Mandibular lengthening by external distraction: an experimental study in the rabbit

Experimental Study on the Bone Morphogenetic Protein 1-Modified Bone Marrow Mesenchymal Stem Cell Sheets to Promote Mandibular Distraction Osteogenesis

Objective

The present study aims to increase the concentration of genetically modified bone marrow mesenchymal stem cells (BMSCs) in the distraction osteogenesis (DO) interstitial space and induce the conversion of BMSCs to osteoblasts to improve the osteogenic efficiency in DO and shorten the treatment period.

Methods

Bone morphogenetic protein 1 (BMP-1) and green fluorescent protein (GFP) gene-modified cell sheets of BMSCs were constructed by tissue engineering. Thirty-six New Zealand white rabbits were randomly divided into three groups: group A (the blank control group), group B (the GFP group) with the injection of GFP gene-modified BMSC sheets into the DO gap, and group C (the BMP-1 group) with the injection of BMP-1 gene-modified BMSC sheets into the DO gap. Rabbits in all three groups were distracted for 5 days at a distraction rate of 2.0 mm/d, once/day. After distraction, the above-mentioned cell sheet suspension was injected into the distraction gap to observe osteogenesis, which was observed by gross specimen observation, micro-computed tomography (Micro-CT) scanning, and histomorphology.

Results

The gross specimen observation showed that all animals had smooth and continuous bone cortex in the distraction region with relatively high hardness. The osteogenesis quality or hardness was ranked from the highest to the lowest, as Group C > Group B > Group A. Micro-CT and histomorphological observation revealed that group C had better maturation and bone volume of the new bone in the DO region at weeks 3 and 6 than groups B and A.

Conclusion

BMP-1 gene-modified BMSC sheets could effectively promote the formation of new bone during rapid DO in the mandible, compensating for the poor osteogenesis caused by rapid distraction and providing a new approach to shorten the DO treatment period in clinical practice.

Effects of bone morphogenetic protein 2 gene therapy on new bone formation during mandibular distraction osteogenesis at rapid rate in rabbits

OBJECTIVE

We investigated the effect of recombinant human bone morphogenetic protein 2 (rhBMP-2) on new bone formation during rapid-rate mandibular distraction osteogenesis. We also explored the feasibility of using local BMP-2 gene therapy to compensate for bad callus formation caused by a rapid distraction rate.

STUDY DESIGN

Bone marrow mesenchymal stem cells (MSCs) from Japanese rabbits were transfected with adenovirus (adv)-BMP-2. The right mandibles of the rabbits were distracted after corticotomy. The distraction rate in group A was 0.8 mm/d. The distraction rate in group B was 2.4 mm/d, and the distraction gap was injected with adv-lacZ-transfected bone marrow MSCs. The distraction rate in group C was 2.4 mm/d, and the distraction gap was injected with adv-BMP-2-transfected bone marrow MSCs. New generation bone tissue in the distraction gap was analyzed by plain radiograph examinations, microfocus computerized tomography (micro-CT) examinations, and biomechanical tests at weeks 2, 4, and 8 of the consolidation period.

RESULTS

Radiographic and micro-CT examinations showed a better bone quality in group C compared with group A at weeks 2 and 4 of the consolidation period. There was no obvious new bone formation in group B. The trabecular parameters (trabecular thickness, trabecular number, volumetric bone mineral density at tissue, and bone volume fraction) were significantly higher in group C than in group A at weeks 2 and 4. At week 8, no significant difference were detected for all parameters except trabecular number between groups A and C. All biomechanical stress parameters were significantly higher in group C than in group A at week 4, and only peak stress was significantly different at week 8.

CONCLUSIONS

Gene therapy using rhBMP-2-modified MSCs promoted new bone formation during mandibular distraction osteogenesis, and effectively compensated for the detrimental effect of rapid distraction rate on new bone formation.

Why high frequency of distraction improved the bone formation in distraction osteogenesis?

Distraction osteogenesis, currently a standard method of bone lengthening, is based upon the "tension-stress principle", as proposed by G.A. Ilizarov. Mechanical stimulation by distraction induces biological responses of skeletal regeneration that is accomplished by a cascade of biologic processes including differentiation of pluripotential tissue, angiogenesis, mineralization, and remodeling. The exact mechanism by which strain stimulates bone formation remains unclear. Distraction rate and rhythm must have great influence on the quality of the newly formed bone generated by mechanical traction. The preliminary results demonstrated that for a given rate higher frequency of distraction improved the bone formation, but the mechanism remains unclear. In this article we present a hypothesis that the reason why higher frequency of distraction improved the bone formation for a given rate is that higher frequency of distraction provides smaller microtrauma to tissues within the gap and longer existence time of the microenvironment stimulating tissues within the gap than low frequency distraction. This hypothesis, if proven to be valid, will not only represent a breakthrough in research of mechanism of distraction osteogenesis, but also will open a new door to the bone regeneration.

Histologic study of the cellular events during rat mandibular distraction osteogenesis

OBJECTIVE

The cellular events, underlying bone regeneration through rat mandibular distraction osteogenesis (DO) was examined using micro computerized tomography (microCT), histology, and histochemistry.

STUDY DESIGN

After 5-day latency, mandibles were distracted at 0.2 mm/12 h for 10 days, and fixed at latency 5 days (L5D), distraction 3, 6, 10 days (D3D, D6D, D10D), and consolidation 1, 3, 6, 10 weeks (C1W, C3W, C6W, C10W).

RESULTS

The microCT demonstrated radiopacity at the distraction gap (DG) during C1W, which was filled with new bone at C6W and C10W. At D3D, collagen fibers were aligned along the axis of the distraction vector. At D6D, alkaline phosphatase-positive osteoblasts and intramembranous ossification was observed. Collagen bundles became thicker with new bony trabeculae at D10D. Type II collagen-immunopositive areas first appeared at C1W. At C3W, cartilage tissue and endochondral ossification were found. By C6W, the entire DG had been bridged by new bone. The C10W specimens showed mature lamellar bone.

CONCLUSION

Mandibular DO produces bone through both intramembranous and endochondral ossification.

Promoted new bone formation in maxillary distraction osteogenesis using a tissue-engineered osteogenic material

Bilateral maxillary distraction was performed at a higher rate in rabbits to determine whether locally applied tissue-engineered osteogenic material (TEOM) enhances bone regeneration. The material was an injectable gel composed of autologous mesenchymal stem cells, which were cultured then induced to be osteogenic in character, and platelet-rich plasma (PRP). After a 5-day latency period, distraction devices were activated at a rate of 2.0 mm once daily for 4 days. Twelve rabbits were divided into 2 groups. At the end of distraction, the experimental group of rabbits received an injection of TEOM into the distracted tissue on one side, whereas, saline solution was injected into the distracted tissue on the contralateral side as the internal control. An additional control group received an injection of PRP or saline solution into the distracted tissue in the same way as the experimental group. The distraction regenerates were assessed by radiological and histomorphometric analyses. The radiodensity of the distraction gap injected with TEOM was significantly higher than that injected with PRP or saline solution at 2, 3, and 4 weeks postdistraction. The histomorphometric analysis also showed that both new bone zone and bony content in the distraction gap injected with TEOM were significantly increased when compared with PRP or saline solution. Our results demonstrated that the distraction gap injected with TEOM showed significant new bone formation. Therefore, injections of TEOM may be able to compensate for insufficient distraction gaps.

Transplantation of osteoblast-like cells to the distracted callus in the rabbit mandible

BACKGROUND

The purpose of this study was to investigate whether injections of marrow-derived mesenchymal progenitor cells could be used to facilitate new bone formation during distraction osteogenesis.

METHODS

Fifteen New Zealand rabbits underwent bilateral osteotomy. After a 1-week latency period, bone distraction was activated at a rate of 2.0 mm/day for 5 days. The marrow-derived mesenchymal progenitor cells derived from the ilium marrow were cultured to a population of 10 in 0.5 ml and then unilaterally transplanted to the gap of distracted callus immediately after distraction had been terminated. Rabbits were killed at 2, 4, and 6 weeks after completion of bone lengthening. The distracted areas were harvested and evaluated by histologic, histomorphometric, radiographic, and scanning electron microscopic analysis. Bone mineral density in the lengthened callus was evaluated using dual-energy x-ray absorptiometry.

RESULTS

Radiographic evaluation indicated a significant increase in bony union of the distraction regenerate in the experimental side compared with the control side. Corresponding to the radiographic findings, the histologic examination showed an earlier and more intensive bone formation in the experimental side after 2, 4, and 6 weeks compared with the control side. Larger chondroid islands were found evident in distracted bone of the control side than in the experimental side.

CONCLUSIONS

The results show that transplantation of osteoblast-like cells promotes maturity of the distracted callus, as observed on the second and fourth weeks after lengthening. The method appears promising as a means of shortening the consolidation period of osteodistraction and decreasing complications during bone lengthening.

Effect of Recombinant Human Bone Morphogenetic Protein-2 on Mandibular Distraction at Different Rates in a Rabbit Model

This study aims to evaluate the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on mandibular distraction at routine and rapid distraction rates. Eighteen New Zealand white rabbits were assigned to 2 groups, 1 treated at a routine distraction rate (0.9 mm/d) and the other at a rapid distraction rate (2.7 mm/d). rhBMP-2 was injected into 1 side of the distraction regenerate at the end of the active distraction period; the contralateral side was used as a control. The distraction regenerates were analyzed by plain radiography, microcomputed tomography, and histologic examination. The results showed that rhBMP-2 can promote bone formation at both rapid and routine distraction rates, but no statistically significant difference was observed between the bone morphogenetic protein injection sides of the rapid and routine distraction groups. In conclusion, the study indicates that rhBMP-2 can enhance bone ossification at both routine and rapid distraction rates. The addition of rhBMP-2 seems to be able to compensate for the rapid distraction rate in mandibular distraction osteogenesis. Further longterm follow-up and mechanical strength test for the support of implants or conventional prostheses are necessary.

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.

Effect of Recombinant Human Bone Morphogenetic Protein-2 on Mandibular Distraction at Different Rates in an Experimental Model

This study evaluates the effect of recombinant human (rh) bone morphogenetic protein (BMP)-2 on mandibular distraction at normal and rapid distraction rates. This study also determines the feasibility of compensating for the increased distraction rate by the addition of rhBMP-2 while maintaining the quality of the distraction regenerate. Twenty-four New Zealand white rabbits were divided into 2 groups, 1 treated at a normal distraction rate (0.9 mm/d) and the other at a rapid distraction rate (2.7 mm/d). At the end of the active distraction period, rhBMP-2 was injected into distraction regenerate, and the contralateral side was used as a control. The distraction regenerates were analyzed by plain radiography, microcomputed tomography, and mechanical testing. The results showed that rhBMP-2 can promote bone formation at both rapid and normal distraction rates. At week 2 and week 4 of consolidation, bone volumes in the BMP-injection sides were significantly higher than in the control sides, but no statistically significant difference was observed between the BMP-injection sides of the rapid and normal distraction groups. At week 8 of consolidation, mechanical testing demonstrated no significant difference of the failure load and stiffness between the BMP-injection and control sides. In conclusion, the study indicates that rhBMP-2 can enhance bone ossification at both normal and rapid distraction rates. The addition of rhBMP-2 can compensate for the rapid distraction rate in mandibular distraction osteogenesis. However, in the long term, the bone quality and stiffness of the distraction regeneration was not influenced by rhBMP-2.

Effects of distraction forces and frequency of distraction on bony regeneration

The rate and frequency of distraction have a decisive influence on the regenerative process. We tested a newly developed hydraulic osteodistractor in 12 pigs, which were assigned to have continuous and intermittent osteodistraction of the mandible after osteotomy. The forces necessary to distract the mandible were recorded during intermittent distraction. These data were then used for continuous distraction of the bone. Continuous osteodistraction resulted in intramembranous regeneration of bone, whereas intermittent osteodistraction caused chondroid ossification in the regeneration of the bone. Continuous osteodistraction caused speedier regeneration, and distraction forces were lower than with intermittent distraction.

Evaluation of recombinant human bone morphogenetic protein-2 in mandibular distraction osteogenesis in rabbits: Effect of dosage and number of doses on formation of bone

We evaluated the dose- and time-dependent response of recombinant human bone morphogenetic protein-2 (rhBMP-2) to the formation of bone in mandibular distraction osteogenesis. Twenty-one adult white New Zealand rabbits (3.0-3.8 kg) were used to establish the mandibular distraction model, 18 of which completed the experiment. Eight rabbits were given rhBMP-2 360 microg and eight 1080 microg; two were given no rhBMP-2. The fluids were injected into the regenerating bone at three different time sequences (days 5, 8, and 11 of active distraction; days 5 and 11 of active distraction; and day 11 of active distraction alone). After four weeks of consolidation, the specimens were harvested and examined radiographically by micro-computed tomography (micro-CT), and histologically. The formation and remodelling of bone in distraction osteogenesis was significantly increased by the addition of rhBMP-2, and the increase was dose-dependent. There was no significant difference between different dosage regimens. A single injection of rhBMP-2 at the end of the distraction phase was as effective as multiple injections.

A Custom-Made Distraction Device for Experimental Mandibular Distraction Osteogenesis

Distraction osteogenesis has recently become popular in craniofacial reconstruction, after it was first described for long bones. Despite the widespread clinical use of this technique, currently, lack of an ideal experimental model for small animals hampers investigations focused on its molecular basis, which warrants further elucidation. The authors developed a new device for distraction of the rat mandible and, to asses its effectiveness, practiced on 30 animals assigned to either an acute 3-mm distraction group (n = 7) or a gradual distraction group (0.25 mm twice a day for 6 days; n = 23). The authors applied the devices to a localization that allowed them to perform the ostomies posterior to the molar teeth. Because of a U-shaped plate that the authors used for posterior pin fixation, their device maintained its stability until the end of the study, despite the delicate anatomy of the bone at the posterior part of the mandible. Additionally, the authors described a practical and easy method of transient mandibular stabilization method that facilitates the manipulations while the mouth is open for safer airway control during surgery. This new nutrition technique with enteral feeding solution solved the problem of progressive weight loss after surgery. Application of the device was easy and practical, without demanding complex manipulations. The authors did not observe any device dislodgement or a high rate of accidental fractures during the manipulations. They demonstrated that the device works properly and is able to create ossified regenerate bones that fill the entire distraction gap, which can be used for various investigations during distraction osteogenesis.

The Effects of Distraction Osteogenesis on Mandibular Growth in Growing Minipigs: A Report on Three-Dimensional Morphologic Changes

BACKGROUND

The purpose of the study was to investigate the morphologic changes of distraction osteogenesis performed on the mandible in growing minipigs.

METHODS

Eighteen piglets were divided into four groups. In group A (n = 6), animals received unilateral osteotomy and the distractor device was activated for 2 weeks after a 1-week latency period. In group B (n = 6), animals underwent the osteotomy procedure and distractor placement. In group C (n = 3), animals received the distractor, and in group D (n = 3), only four reference pins were placed. After completion of distraction, the head portions were sent for computed tomography scanning. The coordinates of each selected mandibular landmark were recorded on three-dimensional computed tomographic reconstruction images for further mathematical linear and angular measurements to quantify morphologic changes.

RESULTS

The sagittal length related to gonial region was increased in group A but decreased in group B. Although all groups had the tendency of increased ramus width, it was only significant in group B. The distraction also reduced the gonial angle and elevated the ramus inclination to the Frankfort horizontal plane at the operated side. On the contrary, osteotomy alone opened the gonial angle and flattened the ramus inclination.

CONCLUSIONS

Distraction could lengthen the mandibles in growing minipigs by reducing the gonial angle and displacing the mandible posteriorly. This effect, which allows for developing a prominent gonial angle, could be further explored in treating syndromic patients with the deficiency in the gonial region. A greater amount of overcorrection should be considered while treating growing patients because the mandibular osteotomy procedure itself seems to retard the growth.

Mandibular Distraction Osteogenesis: A Rabbit Model Using a Novel Experimental Design

PURPOSE

Distraction osteogenesis (DO) is a surgical procedure that targets bone regeneration and elongation, currently used in the treatment of many craniofacial deformities. The quest for optimization of DO clinical parameters has led to the development of a variety of animal models. Our study aims to establish a rabbit animal model of mandibular DO, in which the control osteotomy and distraction device are placed on the opposite hemimandible from the one being distracted, within the same animal host. Furthermore, we propose to histologically characterize the different stages or distraction and consolidation in the same animal model.

MATERIALS AND METHODS

Twenty-five rabbits underwent mandibular osteotomies and bilateral placement of distraction devices. After a latency of 3 days, the distraction device was activated on one side of each animal at a rate of 0.5 mm/12 hours for 7 days, while the other side remained inactive (control). This was followed by a consolidation period of 14 days. Five animals per time-point were killed on days 3, 7, 10, 17, and 24.

RESULTS

Gross tissue analysis showed a 7-mm callus formation at the distracted side and a well-healed osteotomy in the non-distracted side. Clinically, a unilateral Class III malocclusion occurred in the distracted side. Histology at each time-point shows new bone formation and orientation of the bony spicules along the axis of the mechanical strain.

CONCLUSIONS

We have established and characterized an animal model of mandibular DO that outlines valid biologic controls and provides thorough monitoring of the DO process.

Histologic, histomorphometric and immunohistologic changes of the gingival tissues immediately following mandibular osteodistraction

OBJECTIVES

Even though osteogenesis after osteodistraction has been investigated in numerous experimental studies, there is limited information focusing on the influence of well-defined mechanical distraction forces on the associated gingival tissues.

MATERIAL AND METHODS

In a study including 48 rabbits, mandibular osteodistraction was performed in vertically osteotomized mandibular body, using defined distraction protocols with physiologic, moderate and hyperphysiologic forces. The soft tissues overlying the distraction gap were harvested finally for histologic, immunohistologic and histomorphometric investigations.

RESULTS

The control group without distraction showed the typical architecture and thickness of normal gingiva. In groups with distracted mandibles, an accelerating atrophy of gingiva depending on the degree of mechanical loading was obvious, characterized by decreasing thickness of epithelial layer, loss of rete ridges and disorganization of the different cell layers with a high number of apoptotic cells. In lamina propria collagen fibres were reduced and elastic fibres increased. Histomorphometric analysis revealed significant correlation between degree of distraction and atrophy in overlying soft tissues.

CONCLUSION

This rabbit model of mandibular lengthening shows an accelerating atrophy in the covering soft tissues following hyperphysiologic distraction. The long-term outcome of these distraction-related soft-tissue alterations remains unclear. The atrophic changes may likely be of temporary nature.

New developments in pediatric plastic surgery research

Pediatric plastic surgery research is a rapidly expanding field. Unique in many ways, researchers in this field stand at the union of multiple scientific specialties, including biomedical engineering, tissue engineering, polymer science, molecular biology, developmental biology, and genetics. The goal of this scientific effort is to translate research advances into improved treatments for children with congenital and acquired defects. Although the last decade has seen a dramatic acceleration in research related to pediatric plastic surgery, the next 10 years will no doubt lead to novel treatment strategies with improved clinical outcomes.

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.

Mechanobiology of mandibular distraction osteogenesis: experimental analyses with a rat model

We analyzed mechanobiological influences on successful distraction osteogenesis (DO). Mandibular distraction surgeries were performed on 15 adult male Sprague-Dawley rats. Animals underwent gradual distraction (GD), progressive lengthening by small increments (5-day latency followed by 0.25 mm distractions twice daily for 8 days followed by 28-day maturation period). Distracted hemimandibles were harvested on postoperative days (POD) 5, 7, 10, 13, and 41. Load-displacement curves were then recorded for ex vivo distractions of 0.25 mm and stresses determined. Histologically, new bone formation appeared in GD specimens on distraction day 2 (POD 7), filling 50-60% of the gap by distraction day 8 (POD 13), with nearly complete bony bridging at end maturation (POD 41). Average tensile strains imposed by each incremental distraction ranged from approximately 10% to 12.5% during distraction days 2-8 and were associated with bone apposition rates of about 260 microm/day. Because this GD protocol was previously determined to be optimal for DO, we conclude that strains within this range provide an excellent environment for de novo bone apposition. Distraction caused tissue damage in distraction day 2, 5, and 8 specimens as evidenced by distinct drops in the load/displacement curves. Taken together, our interpretation of these data is that daily distractions cause daily tissue damage which triggers new mesenchymal tissue formation.

Spring-Mediated Mandibular Distraction Osteogenesis

Successful performance of distraction osteogenesis requires rigorous patient compliance with a daily activation regimen of a percutaneous screw. Previous clinical studies have found that failure of patient compliance with this regimen is the most common complication leading to technical failure of the distraction process. The authors have developed an internalized spring-mediated device for mandibular distraction osteogenesis that can potentially abrogate the risks associated with patient compliance by allowing for automated distraction across an osteotomy. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A segment of nickel-titanium shape memory alloy reinforced at both ends with a pinball was fashioned into an inferiorly based arc and secured to the mandible with stainless steel wire. On postoperative day 12, spring activation commenced by cutting a wire binding the two pinballs to one another. Animals were observed for 6 weeks before they were killed. Radiographic studies and decalcified histologic analysis were performed on extracted mandibles. Temperature- and displacement-dependent properties of the shape memory alloy were also examined. Five animals were excluded from the study due to infection, nonunion, or device failure. A mean distraction of 1.2 mm in the distracted hemimandible relative to the nonoperated hemimandible was found (P <.001, two-tailed paired t test). The maximum distraction achieved in an experimental specimen using the spring distractor was 3.7 mm. There were no other histologic or radiographic differences found between study specimens and specimens subjected to traditional distraction methods. Biomechanical testing of the shape memory alloy revealed a temperature-dependent increase in force at body temperature compared with room temperature and a reduction in force with increased displacement of the spring. This study demonstrates the feasibility of spring-mediated distraction osteogenesis across an osteotomy. As the field of distraction osteogenesis matures, the next level of sophistication in the clinical development of devices will incorporate technology that permits fully internalized and automated distraction to occur.

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.

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.

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

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

Role of BMP, betaig-h3, and chitosan in early bony consolidation in distraction osteogenesis in a dog model

The purpose of this investigation was to study the effect of bone morphogenetic protein (BMP), transforming growth factor beta-induced gene h3 (betaig-h3), and chitosan on early bony consolidation in distraction osteogenesis in a dog 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 2 mm/day up to a 10-mm distraction after 5 days. The experimental group was then divided into a control group, a BMP group, a betaig-h3 group, and a chitosan group, depending on the type of implantation material used in the distracted area. On the same day after completing the distraction, BMP, betaig-h3, or chitosan was implanted into the distracted area. No material was implanted into the distracted area in the control group. After implanting the materials, the distraction device was left in place for 7 weeks to allow for bony consolidation. Four dogs were allocated to each group. Two dogs in each group, a total of eight dogs, were killed 4 weeks after completing the distraction and the other eight dogs were killed after 7 weeks. Serial radiographs were obtained every week after completing the distraction. New bone was generated in the distracted zone in all groups. In the BMP group, the formation of active woven bone was observed throughout the distracted zone, and the new bone appeared to be nearly normal cortical bone 7 weeks after implantation. In the betaig-h3 and chitosan groups, the development of new bone was observed in the distracted zone after 7 weeks; however, the amount was less than that in the BMP group. In the control group, the new bone was observed at the edges of the distracted zone. These findings suggest that BMP seems to be very effective in early bony consolidation in distraction osteogenesis.

A custom mandibular distraction device for the rat

In the last several years, the rat model has been used as a reliable means of studying distraction osteogenesis (DO). This model has several benefits, including lower cost, the availability of molecular reagents for the rat, and the ability to perform a large number of operations in a short time. We have recently developed an external device that is custom-made for the rat mandible and secured at the mandibular ramus. The device consists of a Leone (Florence, Italy) jackscrew distraction assembly (0.2 mm per one-quarter turn), 2 Luhr L-shaped 0.8-mm five-hole microplates, and four 0.8-mm x 3-mm microscrews (Stryker-Leibinger Corp., Kalamazoo, MI) for fixation. Additionally, there is a methylmethacrylate block that is placed on the lingual surface of the angle of the mandible to support the posterior screws. Sterile surgical technique was used, and the same two surgeons performed all operations. To date, we have operated on 153 Sprague-Dawley rats. The procedure has been well tolerated by the animals. We had 17 postoperative deaths (11% mortality), largely as a result of anesthetic complications. There were no wound infections or dehiscence. A mandible fracture was noted in 6 rats (4%), which occurred at the time of device placement. There were no device dislodgments. Postmortem examination showed the device to be well positioned in all rats, with good callous formation at the distraction site. The rats surpassed their preoperative weight after an average of 9.2 days. These results compare favorably with those of other models currently in use. We have developed a device that is currently being used in the study of DO in the rat mandible. Our device is small in size, does not require wide undermining for its placement, and has had a low incidence of device dislodgment or infection. This model has shown great reproducibility and thus should be effective in its application for the histologic and biochemical investigation of DO in the rat.

Callus stimulation in distraction osteogenesis

Distraction osteogenesis has been described as in vivo tissue engineering. The ability to stimulate this process for the repair of bony defects or lengthening of congenitally shortened facial structures is likely to significantly impact the field of craniofacial surgery. The purpose of this study was to determine whether mechanical stimulation of the distracted rabbit mandible would accelerate the maturation of the bony callus when applied during the early consolidation period. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A uni-directional internal distractor device (Synthes, Paoli, Pa.) was positioned along a plane perpendicular to the line of osteotomy. After a 7-day latency period, distraction was commenced at a rate of 1.0 mm/day for 12 days in all animals. In a control group of 10 rabbits, a consolidation period of 8 weeks was observed before they were killed. In the experimental group of 10 rabbits, daily alternate compression and distraction of 1 mm (sequential compression and distraction) was performed for 3 weeks followed by a 5-week period of rigid fixation. Each animal received a dose of a fluorescent label at three different time points during the study: at the end of the distraction period, 3 weeks after the completion of the distraction phase, and 3 days before it was killed. All animals were killed 8 weeks after the completion of the distraction phase. Undecalcified histologic analysis and 3-point bending tests to failure were performed on the extracted mandibles. The results of the experimental and control groups were compared. Four animals in the control group and three animals in the experimental group were excluded from the study because of screw loosening resulting in distractor dislodgment or because of infection. On histologic analysis, cortical thickness at the center of the callus was found to be significantly greater in the experimental group compared with the control group when normalized to the contralateral hemimandible (83 percent versus 49 percent, respectively; p < 0.007). The ratio of cortical to cancellous bone in the distracted callus was uniformly found to be greater in the experimental specimens. The mineral apposition rate was calculated by using fluorescence microscopy and found to be significantly greater in the experimental group both during the period of sequential compression and distraction (3.2 microm/day versus 2.1 microm/day, p = 0.02) and after the period of sequential compression and distraction (1.4 microm/day versus 1.1 microm/day, p = 0.006). Mechanical testing revealed no significant differences in bending strength or stiffness between experimental or control groups (p = 0.54 and 0.47, respectively). This study has demonstrated that daily alternating compression and distraction of 1 mm amplitude during the early consolidation period has a stimulatory impact on callus formation with respect to osteoblastic activity, remodeling, and maturation of bone. Optimal timing and amplitude of sequential movement, long-term biomechanical differences, and molecular pathways have yet to be elucidated.

Cranio-facial distraction osteogenesis: a review of the literature. Part II: Experimental studies

In this study the literature dealing with experimental cranio-facial distraction osteogenesis (DO) was reviewed. A PUBMED search (National Library of Medicine [NCBI] revised 1 April 2001) from 1966 through December 2000 was conducted. Key words used in the search were: distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, cranio-facial, maxillofacial. This search revealed a total of 120 experiment-orientated articles that were all analyzed in detail in this study. The purpose of the experimental study, animal model, animal growth status, type of distraction, type of surgery, distraction rate and rhythm, latency and contention period, amount of lengthening, relapse, complications and nature of the distraction device were analyzed. This review revealed that a total of 1207 animals were used in seven different animal models for research on cranio-facial DO: 54 using dogs (45.0%), 25 using rabbits (20.8%), 18 using sheep (15.0%), 11 using minipig (9.2%), seven using monkeys (5.8%), four using rats (3.3%) and one using a cat model (0.8%). Based on the results of this study, an attempt was made to provide biological DO parameters and guidelines for future research on experimental cranio-facial DO related to the appropriate animal model.

IGF-I, TGF-beta, and BMP-4 are expressed during distraction osteogenesis of the pig mandible

The mechanisms that regulate bone formation during distraction osteogenesis (DO) are not completely understood. Our hypothesis is that local cytokines that stimulate osteoblast activity are potential regulators of this process. The purpose of this study was to determine gene expression of insulin-like growth factor I (IGF-I), transforming growth factor-beta (TGF-beta), and bone morphogenetic protein 4 (BMP-4) in distracted wounds. A semiburied, rigid distraction device was placed across an osteotomy at the right mandibular angle in 9 Yucatan minipigs. Distraction was begun immediately at a rate of 1 mm/day. The animals were sacrificed after 4 and 7 days of distraction, and after 7 days of distraction plus 4 days of neutral fixation. Excised wound tissues were processed for histologic and gene expression analyses. Competitive reverse-transcription polymerase chain reaction (RT-PCR) assays were developed and validated for porcine genes. Histologic analysis showed membranous ossification within the DO wound. Gene expression of IGF-I, TGF-beta and BMP-4 was detected during distraction and neutral fixation. These results show that gene expression analyses can be performed in a large animal model of mandibular DO. As the pig mandible closely resembles that of the human in morphology and physiology, this is an important step toward characterization of the early molecular events in the DO wound.

The molecular biology of distraction osteogenesis

Distraction osteogenesis has become a mainstay in bone tissue engineering and has significantly improved our armamentarium for reconstructive craniomaxillofacial procedures. However, although the biomechanical, histological, and ultrastructural changes associated with distraction osteogenesis have been widely described, the molecular mechanisms governing the formation of new bone in the interfragmental gap of gradually distracted bone segments remain largely unclear. Recently, a rat model of mandibular distraction was described that provides an excellent environment for deciphering the molecular mechanisms that mediate distraction osteogenesis. This article presents the hypotheses and current research that have furthered knowledge of the molecular mechanisms that govern distraction osteogenesis. Recent studies have implicated a growing number of cytokines that are intimately involved in the regulation of bone synthesis and turnover. The gene regulation of numerous cytokines (transforming growth factor-beta1, -beta2, -beta3, bone morphogenetic proteins, insulin-like growth factor-1, fibroblast growth factor-2) and extracellular matrix proteins (osteonectin, osteopontin) during distraction osteogenesis have been best characterized and are discussed in this article. It is believed that understanding the biomolecular mechanisms that mediate membranous distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone healing.

The versatility of distraction osteogenesis in craniofacial surgery

OBJECTIVES

To review our preliminary results using distraction osteogenesis for the correction of craniofacial deformities and to determine its role in treating anatomic deformities and functional deficits relative to conventional craniofacial surgery.

DESIGN AND SETTING

Retrospective clinical review; tertiary care center.

METHODS

Twenty-four consecutive patients were treated with distraction osteogenesis during a 34-month period. Outcomes were compared with preexisting anatomic deformities and functional deficits using records of clinical assessments, photodocumentation, diagnostic imaging, and treatment planning aids.

MAIN OUTCOME MEASURES

Distraction achieved vs planned distraction based on clinical and radiographic assessment, clinical status of functional deficits before and after treatment, and objective rating of aesthetic improvement.

CONCLUSIONS

Preliminary results demonstrated good-to-excellent outcome in correcting facial skeletal deformity in 80% of patients. Functional outcomes included resolution or significant improvement of upper airway obstruction in 13 of 14 patients and correction of corneal exposure for all 5 patients with preexisting exorbitism. Correction of malocclusion was less reliable. Problems related to the distraction devices, including failure of the advancement mechanism and fixation, were the most prevalent complications. Distraction osteogenesis represents an exciting new development in craniofacial surgery with several potential benefits, including less invasive surgery, the ability for earlier intervention, and the potential for correction of more severe deformities with improved posttreatment stability. The exact role of distraction osteogenesis relative to conventional techniques requires ongoing assessment.

The effects of magnitude and frequency of distraction forces on tissue regeneration in distraction osteogenesis of the mandible

Callus distraction has become an accepted treatment procedure to lengthen hypoplastic mandibles in humans. For this purpose, extraoral and intraoral devices have been applied successfully. The effects of the distraction vector, distractor stability, and rate and frequency of callus distraction on the regenerating tissues have been examined in various studies. In an experimental animal trial on pigs (n = 12), a newly developed microhydraulic osteodistractor was tested. The animals were evenly assigned to two groups to perform a continuous and noncontinuous osteodistraction of the mandible. Initially, the forces necessary to distract the pig mandibles were recorded from a noncontinuous distraction procedure; the results were then used to perform continuous bone distraction. Besides testing the new distractor, the study proved that in continuous osteodistraction, intramembranous bone regeneration occurred, whereas in noncontinuous osteodistraction the bone regeneration process followed a chondroid ossification. In continuous osteodistraction, the bone regeneration proceeded at a higher speed with the lower distraction forces compared with noncontinuous distraction, thereby reducing the consolidation period. Clinical and microscopical results are presented.

Influence of distraction rates on the temporomandibular joint position and cartilage morphology in a rabbit model of mandibular lengthening

PURPOSE

Although various aspects of bone formation during distraction osteogenesis have been studied extensively, there are only limited experimental data concerning the influence of mandibular distraction rates on structural alterations in the temporomandibular joint (TMJ). In this study, a rabbit model of unilateral mandibular distraction was used to test the effects of various strain schedules on the position and morphology of the TMJ.

MATERIAL AND METHODS

Fifty-two immature white female rabbits were used. The distraction procedure was performed using physiologic (2,000 microstrains, 1 per day) and elevated strain magnitudes (20,000 microstrains, 1 per day), as well as high strain magnitudes (200,000 and 300,000 microstrains, 1 per day). The investigation of the TMJ included clinical, radiologic, and histologic aspects.

RESULTS

Clinical and radiologic examinations at the end of the distraction period showed no evidence of joint luxation even at maximal distraction rates. Histologic and ultrastructural analyses revealed a positive correlation between the degree of mechanical loading and the development of degenerative alterations in the cartilage. In samples distracted at hyperphysiologic strain magnitudes, all cartilaginous layers were reduced in the regions of the TMJ that had been exposed to the higher pressure forces. The fibrous layer became nearly completely destroyed.

CONCLUSIONS

These experimental data show that distraction schedules with single but hyperphysiologic loads may lead to degenerative or even early arthrotic changes in the condyle. These data support the principle that distraction protocols should be performed without extensive mechanical loading on the TMJ.

Orthodontic spring guidance of bilateral mandibular distraction in rabbits

Although distraction osteogenesis can lengthen congenitally small mandibles, the distraction procedure can be difficult to control. To study the efficacy and safety of orthodontic spring guidance on bilateral mandibular distraction, an 8-mm anterior open bite was experimentally produced and corrected during bilateral mandibular distraction in rabbits. Orthodontic springs were attached to the anterior maxilla and mandible to redirect an ongoing distraction procedure. Sixteen rabbits underwent mandibular distraction: 6 rabbits received heavy springs (8 oz), 6 rabbits received light force springs (2 oz), and 4 rabbits served as control animals with anterior open bites without spring guidance. Nickel-titanium springs were applied during the last week of osseous distraction and the first week of consolidation. Distractors were left in place throughout a 2-month consolidation period. None of the animals developed fibrous union as a result of spring guidance. The 8-mm open bite did not close in the control group or in the light spring group after 2 weeks of spring wear or during the consolidation period. Heavy springs completely closed the experimental open bites within 2 weeks (P <.01, analysis of variance). Bite corrections did not change during the consolidation period. This study indicated that the addition of an orthodontic spring to a mandibular distraction procedure did not impair bone healing. With the distraction device in place, heavy spring forces redirected an ongoing mandibular distraction procedure and corrected an open bite, distraction side effect. Direct measurements, radiographic measurements, and tissue histologic factors described changes in segment position and shape of the distraction site.

Distraction osteogenesis after membranous bone onlay grafting in a dog model

PURPOSE

The purpose of this experiment was to study the possibility of distraction osteogenesis in a membranous bone onlay graft to the mandible and to clarify the histology of the bone repair.

MATERIALS AND METHODS

Four dogs, 5 months of age at the beginning of the experiment, were used for this study. The zygomatic arch was exposed in the subperiosteal plane, and a 3-cm long, full-thickness portion of the arch was harvested. The lateral surface of the mandibular body was exposed in the subperiosteal plane, and the bone was fixed to the lateral surface as a membranous onlay graft using screws. A vertical osteotomy through the graft and underlying mandibular body was done postoperatively at week 1 in dog 1, week 2 in dog 2, week 3 in dog 3, and week 4 in dog 4. An external distraction device was applied to the mandibular body, and distraction was started 7 days after the operation at a rate of 1 mm/d for 10 days. After completion of distraction, the device was left in place for 6 weeks to allow for bony consolidation. Radiographs were carried out at 2, 4, and 6 weeks postdistraction. All dogs were killed 6 weeks after distraction.

RESULTS

New bone between the native underlying mandibular segments was generated in the distraction zone in all dogs. New bone was not generated between the segments of the membranous bone onlay graft in dog 1, but was generated in dog 2, dog 3, and dog 4. However, in dogs 2 and 3, the new bone between the segments was less firm, with more fibrous tissue, than the bone between the native underlying mandibular segments. Histologically, the distraction gap between the segments of the membranous bone onlay graft in dogs 2 and 3 was composed of considerable fibrous tissue in the central zone and activated osteoblastic cells forming new bone in the margins. In dog 4, there was much more osteoblastic activity in the distraction gap, and the new bone had the appearance of almost normal cortical bone.

CONCLUSION

These findings show that distraction osteogenesis is possible in a membranous bone onlay graft and suggest that the distraction should be performed at least 4 weeks after the onlay grafting.

Bending of the distraction site during mandibular distraction osteogenesis in the rabbit: a model for studying segment control and side effects

PURPOSE

The purpose of this investigation was to develop an animal model for studying and correcting mandibular distraction side effects.

MATERIALS AND METHODS

Twenty-nine rabbits underwent bilateral mandibular distraction. Bending of the mandible was accomplished by offsetting a linear distraction by 35 degrees from the occlusal plane (4 screws per distractor), rotating the anterior segment inferiorly (2 screws per distractor), and removing a 3- or 6-mm wedge of the distraction site. The amount of bite opening varied according to the surgical design. Direct measurements, radiographs, and histology samples were compared.

RESULTS

Linear distraction produced a 4-mm anterior open bite and a Class III malocclusion after 2 weeks of distraction. Segmental rotation produced an 8-mm anterior open bite without complications. Removal of a wedge initiated rotation of the anterior segment. A large wedge (6 mm) produced fibrous union in the distraction site. The amount of bite opening or closure depended on the number of surgical screws and position of the distractor. Serial histologic sections showed bone formation at the rotated, triangular distraction site.

CONCLUSION

Bite opening or closure can occur from loss of segment control or by altering surgical design. This information is needed to counter unwanted side effects or to plan segment rotations.

Comparison of different distraction rates in the mandible: an experimental investigation

This study evaluated bone distracted in rabbit mandibles at different intervals and with different daily rates of distraction histologically with the goal of attaining a universally accepted distraction protocol. Osteogenesis was investigated in mandibles distracted at different rates in 24 New Zealand rabbits using a custom-made submerged distractor. Distraction was started on the third postoperative day for a total of 10 mm. The animals were divided into four groups each containing six rabbits. Group 1 was distracted 0.5 mm twice a day; Group 2 was distracted 1.0 mm once a day; Group 3 was distracted 1.0 mm twice a day and Group 4 was distracted 2.0 mm once a day. All the animals were sacrificed 6 weeks after completion of distraction. Half of the distracted mandibles were decalcified for H&E staining and polarized light microscopy studies. Sections of the undecalcified half of the samples were stained with Goldner's stain. The results indicate that a distraction rate of 1.0 mm per day produced the best osteogenesis among the tested rates. There was no great difference in osteogenesis between 1.0 mm once a day and 0.5 mm twice a day. However, 0.5-mm distraction may result in immature bone healing. Distraction of 1.0 mm twice a day resulted in incomplete osteogenesis, while distraction of 2.0 mm once a day resulted in fibrous union. It is clear from these results that a shorter period of device fixation should be achieved by methods other than rapid distraction.

Rat mandibular distraction osteogenesis: part III. Gradual distraction versus acute lengthening

Distraction osteogenesis is a well-established method of endogenous tissue engineering. This technique has significantly augmented our armamentarium of reconstructive craniofacial procedures. Although the histologic and ultrastructural changes associated with distraction osteogenesis have been extensively described, the molecular mechanisms governing successful membranous distraction remain unknown. Using an established rat model, the molecular differences between successful (i.e., osseous union with gradual distraction) and ineffective (i.e., fibrous union with acute lengthening) membranous bone lengthening was analyzed. Herein, the first insight into the molecular mechanisms of successful membranous bone distraction is provided. In addition, these data provide the foundation for future targeted therapeutic manipulations designed to improve osseous regeneration. Vertical mandibular osteotomies were created in 52 adult male Sprague-Dawley rats, and the animals were fitted with customized distraction devices. Twenty-six animals underwent immediate acute lengthening (3 mm; a length previously shown to result in fibrous union) and 26 animals were gradually distracted (after a 3-day latency period, animals were distracted 0.25 mm twice daily for 6 days; total = 3 mm). Four mandibular regenerates were harvested from each group for RNA analysis on 5, 7, 9, 23, and 37 days postoperatively (n = 40). Two mandibular regenerates were also harvested from each group and prepared for immunohistochemistry on postoperative days 5, 7, and 37 (n = 12). In addition to the 52 experimental animals, 4 control rats underwent sham operations (skin incision only) and mandibular RNA was immediately collected. Control and experimental specimens were analyzed for collagen I, osteocalcin, tissue inhibitor of metalloproteinase-1, and vascular endothelial growth factor mRNA and protein expression. In this study, marked elevation of critical extracellular matrix molecules (osteocalcin and collagen I) during the consolidation phase of gradual distraction compared with acute lengthening is demonstrated. In addition, the expression of an inhibitor of extracellular matrix turnover, tissue inhibitor of metalloproteinase-1, remained strikingly elevated in gradually distracted animals. Finally, this study demonstrated that neither gradual distraction nor acute lengthening appreciably alters vascular endothelial growth factor expression. These results suggest that gradual distraction osteogenesis promotes successful osseous bone repair by regulating the expression of bone-specific extracellular matrix molecules. In contrast, decreased production or increased turnover of bone scaffolding proteins (i.e., collagen) or regulators of mineralization (i.e., osteocalcin) may lead to fibrous union during acute lengthening.

Evaluation of the consolidation period during osteodistraction using computed tomography

The use of distraction osteogenesis offers an alternative approach to the correction of craniofacial deformities. However, little is known with respect to the appropriate length of the consolidation period for the newly formed bone. The objective of this study was to evaluate, by quantitative computed tomography, the regenerate bone produced during osteodistraction of the dog mandible at three different consolidation times. Twelve skeletally mature male beagle dogs were equally separated into three experimental groups. Each dog underwent 10 mm of bilateral distraction osteogenesis to lengthen the mandible. After the distraction period, the bone was allowed to consolidate for 4, 6, or 8 weeks, at which time the animals were sacrificed and the mandibles harvested for computed tomographic imaging. The results demonstrate a significantly lower mean bone density of the regenerate in the 4 week group when compared with either the 6 or 8 week groups (P < .01). There was no significant difference, however, in mean bone density between the 6 and 8 week groups.

Decreased expression of osteocalcin and osteonectin in relation to high strains and decreased mineralization in mandibular distraction osteogenesis

In a rabbit model of mandibular distraction osteogenesis, high strains resulted in a substantial reduction in the expression rate of the two osteogenic marker proteins, osteocalcin and osteonectin. In non-distracted samples and mandibles exposed to 2000 microstrains, staining for osteocalcin in the osteotomized area was detected in osteoblasts and diffusely dispersed in the mineralized matrix of the surrounding bone. However, in osteotomized mandibles distracted at strains above physiological levels (200,000 and 300,000 mustrains, respectively) the majority of osteoblast-like cells failed to express immunodetectable amounts of osteocalcin. Similarly, in the extracellular matrix of the distraction area the expression of osteonectin decreased by applying higher strains. Ultrastructural analyses of mandibular samples exposed to hyperphysiological strains revealed that the reduced expression rate of osteocalcin and osteonectin was paralleled by a significant loss of crystal formation, suggesting a functional role of both proteins related to mechanical loading.

Intraoral widening and lengthening of the mandible in baboons by distraction osteogenesis

PURPOSE

The purpose of this study was to analyze the skeletal and dental positional changes and histomorphology of the distraction regenerates and mucogingival periosteal tissues that occurred after simultaneous widening and bilateral lengthening of the mandible in baboons by a miniaturized intraoral bone-borne distraction appliance.

MATERIALS AND METHODS

Distraction appliances were activated 5 days after vertical ramus and symphyseal osteotomies at a rate of 0.9 mm/d for 10 days. The appliances were then stabilized for 8 weeks, after which the animals were killed. The distraction gaps and gingival tissues were analyzed clinically, histologically, and by standardized radiographic studies.

RESULTS

Positional changes of the canines and incisor apices were proportional to the skeletal movements. Tipping of both incisors toward the center of the distraction gap was observed. Proportionate movement of the superior and inferior portion of the distracted segments was noted. Newly formed longitudinal trabecular columns parallel to the vector of distraction originated from the intact margins of alveolar bone contiguous with the adjacent teeth. Active histogenesis occurred in the stretched mucogingival periosteal tissues located in the distraction gaps.

CONCLUSIONS

The results of this investigation support the clinical use of the miniaturized intraoral bone-borne distraction appliance to selectively widen and lengthen the mandible. The orientation of the mandibular distractors must be parallel to the common vector of distraction, which should be parallel to the maxillary occlusal plane. The formation of a bone regenerate in the alveolar region depends on the presence of an adequate bone interface on either side of the distraction gap.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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