Experimental mandibular fracture: studies on bone repair and remodellation

HIF-1α regulates osteoclast activation and mediates osteogenesis during mandibular bone repair via CT-1

OBJECTIVES

Hypoxia is one of the characteristics of microenvironmental changes after orthognathic surgery for fractures. HIF-1α is a main regulator of the hypoxic response and plays a crucial role in bone formation, remodelling, and homeostasis. Osteoclasts participate in bone absorption and affect osteogenesis, and osteoclasts differentiate in a path from the oxygen-rich bone marrow to oxygen-deficient bone lesions. Thus, we aimed to study the key functions of HIF-1α in osteoclasts during mandibular healing after osteotomy.

MATERIALS AND METHODS

The function of HIF-1α in osteoclasts during fracture healing in osteoclast-specific HIF-1α-conditional-knockout mice was investigated in mandibular osteotomy. Primary osteoclasts were used to explore the expression of HIF-1α and cardiotrophin-1 (CT-1) at both the mRNA and protein levels. The ability of BMSCs co-cultured with conditioned media from osteoclast-specific HIF-1α-knockout primary osteoclasts was detected using osteoclast-mediated osteogenesis experiments.

RESULTS

Hypoxia-inducible factor-1α increased osteoclastogenesis and bone resorption, and a delay in bone healing was found in osteoclast-specific HIF-1α-conditional-knockout mice compared with normal mice. HIF-1α-knockout primary osteoclasts inhibited bone resorption and CT-1 expression, and HIF-1α enhanced the osteoclast-mediated stimulation of BMSC differentiation by secreting CT-1.

CONCLUSIONS

Hypoxia-inducible factor-1α can play a key role in the physiology and pathogenesis of bone resorption by promoting osteoclastogenesis during fracture and influencing osteogenesis through CT-1 during bone healing.

Influence of anabolic steroid on tibial fracture healing in rabbits - a study on experimental model

INTRODUCTION

Anabolic steroid is an established drug for treating catabolic states. The said drug has been shown to restore the lean body mass, to prevent osteoporosis and to correct the impaired immune response, but only few studies have evaluated the effect of the same on fracture healing.

METHODS

Fracture was produced by an impact device in 24 rabbits which were divided into experimental (I) and control (II) groups of 12 animals each. The experimental groups were further divided into the subgroups IA and IB of equal animals, which received Nandrolone Decanoate 10 mg/kg intramuscularly, biweekly for 2 weeks and 4 weeks respectively.

RESULTS AND CONCLUSION

Radiographs taken on the post fracture day15 and 40 showed better healing in the Nandrolone Decanoate administrated groups as a dense periosteal bone formation and prevention of the local osteoporosis. Histochemical examination of the callus and high serum alkaline phosphatase levels on day 15 and 40 confirmed better mineralization in experimental animals.

Adverse effects of the amlodipine on bone healing of the mandibular fracture: an experimental study in rats

BACKGROUND

Calcium channel blockers are effective antihypertensive agents, but they may affect many metabolic processes, including bone metabolism.

PURPOSE

The aim of this study was to evaluate by radiographic, histologic, and biochemical analyses the effects of amlodipine on bone healing of a defect simulating a fracture in mandibular ramus of rats.

METHODS

Fifty male Wistar rats were submitted to the same unilateral surgical procedure simulating a mandibular fracture. Experimental group received oral doses of amlodipine 0.04 mg/rat/day starting 12 days before procedure, while control group received water. Animals were sacrificed at 1, 7, 14, 30, and 90 days postoperatively. Numerical values were submitted to statistical analyses.

RESULTS

Radiographic analysis showed larger radiolucent area into bone defect to the experimental group at the periods of 14 (p = 0.016), 30 (p = 0.009), and 90 (p = 0.028) days. In the histological analysis, the experimental group had a slight delay in the chronology of the repair process. In the histomorphometric analysis, the experimental group presented significant lowering of newly formed bone volume at 7 and 14 days periods (p = 0.049). There was a significant decrease of alkaline phosphatase levels in experimental group in the initial periods (p = 0.049).

CONCLUSIONS

It was concluded that chronic use of amlodipine compromised bone neoformation in the repairing process of surgical defect in the mandibular ramus of rats, but no precluded occurrence of fracture consolidation.

Rotated subcondylar process fracture in the growing animal: an experimental study in rats

Unilateral, rotated subcondylar fractures were surgically induced in young rats under general anaesthesia. A decrease in body weight was observed in the fractured animals, with recovery at the end of the experimental period. A tendency of deviation of the mandible to the fracture side was noticed on axial radiographs, but without significant difference between experimental and sham-operated animals. Histological data initially demonstrated acute inflammation along the articular capsule and adjacent muscle fibres. Within 2 weeks, exuberant callus formation occurred. Neither devitalized bone ends nor intra-articular granulation tissue were seen. After 1 month, the temporomandibular joint presented characteristics of normality, with the condylar process centralized into the temporal fossa, interposed by the articular disc. These results were preserved after 3 months. We concluded that rotational subcondylar fractures in young rats heal by callus formation, with simultaneous and prompt repositioning of the condyle.

Healing of the displaced condylar process fracture: an experimental study

Healing of the displaced condylar process fracture was analysed by means of an experimental model using adults rats. Displaced fractures of the right condylar process were achieved under general anaesthesia. Histological data initially demonstrated neutrophilic exudation along the articular capsule and adjacent muscle fibres. One week later, devitalized bone areas at the fracture site, as well as proliferation of cartilaginous and osseous tissue were observed. Subsequently, exuberant callus formation and a decrease in the inflammatory process occurred. After 3 months, the condylar process presented characteristics of normality and was centralized into the temporal fossa, with interposition of the articular disc. These results indicate that experimentally induced, displaced condylar process fractures heal by callus formation with simultaneous repositioning of the condyle.

Behavior of fetal rat chondrocytes cultured on a bioactive glass-ceramic

We examined the behavior of fetal rat chondrocytes cultured on a bioactive glass-ceramic containing apatite and wollastonite (A.W.G.C.). Biomaterial surface topography and profiles were evaluated by bidimensional profilometry and revealed a rough surface for the glass-ceramic compared to the plastic coverslips used as controls. Chondrocyte attachment was evaluated by measuring the number of attached cells after one day of culture and by morphological observations. Chondrocytes attached in great numbers to the material surface by means of focal contacts containing vinculin and beta1-integrin. Fluorescent labeling of actin and vimentin revealed a poor spreading of chondrocytes on the bioactive glass-ceramic compared to the plastic coverslips, where the cells appeared to adhere intimately to the surface and exhibited polygonal arrays of stress fibers. During the following days of culture, chondrocytes proliferated, colonized the surface of the material, and, finally, on day 10, formed nodular structures composed of round cells separated by a dense extracellular matrix. Furthermore, these clusters of round cells were positive for type II collagen and chondroitin sulfate, both hard markers of the chondrocyte phenotype. In addition, protein synthesis, alkaline phosphatase activity, and proteoglycan production were found to increase gradually during the culture period with a pattern similar to that observed on control cultures. These results demonstrate that the bioactive glass-ceramic tested in this study appears to be a suitable substrate for in vitro chondrocyte attachment, differentiation, and matrix production.

A method for measuring the structural properties of the rat mandible

The rat mandible has been used to study fractures, ridge augmentation, bone defects, and the effects of cryosurgery, all of which affect the structural properties of the mandible. The only previously described mechanical test of the rat mandible used three-point bending with a piece of foam placed between the lingual surface of the mandible and the support. The accuracy and reproducibility of this test were not determined. Two different, three-point bending tests for characterizing the structural properties of the rat mandible have now been evaluated. Acrylic specimens representing three different-sized mandibles were tested in three-point bending with either potted ends or foam interposed between the specimen and the outer load points. Flexural stiffness and failure load were compared against data from a conventional three-point bending test. In addition, five paired halves of 90- and 210-day-old rat mandibles were tested either with interposed foam or with potted ends and the mean coefficients of variation of the stiffness and failure loads were determined. Failure loads of the acrylic specimens with the potted and foam methods were significantly higher (50 and 10%, respectively; p < 0.05) than with the conventional method. The stiffness of the acrylic specimens with the potted and foam methods was significantly different (75% higher and 21% lower, respectively; p < 0.05) than with the conventional test. In addition, there was no difference between the coefficient of variation in stiffness (26 + 11%) or failure load (10 + 4%) measured with the foam test and the comparable values (16 + 11%) and (18 + 13%) in the potted test.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair of intra-membranous bone fractures and defects in rats. Immunolocalization of bone and cartilage proteins and proteoglycans

Osseous healing of experimental fractures and defects in membranous bone was studied in an animal model and the appearance and localization of selected bone and cartilage proteins and proteoglycans determined by polyclonal antibodies. The bone lesions were made in the parietal bone of young rats and subsequently studied on days 3, 5, 8, 15, 30, and 100 after surgery. The bone matrix proteins investigated (62 kDa, bone sialoprotein I and II, and osteopontin) appeared early, adjacent to the periosteal surfaces (pericranium and dura mater) and the marginal bone. The staining reactions were maximal at days 8 or 15 after trauma. Similar patterns were discerned for some cartilage macromolecules studied (58 kDa, 59 kDa, and chondrocalcin), although others showed no labelling whatsoever (148 kDa, and 400 kDa proteins). The proteoglycans PG-S1, PG-S2, and PG-LA were not identified. No callus or cartilage formation were associated with the bone healing process, and the differences between the regenerative pattern of the fractures and defects were limited. The findings emphasize the importance of rigid fixation in craniomaxillofacial surgery.

Quantitation of blood flow in the rat mandible after vertical osteotomy

Vertical osteotomies were performed in the mandibles of rats and combined with elevations of the buccal or bilateral mucoperiosteal pedicles. Isotope fractionation and particle distribution were used to measure blood flow in the distal and proximal segments of the mandible, the masseter muscle and the submandibular gland. Average decrease in blood flow ranged from 9-39% in the distal segment and from 8-24% in the proximal segment. Decrease in blood flow was most pronounced when bilateral mucoperiosteal pedicles were performed. Blood flow in the masseter muscle increased by 16-26% after osteotomy with mucoperiosteal elevations.

Experimental mandibular fracture: effect on bone circulation and metabolism after treatment with anticoagulants

An experimental model was designed for the study of mandibular fracture healing in Sprague-Dawley rats. Healing and remodellation were studied by routine histology and the vascular supply of the mandible by micro-angiography. The blood supply to the body of the mandible was similar to that seen in long bones. The arterial vascular system appeared to be intimately involved with the formation of bone. The vessel configuration varied in relation to the progress of healing. The effect of heparin, dextran 40 and dextran 70 therapy to increase blood flow in the fracture region was tested. Dextrans had no effect on fracture healing whereas heparin induced an increased chondroid reaction in the callus. Serum alkaline phosphatase was measured as a marker for hard-tissue formation. The enzyme activity was reduced after fracture with a minimum activity three days after fracture.