Strain-related bone remodeling in distraction osteogenesis of the mandible

Matrix metalloproteinases and their inhibitors in bone remodelling following distraction osteogenesis of the sheep mandible

AIM

Matrix metalloproteinases (MMPs), together with their tissue inhibitors (TIMPs), are responsible for the controlled degradation of collagen and other matrix substrates in bone and other tissues. This study evaluated the expression of MMPs and TIMPs in bony remodelling in a bilateral sheep mandible model up to 12 months following lengthening by distraction osteogenesis.

METHODOLOGY

Sheep mandibles were harvested 3, 6, 9 or 12 months following lengthening by bilateral mandibular distraction (1 mm/day for 20 days). Undistracted sheep mandibles were used as controls. The tissues underwent routine histology and immunohistochemical staining with monoclonal antibodies specific to MMPs 1-3 and TIMP-1, 2. Matrix and cell staining was assessed using a semi-quantitative analysis.

RESULTS

Matrix metalloproteinases and their tissue inhibitors (TIMPs) expression levels were marked at 3 months and decreased thereafter becoming similar to undistracted controls by 12 months. The histologic development of mature lamellar cortical bone was similar to undistracted controls by 9 months following distraction.

CONCLUSIONS

A temporal expression of MMPs and TIMPs was found in distraction osteogenesis. MMPs and TIMPS may, in part, reflect the state of bony remodelling following mandibular lengthening by distraction osteogenesis. Matrix metalloproteinases and TIMP expression were comparable to undistracted controls by 12 months, suggesting that equilibrium had been achieved and that bony relapse is unlikely.

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.

Clinical application of injectable calcium sulfate on early bony consolidation in distraction osteogenesis for the treatment of craniofacial microsomia

The purpose of this project was to study the effect of calcium sulfate on early bony consolidation in distraction osteogenesis. A total of eight patients with craniofacial microsomia were treated between April 2000 and February 2001. The age of the patients ranged from 2 to 40 years, and all were male. The follow-up period was 1 to 15 months. The operative procedure in adults was based on Ortiz Monasterio's simultaneous mandibular and maxillary distraction technique. In children, osteotomy of the mandible was performed for distraction. On the fifth day after the operation, distraction was performed at a rate of 1 mm/d in three adults. In children, distraction was performed at a rate of 1 mm/d in one patient and 2 mm/d in four patients without a latent period. On the day of completion of distraction, calcium sulfate was implanted into the distracted zone. Radiographs showed bony consolidation at 4 weeks in one child at a rate of 1 mm/d, at 5 to 7 weeks in four children at a rate of 2 mm/d, and at 5 weeks in three adults after implantation of the calcium sulfate. In conclusion, these findings suggest that calcium sulfate is effective for early bony consolidation in distraction osteogenesis and that it would shorten the whole treatment period.

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.

Experimental mandibular regeneration by distraction osteogenesis with submerged devices: preliminary results of a canine model

The authors describe a new technique for reconstruction of mandibular body defects. The feasibility of distraction osteogenesis with submerged (internal) devices for reconstruction of segmental mandibular defects is investigated in an experiment with five adult dogs. A segmental mandibulectomy was performed on the horizontal ramus. The bony defect was regenerated using distraction osteogenesis (bone transport) at a rate of 1 mm daily. The animals were killed after the consolidation period. Complete bone regeneration of the surgically created gap was successful in three of five dogs. Two animals failed to create new bone. In these two cases, the screws did not offer proper stability to the bony fragments, and this caused a lack of ossification. This experimental study demonstrates the possibility to use internal distraction devices to reconstruct segmental mandibular defects in a canine model. Internal devices show enormous advantages in comparison with the external ones. This method with no donor-site morbidity may become a very useful option in human mandibular reconstruction.

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.

Microstructural investigations of strain-related collagen mineralization

Distraction osteogenesis in rabbit mandibles after osteotomy can be used as an experimental model to study the microstructural features of mineralization of callus under defined mechanical loads. Our aim was to study the relation between the micromotions in the gap and the resulting features of mineralization of the matrix. We found that assembly of collagen and formation of crystals depended on the magnitude of the mechanical stress applied. At physiological bone strains (2000 microstrains), the callus had collagen type I in a mature bone-like extracellular arrangement, whereas at 20000 microstrains bundles were orientated predominantly towards the tension vector. Maximum loads (200000 microstrains) resulted in disorganized assembly of the collagen. Quantitative energy-dispersive analysis by X-rays confirmed that high strains were associated with substantially lower concentrations of calcium and phosphate. In contrast to bone-like apatitic formation of crystals at physiological strains, significantly fewer but larger crystals were detected by electron diffraction analysis in samples exposed to high strains. We suggest that mechanical stress regulates the assembly and mineralization of collagen during distraction osteogenesis.

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.

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.

Expander elements in craniofacial surgery: an experimental study in rabbits

With the inception of craniofacial surgery elaborate surgical procedures were introduced for the treatment of craniosynostosis. Recently the use of implantable springs to aid simple strip craniectomies for these conditions has been described. Having shown the feasibility of using springs for dynamic skull reshaping, several questions remain to be answered, all of them about how to control the spring action clinically. One of the most important questions concerns force. The purpose of this study was to evaluate experimentally the effect of two springs of different strengths on the growth of rabbit calvaria after strip craniectomy. Thirty-two 6-week-old rabbits were randomised into one of four groups: sham-operation where only amalgam markers were inserted after subperiostal dissection; strip craniectomy of the sagittal suture, no expansion; strip craniectomy of the sagittal suture and insertion of an expander element made of titanium molybdenum alloy (TMA); and strip craniectomy sagittal suture and insertion of an expander element made of stainless steel (SS). SS springs delivered a range of forces from 2.42-2.18 N, whereas the TMA expander elements delivered a range from 1.39-1.09 N. The parietal bone marker separation after 12 weeks was 4.9 mm in the TMA group and 7.4 mm in the SS group. This resulted in a significant increase of the calvarian height compared with control groups. Histological examination showed intramembranous bone formation in the bone gap in all groups.

Bone loading pattern around implants in average and atrophic edentulous maxillae: a finite-element analysis

INTRODUCTION

Oral implants placed in the maxilla, especially the posterior region, have a lower success rate than those placed in the mandible. Poor bone quantity and quality have been suggested as a reason for this differential success rate.

OBJECTIVE

The purpose of this study was, therefore, to evaluate stress and strain distributions around loaded implants in the normal and atrophic maxilla by finite-element (FE) analyses.

MATERIAL

FE models of a solitary implant were generated to determine stresses and strains in the bone adjacent to the implant surface under loading conditions.

STUDY DESIGN

Different bony situations and implant lengths were used in a FE model. Static loads were applied axially and the resulting stresses and strains calculated.

RESULTS

Bone quality and quantity play a major role in decreasing bone strains adjacent to the implant surface under loading. It was found that stresses were more homogeneously distributed when more spongy bone was present. Decreased bone height was found to have less pronounced effects on strain and stress alterations than poor bone quality. Atrophic bony dimensions in combination with poor bone quality were associated with surface strains exceeding physiological levels (> 6,000 microstrains).

CONCLUSION

Our investigation indicates that supraphysiological bone strains adjacent to the implant surface should be expected under mechanical loading in the atrophic maxilla.

Mechanical regulation of localized and appositional bone formation around bone-interfacing implants

The local mechanical environment around bone-interfacing implants determines, in large part, whether bone formation leading to functional osseointegration will occur. Previous attempts to relate local peri-implant tissue strains to tissue formation have not accounted for implant surface geometry, which has been shown to influence early tissue healing in vivo. Furthermore, the process by which mechanically regulated peri-implant bone formation occurs has not been considered previously. In the current study, we used a unit cell approach and the finite element method to predict the local tissue strains around porous-surfaced and plasma-sprayed implants, and compared the predictions to patterns of bone formation reported in earlier in vivo experiments. Based on the finite element predictions, we determined that appositional bone formation occurred when the magnitudes of the strain components at the tissue-host bone interface were <8%. Localized, de novo bone formation occurred when the distortional tissue strains were less than approximately 3%. Based on these threshold tissue strains, we propose a mechanoregulatory model to relate local tissue strains to the process of peri-implant bone formation. The mechanoregulatory model is novel in that it predicts both appositional and localized bone formation and its predictions are dependent on implant surface geometry. The model provides initial criteria with which the osseointegration potential of bone-interfacing implants may be evaluated, particularly under conditions of immediate or early loading.

Distraction osteogenesis of the maxilla and midface using a subcutaneous device: report of four cases

The use of distraction osteogenesis in the hypoplastic maxilla and midface is still controversial. Since the beginning of 1998, 25 patients have been treated with osteodistraction techniques for various reasons. Among them were four patients who were treated by high LeFort I osteotomies and insertion of a newly developed subcutaneous distraction device in the malar region. Distraction osteogenesis was successful in all four cases resulting in a mean sagittal bone gain of 12.0 mm (range 7-14) at the level of distractor fixation. All patients were kept under orthodontic supervision during osteodistraction. The final occlusal relation was satisfactory. Cephalometric measurements after distraction showed an anterior rotational movement of the midface region. As the question of relapse and further growth is still not clear, Delaire masks are used to stabilize the surgical result after removal of the distractor. The importance of long-term follow-up is stressed.

Tissue differentiation and cytokine synthesis during strain-related bone formation in distraction osteogenesis

To investigate the contributions of various cytokines that are involved in mechanically related bone formation, we applied defined uniaxial strains in a rabbit model of mandibular elongation and examined the regenerating bone during early stages of dist raction osteogenesis by histomorphometry. We also measured serum concentrations of various cytokines during the distraction. Cell proliferation and differentiation indices correlated significantly (P<0.001) with the extent of load application. Serum concentrations of insulin-like growth factor-1 (IGF-1) decreased after osteotomy whereas transforming growth factor beta1 (TGFbeta1) showed a postoperative increase. Prostaglandin E2 (PGE2) concentrations were constant throughout the experimental period. Collagen degradation decreased slightly postoperatively and increased in samples exposed to higher magnitudes of strain. Our data show that it is the magnitude of mechanical strain that decides tissue response by a characteristic cell proliferation and differentiation. The operative trauma leads to inverse changes in serum concentrations of TGFbeta1 and IGF-1, thereby promoting the recruitment of osteoblastic precursor cells as well as collagen matrix synthesis.