Rat Mandibular Condyle Research Articles

Circadian rhythm disruption upregulating Per1 in mandibular condylar chondrocytes mediating temporomandibular joint osteoarthritis via GSK3β/β-CATENIN pathway

BackgroundTemporomandibular joint osteoarthritis (TMJOA) has a high incidence rate, but its pathogenesis remains unclear. Circadian rhythm is an important oscillation in the human body and influences various biological activities. However, it is still unclear whether circadian rhythm affects the onset and development of TMJOA.MethodsWe disrupted the normal rhythm of rats and examined the expression of core clock genes in the mandibular condylar cartilage of the jaw and histological changes in condyles. After isolating rat mandibular condylar chondrocytes, we upregulated or downregulated the clock gene Per1, examined the expression of cartilage matrix-degrading enzymes, tested the activation of the GSK3β/β-CATENIN pathway and verified it using agonists and inhibitors. Finally, after downregulating the expression of Per1 in the mandibular condylar cartilage of rats with jet lag, we examined the expression of cartilage matrix-degrading enzymes and histological changes in condyles.ResultsJet lag led to TMJOA-like lesions in the rat mandibular condyles, and the expression of the clock gene Per1 and cartilage matrix-degrading enzymes increased in the condylar cartilage of rats. When Per1 was downregulated or upregulated in mandibular condylar chondrocytes, the GSK3β/β-CATENIN pathway was inhibited or activated, and the expression of cartilage matrix-degrading enzymes decreased or increased, which can be rescued by activator and inhibitor of the GSK3β/β-CATENIN pathway. Moreover, after down-regulation of Per1 in mandibular condylar cartilage in vivo, significant alleviation of cartilage degradation, cartilage loss, subchondral bone loss induced by jet lag, and inhibition of the GSK3β/β-CATENIN signaling pathway were observed. Circadian rhythm disruption can lead to TMJOA. The clock gene Per1 can promote the occurrence of TMJOA by activating the GSK3β/β-CATENIN pathway and promoting the expression of cartilage matrix-degrading enzymes. The clock gene Per1 is a target for the prevention and treatment of TMJOA.

The effect of low intensity pulsed ultrasound on mandibular condylar growth in young adult rats

There is a need for more effective methods to enhance mandibular growth in young adults with mandibular deficiency. Previous studies suggest that low intensity pulsed ultrasound (LIPUS) can enhance mandibular growth in growing individuals. This study aimed to evaluate the potential growth changes of the mandible following 4-week LIPUS application in young adult rats. Nineteen ≈120-day-old female rats were allocated to experimental (n = 10) and control (n = 9) groups. The animals in the experimental group were treated with LIPUS to their temporomandibular joints (TMJs) bilaterally, 20 min each day for 28 consecutive days. Animals were then euthanized; gross morphological evaluation was performed on 2D photographs and 3D virtual models of hemi-mandibles, and microstructural assessment was done for the mandibular condyle (MC). Evaluation of mineralization and microarchitecture properties of subchondral cancellous bone was performed by micro-computed tomography (μCT) scanning. Qualitative and histomorphometric analysis was done on condylar cartilage and subchondral bone following Alcian Blue/PAS and Goldner's Trichrome staining. Vital flourochrome (calcein green) labeling was also utilized to determine the amount of endochondral bone growth. Gross morphological evaluations showed a slight statistically non-significant increase especially in the main condylar growth direction in the LIPUS group. Moreover, 3D evaluation depicted an enhanced periosteal bone apposition at the site of LIPUS application. Microstructural analysis revealed that LIPUS stimulates both chondrogenesis and osteogenesis and enhances endochondral bone formation in young adult rat MC. Furthermore, the effect of LIPUS on osteogenic cells of subchondral cancellous bone was notable. To conclude, LIPUS can enhance young adult rats' MC residual growth potential.

EFFECTS OF LOW-LEVEL LASER IRRADIATION ON THE GROWTH OF THE RAT MANDIBULAR CONDYLE IN ORGAN CULTURE

<h3>Objective</h3> The present study was carried out to histologically, immunohistochemically, and histometrically investigate the effect of low-level laser irradiation by a diode laser on the growth of the rat mandibular condyle in organ culture. <h3>Methods</h3> The mandibular condyles were removed from rats' embryos on the 21st day and then cultured for 8 days. The 20 cultured condyles were divided into 4 groups: F−L− group (serumless BGJb); F+L− group (serumless BGJb with bFGF 100 ng/mL); F−L+ group (serumless BGJb and laser irradiation); and F+L+ group (serumless BGJb with bFGF 100 ng/mL and laser irradiation). The laser irradiation (output 1.3 W/cm² and wavelength 633 nm) was performed on the cultured condyle for 30 seconds every 24 hours for 5 days. Immunohistochemically, PCNA was used to analyze cell proliferation. <h3>Results</h3> The mesenchymal cells in the layer of differentiation and hypertrophy in the F+L+ group showed a marked increase in cell number and the size of the condyle. The positive cell number of PCNA in F+L− and F+L+ group was significantly higher compared with the control group. <h3>Conclusions</h3> Our data showed that low-level laser irradiation promotes cell proliferation in the cultured condyle same as in bFGF addition. It is suggested that low-level laser irradiation by a diode laser (wavelength 633 nm) stimulated the proliferation of mesenchymal cells, which resulted in an increase in the number of chondrocytes in the layers of differentiation and hypertrophy by leading to the enlargement of the condylar size.

Study of changes in rat mandibular condyle under intermittent cyclic and continuous compressive stress

ObjectivesThis study aimed to investigate the effects of intermittent and continuous compressive stress on rat mandibular condyles. DesignNinety rats were randomly divided into 5 groups: non-loading control groups and 1-day intermittent cyclic loading, 3-day intermittent cyclic loading, 7-day intermittent cyclic loading, continuous loading groups. In the loading groups, compressive mechanical stresses were loaded onto the condyles. The rats were euthanized after one, two, or four weeks. Histomorphometric and immunochemical staining of the cartilage and the micro-CT scanning of subchondral bone were investigated. ResultsUnder continuous loading following the first week, cartilage thickness, numbers of chondrocytes, extracellular matrix (Type-II collagen) and proliferation decreased significantly, and there was no apparent repair response after the second and fourth weeks. The cartilage of 1-day and 3-day intermittent cyclic loading groups showed similar pathological changes but better proliferative activity compared with the continuous loading group. The 7-day intermittent loading group had significant recovery after 2 weeks, including the increase of cartilage thickness and the number of chondrocytes, cell swelling and rearranging. However, the remodeling of subchondral bone showed no significant difference between the intermittent and continuous loading stress compared to the control group. ConclusionsUnder moderate mechanical stress, the condylar cartilage actively remodeled, whereas the subchondral bone, as supportive rigid structure, was less sensitive to mechanical pressure. The intermittent compressive stress protects the condylar cartilage from excessive damage, which is different from continuous compressive stress. With longer intervals, the cartilage has the potential capability for recovery as the initial state.

Rat mandibular condyle and fossa grew separately then unified as a single joint at 20 days old, which was the weaning age.

Magnetic resonance imaging (MRI) was used to observe growth of the mandibular condyle, mandibular fossa, and articular disc as a single unit. Changes in each component's relative position and size were observed using 7-tesla MRI. Mandibular condyle chondrocytes' growth was evaluated with immunohistochemistry, using the expression of zinc transporter ZIP13. Three-dimensional T1-weighted (T1w) MRI was used to obtain images of the TMJ of Sprague Dawley rats at 4-78 days old (P4-78) with a voxel resolution of 65 μm. Two-dimensional T1w MR images were acquired after a subcutaneous injection of the contrast reagent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The T1w MR images showed that the mandibular condyle was located posterior to the mandibular fossa until P20; however, it then moved to a location underneath the mandibular fossa. In the Gd-DTPA enhanced images, the articular disc was identified as a region with lower signal intensity from P20. The number of ZIP13-positive chondrocytes at P6 was larger than the number at P24. In conclusion, the mandibular condyle with cartilage and disc grows on the posterior side of the mandibular fossa until P20, which was the weaning age. Then, the condyle fit into the mandibular fossa and completed the functional unit.

Histological Changes to the Rat Mandibular Condyle in Response to Long-term Exposure to an Extremely Low Frequency Magnetic Field

Background : The need for electrical power continues to increase along with the rapidly growing economies of industrialized countries. However, the effects of electrical fields (EFs) on human health remain unclear. Hence, the aim of the present study is to evaluate the histological effects of an extremely low frequency magnetic field (ELF-MF) on the rat mandibular condyle. Methods : Twenty female Sprague-Dawley rats were randomly allocated to one of two groups (n = 10): an untreated control group and an ELF-MF group exposed to a 1.5-mT ELF-MF for 4 h per day for 6 months. After exposure, the left mandibular condyles of all rats were collected for histopathological examinations. Results : The histopathological changes to the ELF-MF group included a non-homogenous appearance and decreased thickness of the hypertrophic layer, irregular appearances of bone marrow cavities, significant deterioration, and delayed calcification and ossification. There were no significant differences in the thicknesses or histomorphometric appearances of the fibrotic, proliferative, and hypertrophic layers of the mandibular condyle of rats between the groups ( p = 0.05). Conclusion : Long-term ELF-MF exposure can induce histopathological changes to the mandibular condyle of rats .

Chondrocyte apoptosis in rat mandibular condyles induced by dental occlusion due to mitochondrial damage caused by nitric oxide

ObjectiveChondrocyte apoptosis is a pathological manifestation of osteoarthritis. The goal of this report was to explore the role of nitric oxide in chondrocyte apoptosis in osteoarthritic mandibular condylar cartilage. DesignThis study used our reported experimental unilateral anterior crossbite in vivo rat model and chondrocyte fluid flow shear stress in vitro model. In the in vivo model, apoptosis in the mandibular condylar cartilage was assessed by detection of the TUNEL-positive cells, the expression levels of inducible nitric oxide synthase (iNOS), caspase-9, and caspase-3. In the in vitro model, mitochondrial injury was evaluated, the nitric oxide and superoxide dismutase (SOD) production levels were measured, and the cytochrome C (Cyt C) expression level was detected. The expression levels of apoptosis-related proteins B cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), caspase-3, and poly-ADP-ribose polymerase 1 (PARP1) were analyzed in both in vivo and in vitro models. The effects of iNOS inhibitor on chondrocyte apoptosis were also investigated. ResultsThe data indicated that the unilateral anterior crossbite induced cartilage degeneration with enhanced cell apoptosis and stimulated the expression of caspase-3/-9 and iNOS. The fluid flow shear stress upregulated the expression of iNOS, SOD, and nitric oxide, reduced mitochondrial membrane potential, and promoted Cyt C to enter the cytoplasm. All of these changes were reversed by iNOS inhibitors. ConclusionThe abnormal occlusion stimulated mitochondrial damage and apoptosis of the chondrocytes in the mandibular condylar cartilage mediated by nitric oxide. Inhibiting nitric oxide production could be a therapeutic strategy.

Calcium-/calmodulin-dependent protein kinase II in occlusion-induced degenerative cartilage of rat mandibular condyle.

Activated calcium-/calmodulin-dependent protein kinaseII (CaMKII) is important to promote chondrocytes from proliferative to pre-hypertrophic state, which probably plays a role in osteoarthritis (OA), a widespread degeneration disease with enhanced aberrant chondrocyte differentiation. Our aim was to detect the role of CaMKII, and its relationship with the feedback loop of Indian hedgehog (Ihh) and Parathyroid-related peptide (PTHrP) in the temporomandibular joints (TMJs) OA. KN93, the competitive inhibitor of CaMKII, was added to the culture medium in vitro and was locally injected to rats TMJs (n=54, female) every other day for 4weeks from the beginning of the 5th and 9th week after installing of unilateral anterior crossbite (UAC), termed as 4wk+4wk and 8wk+4wk, accordingly. The RNA expression of CaMKII α (1.49±0.09), CaMKII β (3.36±0.20), Ihh (1.88±0.06) and PTHrP (1.87±0.12) was all enhanced, especially at 24dyn/cm2 in vitro (all P<.05), accompanied with downregulated expression of cartilage matrix, but upregulated markers of chondrocytes differentiation (all P<0.05). Similarity was observed in the 4wk+4wk group in vivo. In the 8wk+4wk group, UAC upregulated the RNA expression of CaMKII α (1.81±0.24), CaMKII β (1.36±0.07) and Ihh (1.70±0.21), however, down-regulated PTHrP (0.53±0.04) (all P<.05), in consonance with the protein expression. All these changes were attenuated by KN93 (all P<.05). In conclusion, CaMKII took a role, via Ihh and PTHrP pathways, in promoting biomechanically induced TMJ chondrocytes differentiation, the initiation issue of UAC stimulated osteoarthritic changes in rodent TMJs. Inhibiting CaMKII is helpful to rescue the biomechanically stimulated cartilage degradation and prospective to be a target treatment of OA.

Vitamin C 欠乏および卵巣摘出によるラット下顎頭変化の免疫組織化学的研究

Vitamin C 欠乏および卵巣摘出によるラット下顎頭変化の免疫組織化学的研究

Effect of early intra ⁃ articular injection of alendronate in reducing subchondral bone loss in rat mandibular condyle after ovariectomy

Effect of early intra ⁃ articular injection of alendronate in reducing subchondral bone loss in rat mandibular condyle after ovariectomy

Effect of low-intensity pulsed ultrasound (LIPUS) on mandibular condyle growth in rats analyzed with micro-CT.

This study examined the effects of a bite-jumping appliance combined with low-intensity pulsed ultrasound (LIPUS) stimulation on the mandibular condyle of growing rats using micro CT (mCT) and histological examinations. Twelve Wistar rats were divided into three groups of four individuals each: Group 1 was an untreated control group, Group 2 received bite-jumping appliances, and Group 3 received bite-jumping appliances and LIPUS stimulation (15 min/day, 2 weeks) to the temporomandibular region. We measured the length and three-dimensional bone volume of each rat's mandibular condyle using mCT. The condylar cartilage was observed after the rats had been sacrificed. There was no significant difference in condylar sagittal width among the groups. The bite-jumping appliance combined with LIPUS stimulation increased the condylar major axis, mandibular sagittal length and condylar bone volume to a greater degree than use of the bite-jumping appliance alone. Histological examination demonstrated hypertrophy of the condylar cartilage layers, the fibrous layer and hypertrophic cell layer of the rats treated with bite-jumping appliances combined with LIPUS stimulation in comparison to rats treated with bite-jumping appliances alone. (J Oral Sci 58, 415-422, 2016).

Effects of estrogen deficiency combined with chronic alcohol consumption on rat mandibular condyle

Effects of estrogen deficiency combined with chronic alcohol consumption on rat mandibular condyle

Effects of estrogen deficiency combined with chronic alcohol consumption on rat mandibular condyle

Estrogen deficiency and chronic alcohol consumption may have a synergistic and deleterious effect on bone tissue. Aim: To investigate the effects of estrogen deficiency associated with chronic alcohol consumption on the mandibular condyle in rats. Methods: Fifty-four female rats were first divided equally into two groups: ovariectomized (Ovx) and simulated ovariectomy (Sham). One month after the surgeries, these groups were equally sub-divided according to their dietary treatment: G1: Sham/ad-libitum diet; G2: Sham/alcohol; G3: Sham/isocaloric; G4: Ovx/ad-libitum diet; G5: Ovx/alcohol, G6: Ovx/isocaloric. Eight weeks after starting the diets, all animals were anesthetized and sacrificed. The condyles were analyzed histologically, histomorphometrically, and immunohistochemically using the antibodies for bone sialoprotein (BSP), osteocalcin (OCC) and receptor activator of nuclear factor kappa-B ligand (RANKL). Results: Histological analysis of the mandibular condyles showed that Ovx and Sham groups presented almost the same characteristics. The histomorphometric analysis showed that there was a statistically significant difference only between Ovx/isocaloric and Ovx/ad-libitum groups (p=0.049). No difference was observed in the intensity of BSP, OCC, and RANKL antibody staining between the Ovx/alcohol and the other groups. Conclusions: It may be concluded that there was no histomorphometric, histological, or RANKL, BSP, and OCC staining differences between the Ovx/alcohol group and other experimental groups.

Rat Articular Condyle Changes During and After Continuous Mandibular Advancement: A Histomorphometric Study

The purpose of this study was to investigate the histological changes in rat mandibular condyle during and after continuous mandibular advancement by using a fixed functional appliance. Materials and methods: Fifty-four male Sprague-Dawley rats (4–weeks-old), weight (100-120gm) were used for three month experimental period; control group (A=24 rats) and experimental group (B=30 rats). Group A and Group B were subdivided into 3 equal groups respectively (A1, A2, A3); (B1, B2, B3). All groups were fed ad libitum and were kept under the same environmental condition. Only group (B1, B2, B3) were subjected to a full time orthodontic inclined bite plane cemented to the incisors (fixed functional appliance) to advance the mandible, while group A still as a control group. At the end of the 1st month only group B1as a (full-time wearer)and A1 were sacrificed, while groups B2 and B3 continue as a half-day-wearer, retention period) till the end of the 2nd month, when group B2 and A2 were sacrificed. Remaining rats (Group B3) stayed without appliance, post retention period) during whole 3rd month were sacrificed at the end of third month with control (A3). Specimens of hemi-cranium for all scarified animals were cut and dissected, histopathological examination had been done. Results: An abundant cellular proliferation expressed at posterior border of the condylar cartilage in group B than in group A. Cellular proliferation without proper ossification was noticed on the condyles of young rats of group A. However, rats revealed a significant Condylar ossification and higher osteoblastic activity towards the last week of treatment and retention period with the mandibular Condylar growth was accelerated by bite-jumping appliance treatment and stable within limits after a certain period of retention. Conclusion:Mandibular Condylar changes were accelerated by using fixed functional appliances that increased osteogenesis noticed during active mandibular advancement.

The PI3K/Akt signalling pathway may play an internal role related to abnormal condylar growth: a preliminary study

Developmental deformity of the mandible is one of the most common craniofacial malformations and is closely related to abnormal condylar growth. In this study, the role of PI3K/Akt signalling in the regulation of chondrocyte proliferation and hypertrophic differentiation in the condylar cartilage was studied. Immunohistochemical staining was used to investigate the expression of PI3K and p-Akt in the rat condyle cartilage. Rat condylar chondrocytes were cultured for the investigation of chondrocyte proliferation and hypertrophic differentiation when PI3K/Akt was inhibited. In addition, organ culture of the rat mandibular condyle was performed to evaluate the condyle cartilage growth while PI3K/Akt was inhibited. PI3K-positive cells and p-Akt-positive cells showing cytoplasmic staining were found to be present in the condylar cartilage. Reduced cell proliferation was observed in the culture of rat condylar chondrocytes when PI3K/Akt was inhibited; however, the hypertrophic differentiation level was increased. The proliferative zone thickness of condylar cartilage in the experimental group was less than that in the control group (P=0.00185), but the hypertrophic zone was greater than that in the control group (P=0.01048). PI3K/Akt signalling exerts opposite influences on chondrocyte proliferation and hypertrophic differentiation of the condylar cartilage, and these data suggest that PI3K/Akt is a potential intracellular regulation signal pathway in condylar cartilage development.

A histologic study of deformation of the mandibular condyle caused by distraction in a rat model.

This study investigated the bone resorption process of the rat mandibular condyle after mandibular distraction. Male Wistar rats at 10 weeks of age underwent unilateral mandibular distraction at 0.175 mm per 12 hours for 10 days. Histologic and histochemical analyses were performed at postoperative day 1 and weeks 1 and 3. High-resolution computed tomography (micro-CT) observations showed that deformation of the condyle occurred in the anterior region, where a discontinuity of the condylar cartilage layer was found in histologic sections. This destroyed area gathered many osteoclasts. In the central region, disorganization with a thin hypertrophic cell layer was recognizable by day 1 but later thickened. Morphologic recovery of the mandibular condyle could be attained by week 3 in this animal model. These morphologic findings indicate that rapid deformation of the condyle, with destruction of the cartilage layer and bone resorption, was caused by artificial distraction.

Three-dimensional ultrastructure of the Golgi region of the formative chondrocyte in newborn rat mandibular condyle.

The three dimensional ultrastructure of Golgi region of formative chondrocytes from newborn rat mandibular condyle was examined by means of the method based on dilute osmium maceration with a high-resolution scanning electron microscope. The large area of formative chondrocytes was occupied by the cytoplasmic organelles related to matrix-synthesis such as Golgi apparatus, rough endoplasmic reticulum (RER) and mitochondria. The Golgi region of formative chondrocytes was composed of the limiting membranous structures such as some groups of the stacks of Golgi cisterns, vesicles, vacuoles, secretory granules, reticular constituents and small tabular or tubular RER. The Golgi cisterns were composed of both small tabular parts and rod-like parts arising from tabular parts. Small tabular parts were furthermore subdivided into three types of many, few and no penetrated ones. Reticular constituents were made up of limiting membrane visible as smooth image by scanning electron microscopy, therefore, are assumed to be one part of the GERL (Golgi apparatus-endoplasmic reticulum-lysosome).

Osteochondral angiogenesis in rat mandibular condyles with osteoarthritis-like changes

ObjectiveTo investigate angiogenesis at the osteochondral junction and changes in expression of pro- and anti-angiogenic factors in rat mandibular condyles with osteoarthritis-like changes. MethodsIn order to evoke osteoarthritis-like lesions in mandibular condyles, disordered occlusion was created experimentally in rats. Osteochondral vascularity was assessed histologically at 20 and 24weeks. Protein and mRNA levels of pro-angiogenic factors including vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF) and matrix metalloproteases 9 (MMP9), and anti-angiogenic factor chondromodulin-I (CHM-I) were investigated by means of immunohistochemical staining and real-time PCR. ResultsOsteochondral angiogenesis was demonstrated as increased numbers of vascular channels terminating in the calcified cartilage and non-calcified cartilage in 20- and 24-week experimental groups compared with controls (all P<0.05). In the experimental groups, VEGF, CTGF and MMP9 were highly expressed in the tissues adjacent to the osteochondral junction. However, CHM-I was more expressed in the superior but not deep hypertrophic chondrocytes. Compared to their age-matched controls, the protein levels of VEGF and CTGF were higher in 20-week experimental group, and the protein and mRNA levels of CTGF, MMP-9, and CHM-I increased in the 24-week experimental group (all P<0.05). ConclusionIn the present rat model, osteochondral angiogenesis was observed in mandibular condyles with osteoarthritis-like changes, accompanied with local upregulation of VEGF, CTGF and MMP9. Although the increase in CHM-I may moderate pro-angiogenic factors effects in the superior cartilage, the deficiency of deep hypertrophic chondrocytes to express CHM-I may permit vascular invasion into condylar cartilage.

Can Histological and Histomorphometrical Changes be Induced in Rat Mandibular Condyle Following Ovariectomy and Long-Term Extremely Low Frequency Magnetic Field Exposure?

ABSTRACTThe quantity and quality of maxillary and mandibular bone have long been a focus of attention for dental clinicians. The mandibular condyle is a major growth site and plays an important role during mandibular growth. The aim of the present study was to evaluate the effects of long-term extremely low frequency magnetic field (ELF-MF) and hormonal changes produced by bilateral ovariectomy on the histologic and histomorphometric structure of rat mandibular condyle.Forty mature female Sprague-Dawley rats were randomly divided into four different groups (n =10): control (Cnt), ovariectomy (OVX), ELF-MF exposure (ELF-MF), ELF-MF exposure with OVX application (ELF-MF+OVX). All rats were subjected to bilateral ovariectomy except those in Cnt and ELF-MF groups. ELF-MF and ELF-MF+OVX groups were exposed to 1.5 mT ELF-MF during 6 months, 4 h a day. After all applications, left condyle of rats were removed to examine histopathologically. Some histopathologic changes were observed, such as irregular appearance in bone marrow cavities in rat condyles of OVX, ELF-MF and ELF-MF+OVX groups. Some disorders in transition from hypertrophic field to ossification layer and irregular appearance in calcification were determined in OVX group. In OVX+ELF-MF and ELF-MF groups, there was significant disruption and latency in calcification and ossification areas. However, no significant differences were found in the thickness of the condylar cartilage layer between groups (P > 0.05). It was suggested that long-term ELF-MF exposure and ELF-MF exposure with ovariectomy application can affect the histologic structure of rats' condyle.Consequently, it was concluded that long-term ELF-MF exposure and ovariectomy application can induce histopathological changes in the structure of the condyle and ELF-MF exposure cannot alter ovariectomy-induced changes.

Dose-dependent effects of genistein on bone homeostasis in rats' mandibular subchondral bone

To investigate the effect of genistein on bone homeostasis in mandibular subchondral bone of rats. Female SD rats were administered with genistein (10 and 50 mg/kg) or placebo by oral gavage for 6 weeks. Then the animals were sacrificed, and histomorphology and micro-structure of mandibular condyle were examined using HE staining and micro-CT analysis, respectively. The expression levels of alkaline phosphatase (ALP), osteocalcin (OC), osteoprotegerin (OPG), the receptor activator of nuclear factor κB ligand (RANKL) and estrogen receptors (ERs) in mandibular condyle were detected using real-time PCR. Cultured osteoblasts were prepared from rat mandibular condyle for in in vitro study. The cells were treated with genistein (10(-7) or 10(-4) mol/L) for 48 h. The expression of the bone homeostasis-associated factors and estrogen receptors (ERs) was detected using real-time PCR, and ER silencing was performed. At both the low- and high-doses, genistein significantly increased the bone mineral density (BMD) and bone volume, and resulted in thicker subchondral trabecular bone in vivo. In both in vivo and in vitro study, the low-dose genistein significantly increased the expression of ALP, OC and OPG, but decreased the expression of RANKL and the RANKL/OPG ratio. The high-dose genistein decreased the expression of all these bone homeostasis-associated factors. Both the low and high doses of genistein significantly increased the expression of ERβ, while ERα expression was increased by the low dose genistein and decreased by the high dose genistein. ERβ silencing abrogated most of the effects of genistein treatment. In rat mandibular condylar subchondral bone, low-dose genistein increases bone formation and inhibit bone resorption, while excess genistein inhibits both bone formation and resorption. The effects of genistein were predominantly mediated through ERβ.