An immunohistochemical study of localization of type I and type II collagens in mandibular condylar cartilage compared with tibial growth plate

The combination of odontogenic stem cells and mandibular advancement promotes the length of the mandible in adult rats by facilitating the development of condylar cartilage

BACKGROUND

Mandibular retraction is a prevalent dental and maxillofacial deformity that negatively affects patients' functional health and facial aesthetics. It has been challenging to achieve optimal outcomes for patients who have passed the peak of growth and development using only functional orthopedic treatment. There is a pressing need to explore innovative methods to promote the adaptive remodeling of adult condylar cartilage and the mandible in response to external stimuli. This study aimed to investigate the impact of varying injection frequencies of stem cells from the apical papilla (SCAPs) on the growth and development of condylar cartilage and the mandible, as well as their potential for adaptive remodeling.

METHODS

The study was conducted on 8-week-old adult male Sprague-Dawley rats. The effects of SCAPs injection and different durations of mandibular advancement (MA) on the adaptive remodeling of condylar cartilage and the mandible were assessed. After the initial experimental findings, various injection frequencies of SCAPs were applied to determine the most effective conditions for promoting the growth and adaptive remodeling of condylar cartilage and the mandible during an 8-week period of mandibular advancement.

RESULTS

The study found that rats with extended mandibular lead times (8 weeks) or an appropriately increased frequency of mandibular leading time (once every 2 weeks or once every 1 week) exhibited increased lengths of the mandibular body and ascending branch, and a thickened full layer of condylar cartilage. The highest proportions of the proliferative layer, mature layer, and hypertrophic layer were observed in these rats. Additionally, there was a significant increase in the expression levels of SOX9 and COL2A1.

CONCLUSION

The data from this study suggest that adult rats, even after missing their peak growth period, retain the potential for continued growth and development of their condylar cartilage. By prolonging the duration of mandibular advancement and administering injections of stem cells from the apical papilla (SCAPs), it is possible to stimulate the growth and development of the mandibular condyle.

Mandibular Endochondral Growth Is Specifically Augmented by Nutritional Supplementation with Myo-Inositol Even in Rabbits

Mandibular retrognathism occurs by insufficient mandibular growth and causes several issues, such as respiratory difficulty and diminished masticatory function. At present, functional orthodontic appliances are used for stimulating mandibular growth in pediatric cases. However, the effectiveness of functional appliances is not always stable in daily practices. A more effective, reliable, and safer therapeutic method for mandibular growth promotion would be helpful for growing mandibular retrognathism patients. As we previously discovered that nutritional supplementation of myo-inositol in growing mice specifically increases mandibular endochondral growth, we performed preclinical animal experiments in rabbits in this study. Briefly, six-week-old male Japanese white rabbits were fed with or without myo-inositol supplementation in laboratory chow until 25 weeks old, and 3D image analysis using micro CT data and histological examinations was done. Myo-inositol had no systemic effect, such as femur length, though myo-inositol specifically augmented the mandibular growth. Myo-inositol increased the thickness of mandibular condylar cartilage. We discovered that the nutritional supplementation of myo-inositol during the growth period specifically augmented mandibular growth without any systemic influence, even in rabbits. Our results suggest the possibility of clinical use of myo-inositol for augmentation of the mandibular growth in growing mandibular retrognathism patients in the future.

An immunohistochemical study of matrix components in primary and secondary cartilages of embryonic chick skull

OBJECTIVES

This study aimed to compare the extracellular matrix of primary cartilage with the secondary cartilage of chicks using immunohistochemical analyses in order to understand the features of chick secondary chondrogenesis.

METHODS

Immunohistochemical analysis was performed on the extracellular matrix of quadrate (primary), squamosal, surangular, and anterior pterygoid secondary cartilages using various antibodies targeting the extracellular matrix of cartilage and bone.

RESULTS

The localization of collagen types I, II, and X, versican, aggrecan, hyaluronan, link protein, and tenascin-C was identified in the quadrate cartilage, with variations within and between the regions. Newly formed squamosal and surangular secondary cartilages showed simultaneous immunoreactivity for all molecules investigated. However, collagen type X immunoreactivity was not observed, and there was weak immunoreactivity for versican and aggrecan in the anterior pterygoid secondary cartilage.

CONCLUSIONS

The immunohistochemical localization of extracellular matrix in the quadrate (primary) cartilage was comparable to that of long bone (primary) cartilage in mammals. The fibrocartilaginous nature and rapid differentiation into hypertrophic chondrocytes, which are known structural features of secondary cartilage, were confirmed in the extracellular matrix of squamosal and surangular secondary cartilages. Furthermore, these tissues appear to undergo developmental processes similar to those in mammals. However, the anterior pterygoid secondary cartilage exhibited unique features that differed from primary and other secondary cartilages, suggesting it is formed through a distinct developmental process.

Abaloparatide and teriparatide enhance mandibular growth in adolescent rats with site-specific and mechano-related effects

OBJECTIVE

Teriparatide (TPTD) and abaloparatide (ABL) are two osteoanabolic drugs targeting parathyroid hormone (PTH)1R signalling. This study aimed to investigate the effects of TPTD and ABL on the adolescent mandibular growth.

METHOD

In total, 70 4-week-old male Sprague-Dawley rats were randomly divided into 14 groups, treated with intermittent TPDT or ABL at various doses, accompanied by mandibular advancement (MA) or not. 3D printing was used to fabricate an innovative splint for MA. After a 4-week treatment, morphological measurement, histological and immunohistochemical analysis were performed. Mandibular condylar chondrocytes (MCCs) were treated with TPTD or ABL, followed by CCK-8 assay, alcian blue staining, real time-PCR and immunofluorescent staining.

RESULT

In vivo, TPTD or ABL alone increased the condylar length and cartilage thickness, with up-regulated SOX9 and COL II, whilst down-regulated COL X; however, when combined with MA, the promotive effects were attenuated. TPTD or ABL alone increased the mandibular body height and mandibular angle width, whilst increased the mandibular body length and alveolar bone width when combined with MA. In vitro, TPTD or ABL enhanced the MCC proliferation, glycosaminoglycan synthesis, COL II and SOX9 expression, whilst down-regulated COL X, Ihh and PTH1R expression.

CONCLUSION

Both ABL and TPTD enhance mandibular growth in adolescent rats with site-specific and mechano-related effects, including propelling chondrogenesis at the condylar cartilage and promoting bone apposition at other mechano-responsive sites. They behave as promising drugs for mandibular growth modification, and in general ABL seems more potent than TPTD in this context.

The visualization of the mineral and protein distribution in the same histological sections of rat calcified growth plate cartilage

OBJECTIVE

To determine whether the combination of scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and immunostaining would visualize the mineral and protein distribution in the same histological sections.

METHODS

Paraffin sections of fixed rat hindlimbs were processed for SEM-EDX and subsequently for immunofluorescence staining.

RESULTS

The localization of calcium, phosphorus, and carbon with type II collagen could be visualized in the same region of calcified growth plate cartilage on the same section.

CONCLUSIONS

The combination of SEM-EDX and immunostaining is effective for visualizing mineral and protein distribution in the same histological sections.

gp130/STAT3 signaling is required for homeostatic proliferation and anabolism in postnatal growth plate and articular chondrocytes

Growth of long bones and vertebrae is maintained postnatally by a long-lasting pool of progenitor cells. Little is known about the molecular mechanisms that regulate the output and maintenance of the cells that give rise to mature cartilage. Here we demonstrate that postnatal chondrocyte-specific deletion of a transcription factor Stat3 results in severely reduced proliferation coupled with increased hypertrophy, growth plate fusion, stunting and signs of progressive dysfunction of the articular cartilage. This effect is dimorphic, with females more strongly affected than males. Chondrocyte-specific deletion of the IL-6 family cytokine receptor gp130, which activates Stat3, phenocopied Stat3-deletion; deletion of Lifr, one of many co-receptors that signals through gp130, resulted in a milder phenotype. These data define a molecular circuit that regulates chondrogenic cell maintenance and output and reveals a pivotal positive function of IL-6 family cytokines in the skeletal system with direct implications for skeletal development and regeneration.

Initiation and progression of dental-stimulated temporomandibular joints osteoarthritis

Temporomandibular joint (TMJ), a site that is often impacted by osteoarthritis (OA), is biomechanically linked with dental occlusion. Tissue responses in TMJ condyle to biomechanical stimulation could be investigated by intervention of the dental occlusion in animals. Unilateral anterior crossbite, an experimental malocclusion, has been demonstrated to induce TMJ-OA lesions, showing primarily as enhanced cartilage calcification and subchondral cortical bone formation at the osteochondral interface, causing the osteochondral interface thickening and stiffening. The changed interface would worsen the local biomechanical environment. At the cartilage side, the matrix degenerates. In the case of insufficient restoration of the matrix, the cells in the deep zone flow into the ones undergoing autophagy, apoptosis, and terminal differentiation while the cells in the superficial zone are promoted to differentiate to supply the loss of the deep zone cells. At the meantime, the bone marrow stromal cells are stimulated to bone formation in the subchondral cortical region which is uncoupled with the sites of the osteoclast-mediated resorption process that is predominantly observed at the subchondral trabecular bone region. Overall, the thickening and stiffening osteochondral interface, due greatly to the enhanced endochondral ossification in deep zone cartilage, should be a central pathological process that links with cartilage decay and subchondral bone remodelling in OA joints. The residual chondrocytes locating in the cartilage superficial zone have the progenitor-like qualities that can proliferate, and also differentiate into the deep zone chondrocytes, thus should be critical in progression and rehabilitation of TMJ-OA.

ScxLin cells directly form a subset of chondrocytes in temporomandibular joint that are sharply increased in Dmp1-null mice

It has been assumed that the secondary cartilage in the temporomandibular joint (TMJ), which is the most complex and mystery joint and expands rapidly after birth, is formed by periochondrium-derived chondrocytes. The TMJ condyle has rich attachment sites of tendon, which is thought to be solely responsible for joint movement with a distinct cell lineage. Here, we used a Scx-Cre ERT2 mouse line (the tracing line for progenitor and mature tendon cells) to track the fate of tendon cells during TMJ postnatal growth. Our data showed a progressive differentiation of Scx lineage cells started at tendon and the fibrous layer, to cells at the prechondroblasts (Sox9 -/Col I +), and then to cells at the chondrocytic layer (Sox9 +/Col I -). Importantly, the Scx + chondrocytes remained as "permanent" chondrocytes to maintain cartilage mass with no further cell trandifferentiation to bone cells. This notion was substantiated in an assessment of these cells in Dmp1 -null mice (a hypophosphatemic rickets model), where there was a significant increase in the number of Scx lineage cells in response to hypophosphatemia. In addition, we showed the origin of disc, which is derived from Scx + cells. Thus, we propose Scx lineage cells play an important role in TMJ postnatal growth by forming the disc and a new subset of Scx + chondrocytes that do not undergo osteogenesis as the Scx - chondrocytes and are sensitive to the level of phosphorous.

The role of BMP6 in the proliferation and differentiation of chicken cartilage cells

Previous studies have indicated that bone morphogenetic protein (BMP) 6 may play an important role in skeletal system development and progression. However, the mechanism underlying the effects of BMP6 in cartilage cell proliferation and differentiation remains unknown. In this study, cartilage cells were isolated from shanks of chicken embryos and treated with different concentrations of Growth Hormone. Cell proliferation potential was assessed using real-time polymerase chain reaction (RT-PCR), western blotting and CCK-8 assays in vitro. The results showed that at 48 h, the Collagen II and BMP6 expression levels in 50 ng/μl GH-treated cartilage cells were significantly higher than in groups treated with 100 ng/μl or 200 ng/μl GH. We further observed that knockdown of BMP6 in cartilage cells led to significantly decreased expression mRNAs and proteins of Collagen II and Collagen X. Moreover, the suppression of BMP6 expression by a specific siRNA led to significantly decreased expression mRNA levels of IGF1R, JAK2, PKC, PTH, IHH and PTHrP and decreased protein levels of PKC, IHH and PTHrP. Taken together, our data suggest that BMP6 may play a critical role in chicken cartilage cell proliferation and differentiation through the regulation of IGF1, JAK2, PKC, PTH, and IHH-PTHrP signaling pathways.

Immunohistochemical and ultrastructural evaluation of matrix components in mandibular condylar cartilage in comparison with growth plate cartilage in cartilage calcification insufficient rats

Matrix components of growth plate cartilage and mandibular condylar cartilage were immunohistochemically analyzed in cartilage calcification insufficient (CCI) rats, a model for dwarf rats. Reduction in total tibial length, elongation of growth plate, and appearance of noncartilaginous regions in the growth plate were observed in CCI rats. Immunoreactivity for type I collagen and hyaluronic acid (HA) staining were observed in the noncartilaginous region. However, weak immunoreactivity was observed for aggrecan, collagen types II and X, and decorin in this region. Transmission electron microscopy indicated that the noncartilaginous region showed a loose network of thin collagen fibrils, indicating that HA is predominantly involved in capturing space of the noncartilaginous region in the growth plate. Meanwhile, the mandibular condylar cartilage in CCI rats also showed elongation of the cartilaginous region and had a noncartilaginous region, predominantly comprising thick collagen fibrils. The structural difference between the two types of cartilages in CCI rats may be due to the presence of the fibrous cell zone and the fibrocartilaginous nature of the normal condylar cartilage. Additionally, the reduction in mandibular length was relatively less than the reduction in tibial length. The outline of the condylar process showed only slight abnormality. These results suggest that the condylar cartilage compensated its growth by supplying the characteristic noncartilaginous region effectively and may adapt to severe structural changes observed in CCI rats.

The effects of elevated fibroblast growth factor 23 on mandibular growth in rats

OBJECTIVE

The aim of this study is to elucidate the local effects of fibroblast growth factor 23 (FGF23) in on mandibular condylar growth in growing rats.

DESIGN

Growing Sprague-Dawley rats received intra-temporomandibular joint injections of phosphate buffer solution (PBS), adenovirus-mediated green fluorescent protein (Ad-GFP) or adenovirus-mediated fibroblast growth factor 23 (Ad-FGF23), which were marked as groups A, B, and C, respectively. In vitro, we treated rat mandibular cartilage chondrocytes with PBS, Ad-GFP, and Ad-FGF23.

RESULTS

The mandibular condyles in group C grew smaller sizes than those in the other control groups due to significant differences among the experimental and control groups with the value of C-D, Q-R (P ≤ 0.05), accompanied by diminished bone mass of sub-cartilage condyles via micro CT analysis. Histologically, the length of the hypertrophic zone was diminished and was associated with decreasing chondrocyte proliferation in group C. Quantitative real-time PCR indicated significant decreases in the expression of chondrogenesis marker genes, including Type X collagen (Col X) and SRY-type box 9 (Sox 9). Moreover, elevated Ad-FGF23 suppressed chondrocyte proliferation and the expression of the chondrogenic differentiation markers Col X and Sox 9 of in vitro.

CONCLUSIONS

Local injection of FGF23 suppressed the development and decreased the bone mass of condyles through the decreasing the formation of condylar cartilage, specifically by regulating condylar cartilage cell viability and chondrogenesis expression.

Asporin stably expressed in the surface layer of mandibular condylar cartilage and augmented in the deeper layer with age

Mandibular condylar cartilage (MCC) exhibits dual roles both articular cartilage and growth center. Of many growth factors, TGF-β has been implicated in the growth of articular cartilage including MCC. Recently, Asporin, decoy to TGF-β, was discovered and it blocks TGF-β signaling. Asporin is expressed in a variety of tissues including osteoarthritic articular cartilage, though there was no report of Asporin expression in MCC. In the present study, we investigated the temporal and spatial expression of Asporin in MCC.

Gene expression profile of MCC and epiphyseal cartilage in tibia of 5 weeks old ICR mice were firstly compared with microarray analysis using the laser capture microdissected samples. Variance of gene expression was further confirmed by real-time RT-PCR and immunohistochemical staining at 1,3,10, and 20 weeks old. TGF-β and its signaling molecule, phosphorylated Smad-2/3 (p-Smad2/3), were also examined by immunohistochemical staining.

Microarray analysis revealed that Asporin was highly expressed in MCC. Real-time RT-PCR analysis confirmed that the fibrous layer of MCC exhibited stable higher Asporin expression at any time points as compared to epiphyseal cartilage. This was also observed in immunohistochemical staining. Deeper layer in MCC augmented Asporin expression with age. Whereas, TGF-β was stably highly observed in the layer. The fibrous layer of MCC exhibited weak staining of p-Smad2/3, though the proliferating layer of MCC was strongly stained as compared to epiphyseal cartilage of tibia at early time point. Consistent with the increase of Asporin expression in the deeper layer of MCC, the intensity of p-Smad-2/3 staining was decreased with age.

In conclusion, we discovered that Asporin was stably expressed at the fibrous layer of MCC, which makes it possible to manage both articular cartilage and growth center at the same time.

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Asporin gene and protein were highly expressed in mandibular condylar cartilage as compared to tibial epiphyseal cartilage.

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Asporin in mandibular condylar cartilage was augmented with age.

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TGF-β signaling is suppressed by augmented Asporin and decreased TGF-β production in mandibular condylar cartilage.

Roles of Chondrocytes in Endochondral Bone Formation and Fracture Repair

The formation of the mandibular condylar cartilage (MCC) and its subchondral bone is an important but understudied topic in dental research. The current concept regarding endochondral bone formation postulates that most hypertrophic chondrocytes undergo programmed cell death prior to bone formation. Under this paradigm, the MCC and its underlying bone are thought to result from 2 closely linked but separate processes: chondrogenesis and osteogenesis. However, recent investigations using cell lineage tracing techniques have demonstrated that many, perhaps the majority, of bone cells are derived via direct transformation from chondrocytes. In this review, the authors will briefly discuss the history of this idea and describe recent studies that clearly demonstrate that the direct transformation of chondrocytes into bone cells is common in both long bone and mandibular condyle development and during bone fracture repair. The authors will also provide new evidence of a distinct difference in ossification orientation in the condylar ramus (1 ossification center) versus long bone ossification formation (2 ossification centers). Based on our recent findings and those of other laboratories, we propose a new model that contrasts the mode of bone formation in much of the mandibular ramus (chondrocyte-derived) with intramembranous bone formation of the mandibular body (non-chondrocyte-derived).

A Joint Less Ordinary: Intriguing Roles for Hedgehog Signalling in the Development of the Temporomandibular Synovial Joint

This review highlights the essential role of Hedgehog (Hh) signalling in the developmental steps of temporomandibular joint (TMJ) formation. We review evidence for intra- and potentially inter-tissue Hh signaling as well as Glioma-Associated Oncogene Homolog (GLI) dependent and independent functions. Morphogenesis and maturation of the TMJ’s individual components and the general landscape of Hh signalling is also covered. Comparison of the appendicular knee and axial TMJ also reveals interesting differences and similarities in their mechanisms of development, chondrogenesis and reliance on Hh signalling.

Genetic Influences on Temporomandibular Joint Development and Growth

The temporomandibular joint (TMJ) is a small synovial joint at which the mandible articulates with the skull during movements involved in speaking and mastication. However, the secondary cartilage lining its joint surfaces is indicative of a very different developmental history than limb cartilages. This review summarizes our current knowledge of genes that regulate the formation of primary components of the TMJ, as well as genes that regulate postnatal growth of the TMJ. Although the TMJ is regulated by some of the same genes that are important in limb joints, others appear unique to the TMJ or have different actions. Runx2, Sox9, and members of the TGF-β/BMP family are critical drivers of chondrogenesis during condylar cartilage morphogenesis, and Indian hedgehog (Ihh) is important for formation of the articular disc and cavitation. Osterix (Osx) is a critical regulator of endochondral bone formation during postnatal TMJ growth.

Bmpr1a Signaling in Cartilage Development and Endochondral Bone Formation

The type IA bone morphogenetic protein receptor (Bmpr1a), encoded by 11 exons and spanning about 40 kb on chromosome 14 in mice and chromosome 10 in human (Derynck & Feng, 1997; Mishina, Hanks, Miura, Tallquist, & Behringer, 2002), is an essential receptor for BMP signaling. This chapter focuses on the current understanding of the role of Bmpr1a in cartilage development and endochondral ossification, including formation of the mesenchymal condensation, chondrocyte differentiation and maturation, and endochondral bone development.

Evaluation of protein undernourishment on the condylar process of the Wistar rat mandible correlation with insulin receptor expression

The mandible condylar process cartilage (CP) of Wistar rats is a secondary cartilage and acts as a mandibular growth site. This phenomenon depends on adequate proteins intake and hormone actions, including insulin.

MicroRNA-200a Regulates the Development of Mandibular Condylar Cartilage

Mandibular condylar cartilage (MCC) is classified as secondary cartilage, the histologic structure of which is unique from that of primary cartilage. MicroRNA (miRNA) is a small noncoding RNA that binds to the messenger RNA (mRNA) target to repress its translation and plays an important role in cell differentiation, proliferation, and death. Microarray analysis revealed that miR-200a was characteristically expressed during embryonic development. We hypothesized that miR-200a may be involved in regulating the formation of cartilage during MCC growth. We investigated the function of miR-200a by transfecting an inhibitor or mimic into MCC organ and cell cultures. A histologic examination revealed the localized inhibitory effects of the miR-200a mimic and widespread enhancing effects of the inhibitor on chondrocytic differentiation in the MCC organ culture system. An immunohistochemical examination and gene expression analysis demonstrated that the miR-200a inhibitor enhanced chondrogenesis, while the mimic had the opposite effect by enhancing cell proliferation. Quantitative reverse transcription polymerase chain reaction analysis revealed that miR-200a downregulated the gene expression of chondrocyte markers. Moreover, transfection of the miR-200a mimic into ATDC5 cells repressed the formation of the cartilaginous matrix. These results indicate that miR-200a contributed to chondrogenesis in developing MCC by controlling proliferation and differentiation in MCC cells.

Osterix couples chondrogenesis and osteogenesis in post-natal condylar growth

Osterix (Osx) is a transcription factor essential for osteoblast differentiation and bone mineralization. Although there are indications that Osx also plays a regulatory role in cartilage, this has not been well-studied. The goal of this study was to define the function of Osx in the post-natal growth of the secondary cartilage at the mandibular condyle. Conditional Osx knockout (cKO) mice that were missing Osx only in cartilage were generated by crossing Osx-loxP mice to Aggrecan-Cre mice. Cre activity was induced by tamoxifen injection twice a week from day 12 to 1 mo of age, and specimens were collected at 1 and 5 mo of age. At 1 mo of age, the condylar hypertrophic chondrocyte zone in the cKO-mice was > three-fold thicker than that in the age-matched control, with little sign of endochondral bone formation. Immunohistochemistry and analysis of histological data revealed a defect in the coupling of chondrogenesis and osteogenesis in the cKO mice. In five-month-old mice examined to address whether late-stage removal of the Cre-deletion event would alleviate the phenotype, the hypertrophic chondrocyte zone in the cKO condyles was considerably larger than in wild-type mice. There were large discrete areas of calcified cartilage in the hypertrophic zone, few signs of endochondral bone formation, and large regions of disorganized intramembranous bone. Analysis of these data further strengthens the notion that Osterix is essential for the coupling of terminal cartilage differentiation and endochondral ossification in mandibular condylar cartilage.

Mastication markedly affects mandibular condylar cartilage growth, gene expression, and morphology

INTRODUCTION

Mandibular growth is believed to be strongly related to mastication. Furthermore, mandibular condylar cartilage is known to be derived from neural crest cells. We examined whether the degree of chewing affects condylar cartilage growth of the mandible.

METHODS

Mice were fed diets with varying hardness. Genes specific to neural crest-derived cells were measured by real-time polymerase chain reaction to compare the expression changes between the mandibular and tibia cartilages. The mandibular condylar cartilage was then evaluated histologically, and proliferation was evaluated using proliferating cell nuclear antigen. Immunostaining was conducted for osteopontin, type X collagen, and Musashi1, and real-time polymerase chain reaction was used to assess the expression levels of osteopontin and type X collagen.

RESULTS

Markers including P75, Wnt-1, Musashi1, and Nestin were upregulated in the mandibular condylar cartilage as compared with the tibial cartilage. Histologic assessment of the mandibular cartilage showed that the hypertrophic chondrocyte zone was statistically significantly thicker in mice fed a hard diet. Chondrocyte proliferation and Musashi1 expression were lower in mice fed a hard diet. After 4 weeks, numerous osteopontin and type X collagen-positive cells were observed in mice fed a mixed diet.

CONCLUSIONS

Mastication affects the balance between differentiation and proliferation in the mandibular condylar cartilage. This phenomenon might be attributed to the presence of neural crest-derived cells.

An immunohistochemical study of matrix proteins in the craniofacial cartilage in midterm human fetuses

Immunohistochemical localization of collagen types I, II, and X, aggrecan, versican, dentin matrix protein (DMP)-1, martix extracellular phosphoprotein (MEPE) were performed for Meckel's cartilage, cranial base cartilage, and mandibular condylar cartilage in human midterm fetuses; staining patterns within the condylar cartilage were compared to those within other cartilaginous structures. Mandibular condylar cartilage contained aggrecan; it also had more type I collagen and a thicker hypertrophic cell layer than the other two types of cartilage; these three characteristics are similar to those of the secondary cartilage of rodents. MEPE immunoreactivity was first evident in the cartilage matrix of all types of cartilage in the human fetuses and in Meckel's cartilage of mice and rats. MEPE immunoreactivity was enhanced in the deep layer of the hypertrophic cell layer and in the cartilaginous core of the bone trabeculae in the primary spongiosa. These results indicated that MEPE is a component of cartilage matrix and may be involved in cartilage mineralization. DMP-1 immunoreactivity first became evident in human bone lacunae walls and canaliculi; this pattern of expression was comparable to the pattern seen in rodents. In addition, chondroid bone was evident in the mandibular (glenoid) fossa of the temporal bone, and it had aggrecan, collagen types I and X, MEPE, and DMP-1 immunoreactivity; these findings indicated that chondroid bone in this region has phenotypic expression indicative of both hypertrophic chondrocytes and osteocytes.

An immunohistochemical study on the localization of type II collagen in the developing mouse mandibular condyle

The present chronological investigation assessed the distribution of type II collagen expression in the developing mouse mandibular condyle using immunohistochemical staining with respect to the anatomy of the anlage of the mandibular condyle, the histological characteristics of which were disclosed in our previous investigation. We analyzed fetuses, obtained by cross breeding of ICR strain mice, between 14.0 and 19.0 days post-conception (dpc) and pups on 1, 3, and 5 days post-natal (dpn) using immunohistochemical staining with 2 anti-type II collagen antibodies. The expression of type II collagen was first detected at 15.0 dpc in the lower part of the hypertrophic chondrocyte zone; thereafter, this type II collagen-positive layer was expanded and intensified (P1 layer). At 17.0 dpc, we identified a type II collagen-negative layer (N layer) around the P1 layer and we also identified another newly formed type II collagen-positive layer (P, layer) on the outer surface of the N layer. The most typical and conspicuous 3-layered distribution was observed at 1 dpn; thereafter, there was a reduction in the intensity of expression, and with it, the demarcation between the layers was weakened by 5 dpn. The P1 layer was derived from the central region of the core cell aggregate of the anlage of the mandibular condyle and participated in endochondral bone formation. The N layer was derived from the fringe of the core cell aggregate of the anlage, formed the bone collar at the side of the condyle by intramembranous bone formation, and showed a high level of proliferative activity at the vault. The P2 layer was formed from the outgrowth of the N layer, and could be considered as the secondary cartilage. The intensive expression of type II collagen from 17.0 dpc to 3 dpn was detected in the fibrous sheath covering the condylar head, which is derived from the peripheral cell aggregate of the anlage. Since its expression in the fibrous sheath was not detected in the neighboring section in the absence of hyaluronidase digestion, some changes in the extracellular matrix of the fibrous sheath appear to participate in the generation of the lower joint space. The results of the present investigation indicate that further studies are required to fully characterize the development of the mouse mandibular condyle.

Age-dependent physiological changes in the histoarchitecture of the articular cartilage of the rabbit mandibular condyle: a morphological and morphometric study

Mandibular condyle articular cartilage participates in condylar postnatal growth and is responsible for adaptations to anatomical and/or biomechanical alterations throughout life. In a preliminary study in rabbits, differences were observed in the thickness of the layers of articular cartilage in control animals at 5 and 6 months (generally considered adults for this purpose). This study aimed to describe sagittally sectioned condylar cartilages stained with Picrosirius-hematoxylin in rabbits at 40 days and 5, 6, 8, 13, and 18 months to determine when histological maturity is reached. At 40 days, 5 layers were seen: fibrous, proliferative, transition, maturation, and hypertrophic. Older animals (5-18 months) lacked the transition layer. Fibrous, proliferative, and hypertrophic regions were considered for morphometric analysis. The thickness of the fibrous region did not change during the analyzed period (p = 0.1899). When proliferative and hypertrophic regions and the total thickness of the cartilage were compared, a difference was detected (p < 0.001). The thickness of the proliferative region was greatest at 40 days and decreased at 5 months; however, it increased at 6 months, when it was significantly thicker than at 5, 8, 13, and 18 months. Both the hypertrophic region and the total thickness were thickest at 40 days, intermediate at 5, 6, and 8 months, and thinnest at 13 and 18 months. In summary, our data suggest a physiological period of increased cartilage growth at 6 months. Additionally, rabbits at this age should be avoided in experiments involving condylar cartilage. Finally, 13-month-old rabbits have reached histological maturity of the condylar cartilage.

Cell fate mediators Notch and Twist in mouse mandibular condylar cartilage

OBJECTIVE

The objectives of this study were to examine if Twist and Notch 1 are present in the mandibular condylar cartilage (MCC) and whether their gene expression can be altered by exogenous FGF-2 and TGF-β2.

DESIGN

Half-heads from CD-1 mice pups harvested at embryonic day 17 (E17) were fixed, decalcified, and sectioned in the sagittal plane for immunohistochemical detection of Notch and Twist using confocal microscopy. Other mandibular condyles and adjacent ramus from E17 mice were cultured in serum-free DMEM containing 0, 3, or 30 ng/mL of FGF-2 (10-12 condyles per treatment group). This experimental design was repeated with medium containing 0, 3, or 30 ng/mL of TGF-β2. After 3 days of culture, the pooled RNA from each group was extracted for examination of Notch and Twist gene expression using quantitative real-time RT-PCR.

RESULTS

Immunohistochemical examination revealed that Notch and Twist were localized to the prechondroblastic and upper chondroblastic layers of the cartilage. Exogenous FGF-2 up-regulated Notch 1, Twist 1 and Twist 2 gene expression in MCC explants from E17 mice, whilst TGF-β2 had the opposite effect.

CONCLUSIONS

The gene expression data demonstrate that MCC explants are sensitive to growth factors known to affect Notch and Twist in other tissues. The subset of cells in which Twist and Notch immunoreactivity was found is suggestive of a role for FGF-2 and TGF-β2 as regulators of cell differentiation of the bipotent MCC cell population, consistent with the role of Notch and Twist as downstream mediators of these growth factors in other tissues.

The radiographic approach to child abuse

BACKGROUND

Osseous injuries are a major facet of child abuse and in most patients radiographic imaging plays a major role in diagnosis. While some injuries are typically produced as a result of excessive and inappropriate force other injuries are nonspecific in terms of their causation, but become suspicious when the history provided by the caretakers is inconsistent with the type of injury produced.

QUESTIONS/PURPOSES

I detail the radiographic imaging of the more characteristic of the highly specific injuries, discuss the major issues that relate to some moderate- or low-specificity injuries, and describe several diseases that mimic abuse.

METHODS

A review of the current and recent literature focused on the radiographic imaging of child abuse was performed by searching the National Library of Medicine database at pubmed.gov. Keywords used included: radiology, fracture, child abuse, and/or nonaccidental trauma.

RESULTS

Injuries that are highly specific for the diagnosis of abuse include metaphyseal corner fractures, posteromedial rib fractures, and sternal, scapular, and spinous process fractures. Lesions of moderate specificity include, among other injuries, multiple fractures of various ages and epiphyseal separations. Long-bone fractures and clavicular fractures, while common, are of low specificity. In addition to the appropriate accurate diagnosis of these injuries, several diseases and syndromes may mimic abuse due to the similarity in the radiographic picture.

CONCLUSIONS

Stratification of fractures sustained in child abuse according to specificity and an understanding of the several diseases that mimic abuse are helpful in the accurate diagnosis of child abuse.

LEVEL OF EVIDENCE

Level V, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Expression of Ten-m/Odz3 in the fibrous layer of mandibular condylar cartilage during postnatal growth in mice

It has been speculated that the mandibular condyle develops via the differentiation of the fibroblast-like cells covering the condyle into chondrocytes; however, the developmental mechanisms behind this process have not been revealed. We used laser-capture microdissection and cDNA microarray analysis to elucidate the genes that are highly expressed in these fibroblast-like cells. Among these genes, the transcription of Ten-m/Odz3 was significantly increased in the fibroblast-like cells compared with other cartilage tissues. For the first time, we describe the temporal and spatial expression of Ten-m/Odz3 mRNA in relation to the expression of type I, II, and X collagen mRNA, as determined by in-situ hybridization in mouse mandibular condylar cartilage and mouse femoral cartilage during the early stages of development. Ten-m/Odz3 was expressed in the fibrous layer and the proliferating and mature chondrocyte layers, which expressed type I and II collagen, respectively, but was not detected in the hypertrophic chondrocyte layer. Furthermore, we evaluated the in-vitro expression of Ten-m/Odz3 using ATDC5 cells, a mouse chondrogenic cell line. Ten-m/Odz3 was expressed during the early stage of the differentiation of mesenchymal cells into chondrocytes. These findings suggest that Ten-m/Odz3 is involved in the differentiation of chondrocytes and that it acts as a regulatory factor in the early stages of the development of mandibular condylar cartilage.

Differential gene expression in the perichondrium and cartilage of the neonatal mouse temporomandibular joint

Our goal was to discover genes differentially expressed in the perichondrium (PC) of the mandibular condylar cartilage (MCC) that might enhance regenerative medicine or orthopaedic therapies directed at the tissues of the temporomandibular joint. We used targeted gene arrays (osteogenesis, stem cell) to identify genes preferentially expressed in the PC and the cartilaginous (C) portions of the MCC in 2-day-old mice. Genes with higher expression in the PC sample related to growth factor ligand-receptor interactions [FGF-13 (6.4x), FGF-18 (4x), NCAM (2x); PGDF receptors, transforming growth factor (TGF)-beta and IGF-1], the Notch isoforms (especially Notch 3 and 4) and their ligands or structural proteins/proteoglycans [collagen XIV (21x), collagen XVIII (4x), decorin (2.5x)]. Genes with higher expression in the C sample consisted mostly of known cartilage-specific genes [aggrecan (11x), procollagens X (33x), XI (14x), IX (4.5x), Sox 9 (4.4x) and Indian hedgehog (6.7x)]. However, the functional or structural roles of several genes that were expressed at higher levels in the PC sample are unclear [myogenic factor (Myf) 9 (9x), tooth-related genes such as tuftelin (2.5x) and dentin sialophosphoprotein (1.6x), VEGF-B (2x) and its receptors (3-4x) and sclerostin (1.7x)]. FGF, Notch and TGF-beta signalling may be important regulators of MCC proliferation and differentiation; the relatively high expression of genes such as Myf6 and VEGF-B and its receptors suggests a degree of unsuspected plasticity in PC cells.

Histologic study of the cellular events during rat mandibular distraction osteogenesis

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

Mandibular DO produces bone through both intramembranous and endochondral ossification.

Dual effects of the membrane-anchored MMP regulator RECK on chondrogenic differentiation of ATDC5 cells

Extracellular matrix (ECM) undergoes continuous remodeling during mammalian development. Although involvement of matrix metalloproteinases (MMPs) in ECM degradation has been well documented, how this process is regulated to allow proper ECM accumulation remains unclear. We previously showed the involvement of a membrane-anchored MMP regulator, RECK (reversion-inducing cysteine-rich protein with Kazal motifs), in vascular development in mice. Here we report that Reck mRNA can be detected in developing cartilage in E13.5 approximately 16.5 mouse embryos and is progressively upregulated during differentiation of a chondrogenic cell line ATDC5 in vitro. In the early phase of ATDC5 differentiation, RECK expression stays low, multiple MMPs are upregulated, and there is ECM degradation at the sites of cellular condensation. In the later phase, RECK is upregulated inside the expanding cartilaginous nodules where type II collagen is accumulated while active ECM degradation persists along the rim of the nodules. Constitutive RECK expression suppressed initial cellular condensation, whereas RECK knockdown suppressed the later ECM accumulation in the cartilaginous nodules. These results suggest that RECK expression at the right place (in the core of the nodules) and at the right time (only in the later phase) is important for proper chondrogenesis and that RECK, together with MMPs, plays a crucial role in regulating dynamic processes of tissue morphogenesis.

Immunohistochemical Examination of Epiphyseal Growth Plates of Japanese Brown Cattle with Chondrodysplasia

A new type of inherited chondrodysplasia is described in Japanese Brown cattle, but the basic defects of the epiphyseal growth plate (EGP) in the limb long bones, and proliferation and differentiation of the chondrocytes in the EGP, are not yet understood. In the present study, the EGPs of the limb long bones in eight cases of chondrodysplasia and four normal (control) cattle were examined histologically and immunohistochemically. In the control cattle, proliferative chondrocytes (PCs) and hypertrophic chondrocytes (HCs) were arranged in columns parallel to the long axis of the bone, and HCs were situated on the metaphyseal side of the EGP. In all the affected cattle, many chondrocytes with a hypertrophic appearance were detected in the inner areas of the central portion of the EGP. The PC columns were short and arranged irregularly. Bone tissue and small blood vessels were found frequently in these areas. Six affected cattle showed complete EGP-closure. Backscattered electron (BSE) imaging showed that the calcified cartilage matrix was restricted to the lower region of the hypertrophic zone (HZ) of the EGP in the control cattle, while the calcified cartilage matrix and bone tissue were scattered in the inner areas of the EGP in all the chondrodysplastic cattle. Immunohistochemistry revealed type X collagen in the HCs and cartilage matrix of the HZ in the control cattle. In all the affected cattle, type X collagen was detected in apparently hypertrophic chondrocytes in the inner areas of the EGP. Type II collagen was detected in the entire EGP in all the affected cattle, as in the controls. BrdU (5-bromo-2'-deoxyuridine), injected intravenously 1h before euthanasia was detected in many PCs in the EGP in the control cattle; none, however, was detected in the central portion of the EGP in any affected animal. These observations indicate that differentiation into HCs and calcification of cartilage matrix occur in the inner areas of the central portion of the EGP in chondrodysplasia of Japanese Brown cattle. Differentiation into the HCs at this abnormal site may be caused by the inadequate proliferation and disorganization of the PCs. Premature EGP-closure, observed commonly in chondrodysplasia of Japanese Brown cattle, was thought to be caused by replacement of the calcified cartilage in the inner areas of the EGP by bone tissue.

Effects of estrogen on chondrocyte proliferation and collagen synthesis in skeletally mature articular cartilage

PURPOSE

Estrogen has been shown to have a modulating effect on cartilage thickness. This investigation was performed to determine the effects of estrogen supplementation on cartilage thickness, cellular proliferation, and type II and X collagen production in skeletally mature rat cartilage, both in an organ culture and cell culture system.

MATERIALS AND METHODS

Mandibular condyles were harvested from 8-week-old female Sprague Dawley rats and placed into tissue culture plates containing culture media with or without 17beta-estradiol supplementation. Organ cultures were labeled with 5-bromo-2'-deoxyuridine on culture day 2 or 4 to determine the effects of estrogen supplementation on the cellular mitotic index. Histomorphometric analysis of the organ culture sections was used to determine the thickness (microm) of the various cartilage zones, as well as the total cartilage thickness following estrogen exposure. Type X collagen was immunohistochemically identified in the ECM of hypertrophic chondrocytes using a rabbit anti-rat collagen type X antibody raised against the NCl domain. The reaction was visualized with an avidin-biotin peroxidase detection system (Vector Laboratories, Burlingame, CA). In a separate experiment, articulating cartilage chondrocytes were harvested by collagenase digestion and cultured at 5 x 10(5) cells per 35 mm tissue culture plate. Second subculture chondrocytes were divided into 2 groups: controls and [10(-8) M] 17beta-estradiol (E(2)-10(-8) M) and grown to confluence. The cell cultures were used to establish growth curves for each group using cell counts at 2-day intervals.

RESULTS

In the organ culture experiment, 17beta-estradiol-treated condyles had a significant decrease in total cartilage thickness after 4 days in culture (P < .05). Estrogen supplementation resulted in a significant reduction in the mitotic index as early as culture day 2 (P < .05). Type X collagen deposition into the extracellular matrix was visibly increased in the hypertrophic chondrocyte zone for the estrogen-supplemented group on experimental days 2 and 4 compared with the control group. In the cell culture system, 17beta-estradiol [10(-8) M] decreased chondrocyte proliferation during logarithmic growth (P < .05) and at confluence (P < .05).

CONCLUSION

These data show that estrogen decreased cartilage thickness by inhibition of chondrocyte proliferation and increased chondrocyte maturation. These observed effects showed the potential role of estrogen in the modulation of skeletally mature cartilage.

Histochemical evidences on the chronological alterations of the hypertrophic zone of mandibular condylar cartilage

The hypertrophic chondrocytes lack the ability to proliferate, thus permitting matrix mineralization as well as vascular invasion from the bone in both the mandibular condyle and the epiphyseal cartilage. This study attempted to verify whether the histological appearance of the hypertrophic chondrocytes is in a steady state during postnatal development of the mouse mandibular condyle. Type X collagen immunohistochemistry apparently distinguished the fibrous layer described previously as the "articular zone," "articular layer," and "resting zone" from the hypertrophic zone. Interestingly, the ratio of the type X collagen-positive hypertrophic zone in the entire condyle seemed higher in the early stages but decreased in the later stages. Some apparently compacted cells in the hypertrophic zone showed proliferating cell nuclear antigen (PCNA) immunoreaction, indicating the potential for cell proliferation at the early stages. As the mice matured, in contrast, they further enlarged and assumed typical features of hypertrophic chondrocytes. Apoptotic cells were also discernible in the hypertrophic zone at the early but not later stages. Consistent with morphological configurations of hypertrophic chondrocytes, immunoreactions for alkaline phosphatase, osteopontin, and type I collagen were prominent at the later stage, but not the early stage. Cartilaginous matrices demonstrated scattered patches of mineralization at the early stage, but increased in their volume and connectivity at the later stage. Thus, the spatial and temporal occurrence of these immunoreactions as well as apoptosis likely reflect the prematurity of hypertrophying cells at the early stage, and imply a physiological relevance during the early development of the mandibular condyles.

Age-related changes in the expression of gelatinase and tissue inhibitor of metalloproteinase genes in mandibular condylar, growth plate, and articular cartilage in rats

Mandibular condylar cartilage acts as both articular and growth plate cartilage during growth, and then becomes articular cartilage after growth is complete. Cartilaginous extracellular matrix is remodeled continuously via a combination of production, degradation by matrix metalloproteinases (MMPs), and inhibition of MMP activity by tissue inhibitors of metalloproteinases (TIMPs). This study attempted to clarify the age-related changes in the mRNA expression patterns of MMP-2, MMP-9, TIMP-1, TIMP-2, and TIMP-3 in mandibular condylar cartilage in comparison to tibial growth plate and articular cartilage using an in situ hybridization method in growing and adult rats. MMP-2 and MMP-9 were expressed in a wide range of condylar cartilage cells during growth, and their expression domains became limited to mature chondrocytes in adults. The patterns of TIMP-1 and TIMP-2 expression were similar to those of MMP-2 and MMP-9 during growth, and were maintained until adulthood. TIMP-3 was localized to hypertrophic chondrocytes throughout the growth stage. Therefore, we concluded that TIMP-1 and TIMP-2 were general inhibitors of MMP-2 and MMP-9 in condylar cartilage, while TIMP-3 regulates the collagenolytic degradation of the hypertrophic cartilage matrix.

Localization of CD44 (hyaluronan receptor) and hyaluronan in rat mandibular condyle

CD44 is a multifunctional adhesion molecule that binds to hyaluronan (HA), type I collagen, and fibronectin. We investigated localization of CD44 and HA in mandibular condylar cartilage compared with the growth plate and the articular cartilage, to clarify the characteristics of chondrocytes. We also performed Western blotting using a lysate of mandibular condyle. In mandibular condyle, CD44-positive cells were seen in the surface region of the fibrous cell layer and in the proliferative cell layer. Western blotting revealed that the molecular weight of CD44 in condyle was 78 to 86 kD. Intense reactivity for HA was detected on the surface of the condyle and the lacunae of the hypertrophic cell layer. Moderate labeling was seen in cartilage matrix of the proliferative and maturative layer. Weak labeling was also seen in the fibrous cell layer. In growth plate and articular cartilage, HA was detected in all cell layers. However, chondrocytes of these cartilages did not exhibit reactivity for CD44. These results suggest that chondrocytes in the mandibular condylar cartilage differ in expression of CD44 from those in tibial growth plate and articular cartilage. Cell-matrix interaction between CD44 and HA may play an important role in the proliferation of chondrocytes in the mandibular condyle.

Distribution of Type VI Collagen in the Cartilaginous Tissue of the Proximal Tibia in the Domestic Cat

To investigate the distribution of the early stage chondrocytes during the formation and closure of epiphyseal growth plate (EGP) of the domestic cat, we examined the EGP of proximal tibiae by immunohistochemistry for type VI collagen. In the epiphyseal cartilage without the secondary ossification center (SOC) and EGP in newborn cats aged 1 and 10 days, type VI collagen-positive chondrocytes were located around the cartilage canals and articular surface. In the epiphyseal cartilage with the SOC and EGP in young cats aged 1 to 3 months, type VI collagen-positive chondrocytes were located in the upper resting zone of the EGP, and then increased throughout the resting zone along with maturation. In the adult cats with the partially closed EGP, type VI collagen-positive chondrocytes were distributed throughout the remaining EGP. These findings indicate that the early stage chondrocytes characterized with type VI collagen are continuously located in the EGP during maturation. In addition, the increase of the early stage chondrocytes and the decrease of the reserve chondrocytes in the EGP along with maturation may cause the cessation of the longitudinal growth of the EGP, and finally bring about the EGP closure.

Mechanical signals as regulators of stem cell fate

In recent years, stem cells have shown significant promise for their potential to provide a source of undifferentiated progenitor cells for therapeutic applications in tissue or organ repair. Significant questions still remain, however, as to the genetic and epigenetic signals that regulate the fate of stem cells. It is now well accepted that the micro-environment of the stem cell can have a significant influence on its differentiation and phenotypic expression. Although emphasis has been placed in previous work on the role of soluble mediators such as growth factors and cytokines on stem cell differentiation, there is now significant evidence, both direct and indirect, that mechanical signals may also regulate stem cell fate. We review a number of in vivo and in vitro studies that have provided evidence that mechanical factors have the ability to influence the differentiation of a number of cells that have been classified as either precursor, progenitor, or stem cells. Taken together, these studies show that specific mechanical signals may promote cell differentiation into a particular phenotype, potentially having an effect on embryonic development. The use of such mechanical signals in vitro in specially designed "bioreactors" may provide important adjuncts to standard biochemical signaling pathways for promoting engineered tissue growth. A further understanding of the biomechanical and biochemical pathways involved in mechanical signal transduction by stem cells will hopefully provide new insight for the improvement of stem-cell based therapies.

Primary and secondary cartilages of the neonatal rat: the femoral head and the mandibular condyle

Primary and secondary cartilages differ in embryonic origin and in histological organization, and are generally considered to have a different mode of growth. However, few studies have directly compared the two types of cartilage of the same animal at the same age. Therefore, we analysed several histological and biochemical differences between secondary cartilage of the mandibular condyle and primary cartilage of the femoral head of 4-d-old rats. We evaluated the tissue organization, the level of DNA and glycosaminoglycan (GAG) synthesis, and the GAG and collagen content. The expression of collagen types I, II and III and of receptors for insulin-like growth factor (IGF)-I, fibroblast growth factor (FGF), and transforming growth factor (TGF)-beta were investigated by immunohistochemistry. The ex vivo DNA and GAG synthesis as well as the GAG content of femoral heads were much higher than that of mandibular condyles. Mandibular condyles expressed both collagen types I and II, while femoral heads expressed only type II collagen. In the mandibular condyles, receptors for IGF-I, FGF, and TGF-beta were observed mainly in the superficial layers, whereas they were found throughout the entire femoral head. In conclusion, major differences were found between both types of cartilage, which might be related to their specific functional demands.

Experimentally induced unilateral tooth loss: expression of type II collagen in temporomandibular joint cartilage

PURPOSE

We sought to examine possible changes in pattern and concentration of type II collagen in the condylar cartilage and articular disc of the temporomandibular joint (TMJ) in response to unilateral extraction of mandibular teeth in a rabbit model as a means of elucidating the effects of unilateral mastication on the TMJ.

METHODS

A total of 12 experimental rabbits were killed either 3 or 6 weeks after the extractions, and 3 additional rabbits without extractions were used as controls. TMJ blocks from both sides of each of the 15 animals were examined for type II collagen via an immunoperoxidase procedure.

RESULTS

Anti-type II collagen antibody (Ab) binding was detected mainly in the hypertrophic chondroblast layer of the condylar cartilage of normal rabbits. At 3 weeks after unilateral extraction of teeth, anti-type II collagen Ab binding to the territorial matrix of the hypertrophic chondroblast layer of the condylar cartilage and to the disc was stronger than normal. The increase in Ab binding appeared more dramatic on the nonfunctional side than on the functional side of TMJ. Variations from the normal pattern of anti-type II collagen Ab binding in terms of distribution through the extracellular matrix and fibrillar appearance were also observed.

CONCLUSION

The findings suggest that the condylar cartilage and disc adapt to the imbalance induced by unilateral extraction of teeth through chondrocyte repair responses involving collagen II expression that appear to differ between the functional and nonfunctional sides of the TMJ.