopaedic and craniofacial surgery. However, its exact mechanism is still poorly understood. The purpose of this study was to find out whether there is systemic recruitment of mesenchymal stem cells (MSC) to the neocallus in the distraction gap by the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis during osteogenesis. We examined the migration of MSC towards a gradient of SDF-1 in vitro. We also transplanted MSC labelled with green fluorescent protein (GFP) intravenously, with or without treatment with CXCR4-blocking antibody, into rats that had had unilateral mandibular distraction osteogenesis, and investigated the distribution of cells labelled with GFP in the soft callus after 24h. We found that SDF-1 facilitated the migration potency of MSC both in vitro and in vivo, and this migration could be inhibited by AMD3100, an antagonist of CXCR4, and promoted by local infusion of exogenous SDF-1 into the distraction gap. This study provides a new insight into the molecular basis of how new bone is regenerated during distraction osteogenesis.

Effect of Eupolyphaga Sinensis Walker on mandibular distraction osteogenesis in rabbits

To study the effect of Eupolyphaga Sinensis Walker on mandibular distraction osteogenesis (DO) in rabbits. 30 Japanese white rabbits (weight 2.0-2.5 kg, about 3 months old) were divided randomly into control group (n = 15) and experimental group (n = 15). Unilateral mandibular DO models were established at the right mandible of the rabbits. Distraction was started 7 days after the surgery at the speed of 0.4 mm per time twice a day and continued for 10 days. From the first day of distraction to the day of execution, the experimental group rabbits were fed with 2 g of ESW power once a day at 9 o' clock. Three animals in each group were executed respectively at 24 hours, 72 hours, 1 week, 4 weeks and 7 weeks after completion of distraction, and the specimens of DO were harvested. The general observation, X-ray examination, histological study and immunohistochemical staining of bone morphogenetic proteins (BMPs) and vascular endothelial growth factor (VEGF) were performed. The images of immunohistochemical staining of BMPs and VEGF were analyzed by the image analysis software, and the results were analyzed by statistical software SPSS 17.0. The rate of the new bone formation in the experimental group was faster than that in the control group, and the immunohistochemical staining of BMPs and VEGF in the experimental group was higher than that in the control group. ESW can promote the formation of the new bone in the distracted gap during mandibular DO in rabbits, which may be due to its enhancement effect on the expression of BMPs and VEGF.

Changes in Width of Lower Face After Unilateral Mandibular Distraction Osteogenesis

Distraction osteogenesis (DO) has been popular to improve hypoplastic mandible in patients with hemifacial microsomia in craniofacial surgery. However, changes in width of the lower face after DO still lack in literatures. The aim of this pilot study was to evaluate cephalometric changes in width of the lower face at different time points after DO and to give an insight into the influence on facial contour. A total of 10 patients (8 males and 2 females) with hemifacial microsomia received DO of the mandibular body measured by posteroanterior cephalograms. Five landmarks (crista galli, latero-orbitale, gonion of the unaffected side, incisor point superior of the unaffected maxilla, incisor point inferior of the unaffected side of the mandible) were chosen for cephalometric analysis. Six distances from the soft tissue contour perpendicularly to the vertical reference line (through crista galli) were calculated through the incisor point superior of the unaffected maxilla, gonion of the unaffected side, incisor point inferior of the unaffected side of the mandible. Measurements were taken preoperatively and postoperatively on the day distraction started (time 1), at the end of distraction (time 2), and at the end of the consolidation period (time 3). Calculations for statistical significance were done for all patients. Mean differences between 3 periods were measured by repeated-measures analysis with significance determined at the 0.05 level of confidence. The results suggested that the values of 6 distances at times 2 and 3 had no significant differences when compared with the values at time 1 (P>0.05). In conclusion, DO of the unilateral mandibular body in patients with hemifacial microsomia should not be beneficial to improve the width of the lower face at a short-term follow-up.

Influence of Low-Dose Nicotine on Bone Healing

Nicotine at a low concentration was suggested as a new topical drug for clinical application. It has been reported to be capable of enhancing skin wound healing. This study was designed to assess the effect of nicotine administration at a low dose on bone regeneration using a rabbit model of mandibular distraction osteogenesis. Twenty New Zealand white rabbits were randomly assigned to nicotine group and control group. A total of 0.75 g, 60-day time release, nicotine pellets or placebos were implanted in the neck subcutaneous tissue of the rabbits. The nicotine or placebo exposure time for all the animals was 7 weeks. Unilateral mandibular distraction osteogenesis was performed. Five animals in each group were killed on week 2 and week 4 of consolidation, respectively. The mandibular samples were subjected to radiographic, histologic, and immunohistochemical analysis. Nicotine at low dose showed no significant effect on the expression of bone morphogenetic protein-2 and on the radiodensity of bone regeneration. However, the delayed bone healing was detected in the nicotine group by histologic examination. These findings imply a potential risk of compromised bone healing in patients taking nicotine medication. Further clinical studies are necessary to assess the risk of nicotine medication on reconstructive surgery.

Regenerate healing outcomes in unilateral mandibular distraction osteogenesis using quantitative histomorphometry.

The authors' goal was to ascertain regenerate bone-healing metrics using quantitative histomorphometry at a single consolidation period. Rats underwent either mandibular distraction osteogenesis (n = 7) or partially reduced fractures (n = 7); their contralateral mandibles were used as controls (n = 11). External fixators were secured and unilateral osteotomies performed, followed by either mandibular distraction osteogenesis (4 days' latency, then 0.3 mm every 12 hours for 8 days; 5.1 mm) or partially reduced fractures (fixed immediately postoperatively; 2.1 mm); both groups underwent 4 weeks of consolidation. After tissue processing, bone volume/tissue volume ratio, osteoid volume/tissue volume ratio, and osteocyte count per high-power field were analyzed by means of quantitative histomorphometry. Contralateral mandibles had statistically greater bone volume/tissue volume ratio and osteocyte count per high-power field compared with both mandibular distraction osteogenesis and partially reduced fractures by almost 50 percent, whereas osteoid volume/tissue volume ratio was statistically greater in both mandibular distraction osteogenesis specimens and partially reduced fractures compared with contralateral mandibles. No statistical difference in bone volume/tissue volume ratio, osteoid volume/tissue volume ratio, or osteocyte count per high-power field was found between mandibular distraction osteogenesis specimens and partially reduced fractures. The authors' findings demonstrate significantly decreased bone quantity and maturity in mandibular distraction osteogenesis specimens and partially reduced fractures compared with contralateral mandibles using the clinically analogous protocols. If these results are extrapolated clinically, treatment strategies may require modification to ensure reliable, predictable, and improved outcomes.

Analysis of the Biomechanical Properties of the Mandible after Unilateral Distraction Osteogenesis

The purpose of this study was to establish biomechanical outcomes measures to evaluate how mandibular distraction osteogenesis affects the overall quality of bone healing. Strength and functional integrity of the regenerate were determined quantitatively after unilateral mandibular distraction osteogenesis in comparison with the contralateral mandible and a partially reduced fracture. The authors hypothesized that the breaking load, yield, and stiffness of mandibular distraction osteogenesis would be significantly reduced in comparison with both the contralateral mandible and a partially reduced fracture. Sprague-Dawley rats underwent mandibular distraction osteogenesis (n = 8) or a partially reduced fracture (n = 6). Distraction was performed using 4 days' latency and then 0.3 mm every 12 hours for 8 days (5.1 mm). Partially reduced fractures had gaps fixed postoperatively at 2.1 mm. Both groups underwent 4 weeks of consolidation. The contralateral mandibles were used as controls (n = 14). Mandibles were tension tested at 0.5 mm/second to failure, and then breaking load, yield, and stiffness were determined. Mandibular distraction osteogenesis had significantly lower breaking load, yield, and stiffness than contralateral mandible, by 40, 30, and 60 percent, respectively. Breaking load was reduced in partially reduced mandibular fractures by 40 percent when compared with distraction osteogenesis. Using a standard Ilizarov protocol, the biomechanical properties of breaking load, yield, and stiffness in mandibular distraction osteogenesis were significantly lower than those in contralateral mandibles. Surprisingly, the breaking load of mandibular distraction osteogenesis was significantly greater than that of partially reduced mandibular fracture. These verifiable metrics of regenerate integrity can be used to discern optimal outcomes of mandibular distraction osteogenesis, potentially enhancing the clinical applications of this powerful technique.

Uncoupled angiogenesis and osteogenesis in nicotine-compromised bone healing

Nicotine is the main chemical component responsible for tobacco addiction. This study aimed to evaluate the influence of nicotine on angiogenesis and osteogenesis and the associated expression of angiogenic and osteogenic mediators during bone healing. Forty-eight adult New Zealand White rabbits were randomly assigned to a nicotine group and a control group. Nicotine pellets (1.5 g, 60-day time release) or placebo pellets were implanted in the neck subcutaneous tissue. The nicotine or placebo exposure time for all the animals was 7 weeks. Unilateral mandibular distraction osteogenesis was performed. Eight animals in each group were euthanized on day 5, day 11 of active distraction, and week 1 of consolidation, respectively. The mandibular samples were subjected to radiographic, histologic, immunohistochemical, and real-time reverse-transcriptase polymerase chain reaction examinations. Nicotine exposure upregulated the expression of hypoxia inducible factor 1alpha and vascular endothelial growth factor and enhanced angiogenesis but inhibited the expression of bone morphogenetic protein 2 and impaired bone healing. The results indicate that nicotine decouples angiogenesis and osteogenesis in this rabbit model of distraction osteogenesis, and the enhanced angiogenesis cannot compensate for the adverse effects of nicotine on bone healing.

Effect of Nicotine on Gene Expression of Angiogenic and Osteogenic Factors in a Rabbit Model of Bone Regeneration

This study aims to evaluate the influence of nicotine on the gene expression of osteogenic and angiogenic factors in bone regeneration by use of a nicotine-compromised rabbit model of mandibular lengthening. Thirty adult New Zealand white rabbits were randomly assigned to the nicotine group or the control group. The total nicotine or placebo exposure time for all animals was 7 weeks. Unilateral mandibular distraction osteogenesis was performed. Five animals in each group were sacrificed at day 5, day 11, and day 18, respectively, after commencement of active distraction. The distraction regenerate samples were harvested, and the messenger ribonucleic acid expression of bone transforming growth factor beta(1), platelet-derived growth factor A, and basic fibroblast growth factor was assayed by real-time polymerase chain reaction analysis. The messenger ribonucleic acid expression of transforming growth factor beta(1), platelet-derived growth factor A, and basic fibroblast growth factor was significantly inhibited by nicotine exposure at a variety of time points. The presence of nicotine inhibited the gene expression of angiogenic and osteogenic factors resulting in compromised bone regeneration.

Effects of Simvastatin on Mandibular Distraction Osteogenesis

The aim of this study was to evaluate the effects of local and systemic simvastatin application on distraction osteogenesis. Eighteen New Zealand white rabbits underwent unilateral mandibular distraction osteogenesis. After 7 days of neutral fixation, 0.4 mm twice per day, distraction was performed for 10 days. Simvastatin was applied locally during the osteotomy phase with a gelatin sponge carrier and systemically during the distraction osteogenesis period by oral gavage. All animals were killed at the end of the consolidation period of 14 days. The distracted mandibles were harvested and evaluated by plain radiography, by peripheral quantitative computed tomography, and with histomorphometry. Radiographic evaluation with peripheral quantitative computed tomography showed that the area of the regenerate increased by 9.6% in the local simvastatin group and by 19.3% in the systemic simvastatin group as compared with the control group. In both experimental groups the density of the regenerate increased by 6.7% as compared with the control group. Statistical evaluation of radiographic data showed that all of these changes were not significant. Histomorphometric evaluation determined that there was no statistical difference among groups with regard to the ratios of bone tissue volume to fibrous tissue volume and bone tissue volume to marrow tissue volume. The results of this study suggest that simvastatin's effect on enhancing distraction regenerate is limited with the applied doses and methods.

Comparison of Skeletal and Soft-Tissue Changes following Unilateral Mandibular Distraction Osteogenesis

The purpose of this study was to investigate the relationship between soft-tissue and underlying skeletal structures before and after unilateral mandibular distraction osteogenesis. The sample consisted of 11 patients (three girls and eight boys) with an average age of 4.6 years at the time of treatment. All patients had unilateral craniofacial microsomia (four right-sided and seven left-sided unilateral craniofacial microsomia) and all underwent unilateral mandibular distraction osteogenesis. Measurements were performed on frontal medical photographs and posteroanterior cephalograms at predistraction (time 1) and postdistraction (time 2) periods. Left and right ramus heights, skeletal midline deviation, and transverse occlusal plane were measured on the posteroanterior cephalograms and compared with the linear distances between the lip commissures and the orbital plane, the circumference of both sides of the faces, and the angulation of the oral commissure plane as recorded on the medical photographs, respectively. To reduce magnification error, ratios of affected to less affected sides of the mandibles and soft-tissue facial structures were selected and studied. A similar relationship was observed between soft-tissue and skeletal components. However, there was no 1:1 relationship between the changes in ramus height and improvement in parallelism of lip commissures to the orbital plane. A significant improvement in soft- and hard-tissue anatomy has been observed following unilateral distraction osteogenesis of the mandible. The relationship between the soft-tissue and skeletal correction was different for all patients because of the large range in severity of the craniofacial malformation. Greater skeletal deficiency requires more correction to achieve symmetry of both hard and soft tissue.

Poster 125: Mandibular Lengthening by Distraction Osteogenesis (DO) in a Porcine Model: Changes in Anterior Digastric Muscle

The effects of mandibular lengthening by distraction osteogenesis on the muscles of mastication are not well understood. The purpose of this investigation was to document the changes, over time, in the digastric muscle in response to unilateral mandibular lengthening. In this experiment, 17 mixed dentition Yucatan minipigs were used: Osteotomy and unilateral (right side) mandibular distraction osteogenesis using a protocol of 0-day latency, 1 mm/day rate of distraction for 12 days, followed by 24 days of fixation (n=14 minipigs); osteotomy and acute lengthening of 12 mm (n=2); and sham control with dissection and 0 mm advancement (n=1). Anterior digastric muscles were harvested from the distraction and contralateral sides at mid-DO, end-DO, mid-fixation, and end-fixation. The same muscle samples were harvested from the acute lengthening and sham control groups 24 days after operation. All muscle samples were fixed, embedded in paraffin, and sectioned transversely and longitudinally. Specimens were stained with Hematoxylin & Eosin (H&E) or immunostained against PCNA. To evaluate histologic changes, a blinded pathologist examined all the H&E slides under light microscopy for the presence of inflammation, hematoma, necrosis, fibrosis, edema and for the size of muscle fibers. Histologic images (400X) from H&E slides were used for computer histomorphometric analysis. The cross-sectional surface area of the muscle fibers was measured by histomorphometric software (Image J, NIH) and the data were analyzed for statistical significance (two sample T-test). Proliferation activity was evaluated by calculating the percentage of PCNA positive nuclei in six randomly chosen fields in each sample. Statistical significance of the means was evaluated using the Wilcoxon’s matched pairs test. In two of 4 pigs, at mid-DO, there was a mild and scattered inflammatory infiltrate in the experimental side muscle. There were no inflammatory changes observed in specimens at end-DO (n=4), mid-fixation (n=4) and end-fixation (n=2). Muscles from the sham control group also demonstrated no inflammatory changes. In the acute lengthening group (n=2), inflammatory infiltrate, fibrosis, edema, and hematoma were present in the digastric on the experimental side. Histomorphometric analysis showed that cross-sectional surface area of the anterior digastric myocyte fibers on the distracted side were significantly (10%) larger than controls at end-fixation. In the acute lengthening group there was a 23% reduction in myocyte fiber cross-sectional surface area 24 days postoperative. The size of myocyte fiber nuclei was increased on the distracted side at all time points. Data from PCNA immunohistochemistry revealed that the anterior digastric muscle, which is parallel to the distraction vector, had a 3.6-fold (mid-DO group), 7.1-fold (end-DO group), 10.4-fold (mid-fixation group), 10.3-fold (end-fixation group) increase in PCNA-positive myocytes compared with the contralateral samples. Anterior digastric muscle in the acute lengthening group had a 2.9-fold increase in PCNA-positive myocytes when compared to the contralateral muscle. The results of this study indicate that the anterior digastric muscle, whose fibers are parallel to the distraction vector, undergoes hypertrophy and proliferation in response to DO.

Poster 185: Treatment of Concomitant Facial Asymmetry and Temporomandibular Joint Disorder With Unilateral Mandibular Ramus Distraction Osteogensis

One of the most difficult challenges confronting the oral and maxillofacial surgeon is the management of a patient with dentofacial deformity who also has temporomandibular joint (TMJ) disorder. Questions arise as to whether biomechanical loading on the TMJ derived from gradual distraction will affect the TMJ, further exacerbating TMJ dysfunction. Four adult patients with concomitant severe facial asymmetry and various types of congenital or acquired TMJ disorder were treated with unilateral mandibular ramus distraction osteogenesis (MRDO).

Masticatory mechanics of a mandibular distraction osteogenesis site: Interfragmentary micromovement

Micromovement at a fracture or distraction osteogenesis (DO) site may play a significant role in bone formation and healing. Mastication is an important physiological process that can cause substantial micromovement at a mandibular disjunction. The purpose of this study is to characterize and quantify the micromovement caused by mastication. Eighteen pigs, divided into three groups based on duration of consolidation, received a unilateral (right) mandibular angle distraction osteogenesis protocol. Differential variable reluctance transducers (DVRTs) and ultrasound crystals were used to measure the change of gap width as well as interfragmentary movement during mastication. Synchronized chewing video and interfragmentary movement recordings were used to determine the magnitude and direction of micromovement at different phases of the chewing cycle. The magnitude of micromovement did not increase significantly with distraction up to almost 5 mm, but did decrease gradually with consolidation. The average micromovement magnitude during the distraction phase was 0.2–0.3 mm, equaling 50,000–250,000 microstrain (με) on interfragmentary tissue. The dominant deformation pattern was bending in the sagittal plane. The most common direction of bending at the power stroke of chewing was concave dorsally, i.e., superior shortening and inferior lengthening. These findings elucidate how masticatory mechanics affect a mandibular distraction site, and the measurements may be useful for future simulation studies.

O.091 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. © 2006 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 64:249-258, 2006