Distraction osteogenesis of the craniofacial skeleton

Monobloc Advancement by Distraction Osteogenesis Decreases Morbidity and Relapse

BACKGROUND

Treatment of midface hypoplasia and forehead retrusion with monobloc advancement is associated with significant complications, including meningitis, prolonged intubation, and frontal bone flap necrosis. To see whether distraction of the monobloc segment offered decreased morbidity, the authors compared clinical outcomes of patients who underwent conventional monobloc advancement with those of patients who underwent monobloc distraction.

METHODS

Group 1 (conventional monobloc; n = 12) underwent traditional monobloc advancement with bone grafting. Group 2 (modified monobloc; n = 11) did not receive ventriculoperitoneal shunts and underwent the above procedures with placement of a pericranial flap and fibrin glue over the midline defect. Group 3 (monobloc distraction; n = 24) underwent advancement of the monobloc segment by distraction osteogenesis using internal distraction devices. Complications included meningitis, cerebrospinal fluid leak, frontal bone flap loss, and wound infection. Preoperative, postoperative, and follow-up lateral cephalograms were used to assess horizontal changes of the forehead, midface, and maxilla.

RESULTS

Group 3 (distraction monobloc) had the lowest complication rate (8 percent), followed by groups 2 (modified monobloc; 43 percent) and 1 (conventional monobloc; 61 percent) (p < 0.05). Group 3 achieved greater advancement (12.6 mm) than did group 2 (9.4 mm) or group 1 (9.1 mm) (p < 0.05). Relapse was least in group 3 (8 percent) compared with groups 2 (67 percent) and 1 (45 percent).

CONCLUSIONS

Monobloc advancement by distraction osteogenesis had less morbidity and achieved greater advancement with less relapse compared with conventional methods of acute monobloc advancement with bone grafting. Monobloc distraction is superior to conventional methods of acute monobloc advancement and is an alternative to staged fronto-orbital advancement followed by Le Fort III advancement.

Bone regeneration in mandibular distraction osteogenesis combined with compression stimulation

PURPOSE

This study compared modified distraction osteogenesis (DO) protocol with conventional DO protocol on healing bone formation. Computer simulation was performed to understand the mechanical environment of modified DO protocol, which applies compression during the consolidation period.

MATERIALS AND METHODS

Fifty rats were used in this study. Twenty-five rats in the conventional DO (control) group were sacrificed at postoperative days 11, 21, 28, 35, and 49 after osteotomy. In the modified DO (experimental) group, compression was applied on day 7 after distraction (day 18 postoperatively) for 4 days during the early consolidation period and 25 rats were sacrificed on postoperative day 19, 28, 39, 46, and 53. The histologic and radiographic findings were used to compare the 2 groups. Further, computer simulation was used to predict the mechanical environment of healing bone under conventional and modified DO protocol.

RESULTS

Radiographic findings showed that the experimental group resulted in denser and wider healing bone. Histologically, the experimental group yielded more mature lamellar bone than the control group. Computer simulation showed that absolute values of tissue strains were nearly double in the control group because of the softer healing tissues. Both the experimental and control groups showed high strains at the ridge crest. Concentrated tensile strain along the distraction direction at the ridge crest might hinder bone formation at the interface, while compressive strain could facilitate the process.

CONCLUSION

This study proposed a modified DO protocol of adding compression during the early consolidation period of conventional DO protocol. This new technique appears to provide faster and denser bone regeneration.

New Osteotomies for Midface Advancement in Patients With Crouzon Syndrome

In some patients with Crouzon's syndrome the typical midface advancement can produce an excessive nasal protrusion which calls for subsequent rhinoplasty. Proposed modification of classical Le Fort III procedure consists in midface osteotomy and external distraction without median orbital walls and nasal component. Limited surgical approach through vestibular incision and split lower eyelids makes the operation quite easy and less extensive. So far, three adult patients were successfully treated according to described modality.

Long-Term Stability and Growth following Unilateral Mandibular Distraction in Growing Children with Craniofacial Microsomia

BACKGROUND

The purpose of this study was to evaluate long-term mandibular skeletal stability and growth following unilateral mandibular distraction in growing children.

METHODS

This retrospective longitudinal study of 12 consecutive patients with unilateral craniofacial microsomia who underwent mandibular distraction had a range of 5 years of postdistraction follow-up; five patients were followed for 10 years. Records included clinical photographs, dental study models, lateral and posteroanterior cephalograms, and panoramic radiographs obtained before distraction, at the time of device removal, and 1, 5, and 10 years after distraction. The mean patient age at the time of distraction was 48 months. The device was activated an average of 21.7 mm at the rate of 1 mm per day. The mean latency period was 6.1 days, and the mean consolidation period was 60.6 days. Fifty-two parameters were examined at each of the five time intervals.

RESULTS

On average, the ramal length (condylion to gonion) increased 13.04 mm in the distracted rami. At 1 year after distraction, this dimension decreased by 3.46 mm. At 5 and 10 years after distraction, the average condylion-gonion dimension increased by 3.83 and 4 mm, respectively, with an average growth rate of 0.87 mm per year; during the same period, the unaffected ramus grew 1.15 mm per year.

CONCLUSIONS

The distraction technique does not eliminate the inherent growth potential of the affected mandibular side. Facial asymmetry is significantly improved after distraction, and despite mild relapse observed during the first year, surgical correction is stable in the later years of follow-up.

Experimental evaluation of the effects of zoledronic acid on regenerate bone formation and osteoporosis in mandibular distraction osteogenesis

PURPOSE

The aim of this study was to evaluate the effects of systemically administered zoledronic acid (ZA) on the bone mineral density (BMD) and bone mineral content (BMC) at mandibular distraction sites in rabbits.

MATERIALS AND METHODS

Eighteen New Zealand white rabbits were randomly divided into 2 groups. Bone lengthening was performed in the left portion of the mandible through distraction osteogenesis at a rate of 0.5 mm every 12 hours for 5 days. While the experimental group rabbits were administered intravenous 0.1 mg/kg ZA, control group rabbits were given only saline infusion during operation. All animals were sacrificed at the end of the consolidation period of 28 days. The mandibles of all animals were removed and both the anterior and posterior pin regions of the regenerate and regenerate region were evaluated by dual energy x-ray absorptiometry (DEXA). BMD and BMC data were statistically analyzed.

RESULTS

Except for 1 rabbit from the experimental group that had an infection at the external pin region, all animals showed complete clinical healing. When the values in the group receiving ZA were compared with those of the control group, it was observed that the BMD values of the anterior pin region of regenerate, regenerate region, and posterior pin region increased by 23%, 20%, and 31%, respectively; and BMC values increased by 22%, 24%, and 32%, respectively. When data of these regions were compared, both BMD and BMC were found statistically different in all regions (P < .05).

CONCLUSION

Results of this study showed that ZA had positive effects on new bone formation at and around the distraction gaps of the lengthened rabbit mandibles by distraction osteogenesis.

Pediatric Feeding Disorder and Growth Decline following Mandibular Distraction Osteogenesis

BACKGROUND

Mandibular distraction osteogenesis has proven to be an effective treatment for upper airway obstruction related to micrognathia. Changes in the aerodigestive space can help facilitate tracheostomy removal in children and prevent tracheostomy in newborns. However, this may also precipitate changes in the ability to orally feed. There are few data on early postoperative feeding and growth rate following mandibular lengthening. The authors found evidence of growth rate decline and feeding difficulty in pediatric patients following mandibular distraction osteogenesis.

METHODS

Ten pediatric patients underwent mandibular distraction osteogenesis for treatment of upper airway obstruction. Outcomes in resolution of upper airway obstruction, oral feeding success, and growth rate were analyzed. Follow-up ranged from 12 to 28 months.

RESULTS

All 10 patients had complete resolution of upper airway obstruction. The length of distraction ranged from 10 to 17 mm. Three patients demonstrated a feeding disorder after mandibular distraction osteogenesis, defined as requiring a long-term (>1 month) alternate feeding method (gastric tube in two patients and gastric gavage in one). Seven of 10 patients exhibited an early decline in growth rate following distraction. Data used to determine growth rate changes were weight measurements at the time of distraction, at the time of distractor removal (6 to 8 weeks after distraction), and at 6 and 12 months after the date of distraction initiation.

CONCLUSION

These results suggest that infants and children undergoing mandibular lengthening by distraction osteogenesis should be carefully monitored for postdistraction feeding disorder and growth rate disturbance.

Mandibular distraction osteogenesis enhanced by bone marrow mesenchymal stem cells in rats

OBJECTIVE

This study was to observe the effects of bone marrow mesenchymal stem cell transplantation on new bone formation in a rat mandibular osteodistraction model.

MATERIAL AND METHODS

Autologous bone marrow stem cells were obtained from tibiae of 40 male rats. Two weeks after cell harvest, the rats underwent right mandibular distraction and were then randomly divided into two groups (group A=20, group B=20). After distraction was complete, the stem cells were injected into the distracted gaps in group A, while the rats in group B only received physiological saline. Twenty rats (10 from each group) were sacrificed on postoperative days 27 and 55, respectively. The distracted mandibles were harvested and processed for radiographic, histological and histomorphometric analysis.

RESULTS

The radiodensity of the distraction zone was higher in group A than in group B at both time points. Histologically callus was found in both groups but more bone was formed in group A. Histomorphometric analysis also demonstrated that both new bone volume and thickness of the new trabeculae were significantly greater in group A than in group B.

CONCLUSION

The results of this study suggest that autologous bone marrow stem cell transplantation may be considered as a potential method to accelerate bone regeneration in the distraction gap, and enhance consolidation.

Distraction Rate and Latency: Factors in the Outcome of Pediatric Mandibular Distraction

BACKGROUND

Distraction osteogenesis was initially devised as a way to lengthen the lower extremity. All the basic tenets of the technique were developed based on this use. This includes both the supposed need for a latency period before distraction begins (3 to 5 days) and the ideal rate of distraction (1 mm/day). There is no evidence that these values apply to craniofacial distraction osteogenesis, particularly in children. Indeed, with the markedly improved blood supply in the face when compared with the lower extremity and the use of the technique in children versus adults, one might assume that a shorter latency period and a more rapid rate of distraction are possible.

METHODS

This study is a retrospective review of 22 pediatric patients with mandibular hypoplasia undergoing mandibular distraction osteogenesis. All patients were operated on by a team consisting of an oral surgeon and a plastic surgeon. All the distraction devices used were external. All patients had a latency period, before activation, of less than 24 hours and a distraction rate of 2 mm/day.

RESULTS

Two patients developed cellulitis at the pin sites, one patient developed premature healing, one patient developed a nonunion that required further surgery. This was the only patient in the series who had distraction of a previous bone graft. No patient undergoing distraction of native mandible developed a nonunion.

CONCLUSIONS

Eliminating the latency period and rapidly distracting the mandible in pediatric cases has an acceptably low complication rate. This benefits the patient in terms of an overall reduction in the amount of time that the child needs to remain in the distraction device. The patient spends less time with the distraction device, thus reducing the potential morbidity and increased cost of the treatment. Potential explanations for why this variation in distraction technique is successful include the improved blood supply in the face of children and the failure of external devices to translate all the distracted movements to the bone interface. Some of this force is translated into both bending of the pins and migration of the pins through bone. Although a latency period might be necessary in the distraction of the lower extremities, the application of this concept to the craniofacial skeleton in children is erroneous.

Guided tissue regeneration enhances bone formation in a rat model of failed osteogenesis

BACKGROUND

Guided tissue regeneration is a technique that uses barrier materials to enhance tissue regeneration. Although previously demonstrated to be an effective way of enhancing craniofacial osteogenesis in several animal models, the ability of guided tissue regeneration to augment bone formation in the context of distraction osteogenesis is unknown. In the current study, the authors applied the principle of guided tissue regeneration to their rat mandibular distraction osteogenesis model in an attempt to enhance bone regeneration.

METHODS

Twelve (n = 6 per group) adult Sprague-Dawley rats underwent routine gradual distraction (5 days' latency, 4-mm distraction over 8 days, 4 to 6 weeks of consolidation) and acute distraction (immediate lengthening to 4 mm, 6 to 8 weeks of consolidation). An additional 10 animals underwent acute distraction followed by application of bioabsorbable Gore Resolut XT membranes (acute distraction plus guided tissue regeneration). Membranes were completely wrapped around the distraction gap. Animals were killed 6 and 8 weeks postoperatively and mandibles analyzed radiographically and histologically.

RESULTS

Quantitative histomorphometric analyses were performed to compare relative bone formation between all three groups. Gradual distraction mandibles achieved bony union by 6 weeks with 86 percent bone formation, which increased to 98 percent by 8 weeks. Acute distraction mandibles healed with a fibrous nonunion and only 37 percent bone formation by 8 weeks. In contrast, acute distraction plus guided tissue regeneration-treated mandibles formed significantly more bone than acute distraction mandibles by 6 weeks (57 percent) and achieved bony bridging by 8 weeks, with 88 percent new bone formation.

CONCLUSION

The authors' data demonstrate that guided tissue regeneration can significantly enhance bone formation in a fibrous nonunion model of mandibular distraction osteogenesis.

Mandibular mechanics after osteotomy and distraction appliance placement I: Postoperative mobility of the osteotomy site

PURPOSE

Fixation at the osteotomy site for mandibular distraction osteogenesis (DO) is probably not rigid, especially during mastication. Micromotion may affect the course of DO. This study aimed to measure the mobility of the fresh distractor-fixed osteotomy site in response to mastication and masticatory muscle stimulation.

MATERIALS AND METHODS

Twenty-eight domestic pigs, 6 to 8 weeks old, underwent osteotomy of the right mandible and placement of a distractor appliance. Immediately after surgery, displacement at 3 different locations (superior-lateral, inferior-lateral, and inferior-medial) of the osteotomy site was assessed using ultrasound piezoelectric crystals or differential variable reluctance transducers (DVRTs). The amount of lengthening or shortening at each location was measured during mastication and muscle stimulation. Displacement was also measured for bilateral osteotomy during muscle stimulation from a subgroup of 12 pigs.

RESULTS

The osteotomy site demonstrated significant mobility during power strokes of mastication with an average magnitude of 0.3 to 0.4 mm. Distinct patterns of displacement were associated with different locations, and the patterns varied between chewing sides. The most common pattern was lengthening at the superior-lateral and shortening at both inferior sites. Similar amounts of displacement were observed during the stimulation of jaw-closers (masseter and medial pterygoid), but the patterns produced by these muscles did not completely explain the masticatory pattern. Opening the osteotomy to 1.5 mm did not alter the displacements observed during muscle stimulation. Bilateral osteotomy tended to decrease displacement.

CONCLUSIONS

The study demonstrates that during mastication and masticatory muscle stimulation, an acute mandibular osteotomy site is mobile despite fixation by a distractor appliance.

Stem cells and distraction osteogenesis: endothelial progenitor cells home to the ischemic generate in activation and consolidation

BACKGROUND

Ischemia is a limiting factor during distraction osteogenesis. The authors sought to determine the extent of ischemia in the distraction zone and whether endothelial progenitor cells home to the distraction zone and participate in local vasculogenesis.

METHODS

Laser Doppler imaging was used to assess the extent of blood flow in the distraction zone in gradually distracted, immediately distracted, and osteotomized rat mandibles during activation and consolidation. Animals (n = 50; 25 rats with unilateral gradual distraction and contralateral osteotomy as an internal control, and 25 rats with unilateral immediate distraction) were examined on postoperative days 4, 6, and 8 of activation, and after 1 and 2 weeks of consolidation. Endothelial progenitor cells isolated from human peripheral blood were labeled with fluorescent DiI dye, and 0.5 x 10 cells were injected intra-arterially under direct vision into each carotid artery at the start of activation in nude rats (n = 18) that then underwent the distraction protocol outlined above.

RESULTS

Doppler flow analysis demonstrated relative ischemia during the activation period in the distraction osteogenesis group and increased blood flow in the osteotomized control group as compared with flow in a normal hemimandible [normal, 1 (standardized); distraction osteogenesis, 0.58 +/- 0.05; control, 2.58 +/- 0.21; p < 0.05 for both results]. We observed a significantly increased endothelial progenitor cell population at the generate site versus controls at midactivation and at 1 and 2 weeks of consolidation [25 +/- 1.9 versus 1 +/- 0.3 DiI-positive cells per high-power field (p < 0.05), 124 +/- 21 versus 8 +/- 4 DiI-positive cells per high-power field (p < 0.05), and 106 +/- 18 versus 9 +/- 3 DiI-positive cells per high-power field (p < 0.05), respectively].

CONCLUSIONS

These data suggest that the distraction zone becomes relatively ischemic during activation and that endothelial progenitor cells home to the ischemic generate site during the activation phase and remain during the consolidation phase. Selective expansion of these stem cells may be useful in overcoming ischemic limitations of distraction osteogenesis. Moreover, their homing capability may be used to effect site-specific transgene delivery to the generate.

The effect of chitosan bead encapsulating calcium sulfate as an injectable bone substitute on consolidation in the mandibular distraction osteogenesis of a dog model

PURPOSE

The purpose of this project was to study the effect of chitosan bead encapsulating calcium sulfate, which provides a sustained release of chitosan and calcium sulfate after implantation, on early bony consolidation in distraction osteogenesis of a dog model.

MATERIALS AND METHODS

Forty-five dogs were used for this study. An external distraction device was applied to the mandibular body after a vertical osteotomy and mandibular distraction was initiated 5 days after the operation at a rate of 1 mm/day up to a 10-mm distraction. The experimental group was divided into a control group (I), hyaluronic acid group (II), chitosan group (III), calcium sulfate group (IV), and chitosan bead encapsulating calcium sulfate group (V). Normal saline was injected in group I. In group II, 1 mL of hyaluronic acid solution was injected into the distracted region. In group III, 1 mL of injectable solution of chitosan mixed with hyaluronic acid was implanted. In group IV, 1 mL of injectable solution of calcium sulfate mixed with hyaluronic acid was implanted. In group V, an injectable form of powdered chitosan bead encapsulating calcium sulfate mixed with 1 mL volume of hyaluronic acid was implanted.

RESULTS

Bone mineral density was 12% of the contralateral normal mandible at 3 weeks, 23.4% at 6 weeks in group I, 15% at 3 weeks, 29.1% at 6 weeks in group II, 16% at 3 weeks and 32% at 6 weeks in group III, 30.4% at 3 weeks and 52.8% at 6 weeks in group IV, and 33.6% at 3 weeks and 55% at 6 weeks in group V with statistical significance (P < .005). The mean 3-point failure load was compared with the intact contralateral mandible and noted to be 12% in the control group, 16% in group II, 18% in group III, 34.3% in group IV, and 31.7% in group V. Difference of mean percentages between one group and another was statistically significant (P < .005). In the histologic findings, new bone was generated in all groups. In groups IV and V, the formation of active woven bone was observed throughout the distracted region at 6 weeks. The amount of new bone formation in the distracted zone was in the order of group IV and V, III and II, and the control group.

CONCLUSIONS

These findings suggest that chitosan bead encapsulating calcium sulfate appears to facilitate early bony consolidation in distraction osteogenesis.

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.

Growth factor expression following clinical mandibular distraction osteogenesis in humans and its comparison with existing animal studies

AIM

Lengthening the mandible by distraction osteogenesis (DO) is nowadays a well recognized technique in maxillofacial surgery. In this study growth factor expression profiles were examined in biopsies taken from six patients undergoing mandibular DO and compared with findings from a sheep model for mandibular DO.

STUDY DESIGN

In all patients (and sheep), the ascending ramus was distracted 10-15 mm at a rate of 1mm/day using an intraoral device. Biopsies were taken from the centre of the distraction zone 21 days after completion of distraction. Using standard immunohistochemical techniques, samples were stained for platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-beta), basic fibroblast growth factor (bFGF) and bone morphogenetic proteins-2, -4 and -7 (BMP-2, -4, -7), matrix metalloproteinases-1 and -3 (MMP-1, -3), the vascular endothelial growth factor (VEGF), a marker for endothelial cells (CD-31) and type IV collagen (Col IV).

RESULTS

Positive staining for PDGF, bFGF, TGF-beta, BMP-2, -4, and -7 was noted in cells and matrix components. There was intense staining for MMP-1. Strong staining for CD-31 and COL IV was observed adjacent to vessels. VEGF staining was less specific. Similar findings were noted in the sheep model.

CONCLUSION

Growth factor expression in the human distraction site is similar to that in the sheep model.

Three-Dimensional Finite Element Analysis of the Mandible and Temporomandibular Joint During Vertical Ramus Elongation by Distraction Osteogenesis

Distraction osteogenesis has been accepted as an alternative treatment modality for hypoplastic mandibles. Knowledge about the changes occurring in the temporomandibular joint region during mandibular distraction osteogenesis is, however, limited and controversial. Stress distribution in the temporomandibular joint region during unilateral vertical mandibular ramus distraction was studied using a finite element model. The finite element model was based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the temporomandibular joint and mandible was analyzed quantitatively at different intervals of the vertical mandibular ramus elongation. During the distraction phase, the condyles, articular disks, and glenoid fossa regions were loaded with a differentiated stress pattern. The affected right condyle, disk, and fossa were submitted to increasing loads with increasing elongation compared with the contralateral temporomandibular joint. Loading on the unaffected left side shifted posteriorly and slightly laterally, because the left condyle was the center of rotation. The loading of the temporomandibular joint regions was low during the active distraction phase, although local areas were subjected to elevated peak stresses.

Using the finite element method to model the biomechanics of the asymmetric mandible before, during and after skeletal correction by distraction osteogenesis

An approach was developed to evaluate the load transfer mechanism in the temporomandibular joint (TMJ) area before, during and after mandibular ramus elongation by distraction osteogenesis (DO). In a concerted approach using computer tomography, magnetic resonance imaging (MRI), and finite element analysis, three-dimensional numerical models based on a young male patient, with a dento-facial deformity were generated. The magnitude and direction of the muscle forces acting on the mandible were assessed using both values derived from the muscles volume and cross-section as retrieved from the MRI-scan data-sets and taken from the literature. The resistance of the soft tissue envelope towards elongation during the DO-phase was also included. The finite element analyses showed that before skeletal correction by DO the load transfer was asymmetrical with high peak stresses in the affected joint. Following ramus elongation a more symmetrical loading in TMJs was predicted. The reaction forces in the TMJs during DO were low.

Effect of platelet-rich-plasma on cranial distraction osteogenesis in sheep: preliminary clinical and radiographic results

The purpose of this study was to investigate the effect of platelet-rich-plasma (PRP) on cranial distraction osteogenesis. Standardized calvaria critical size defects (6 cm x 5 cm) were created in 16 adult female sheep. Bifocal cranial transport distraction osteogenesis with autogenous free calvaria bone grafts (2 cm x 4 cm) was performed at a rate of 1mm once daily to a total of 30 mm. The 16 sheep involved in the experiment were randomly divided into four groups, four animals in each: Group 1 (no PRP, latency 5 days); Group 2 (no PRP, latency 0 day), Group 3 (PRP, latency 5 days) and Group 4 (PRP, latency 0 day). After a consolidation phase of 6 weeks, the animals were sacrificed and specimens harvested for conventional radiological and 3D quantitative computer tomographic (3D-QCT) assessment. New bone was generated in the distraction zone in all groups. There were significantly (P < 0.05) higher densities in the proximal region of the distraction regenerate in Group 4 (PRP, latency 0 day) compared to Group 2. However, no significant differences in mean density of the total distraction regenerate were found, neither in volume of the bony regenerate between the experimental groups. This study showed that PRP only had an effect on bone regeneration if active distraction was started immediately after application of PRP in the distraction gap.

Three-Dimensional Finite Element Analysis of the Mandible and Temporomandibular Joint on Simulated Occlusal Forces before and after Vertical Ramus Elongation by Distraction Osteogenesis

Distraction osteogenesis has recently become a mainstay for treatment of mandibular hypoplasia. Thorough knowledge about changes in the temporomandibular joint (TMJ) and the surrounding parts of the mandible and the skull after mandibular distraction is still lacking. The purpose of the current study was to investigate the stress distribution in the mandible and the TMJ before and after skeletal correction by intraoral unilateral vertical mandibular ramus distraction, using a finite element (FE) model. The FE models were based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the mandible and TMJ before and after skeletal correction by 15 mm of vertical distraction of the mandibular ramus was analyzed quantitatively and compared during centric occlusion. Before the distraction osteogenesis treatment, the condyles, articular discs, and glenoid fossa regions are loaded with a different stress pattern. The affected right condyle, disc, and fossa are loaded diffusely and externally in comparison with the anterior and with centralized loading on the normal left side. After unilateral mandibular distraction osteogenesis, the load became more centric and symmetrical. The results suggest that correction of the mandibular deformity by distraction osteogenesis tends to normalize the stress patterns in the TMJ.

Sequential histomorphometric analysis of regenerate osteogenesis following mandibular distraction in the rat

Few studies of distraction osteogenesis in the craniofacial region have examined the dynamic nature of the bone healing process. This study investigated bone formation in distraction sites at various times following slow, moderate, and rapid rates of mandibular distraction in adult rats. After a 3-day latency period, 16 groups of 8-9 rats underwent unilateral mandibular distraction for 5 days at four different rates (0, 0.2, 0.4, and 0.6 mm/day) and were sacrificed at four different time points (6, 10, 24, and 38 days). Vital bone labels were injected prior to sacrifice and histological sections were examined under epifluorescence to measure mineral apposition rate (MAR) and the number of red and green pixels that corresponded to the wavelengths of the two bone labels. These pixel counts were designed to quantify the amount of fluorescent bone formation. For MAR and the pixel counts, no significant differences were found between the distraction rate groups. Over time, MAR was significantly higher (p < 0.001) at 24 days (4.50 microm/day) compared to 38 days (3.78 microm/day). Thus, MAR appears to be elevated at mid-consolidation compared to late consolidation. The pixel counts showed that the 6-day (mid-distraction) and 10-day (early consolidation) time points had significantly lower total fluorescent activity compared to the 24-day (mid-consolidation) and 38-day (late consolidation) time points (p < 0.001). The red, green, and red + green pixel counts were found to correlate significantly but weakly with microdensity (r = 0.318, 0.307, and 0.334, respectively). The pixel counts and microdensity both showed similar patterns over time.

Unilateral Mandibular Ramus Elongation by Intraoral Distraction Osteogenesis

Successful correction of facial asymmetry by mandibular distraction osteogenesis relies on mastering vector control. Lack of necessary vector control continues to compromise the treatment modality. The purpose of this study was to describe a new simplified method for vector transfer and to evaluate this method according to the outcome and the efficacy of distraction osteogenesis in the correction of unilateral mandibular hypoplasia and asymmetry. Twenty-seven patients with unilateral hypoplasia of the mandibular ramus underwent unilateral mandibular distraction osteogenesis with intraoral distraction devices. Posterior-anterior and lateral cephalograms were analyzed by digitalization. Changes in sagittal, vertical, and transversal linear and angular dimensions after the distraction treatment were evaluated by measurements performed on headfilms taken before and after surgery. Means and variances were calculated for selected cephalometric variables for each time point. The differences between the control and the treatment side were calculated, statistically described, and compared with a paired Student t test. Correction of the mandibular asymmetry, chin position, and the canting of the occlusal plane was obtained in all patients clinically, as well as radiographically, by the use of intraoral unidirectional distraction osteogenesis.

Apoptosis in the regenerate produced by mandibular osteodistraction in the mature rat*

AUTHORS: Liu ZJ, Anderson MW, Gu GM, King GJ.

OBJECTIVE

Little is known about the contribution of apoptosis to the formation of the regenerate in distraction osteogenesis. This study investigated the role of apoptosis in the regulation of osteogenesis in relation to mandibular distraction rate and recovery time.

METHODS

One hundred and twenty-nine 3-month rats received unilateral mandibular ramus osteotomy and distraction device placement. After 3-day latency, these were distracted for 5 days. The slow group was distracted a total of 1 mm (0.2 mm/day), the moderate 2 mm (0.4 mm/day), the rapid 3 mm (0.6 mm/day), and the sham was not distracted (0.0 mm/day). Eight to nine rats from each group were killed at 6 (mid-distraction), 10 (early-consolidation), 24 (mid-consolidation) and 38 (late-consolidation) days following device placement. Baseline data were obtained from an additional eight rats killed at day 3 (end of latency). Sagittal sections (7 mum) of the harvested hemi-mandibles were embedded in paraffin, double-stained with the DeadEnd(TM) Colorimetric TUNEL system for apoptotic cells and tartrate-resistant acid phosphatase for osteoclasts. Cell counts of apoptotic cells and osteoclasts (apoptotic or otherwise) were preformed at 40x magnification using a calibrated grid at the middle regions of the caudal, central and rostral parts of the distraction gap. Counting reproducibility was verified as <13%.

RESULTS

Counts from all three regions were combined because no significant regional difference was found. The majority of the fibrous matrix regenerate was seen at days 6 and 10 while osseous regenerate occurred mainly at days 24 and 38. Significantly higher levels of apoptotic activity were seen at day 24. Apoptotic osteoclasts also peaked at day 24. Apoptotic cell numbers in the slow and moderate groups most closely followed the pattern of the sham in which the apoptosis activity peaked at days 10 or 24. However, those in the rapid group showed delayed peaks at days 24 or 38.

CONCLUSIONS

Chalmers Street, Surry Hill, NSW 2010, Australia. gshe6437@mail.usyd.edu.au The transition from fibrous to osseous regenerate during mandibular distraction osteogenesis is accompanied by an increase in cell clearance via apoptosis. A slow to moderate distraction rate allows for the most typical pattern of bone healing while a rapid rate prolongs the healing process.

Reliability of Distraction Vector Transfer in Unilateral Vertical Distraction of the Mandibular Ramus

Mandibular distraction osteogenesis fails in correcting the skeletal deformities if the vector of distraction is incorrect. Lack of vector control is caused mainly by two factors: first, deficient vector planning and transfer, and, second, resistance of the masticatory muscles and the remaining soft tissue envelope toward elongation. To enhance predictable placement of intraoral distraction devices during surgery and thereby the treatment outcome, a method combining planning, simulation, and transfer was developed. The presurgical planning was based on frontal and lateral head films, and the planned position and orientation of the distraction device was applied on the stereolithographic model. This model was cut according to the planned osteotomy, and the distraction was simulated. The transfer procedure copied the planned and simulated position of the distraction device during surgery by use of an individual guiding splint. The guiding splint was fabricated on plaster models, and transferred to the stereolithographic model to reproduce the planned and simulated distraction treatment during surgery. The reliability of the vector-transfer method was evaluated cephalometrically in a homogenous group of 13 patients and their respective stereolithographic models in comparison with the planned, simulated, and transferred distraction vectors.

Assessment of the distraction regenerate using three-dimensional quantitative computer tomography

This study presents a new method for objective assessment of the distraction regenerate using three-dimensional quantitative computer tomography (3D-QCT). The distraction specimens of 16 sheep that underwent bifocal cranial distraction osteogenesis to reconstruct a critical size defect were used to evaluate this method. To analyse the validity of this method the results were compared to conventional quantitative computer tomography (QCT). Squared correlation coefficients (r(2)) according to Sackett showed a high reliability (r(2) > 70% for the total DO regenerate, DO Regions 2-4). Method comparison according to Bland-Altman (< or =6.25% of measurements out of 95% limits of agreement) showed that three-dimensional computer tomography based bone densitometry is valid for future DO research.

Distraction Osteogenesis of the Craniofacial Skeleton

LEARNING OBJECTIVES:: After studying this article, the participant should be able to: 1. Review the biomechanical principles and pertinent cellular and molecular biology of distraction osteogenesis of the craniofacial skeleton. 2. Describe the clinical indications and applications of distraction osteogenesis of the craniofacial skeleton. 3. Describe maxillary, mandibular, midface, and calvarial procedures in distraction osteogenesis. 4. Discuss the clinical outcomes and complications of distraction osteogenesis of the craniofacial skeleton.The year 2002 marked the end of the first decade in clinical distraction osteogenesis of the craniofacial skeleton. In this short period, its application has increased exponentially. More than 3000 cases have been performed according to a recent survey, and more than 700 articles have been written on this subject in the MEDLINE database since 1996. It is a powerful surgical tool and enables surgeons to achieve results not previously attainable. Despite all this, distraction osteogenesis is practiced by only a small number of plastic surgeons. This article reviews the biomechanical principles; the pertinent cellular and molecular biology; and the clinical indications, applications, controversies, and complications of distraction osteogenesis of the craniofacial skeleton.

The bone regenerative effect of chitosan microsphere-encapsulated growth hormone on bony consolidation in mandibular distraction osteogenesis in a dog model

The purpose of this project was to study the effect of chitosan microsphere-encapsulated human growth hormone, which causes sustained release of chitosan and human growth hormone after implantation on early bony consolidation in distraction osteogenesis of a canine model. Forty-eight dogs were used for this study. An external distraction device was applied to the mandibular body after a vertical osteotomy, and the mandibular distraction was started 5 days after the operation at a rate of 1 mm/d up to a 10-mm distraction. The experimental group was divided into a control group (I), hyaluronic acid group (II), chitosan microsphere group (III), and chitosan microsphere-encapsulated human growth hormone group (IV). Normal saline was injected in group I. In group II, a 1-ml volume of hyaluronic acid solution was injected into the distracted area. In the group III, powder of chitosan microspheres and hGH were mixed with a 1-ml volume of hyaluronic acid to make an injectable form, and it was implanted into the distracted area. In group IV, powder of chitosan microsphere-encapsulated hGH was mixed with a 1-ml volume of hyaluronic acid. A total of 1-ml volume of the solution mix was implanted into the distracted area. Five dogs in each group (total of 20 dogs) were killed 3 weeks after completion of distraction. Twenty-eight dogs were killed at 6 weeks. Bone mineral density was 13.1% of the contralateral normal mandible at 3 weeks and 29.6% at 6 weeks in group I, 16.4% at 3 weeks and 40.4% at 6 weeks in group II, 16.6% at 3 weeks and 45.95% at 6 weeks in group III, and 29.6% at 3 weeks and 66.7% at 6 weeks in group IV. The mean three-point failure load was 16.1% in the control group, 34.7% in group II, 41.5% in group III, and 52.1% in group IV compared with the intact contralateral mandible, with statistical significance. In the histological findings, new bone was generated in all groups. In group IV, the formation of active woven bone was observed throughout the distracted area at 6 weeks. The amount of new bone formation in the distracted zone was in the order of group IV, group III, group II, and the control group. In conclusion, these findings suggest that chitosan microsphere-encapsulated hGH seems to be quite effective in early bone consolidation in distraction osteogenesis.

Bone Morphogenic Protein-2 Gene Therapy for Mandibular Distraction Osteogenesis

Distraction osteogenesis (DO) requires a long consolidation period and has a low but real failure rate. Bone morphogenic proteins (BMPs) accelerate bone deposition in fractures and critical-sized bone defects, but their effects on mandibular DO are unknown. We investigated the effect of local delivery of adenovirus containing the gene for BMP-2 (Adbmp-2) on mandibular DO in a rat model. Rats (n = 54) were distracted to 3 mm over 6 days. At the start of consolidation (POD 10), Adbmp-2 or adenovirus containing the lacZgene (AdlacZ) was injected directly into the distraction zone. After 1, 2, and 4 weeks of consolidation, mandibles were evaluated for amount of bone deposition. Adbmp-2-treated specimens demonstrated an increased amount of new bone formation by radiographic, histologic, and histomorphometric analysis. This study demonstrates that local, adenovirally-mediated delivery of BMP-2 can increase bone deposition during DO, potentially shortening consolidation and enhancing DO in poorly healing mandibles, such as occurs postirradiation.

Removal of Mandibular Tooth Follicles before Distraction Osteogenesis

Distraction osteogenesis is an innovative technique that has transformed the treatment of craniofacial malformations in young children. Bone generation obviates the need for graft material, which is in short supply in young patients, thus making possible surgical procedures on the craniofacial skeleton in young children. Sufficient mandibular volume is required for the osteotomy and placement of the device screws and/or pins. To have adequate bone stock and to facilitate distraction, the authors preoperatively examined all patients radiographically and selected those with tooth follicles that precluded successful osteotomy and pin placement for planned mandibular distraction. This report is of the first 13 children, aged 9 months to 6 years, who underwent predistraction enucleation. The osteotomy and device placement were performed successfully at least 4 months after enucleation. The described procedure has minimal morbidity and has resulted in successful subsequent distraction. The advantages, disadvantages, and cost-benefit issues are discussed.

Occlusal Difficulties After Simultaneous Mandibular and Maxillary Distraction in an Adult Case of Hemifacial Microsomia

A 23-year-old woman with hemifacial microsomia type IIB was treated by simultaneous mandibular and maxillary distraction. During the course of the distraction, cephalometric analysis showed that the maxilla was not moving downward and that the upper edge of the mandibular condyle was moving upward into the space between the condyle and the glenoid fossa. This phenomenon could lead to early consolidation of the osteotomized maxilla, resulting in malposition and occlusal difficulties. This is thought to be a problem unique to bimaxillary distraction of hemifacial microsomia type IIB with severe hypoplasia of the mandibular ramus and space between the condyle and the glenoid fossa. Surgeons should be alerted to this risk and prepared to address it when performing this procedure.

Stoppers in Red II Distraction Device: Is it Possible to Prevent Pin Migration?

Distraction osteogenesis has become popular for the treatment of hypoplastic congenital craniomaxillofacial anomalies. Rigid external distraction (RED II) after Le Fort III osteotomy was shown to be a highly effective treatment for the management of midface hypoplasia. This device is used with a halo vest, which is placed at the cranial equator. Intracranial penetration of the fixation pins of the halo is one of the complications of an external distraction device. To prevent pin penetration in rigid external distraction, the authors designed polylactic acid/polyglycolic acid (PLA/PGA) plates that were circular; the plates were 0.8 cm in diameter and had 1.5-mm holes in the center, through which the tip of the pins would pass. To quantify the applied torque by manual tightening of the screws of the distraction device and to measure intraosseous cone depth created by the penetration of the conical part of the screws with and without the PLA/PGA composite stopper, first an in vitro experiment was undertaken on cadaver. Then these PLA/PGA plaques, or stoppers, were placed over the bone surfaces of the cranium of the patients where the tip of the pins press. PLA/PGA stoppers are malleable and adapt their shape to the interactive forces between bone and the pins. They act as a second barrier, and spread the pressure of the screws to larger surfaces, thus securing better stabilization. The penetration of wider portions of the screw into scalp is reduced, minimizing the scalp damage caused by the screws. Biodegradable and biocompatible PLA/PGA stoppers avoid intracranial migration of the fixation pins, especially in children.

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.

Longitudinal Results of Mandibular Distraction Osteogenesis in Hemifacial Microsomia

The aim of this study was to evaluate mandibular distraction therapy by three-dimensional (3-D) computed tomography (CT) imaging so as to be able to improve the treatment results. The study group consisted of eight children (3 male and 5 female) with hemifacial microsomia. For each child, CT scans of the head were available (Pro Speed S Fast Spiral scanner; General Electric). Longitudinal measurements of the mandible, bony and soft tissue 3-D reconstructions, and masticatory muscles were demonstrated. Three-dimensional CT scans provide important data concerning the results of mandibular distraction therapy and should be used in treatment evaluation. In some patients and for some muscles only, a small increase in the volume of the affected side of the masticatory muscles in comparison to the normal side was found 3 years after mandibular distraction. In around 50% of the cases, there seems to be a relapse occurring 1 year after distraction osteogenesis, and this relapse has a progressive character when seen 3 years after distraction osteogenesis in comparison to 15 weeks after distraction osteogenesis.

Complications in bilateral mandibular distraction osteogenesis using internal devices

OBJECTIVE

We sought to evaluate the possibility of distraction osteogenesis as an alternative to conventional bilateral sagittal split osteotomy. Complications (intraoperative, intradistraction, and postdistraction) were evaluated retrospectively.

STUDY DESIGN

Seventy consecutive patients (40 males and 30 females, 11.2-37.3 years old; mean, 14.2 years) underwent distraction osteogenesis to lengthen the mandible. The surgical procedure was carried out with the patient under general anesthesia. After the osteotomy was performed, 2 intraoral monodirectional distraction devices were placed on the mandibular cortex in the third molar region. The rate of distraction was 1 mm/day. The different complications encountered during all phases of the distraction procedure were recorded.

RESULTS

A total of 28 complications (40%) were recorded. In 10 patients (14.3%), the complications were technique- or device-related, or both, and occurred early in the learning period. Five patients (7.1%) had infection occur, and 3 patients (4.3%) had prolonged sensory loss in the distribution of the alveolar nerve. Severe complications occurred in 6 patients (8.6%). Rehospitalization was necessary in 5 patients (7.1%), 4 of whom (5.7% of the series) required further surgery under general anesthesia.

CONCLUSION

Distraction osteogenesis can be considered a safe and predictable procedure for lengthening the mandible, with a low incidence of major complications. The infection rate and the incidence of damage to the inferior alveolar nerve (2.1%) are low. Compliance of both patients and parents during the whole treatment period is of the utmost importance.

Distraction Osteogenesis of the Mandible With an Internal Bioresorbable Device

Lengthening of the mandible by distraction osteogenesis has been shown to be an effective treatment of hypoplastic mandibles. Use of an internal technique with a bioresorbable distraction device is presented. Mandibular lengthening was performed in seven patients aged 3.2 to 7 years. Six of the patients were diagnosed with craniofacial microsomia, anthe buccal aspect of the mandible, and distraction was started on the second postoperative day at the rate of d one was diagnosed with Nager syndrome. An internal bioresorbable device was placed along 1 mm/d and continued for 17 to 20 days. The distractor screw was maintained for retention for an additional 6 weeks and was then removed. All the patients showed clinical improvement. The postdistraction craniofacial computed tomography scans demonstrated elongation of the mandible with increase in the bony mass. The complications included device failure in one patient. The advantage of this method compared with the internal metal device is that it does not necessitate an additional procedure for device removal.

Segmental Unilateral Transpalatal Distraction in Cleft Patients

Patients with unilateral cleft lip and palate (UCLP) can present with an asymmetric transversal deficiency caused by collapse of the lateral maxillary segment at the cleft side. The surgical technique and orthodontic implications of segmental unilateral transpalatal distraction (TPD) after a posterior maxillary subapical osteotomy using the transpalatal distractor (TPD(R)) are described. The differences between unilateral posterior surgical-assisted rapid palatal expansion (SA-RPE) and segmental unilateral TPD are discussed. The proposed orthodontic-surgical treatment strategy certainly has to be validated by long-term studies in the future.

Pediatric Mandibular Distraction Osteogenesis: The Present and the Future

Pediatric mandibular distraction osteogenesis (MDO) has become a mainstay of treatment for patients with micrognathia and retrognathia. As craniofacial surgeons have gained experience with MDO, the technique has become a safe and durable means of mandibular lengthening that avoids the significant morbidity of conventional surgical treatments. The full impact of this technique has not yet been realized for pediatric patients. Although studies have confirmed durable reconstruction of mandibular length with MDO, the range of applications of this technique is currently limited. As innovative clinicians continue to apply MDO to pediatric clinical craniofacial problems not easily treated with conventional means, the field of MDO will continue to mature. This article discusses current uses and examples of potential future applications of pediatric MDO. The development of novel and creative applications of MDO will advance the management of complex craniofacial anomalies, taking the field of craniofacial surgery into the future.

Alterations of morphology and microdensity in the condyle after mandibular osteodistraction in the rat

PURPOSE

In this study, we examined the effects of mandibular distraction osteogenesis on the morphology and the microdensity of the rat condyle.

MATERIALS AND METHODS

One hundred twenty-nine rats were allocated to 4 experimental groups (n = 32 or 33). Each received unilateral mandibular ramus osteotomy and distraction device placement. After a 3-day latency, these were distracted once a day for 5 days. The slow distraction group was distracted a total of 1 mm (0.2 mm/d); the moderate group, 2 mm (0.4 mm/d); the rapid group, 3 mm (0.6 mm/d); and the sham group, no distraction (0.0 mm/d). Eight to 9 rats in each group were sacrificed at each of 4 time points after device placement (6, 10, 24, and 38 days). Baseline data were obtained 3 days after osteotomy and device placement without distraction from an additional 10 rats. Radiographs of the hemimandibles were scanned and measured to evaluate changes in condylar size (height, width, and area), angulation, and bone microdensity converted to equivalent bone thickness using a stepwedge. The wet weights of masseter muscle were measured at the time of harvest.

RESULTS

1) Muscle weight gains over time were significantly lower in the treated than the untreated sides throughout the consolidation period (P <.001). 2) Condylar size and angulation on the untreated side increased postoperatively, whereas there was a significant reduction of these parameters (P <.01 to.001) on the treated side at 24 and/or 38 days. 3) Condylar microdensity significantly increased on the untreated side at 24 and 38 days (P <.05 to.01) but not on the treated side. 4) Faster or larger distraction caused more severe size reduction and more upright condylar angulation, prevented an increase in bone microdensity on the treated side, especially during the consolidation periods (P <.05 to.01), and retarded increase in muscle weight, whereas a slower distraction rate showed few negative, and even some positive effects. 5) Correlations in size, angulation, and microdensity between right and left condyles became less significant over time. 6) There were positive correlations between muscle weight and condylar size, angulation, and microdensity.

CONCLUSION

An increased rate of mandibular distraction has significant negative effects on condylar morphology and microdensity.

Radiologic characterization of new bone generated from distraction after maxillary bone transport

OBJECTIVE

The purpose of this study was to characterize the radiologic features of the new bone generated from distraction following maxillary bone transport.

STUDY DESIGN

Maxillary dentoalveolar segments were transported by distraction to close posterior maxillectomy defects in 9 rhesus monkeys. The distracted dentoalveoli were harvested at 1, 2, 3, and 6 months after the completion of the distraction. The specimens were evaluated by plain radiography and microcomputerized tomography scanning, which included 2- and 3-dimensional quantitative analyses of bone regeneration volume and microstructural indices.

RESULTS

Plain radiographs showed that radiolucency in the distraction regenerate reduced with time. Microcomputerized scanning found that bone formation and trabecular thickness increased in the new bone with longer consolidation. The high orientation and connectivity of the trabeculae were reduced at longer consolidation intervals. Within the whole distraction gap, bone volume was found to be site-specific.

CONCLUSION

Morphologic analysis in the high resolution offered by microcomputerized tomography shows that active bone mineralization and remodeling occur in the new bone within 3 months after distraction in maxillary dentoalveolus.

Stability consideration for internal maxillary distractors

PURPOSE

Stability in distractor design ensures distraction osteogenesis healing with good bone regenerate formation. The aim of this study was to compare the holding strengths of different fixation systems for maxillary distractor design on bone pieces of different thicknesses.

MATERIAL AND METHODS

Cross-sectional images of 10 dry skulls were obtained by computer tomography and the bone thickness of the maxillae were measured according to five individual anatomical regions (paranasal, infra-orbital, posterior sinus wall, zygomatic and alveolar regions). According to the measurements, the screws of 1.5 and 2mm in diameter and the three-screw mini-plates in triangular and straight configurations were evaluated for holding strength by pull-out tests on fresh animal bone pieces of defined thickness.

RESULTS

The paranasal and zygomatic regions of the human skulls had the thickest cortical bone (4mm) followed by the alveolar region (2mm). In the bones of 2 and 4mm thickness, the 2mm screws were confirmed stronger than the 1.5mm ones in pull-out tests. However, the pull-out behaviour of screws of different diameters in 1mm thick bones and the mini-plates in two different configurations showed no significant differences.

CONCLUSION

This study confirms that the paranasal and zygomatic bones are the thickest for fixation of internal maxillary distractors. Fixation screws of 2mm diameter in either triangular or straight miniplates can produce good stabilization for distractors.

The bone regenerative effect of growth hormone on consolidation in mandibular distraction osteogenesis of a dog model

The purpose of this project was to study the effect of growth hormone on early bony consolidation in distraction osteogenesis of a dog model. Sixteen dogs were used for this study. The vertical osteotomy on the mandibular body was extended downward. An external distraction device was applied to the mandibular body and the mandibular distraction was started 5 days after the operation at a rate of 1 mm/d up to a 10-mm distraction. The experimental group was divided into a control group and growth hormone group. Dogs in the growth hormone group received a daily subcutaneous injection of 100 microg (1 IU) of recombinant human growth hormone per kilogram of body weight. The daily administration of growth hormone was performed from the day of the osteotomy through the whole distraction period to the sacrifice. Normal saline was injected in the control group. Eight dogs were allocated to each group. Two dogs in each group, a total of four dogs, were killed at 2 weeks after completion of distraction, four dogs were killed at 4 weeks, and the other eight dogs were killed at 6 weeks. The level of serum IGF-I in the growth hormone group was elevated and peaked between 8 days and 12 days after systemic administration of growth hormone. Bone mineral density was higher in the growth hormone group and lower in the control group for the whole period. Bone mechanical strength was 300% higher in the growth hormone group than in the control group. However, results were more suggestive than conclusive. On histological examination, the formation of a substantial amount of active woven bone was observed throughout the distracted zone at six weeks in the growth hormone group. In the control group, new bone was generated from the edge to the center of the distracted zone. In addition, most of the central area of the distracted zone was filled with fibrous tissue at six weeks. In conclusion, these findings suggest that growth hormone appears to be effective in early bony consolidation in distraction osteogenesis.

Mechanobiology of craniofacial sutures

Craniofacial sutures are soft connective-tissue joints between mineralized skull bones. Suture mechanobiology refers to the understanding of how mechanical stimuli modulate sutural growth. This review's hypothesis is that novel mechanical stimuli can effectively modulate sutural growth. Exogenous forces with static, sinusoidal, and square waveforms induce corresponding waveforms of sutural strain. Sutural growth is accelerated upon small doses of oscillatory strain, as few as 600 cycles delivered 10 min/day over 12 days. Interestingly, both oscillatory tensile and compressive strains induce anabolic sutural responses beyond natural growth. Mechanistically, oscillatory strain likely turns on genes and transcription factors that activate cellular machinery via mechanotransduction pathways. Thus, sutural growth is determined by hereditary and mechanical signals via the common pathway of genes. It is concluded that small doses of oscillatory mechanical stimuli have the potential to modulate sutural growth effectively: either accelerating it or initiating net sutural bone resorption for various therapeutic objectives.

The role of hyaluronic acid, chitosan, and calcium sulfate and their combined effect on early bony consolidation in distraction osteogenesis of a canine model

The purpose of this project was to study the effect of hyaluronic acid, calcium sulfate, and chitosan on early bony consolidation in distraction osteogenesis of a canine model. Sixteen dogs were used for this study. The lateral surface of the mandibular body was exposed in the subperiosteal plane, and the vertical osteotomy on the mandibular body was extended downward. An external distraction device was applied to the mandibular body, and the mandibular distraction was started 5 days after the operation at a rate of 1 mm/d up to a 10-mm distraction. The experimental group was then divided into a control group, chitosan group, hyaluronic acid group, calcium sulfate combined with hyaluronic acid group, and calcium sulfate combined with chitosan group, depending on the type of implantation material in the distracted area. After completing the distraction, implantation material was injected into the distracted area, although no material was implanted into the distracted area of the control group. After implanting the materials, the distraction device was left in place for 6 weeks to allow for bony consolidation. Four dogs were allocated to each group. Two dogs in each group (total of 8 dogs) were killed 3 weeks after implantation of the material, and the other 8 dogs were killed after 6 weeks. New bone was generated in the distracted zone of all groups. In the calcium sulfate combined with chitosan group and calcium sulfate combined with hyaluronic acid group, the formation of active woven bone was observed throughout the distracted zone. Moreover, the new bone seemed to be nearly normal cortical bone at 6 weeks after implantation. In the chitosan group and hyaluronic acid group, the development of new bone was observed in the distracted zone at 6 weeks. The amount was less than that in the calcium sulfate combined with hyaluronic acid group and calcium sulfate combined with chitosan group. These findings suggest that calcium sulfate and its combined materials seem to be quite effective in early bony consolidation in distraction osteogenesis.

Is early osteodistraction a solution for the ascending ramus compartment in hemifacial microsomia? A literature study

AIM

In hemifacial microsomia, osteodistraction before skeletal maturation claims to induce both bone- and soft-tissue generation in such a way that conventional bone grafting and soft-tissue grafts are not necessary. Early osteodistraction in facial microsomia would have a positive effect on the 'functional matrix', and allow symmetrical vertical and sagittal expansion of the midface and mandible. The aim of this literature survey was to find evidence for this hypothesis by analysing long-term follow-up reports on distraction histiogenesis in the ascending ramus.

MATERIAL

Only eight published studies were found, of which only two had more than ten patients, two were case reports, and three were from the same institution.

RESULT

Invariably, the results pointed towards over-correction, repeated osteodistraction procedures, soft-tissue stretching (but no lateral augmentation), and to soft-tissue complications. The studies did not allow a conclusion to be made as whether increased vertical gain in the ascending ramus was unstable because of decreased growth on the affected side, inborn or iatrogenic, or due to resorption of the bone generated by distraction. To date, there is no evidence that osteodistraction produces better results and has lower morbidity than conventional growth centre transplantation and separate soft-tissue augmentation.

CONCLUSION

Recommendations for prospective studies are: sharp differentiation between the four Pruzansky-Kaban mandibular types, multi-centre study of a surgical protocol to increase the sample number using a standard three-dimensional evaluation protocol, and differentiation between decreased growth and collapse of the newly generated bone.