The effect of gradual distraction of the mandible on the sheep temporomandibular joint

The autogenous graft versus transport distraction osteogenesis for reconstruction of the ramus-condyle unit: a prospective comparative study

This study aimed to compare the joint function and morphology achieved following condylar reconstruction using sternoclavicular grafts (SCG) versus transport distraction osteogenesis (TDO) in temporomandibular joint (TMJ) ankylosis patients. Twenty-two patients with TMJ ankylosis underwent TMJ reconstruction with SCG or TDO (n=11 each). Radiographic and clinical evaluations were performed at 1 week and at 1, 3, and 6 months post-surgery. Clinical criteria examined included the duration of surgery, mean postoperative mouth opening, excursive jaw movements, and pain scores. The radiographic evaluation 6 months postoperatively (computed tomography) included subjective assessment of joint morphology and measurements of the mean condylar height, width achieved, and amount of condylar resorption. The χ² test and Student t-test were used to compare qualitative and quantitative variables, respectively. Similar mean mouth opening (SCG=31.8mm, TDO=32.1mm at 6 months), excursive movements, and pain scores were observed in the two groups throughout follow-up. Mean condylar resorption was significantly greater in the TDO group (TDO=7.0mm, SCG=2.7mm; P=0.005). The duration of reconstruction surgery was greater in the SCG group (P=0.035). A greater incidence of complications was observed with TDO. In conclusion, based on the protocols used in this study, SCGs are superior to TDO in terms of condylar morphology, stability, and surgical safety.

Histomorphometric analysis of the temporal bone after change of direction of force vector of mandible: an experimental study in rabbits

Objectives

The present study aimed at performing a histological evaluation of the response of temporal bone tissue to a change of direction of the force vector of the mandible in relation to the base of the skull.

Material and methods

Adult rabbits were assigned into four groups with two control and four experimental animals in each group. Experimental animals underwent surgery, which resulted in a change of direction of the force vector on the right temporomandibular joint. Samples were collected after 15, 30, 60 and 90 days for histological analysis.

Results

In the two-way analysis of variance, the effect of group and time was statistically significant (p<0.001). Additionally, a statistically significant interaction between group and time was observed (p<0.001). Control animals showed normal growth and development of the temporal region. In the experimental group, the change in direction of the force vector of the mandible induced significant changes in the temporal bone, with a bone modeling process, which suggests growth of this cranial structure.

Conclusions

The methodology used in this experiment allows us to conclude that the change in direction of the force vector of the mandible in relation to the skull base induces remodeling and modeling processes in the temporal bone. The resumption of normal oral functions after bone healing of the mandibular fracture appears to increase cell activation in the remodeling and modeling of the temporal bone structure. The observation of areas of temporal bone modeling shows the relevance of further investigation on the correlation between the joint structures and craniofacial growth and development.

Histomorphometric examination of long-term changes in temporomandibular joints after mandibular lengthening by distraction osteogenesis in rabbits

OBJECTIVE

The purpose of this study was to evaluate long-term histomorphometric changes in temporomandibular joints (TMJs) of rabbits after mandibular distraction osteogenesis (DO).

STUDY DESIGN

Twenty-six rabbits were used in this study. Two of them served as control subjects, and the remaining 24 underwent DO procedures in their left mandibular bodies. After a latency period of 5 days, 5 mm lengthening was performed at a rate of 1 mm/d. The rabbits in the experimental group were randomly divided into 4 subgroups and killed after 1, 2, 4, and 6 months. TMJs from both sides were harvested and prepared with hematoxylin and eosin stain for histomorphometric examination under an optical microscope.

RESULTS

Compared with control subjects and nondistracted sides, fibrous articular, proliferative, and hypertrophic areas were significantly increased (P < .05) in the first 2 months in distracted sides. The changes were insignificant in the fourth and sixth postoperative months.

CONCLUSION

Unilateral mandibular distraction of 5 mm was found to be well tolerated and no degenerative changes were observed histologically in the rabbit TMJs in the long-term period.

Autogenous grafts for condylar reconstruction in treatment of TMJ ankylosis: current concepts and considerations for the future

Temporomandibular joint (TMJ) ankylosis is characterized by difficulty or inability to open the mouth due to fusion of the temporal and the mandible, resulting in facial symmetry/deformity, malocclusion and dental problems. The only treatment option for TMJ ankylosis is surgical with or without condylar reconstruction. Various autogenous grafts are available for condylar reconstruction after freeing the ankylotic mass such as costochondral, sternoclavicular, fibular, coronoid, and metatarsophalangeal. Costochondral graft is preferred by surgeons, but distraction osteogenesis is slowly gaining popularity and may ultimately become the standard procedure, providing a cost-effective approach with low morbidity and excellent functional outcomes. Tissue engineering is another budding field which has shown promising results in animal studies but has not been applied to humans. To date, there is no ideal autogenous graft for condylar reconstruction that satisfies the complex anatomy and the myriad of functions of a missing condyle.

Stress distribution in mandible and temporomandibular joint by mandibular distraction: a 3-dimensional finite-element analysis

The effects of mandibular distraction on the mandible and its surrounding tissue remain to be clarified. Here, we used a 3-dimensional finite-element method to investigate the effects of unilateral horizontal lengthening of the mandibular body and vertical lengthening of the mandibular ramus on the mandible and temporomandibular joint (TMJ). With horizontal loading that assumed mandibular body lengthening, tensile and compressive stresses were great near the anterior region of the mandibular angle (the loading area). With vertical loading that assumed mandibular ramus lengthening, tensile and compressive stresses were great at the center of the mandibular ramus (the loading area). Under both loading conditions, stress distribution in the TMJ was greater on the loading side than on the non-loading side. With mandibular body lengthening, the center of the mandible deviated in the direction of the non-lengthened side to widen the mandible in the lateral direction. With mandibular ramus lengthening, the occlusal plane tilted in the inferior direction on the lengthened side. In the TMJ, stress was greatest on the affected side during mandibular ramus lengthening, suggesting the need to consider the mandibular condyle on the affected side during this procedure.

Prediction of the articular eminence shape in a patient with unilateral hypoplasia of the right mandibular ramus before and after distraction osteogenesis-A simulation study

The aim of this work was to predict the shape of the articular eminence in a patient with unilateral hypoplasia of the right mandibular ramus before and after distraction osteogenesis (DO). Using a patient-specific musculoskeletal model of the mandible the hypothesis that the observed differences in this patient in the left and right articular eminence inclinations were consistent with minimisation of joint loads was tested. Moreover, a prediction was made of the final shape of the articular eminence after DO when the expected remodelling has reached a steady state. The individual muscle forces and the average TMJ loading were computed for each combination of articular eminence angles both before and after DO. This exhaustive parameter study provides a full overview of average TMJ loading depending on the angles of the articular eminences. Before DO the parameter study resulted in different articular eminence inclinations between left and right sides consistent with patient data obtained from CT scans, indicating that in this patient the articular eminence shapes result from minimisation of joint loads. The simulation model predicts development of almost equal articular eminence shapes after DO. The same tendency was observed in cone beam CT scans (NewTom) of the patient taken 6.5 years after surgery.

Effect of bilateral mandibular osteodistration on the condylar cartilage: an experimental study on rabbits

Although various aspects of bone formation during distraction osteogenesis have been studied extensively, there are only limited experimental data concerning the influence of hyper-physiologic mandibular distraction rate on structural alterations in the temporomandibular joint (TMJ) condylar cartilage. The purpose of this study was to evaluate the effect of bilateral distraction osteogenesis of the mandibular body, at a hyper-physiologic rate and length, on the integrity of the condylar cartilage in rabbits. MATERIALS AND METHODS: Eighteen healthy adult male rabbits weighing 2 to 3 kg were assigned to 1 of 2 groups: the control group (n = 2 rabbits, 4 joints) or the study group (n = 16 rabbits, 32 joints) four rabbits (8 joints) in each subgroup according to the post-distraction period (1,2,3 or 4 weeks). In the control group, rabbits received sham surgery (Osteotomy without distraction) and then left to live for 4 weeks under the same condition of the study group then euthanized using intravenous overdose of pentobarbital sodium. In the study group, an extra oral custom-made distracter was employed to achieve bilateral mandibular hyper physiologic distraction (1.5 mm twice daily for 5 days) distraction. All animals were evaluated clinically and histomorphometrically and results analyzed by MINITABE 13.1 statistical package using ANOVA test. RESULTS: Animals underwent distraction showed obvious changes in condylar surface contour related to length of the follow up period, compared to the control; these changes seemed to be partly reversible. The most pronounced observation was the irregularities and resorption in the anterior part of the condylar cartilage and the subcondylar bone. Moreover, at the first two weeks, the area of resorption was invaded by large number of osteoclasts and chronic inflammatory cells which declined later in the 3rd and 4th weeks and replaced with osteoblastic activities. CONSLUSION: These experimental data showed that distraction rate of 3 mm per day may lead to degenerative or even early arthritic changes in the TMJ condylar cartilage in the 1st and 2nd post-distraction weeks. However, all condyles showed adaptive and remodeling sings in the following 3rd and 4th weeks.

Biomechanical Properties of the Condyle Created by Osteodistraction

A new condyle can be reconstructed by osteodistraction, but the biomechanical properties of the neocondyle remain unknown. This study examined the hypothesis that the biomechanical properties of neocondylar cancellous bone could reach control levels 24 weeks after its creation by osteodistraction. The right mandibular condyles were removed and reconstructed by osteo-distraction in 16 adult goats. Their contralateral condyles served as controls. Microstructural and mechanical properties were examined by microcomputed tomography and mechanical testing. At 24 weeks after distraction, the neocondyle grew larger in size, but the shape and histological features were similar to those of the controls. The cancellous bone of the neocondyle even appeared to be more dense and stiffer in comparison with the control condyle. The results of this study suggest that the neocondyle created by osteodistraction develops nearly normal biomechanical properties for functional loading by 24 weeks after creation.

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

OBJECTIVE

Loading of temporomandibular tissues during mandibular distraction may cause changes in condylar growth and cartilage thickness. This study examines the effects of distraction on the condyle in a large animal model by explicitly measuring growth and in vivo loading.

DESIGN

Unilateral mandibular distraction was carried out on 20 growing minipigs divided into three groups. One group underwent distraction but not consolidation, whereas the other two groups were allowed a period of consolidation of either 1 or 2 weeks. Animals received fluorochrome and 5-bromo-2'-deoxyuridine (BrdU) labelling and masticatory strain was measured from the condylar neck. Condylar strain was also recorded in an age-matched sample of eight animals that received no distraction surgery. Immunohistochemical procedures were used to identify dividing prechondroblasts and histological analysis was used to measure mineral apposition rate, count dividing cells, and measure the thickness of condylar cartilage.

RESULTS

Strain magnitude, particularly compressive strain, was much larger on the non-distraction side compared to the distraction side condyle. Compared to normal loading levels, the distraction side condyle was underloaded whereas the condyle on the intact side was overloaded. Mineral apposition and cartilage thickness were greater on the distraction side condyle compared to the opposite side. Differences between the sides were most pronounced in the group with no consolidation and became progressively reduced with consolidation time.

CONCLUSIONS

Increased mineralisation and cartilage thickness on the distraction side condyle are associated with reduced, not increased loading, perhaps because of disruption of the distraction side masseter muscle.

Mandibular distraction osteogenesis in a skeletal Class II patient with obstructive sleep apnea

We report the orthodontic treatment of a 31-year-old man with severe skeletal Class II malocclusion and documented obstructive sleep apnea (OSA). He had a retrognathic profile with an overbite of 4 mm and an overjet of 14 mm. Mandibular distraction osteogenesis was performed to lengthen the small, retruded mandible by 18 mm and improve the symptoms of OSA. Orthodontic treatment after the mandibular distraction osteogenesis procedure lasted 3 years 1 month. An acceptable occlusion was obtained, and the patient's OSA was significantly alleviated. Although the patient was satisfied with the treatment, condylar resorption was observed. The relevance of condylar resorption with reference to a comprehensive evaluation of the treatment outcome is discussed.

Histological evaluation of the temporomandibular joint after bilateral vertical ramus mandibular distraction in a canine model

The aim of this pilot study was to histologically evaluate the effect of bilateral vertical mandibular distraction osteogenesis (DO) on the temporomandibular joint (TMJ) in a canine model. Eight male beagle dogs underwent DO, with the placement of single-vector internal distractors. One unoperated animal served as control. After a latency period of 7 days, distraction was performed at a rate of 1 mm a day for an average of 12 days. The animals were divided into two groups (n = 4) and sacrificed after one or two months of consolidation. Eighteen TMJs were prepared for histological evaluation. Control TMJs surfaces were smooth, with no irregularities and trabecular bone was thick and multiply connected. In the one-month group, thinning of the trabecular bone was evident. The trabeculae were long, not multiply connected, parallel to each other and perpendicular to the articular surface. Although overall fibrous-cartilaginous tissues covering the TMJs were maintained with no signs of degenerative changes, one condyle from the one-month group had depressions and erosions of the fibro-cartilage layer and subcortical bone. In the two-month group, overall bone and cartilage architecture was more similar to the control specimens. This study indicates that, in the short term, gross changes can occur in the TMJ after bilateral mandibular vertical ramus distraction. These changes seem to be a process of biological adaptation to the pressure and functional changes secondary to surgery and distraction. However, long-term studies are needed to confirm whether the changes are completely reversible.

Condylar mineralization following mandibular distraction in rats

The impact of mandibular distraction on condyles is poorly understood. To examine how condylar mineralization is affected, we performed distraction in 128 one-month-old rapidly and 126 three-month-old slowly growing rats. The rate of distraction was 0.0 mm (sham), 0.2 mm (slow), 0.4 mm (moderate), or 0.6 mm (rapid). From 7 to 9 rats from each rate (n = 29-32) were killed at 4 time periods (D6, D10, D24, and D38) following osteotomy. Calcein and alizarin were injected 6 and 3 days, respectively, prior to death. Methacrylate-embedded sagittal condylar sections were examined under epifluorescence, and mineral apposition rates were measured. Results indicated that: (1) rapidly growing rats showed higher mineral apposition rates (p < 0.01-0.001) than did slowly growing rats; (2) mineral apposition rates were lower in distracted sides at all times in rapidly growing rats (p < 0.05-0.01), while this side-dependency was seen only at D24 in slowly growing rats (p < 0.05); and (3) distraction rates had little effect on mineral apposition rates. Thus, mandibular distraction decreases condylar mineral apposition rates, but only in rapidly growing rats, which is related to surgery and its functional consequences, not to the distraction rate.

Micro-Computed Tomography Evaluation of the Glenoid Fossa and Mandibular Condyle Bone After Bilateral Vertical Ramus Mandibular Distraction in a Canine Model

The aim of this study was to quantify bone microarchitecture within the glenoid fossa and mandibular condyle following mandibular distraction osteogenesis. Eight 6- to 9-month-old male beagle dogs underwent bilateral vertical mandibular distraction with semiburied distractors (12 days of distraction at 1 mm per day). One unoperated animal served as control. After distraction the animals were divided into two groups (N = 4) and killed after 1 or 2 months of consolidation. Three-dimensional trabecular architecture was analyzed by micro-computed tomography (microCT). At both sites the overall trends were similar. In the glenoid fossa, there was decreased bone volume, trabecular number, and connectivity density and increased trabecular separation at 1 month and decreased trabecular thickness and increased structure model index compared with the control (P < 0.05). In the mandibular condyle, there was decreased bone volume, trabecular number, and connectivity density at both 1 and 2 months, with decreased trabecular thickness and increased structure model index at 2 months only compared with the control (P < 0.05). The bone became less dense and more rodlike. These bone changes are similar to those seen by the effects of aging or impaired normal function. Thus, in the short term, changes occur in the bone microstructure of the glenoid fossa and mandibular condyle after vertical mandibular ramus distraction in the canine model.

Micro-computed tomography evaluation of the glenoid fossa and mandibular condyle bone after bilateral vertical ramus mandibular distraction in a canine model

The aim of this study was to quantify bone microarchitecture within the glenoid fossa and mandibular condyle following mandibular distraction osteogenesis. Eight 6- to 9-month-old male beagle dogs underwent bilateral vertical mandibular distraction with semiburied distractors (12 days of distraction at 1 mm per day). One unoperated animal served as control. After distraction the animals were divided into two groups (N = 4) and killed after 1 or 2 months of consolidation. Three-dimensional trabecular architecture was analyzed by micro-computed tomography (muCT). At both sites the overall trends were similar. In the glenoid fossa, there was decreased bone volume, trabecular number, and connectivity density and increased trabecular separation at 1 month and decreased trabecular thickness and increased structure model index compared with the control (P < 0.05). In the mandibular condyle, there was decreased bone volume, trabecular number, and connectivity density at both 1 and 2 months, with decreased trabecular thickness and increased structure model index at 2 months only compared with the control (P < 0.05). The bone became less dense and more rodlike. These bone changes are similar to those seen by the effects of aging or impaired normal function. Thus, in the short term, changes occur in the bone microstructure of the glenoid fossa and mandibular condyle after vertical mandibular ramus distraction in the canine model.

Mandibular mechanics following osteotomy and appliance placement II: Bone strain on the body and condylar neck

PURPOSE

The purpose of this investigation was to determine if the mechanical environment of the mandible is changed by osteotomy and fixation, as assessed by the measurement of bone strain on the condylar neck and mandibular corpus.

MATERIALS AND METHODS

Immediately following unilateral mandibular osteotomy and distractor placement, strain gauges were attached directly to the corpus and condylar neck in a sample of domestic pigs. Bone strains were recorded during mastication and muscle stimulation. Comparisons of principal strain magnitudes and orientations were made between sides and between the osteotomy sample and a control database.

RESULTS

The animals preferred to chew on the non-osteotomy side. Corpus strains were higher for osteotomy-side chewing but were comparable to the control database, regardless of chewing side. For the condyle, compared with the control database and the non-osteotomy side, the osteotomy side was underloaded in compression. Furthermore, the orientation of compressive strain was highly variable and more horizontally oriented than that of control and non-osteotomy condyles. Stimulation of the masseter and medial pterygoid loaded the mandible to normal levels.

CONCLUSION

Masticatory behavior was altered, probably as a combined result of disruption of the occlusion, changes in muscle recruitment, and probable loss of sensory feedback. However, neither these changes nor damage to the muscles explain the decrease and reorientation of compressive strain on the condylar neck. Alternatively, the modified strain pattern could have arisen from positional instability of the proximal bone fragment.

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

PURPOSE

Unilateral mandibular distraction osteogenesis (DO) has been shown to cause gross changes in the mandibular condyle and articular disc. The purpose of this study was to correlate histologic findings with these gross changes in a minipig distraction model.

MATERIALS AND METHODS

Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0-day latency and rates of 1, 2, or 4 mm/day for a 12-mm gap. After the minipigs were killed (at 0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested, decalcified, prepared for standard paraffin embedding, and evaluated to determine changes in 1) morphology and thickness of the articular cartilage and subchondral bone and 2) morphology of the disc.

RESULTS

In control animals, there were no degenerative changes in the articular cartilage and underlying condylar bone; there were no significant differences in the mean articular cartilage thickness. The temporomandibular joint discs were normal. In experimental animals, distracted condyles showed increasing degenerative changes and mean articular cartilage thickness as the DO rate increased. The discs were thinner. These changes were present, but to a lesser degree, in the contralateral condyles. After 90 days, degenerative changes in the condyles and discs were reduced, after remodeling, except in the 4 mm/day DO group.

CONCLUSIONS

Histologic changes in the condyles and temporomandibular joint discs in response to mandibular DO correlated with previously reported gross changes. These changes were greater at higher distraction rates and remodeling back to normal occurred in mandibular condyles distracted at 1 mm/day.

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

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

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.

A Comparison of Synovial Fluid Pressure After Immediate Versus Gradual Mandibular Advancement in the Miniature Pig

PURPOSE

Mandibular advancement is a commonly performed surgical procedure for the treatment of mandibular hypoplasia. With the increased use of rigid fixation, there has been a decrease in the amount of relapse but an increase in the amount of force transmitted to the condyles. Gradual advancement of the mandible by distraction osteogenesis slowly overcomes the soft-tissue envelope and may decrease the amount of force exerted on the condyles. The purpose of this study was to develop an animal model to measure the magnitude of pressure associated with immediate versus gradual mandibular advancement.

MATERIALS AND METHODS

A 2.0-mm pressure transducer was placed in the superior joint space in 2 miniature pigs. In the first animal, immediate advancement of the mandible with rigid fixation was performed. The synovial fluid hydrostatic pressures were measured prior to surgery and postoperatively. A second animal underwent gradual advancement with distraction osteogenesis. The synovial fluid hydrostatic pressures were measured prior to and after each activation of the distraction device. The condyles were examined radiographically and microscopically.

RESULTS

The superior joint space fluid pressures increased and remained elevated over a 5-week period after immediate advancement. In the gradually advanced mandible, the pressures were elevated but returned to near baseline prior to the activation the following day.

CONCLUSION

This animal model is useful to directly measure the pressure that is exerted on the condyle. This will allow further studies to compare methods for mandibular advancement. It is likely that gradual advancement of the mandible by distraction osteogenesis produces less force and causes less condylar resorption than large mandibular advancement stabilized with rigid fixation.

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.

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.

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

PURPOSE

Distraction osteogenesis (DO) is commonly performed for mandibular reconstruction during the growth period. We tested the hypothesis that parathyroid hormone-related protein (PTHrP) in mandibular condylar cartilage and underlying trabecular bone in growing individuals undergo changes in response to distraction forces.

MATERIALS AND METHODS

Forty-eight 6-week-old male Sprague-Dawley rats were used. Animals underwent unilateral mandibular distraction using a distractor that we devised, and unoperated animals were evaluated as controls. DO procedure was performed: 3 days' latency period, 0.4 mm/day rate, total 4.0 mm. Changes in cartilage morphology, PTHrP activity, and 3-dimensional trabecular bone structure changes measured by micro-computed tomography were examined at 0, 2, 4, and 6 weeks of consolidation.

RESULTS

A marked irregularity was noted in the superior portion of the distracted side's condylar cartilage that resolved after distraction ceased. PTHrP was more strongly expressed in the hypertrophic layer of condylar cartilage on the distracted side than in controls, up to 6 weeks after the end of distraction. Subchondral trabecular bone volume, percent bone volume, and trabecular number in the superior and posterior regions of the condyle decreased significantly by 2 weeks after distraction. These parameters returned to normal in the posterior condyle, but not in the superior part of the condyle by 6 weeks following distraction.

CONCLUSION

These results suggest that unilateral mandibular distraction in growing rats causes temporary morphologic alterations of trabecular bone structure on the distracted side accompanied by increased production of PTHrP in the mandibular condyle.

Backward distraction osteogenesis of condylar segment in patient with mandibular ramus deficiency—Report of a case

A backward distraction osteogenesis (BDO) of the condylar segment for treatment of mandibular ramus deficiency was developed. This report describes the clinical progress of a patient with mandibular ramus deficiency in whom satisfactory occlusion was achieved and maintained by gradual posterosuperior repositioning of the displaced condyles into the glenoid fossae during intermaxillary fixation. Findings of pre- and postoperative clinical and magnetic resonance imaging indicate that the effect of BDO on the temporomandibular joint was negligible.

Correlation of immunohistochemical characteristics of the craniomandibular joint with the degree of mandibular lengthening in rabbits

PURPOSE

This study examined immunohistochemical changes in the craniomandibular joints of rabbits after distraction osteogenesis following mandibular corticotomy.

MATERIALS AND METHODS

The experimental animals (n = 8) were divided into 3 groups that underwent 2, 3.5, and 5 mm of unilateral distraction osteogenesis (groups 1, 2, and 3, respectively). After corticotomy of the left mandibular body and a 7-day healing period, a second operation was performed to expose the device. Distraction was then performed at the rate of 0.5 mm/d. A 14-day consolidation period was allowed after the distraction was complete. Changes in cartilage, osteoblast activity, and osteoclast activity were then examined.

RESULTS

The differentiation and proliferation of cartilage increased in groups 1 and 2, were highest in group 2, and decreased in group 3. Group 2 also showed the greatest increase in the width of the hypertrophic chondrocyte layer. Relative to the control group, osteoclast activity was only somewhat higher in groups 1 and 2 but was significantly higher in group 3. Osteoblast activity was significantly higher in groups 1 and 2 than in the control group. However, the osteoblast activity in group 3 was slightly lower than that in group 2. At the time of unilateral mandibular distraction, no degenerative changes of the temporomandibular joint were observed in groups 1 or 2, but bone resorption was observed in group 3.

CONCLUSIONS

The unilateral mandibular distraction of 2 or 3.5 mm was acceptable in that no degenerative changes of the temporomandibular joint were observed on either the distraction or the nondistraction sides. Five millimeters of distraction might be beyond physiologic limits.

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.

Cephalometric analysis of the consolidation phase following bilateral pediatric mandibular distraction

OBJECTIVE

The goal of the consolidation phase of mandible distraction is to maintain the improvement in maxillomandibular form and relationship while the generated tissue ossifies. During this period, external deforming forces can act on the healing generated bone. The purpose of this study was to describe the potential cephalometric changes that occur following pediatric bilateral mandibular distraction using external devices.

DESIGN

Retrospective lateral superimposition cephalometric analyses.

PARTICIPANTS

Thirty-five cases of pediatric mandible distraction were reviewed. Seven of these cases were included in the study after exclusion criteria were applied. These cases represented a group with severe congenital dysmorphology and a mean device activation of 26.5 mm.

MAIN OUTCOME MEASURES

Changes in pogonion position, symphyseal plane rotation, mandible length, and mandible length relative to maxillary length during the 18 to 36 days of activation, the eight weeks of consolidation, and the 1-year period following removal of the distraction device were measured.

RESULTS

All patients demonstrated variable changes in position of the mandible during the consolidation phase. The most common were retrusion of pogonion, a decrease in mandible length, and a clockwise rotation of the symphyseal plane. In some cases the changes that occurred during consolidation were greater than those that occurred on 1-year follow-up.

CONCLUSIONS

The consolidation phase of distraction osteogenesis is a dynamic phase and should not be assumed to be static. Multicenter use of this cephalometric technique would help to identify potential risk factors associated with postactivation changes.

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

PURPOSE

Distraction osteogenesis (DO) is a commonly used technique for mandibular lengthening, but changes in the temporomandibular joint have not been well documented. The purpose of this study was to evaluate the effect of DO, at varying rates, on the mandibular condyle and articular disc.

MATERIALS AND METHODS

Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0 day latency and rates of 1, 2, or 4 mm/d for a 12-mm gap. After the animals were killed (0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested and evaluated to determine changes in 1) condylar form and size, 2) condylar surface, and 3) the articular disc.

RESULTS

Articular surfaces of the condyles in control animals were smooth, with no irregularities or erosions. In animals undergoing distraction, ipsilateral condyles showed increasing changes in morphology and AP dimension, and surface contour irregularities as the DO rate increased. These changes were present, but to a lesser degree, in the contralateral condyles. Articular discs of both ipsilateral and contralateral sides showed variable thinning at the medial aspect at end DO. After 90 days, changes in the condyles and discs were reduced by remodeling except in the 4 mm/d DO groups.

CONCLUSIONS

Results of this preliminary study indicate that gross changes occur in condyles and discs after unilateral mandibular DO. These changes are more severe at faster distraction rates (4 mm/d) and tend to resolve during neutral fixation when a rate of 1 mm/d is used.

Effect of mandibular distraction osteogenesis on temporomandibular joint after previous irradiation and hyperbaric oxygenation

The purpose was to evaluate the effect of mandibular distraction osteogenesis (DO) on condylar cartilage after radiotherapy and hyperbaric oxygenation (HBO). Unilateral DO was performed on low- and high-dose irradiated rabbits with or without accompanying HBO, and non-irradiated animals. High-dose irradiated animals were given irradiation in the temporomandibular joint (TMJ) equivalent to 50 Gy in 25 fractions. Low-dose irradiated rabbits received scattered irradiation of 10% of that of high-dose irradiated animals. After radiotherapy, some of the animals were given HBO 18 times at 2.5 ATA for 90 min/day. One month after completion of radiotherapy, distraction osteotomy with distractor placement was performed. After a latency period, distraction was started at the rate of 1 mm/day, continued for 2 weeks, and the regenerate was allowed to consolidate for 1 month. Condyles of non-operated rabbits served as controls. Histological changes were more evident on the distracted than on the non-distracted side. In distracted, non-irradiated animals, condylar cartilage changes were minor and probably clinically insignificant. In irradiated rabbits, condylar cartilage changes on the lengthened side were severe, and often cartilage was either totally or partially sealed off by bone. Condylar heads were morphologically deformed. Even low doses of irradiation resulted in notable changes on the operated side, and HBO did not prevent disadvantageous effects.

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.

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

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

Proximal segment displacement in mandibular distraction osteogenesis

Distraction osteogenesis has been advocated for treatment of the mandibular deformity in patients with hemifacial microsomia (HFM). During the active phase, the force of distraction pushes the distal segment of the mandible down, creating a distraction gap. Because of the abnormal temporomandibular joint anatomy in HFM patients, the proximal segment may not seat in the glenoid fossa and thus may be displaced with distraction. The purpose of this study was to determine the vector(s) of proximal segment movement during mandibular distraction using a semiburied device. Two investigators traced the immediate pre-and postdistraction panoramic radiographs of 12 HFM patients (mean age at operation = 8.4 years, mean distraction = 28 mm) who had mandibular distraction with a semiburied device. Radiographic analysis, based on a vertical maxillary reference line, measured change in condylar position with angular and linear measurements. Inter-rater reliability for the tracing and analysis was shown with a correlation coefficient between 0.89 and 0.99 for all measures. Based on the angular and linear measurements, 10 of the 12 patients had superior movement of the proximal segment with distraction. Sagittal movement of the proximal segment could not be judged adequately. This study was based on measurements made on panoramic radiographs. Direct measurements could not be made; thus, it was not possible to estimate proximal segment movement in millimeters or as a percentage of total movement. Further studies to document proximal segment movement using computed tomography scans may provide more quantitative data.

Experimental forward mandibular displacement in sheep

In order to investigate growth modifications of the temporomandibular joint (TMJ) during dentofacial orthopaedic treatment, specific functional appliances have been used experimentally to prompt the mandible into a protrusive position in various animal models. The purpose of this study was to test the effectiveness of a functional appliance specially designed for sheep and to evaluate the sheep as a model for dentofacial orthopaedic research. Eight, 4-month-old, castrated male Merino sheep were randomly assigned to experimental or control groups, with four in each group. Cast functional appliances were fabricated for the animals in the experimental group. The treatment period was 15 weeks. Dental casts, endosseous implant markers and cephalograms were used to analyse the displacement of the mandible. Undemineralised sagittal sections of TMJ were used to evaluate the tissue responses induced by the appliances. The weight of the animals was measured monthly to monitor their growth. The growth of the metacarpus was also measured. During the experimental period, the animals maintained their weight within the normal range and grew normally. The appliance displaced the mandible to a downward and forward position. The adaptive responses in the TMJ induced by the appliances included changed anteroposterior shape of the condylar process, anteriorly thickened condylar cartilage, and a thickened compact bone layer along the anterior surface of the posterior wall of the glenoid fossa. The sheep coped well with the experimental procedures and the appliance used was demonstrably effective in inducing adaptive responses in the TMJ. Consequently, it is believed that the sheep is an appropriate animal model to study growth modifications in the TMJ region.

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.

Mandibular advancement using an intra-oral osteogenic distraction technique: a report of three clinical cases

Osteogenic distraction has been used for decades to lengthen limbs and now attention is focused upon its use within the craniofacial skeleton. This paper addresses distraction of the mandible. It is proposed that mandibular osteogenic distraction could be a possible adjunct to the orthodontic treatment of those adult patients with skeletal anomalies, who would benefit from combined orthodontic/orthognathic treatment. Three consecutive cases from one unit are presented, where adult patients with severe Class II division 1 malocclusions have undergone orthodontic treatment combined with mandibular osteogenic distraction, instead of conventional bilateral sagittal split osteotomies.

Reconstruction of a neocondyle using transport distraction osteogenesis

The process of slow bone expansion by distraction osteogenesis in conjunction with functional remodeling can also be used for the reconstruction of a neomandible and neocondyle. This is the technique of transport distraction osteogenesis. A transport disc is surgically created adjacent to the area of a discontinuity defect, and the transport disc is advanced by the process of distraction osteogenesis, using the Ilizarov principles. The mandible therefore acts as the bony template for reconstruction such that the neomandible created from the distraction process has the same size and shape as the native mandible covered by gingiva. This allows for enhanced prosthetic reconstruction. A reverse-L osteotomy of the ramus can also be performed to create a transport disc to reconstruct a neocondyle. Because the leading edge of the transport disc becomes enveloped by a fibrocartilagenous cap, the ramal transport disc can be moved superiorly to create a new articulation. Patients are encouraged to open and close their mouths during the distraction process, such that the transport disc remodels to form a neocondyle. This technique was successfully used to treat patients with degenerative joint disease, condylar resorption, and bony ankylosis.

The role of latency in mandibular osteodistraction

Even though osteodistraction has been well established in the extremities, the parameters used in craniofacial distraction have been essentially borrowed from orthopaedic experience. Latency is widely practised but its relevance has not been fully investigated. The purpose of this study was to establish the role of latency in mandibular distraction osteogenesis. Twenty-two growing Wethers sheep were allocated to four experimental groups. Six animals were allocated to each of Groups A, B and C and underwent bilateral mandibular corticotomies and attachment of an external lengthening device. Latent periods of 0, 4 and 7 days respectively were observed prior to beginning distraction. The distraction protocol consisted of a rate of 0.5 mm twice daily for 20 days, followed by a consolidation phase of 20 days after which the sheep were killed. Histology, bone densitometry and 3-point mechanical testing were performed on the harvested mandibles. Group D formed the control group (n = 4). Histologically, the distracted bone exhibited bone formation primarily via intramembranous ossification with scattered islands of cartilage. The regenerated bone had mechanical properties significantly weaker than the undistracted control group (P < 0.05), but between the experimental groups no statistically significant differences were demonstrable either in mechanical strength or DEXA density. These data indicate that a change in latency does not alter the properties of the regenerated bone in mandibular distraction osteogenesis and indeed no latent interval may be necessary at all in craniofacial distraction. This has implications for the duration of device fixation in distraction procedures.

Distraction osteogenesis: application to dentofacial orthopedics

Distraction osteogenesis is a surgical-orthopedic method for lengthening bone by separating or distracting a fracture callus. This technique has a long history in limb lengthening and has recently been used to lengthen mandibles and maxillae in human patients. Distraction osteogenesis represents a powerful method of producing unlimited quantities of living bone which can be formed along any plane of space. Because this method uses local host tissue, it offers many advantages over bone grafting. In the author's experience, large (10-22 mm) antero-posterior and vertical corrections of mandibles can be achieved using this technique. The purpose of this article is to review its biological basis and discuss recent clinical applications. This article reviews the history, theory, current management, and limitations of distraction osteogenesis in treating craniofacial anomalies.

Reactive changes in the temporomandibular joint after mandibular midline osteodistraction

The purpose of this study was to evaluate the histologic changes within the condyle in response to mandibular widening using osteodistraction. Mandibular midline osteotomies were made in nine Macaca mulatta monkeys and tooth-borne distraction devices were bonded to the mandibular dentition. Distraction was continued until a 3-5 mm widening was achieved. The appliances were then stabilized for a period of 4 weeks. Non-decalcified sagittal sections of the lateral, middle and medial thirds of the condyles were analyzed. Although three of the seven animals showed no unusual morphology, four others exhibited morphologic differences within the fibrous layer, cartilage layer or bone/cartilage interface. Histologic changes were seen to occur in the fibrous layer, cartilaginous layer and cartilage/bone interface. The severity of these changes were correlated with the likely rotational forces directed at the condyle on the postero-lateral and antero-medial surfaces.