Local injection of abaloparatide promotes mandibular condyle lengthening in adolescent rats via enhancing chondrogenesis and ossification.

BACKGROUND: Mandibular condylar hypoplasia negatively affects patient's facial appearance and dentofacial function. OBJECTIVE: To investigate the effect of local injection of the drug abaloparatide (ABL), an analogue of parathyroid hormone related protein (PTHrP), on promoting lengthening of the mandibular condyle. METHODS: Thirty adolescent male Sprague-Dawley rats were randomly divided into two groups, which received the injection of ABL or normal saline (the control) every 3 days in the temporomandibular joint (TMJ) cavity. Cone-beam computed tomography and immunohistochemistry assays were performed at 2, 4 and 6 weeks since the injection. Mandibular condylar chondrocytes (MCC) and pre-osteoblasts were treated with ABL or PBS, followed by the CCK-8 detection, IC50, real-time PCR assay, Western Blot and immunofluorescence staining. RESULTS: In vivo, compared with the control, the ABL group significantly increased the mandibular condylar process length (by 1.34 ± 0.59 mm at 6 weeks), the thickness of the cartilage layer, and enhanced the matrix synthesis. The ABL group had significant up-regulation of SOX 9, COL II, PTHrP and PTH1R, down-regulation of COL X in the cartilage, up-regulation of RUNX 2, and unchanged osteoclastogenesis in the subchondral bone. In vitro, the intra-TMJ injection of ABL promoted the MCC proliferation, with up-regulated expression of chondrogenic genes, and enhanced osteogenic differentiation of the pre-osteoblasts. CONCLUSIONS: Intra-TMJ injection of abaloparatide promotes mandibular condyle lengthening in the adolescent rats via enhancing chondrogenesis in the mandibular condylar cartilage and ossification in the subchondral bone.

Mechanical stress can regulate temporomandibular joint cavitation via signalling pathways.

The temporomandibular joint (TMJ), composed of temporal fossa, mandibular condyle and a fibrocartilage disc with upper and lower cavities, is the biggest synovial joint and biomechanical hinge of the craniomaxillofacial musculoskeletal system. The initial events that give rise to TMJ cavities across diverse species are not fully understood. Most studies focus on the pivotal role of molecules such as Indian hedgehog (Ihh) and hyaluronic acid (HA) in TMJ cavitation. Although biologists have observed that mechanical stress plays an irreplaceable role in the development of biological tissues and organs, few studies have been concerned with how mechanical stress regulates TMJ cavitation. Based on the evidence from human or other animal embryos today, it is implicated that mechanical stress plays an essential role in TMJ cavitation. In this review, we discuss the relationship between mechanical stress and TMJ cavitation from evo-devo perspectives and review the clinical features and potential pathogenesis of TMJ dysplasia.

Clock gene Per1 regulates rat temporomandibular osteoarthritis through NF-κB pathway: an in vitro and in vivo study.

PURPOSE: Temporomandibular joint osteoarthritis (TMJOA) is a common disease that negatively affects the life quality of human beings. Circadian rhythm acts an important role in life activities. However, whether the clock genes are rhythmic expressed in mandibular condylar chondrocytes, or the clock genes have an effect on the progression of TMJOA remains unknown. In this study, we aim to explore expression of clock genes and regulatory mechanism of TMJOA in rat mandibular condylar chondrocytes. METHODS: After synchronized by dexamethasone, the expression of core clock genes Per1, Per2, Clock, Cry1, Cry2 and Bmal1 and cartilage matrix degrading factor gene Mmp13 were analyzed in mandibular condylar chondrocytes every 4 h with RT-qPCR. The mandibular condylar chondrocytes were stimulated with IL-1ß, and expression of Per1, Mmp13, P65 and p-P65 was assessed by RT-qPCR and Western blot. Sh-Per1 lentivirus was used to assess the effect of clock gene Per1 in IL-1ß-induced chondrocytes, and expression of Mmp13, P65 and p-P65 was measured. After establishing a rat TMJOA model using unilateral anterior crossbite (UAC), micro-CT, H & E, Alcian Blue & Nuclear Fast Red and Safranin O & Fast Green, cartilage thickness was utilized to assess the damage of cartilage and subchondral bone. Immunohistochemistry of PER1, MMP13 and P65 was performed in condylar sections. RESULTS: All core clock genes and Mmp13 were rhythmically expressed. And Mmp13 expression curve was closed in phase and amplitude with Per1. After stimulation with IL-1ß, the expression of MMP13, PER1 and P65 and ratio of p-P65/P65 increased in condylar chondrocytes. After Per1 was down-regulated in condylar chondrocytes, the expression of MMP13 and P65 and ratio of p-P65/P65 decreased. Compared with the condyles of Sham group, the bony parameters of UAC group were significantly worse. The thickness of cartilage in UAC group significantly reduced. The modified Mankin scores and the expression of PER1, MMP13 and P65 in cartilage of UAC group significantly increased compared with Sham group. CONCLUSION: Core clock genes and Mmp13 are rhythmic expressed in rat mandibular condylar chondrocytes. PER1 can regulate the expression of MMP13 through NF-κB pathway in IL-1ß-induced mandibular condylar chondrocytes.

Mechanical loading and autophagy: A study on the BoNT-A injection-induced condylar cartilage degeneration.

Botulinum toxin A (BoNT-A) has emerged as a treatment option for temporomandibular disorder (TMD). By injecting BoNT-A into the masseter muscle, it is possible to reduce mechanical loading on the temporomandibular joint (TMJ). However, numerous prior studies have indicated excessive reduction in mechanical loading can have detrimental effects on TMJ cartilage. This study proposes that autophagy, a process influenced by mechanical loading, could play a role in BoNT-A-induced mandibular condyle cartilage degeneration. To explore this hypothesis, we employed both BoNT-A injection and an excessive biting model to induce variations in mechanical loading on the condyle cartilage of C57BL/6 mice, thereby simulating an increase and decrease in mechanical loading, respectively. Results showed a significant reduction in cartilage thickness and downregulation of Runt-related transcription factor 2 (Runx2) expression in chondrocytes following BoNT-A injection. In vitro experiments demonstrated that the reduction of Runx2 expression in chondrocytes is associated with autophagy, possibly dependent on decreased YAP expression induced by low mechanical loading. This study reveals the potential involvement of the YAP/LC3/Runx2 signaling pathway in BoNT-A mediated mandibular condylar cartilage degeneration.

Age-Related Gene and Protein Expression in Mouse Mandibular Condyle Analyzed by Cap Analysis of Gene Expression and Immunohistochemistry.

INTRODUCTION: Aging, an inevitable physiological process, leads to morphological and histological degenerative changes in the mandibular condylar cartilage (MCC); however, the molecular mechanism has not yet been elucidated, and little information is available on age-related factors. Therefore, this study was designed to identify age-related factors by investigating the age-related differentially expressed genes (DEGs) and localization of their translated protein expression in the mandibular condyle. METHODS: Mandibular condyles were collected from 10- and 50-week-old mice. Total RNA was extracted from the samples and then analyzed using cap analysis of gene expression (CAGE) to identify age-related DEGs. Gene ontology (GO) enrichment analysis was performed to determine which biological processes were most affected by aging in terms of gene expression using Metascape. The mandibular condyle samples were processed for histology to investigate morphological changes caused by aging and for immunohistochemistry to localize the protein expression encoded by age-related genes identified with CAGE. Semi-quantitative immunohistochemistry was performed to assess age-related extracellular matrix (ECM) protein levels in the MCC. The histological sections were also used for Alcian blue histochemistry to detect glycosaminoglycans (GAGs). RESULTS: GO enrichment analysis revealed that the genes related to "extracellular matrix organization," including Acan, Col1a1, Col1a2, Col2a1, Mmp3, Mmp9, and Mmp13, were most differentially expressed in the aged mandibular condyle. Among these seven genes, Mmp3 was upregulated, and the others were downregulated with aging. Histological examination showed the age-related morphological and histological changes in the MCC. Immunohistochemical investigation showed the localization of matrix metalloproteinases (MMPs)-3, -9, and -13 and their substrate proteins, aggrecan, type I collagen, and type II collagen, in the mandibular condyle at 10 and 50 weeks, indicating different localizations between the young and the aged. In the aged MCC, semi-quantitative immunohistochemistry showed a significant decrease in the aggrecan protein level, and Alcian blue histochemistry showed a decrease in GAGs. CONCLUSION: MMP-3, MMP-9, and MMP-13 contribute to the remodeling of the ECM of the MCC and subchondral bone during aging by degrading ECM proteins at specific times and sites under the regulation of their production and secretion.

Spatial and Temporal Expression of Ectodysplasin-A Signaling Pathway Members During Mandibular Condylar Development in Postnatal Mice.

A growing body of evidence emerging supported that ectodysplasin-A (EDA) signaling pathway contributed to craniofacial development. However, their expression in condyle has not been elucidated yet. This study investigated the expression patterns of EDA, EDA receptor (EDAR), and EDAR-associated death domain (EDARADD) in condyle of postnatal mice. Histological staining and micro-computed tomography (CT) scanning showed that as endochondral ossification proceeded, the thickness of chondrocyte layer decreased, and the volume of mandibular condyle increased. Osteoclasts remained active throughout the condylar development. Immunohistochemistry staining demonstrated that EDA was expressed in almost all layers during the first 2 weeks after birth. EDA shifted from the mature and hypertrophic layers to fibrous and proliferating layers at postnatal 3 weeks. As condyle matured, the distribution of EDA tended to be limited to hypertrophic layer. The distribution patterns of EDAR and EDARADD were consistent with EDA, while the level of EDAR expression was slightly lower. mRNA expression levels of EDA signaling pathway-related components increased after birth. Furthermore, we evaluated the expression of EDA using ATDC5 in vitro. EDA increased during the late stage of chondrogenesis. These findings proved that EDA signaling pathway was involved in condylar development and acted as a regulatory factor in condylar maturation and differentiation.

Spatial Heterogeneity Directs Energy Dissipation in Condylar Fibrocartilage.

Condylar fibrocartilage with structural and compositional heterogeneity can efficiently orchestrate load-bearing and energy dissipation, making the temporomandibular joint (TMJ) survive high occlusion loads for a prolonged lifetime. How the thin condylar fibrocartilage can achieve efficient energy dissipation to cushion enormous stresses remains an open question in biology and tissue engineering. Here, three distinct zones in the condylar fibrocartilage are identified by analyzing the components and structure from the macro-and microscale to the nanoscale. Specific proteins are highly expressed in each zone related to its mechanics. The heterogeneity of condylar fibrocartilage can direct energy dissipation through the nano-micron-macro gradient spatial scale, by atomic force microscope (AFM), nanoindentation, dynamic mechanical analyzer assay (DMA), and the corresponding energy dissipation mechanisms are exclusive for each distinct zone. This study reveals the significance of the heterogeneity of condylar fibrocartilage in mechanical behavior and provides new insights into the research methods for cartilage biomechanics and the design of energy-dissipative materials.

Immunohistochemical characterization of the mandibular condyle for type I and II collagen, aggrecan, MMP-9, and MMP-13 in MMP-2-deficient mice.

Mice devoid of matrix metalloproteinase (MMP)-2 due to gene targeting have been reported to show articular cartilage destruction in the knee joint; however, the phenotype of the mandibular condylar cartilage remains unknown. Thus, in the present study, we investigated the mandibular condyle in Mmp2-/- mice. We obtained and bred Mmp2-/- mice from the same source as the previous study, and performed genotyping using genomic DNA extracted from finger snips. The mandibular condyle of Mmp2-/- mice and wild-type (WT) mice was immunohistochemically examined for the localization of extracellular matrix (ECM) proteins (type I and II collagen, and aggrecan), and MMP-9 and MMP-13. No cartilage destruction was observed in the mandibular condyle of Mmp2-/- mice, and no difference was found in the localization of the ECM proteins between the Mmp2-/- mice and WT mice. However, the bone marrow cavity in the subchondral bone of the mandibular condyle was more distinct in Mmp2-/- mice than in WT mice at the age of 50 weeks. Of note, MMP-9 characteristically localized in multinucleated cells in the mandibular condyle in 50-week-old Mmp2-/- mice. MMP-2 may be involved in the regulation of osteoclast differentiation and the formation of the bone marrow cavity in aged mice.

Bulk RNA-seq analyses of mandibular condylar cartilage in a post-traumatic TMJ osteoarthritis rabbit model.

OBJECTIVE: The temporomandibular joint (TMJ) is anatomically comprised of the mandibular condylar cartilage (CC) lined with fibrocartilaginous superficial zone and is crucial for eating and dental occlusion. TMJ osteoarthritis (OA) leads to pain, joint dysfunction and permanent loss of cartilage tissue. However, there are no drugs clinically available that ameliorate OA and little is known about global profiles of genes that contribute to TMJ OA. Furthermore, animal models that recapitulate the complexity of signalling pathways contributing to OA pathogenesis are crucial for designing novel biologics that thwart OA progression. We have previously developed a New Zealand white rabbit TMJ injury model that demonstrates CC degeneration. Here, we performed genome-wide profiling to identify new signalling pathways critical for cellular functions during OA pathology. MATERIALS AND METHODS: Temporomandibular joint OA was surgically induced in New Zealand white rabbits. Three months following injury, we performed global gene expression profiling of the TMJ condyle. RNA samples from TMJ condyles were subjected to sequencing. After raw RNA-seq data were mapped to relevant genomes, differential expression was analysed with DESeq2. Gene ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis were conducted. RESULTS/CONCLUSIONS: Our study revealed multiple pathways altered during TMJ OA induction including the Wnt, Notch and PI3K-Akt signalling pathways. We demonstrate an animal model that recapitulates the complexity of the cues and signals underlying TMJ OA pathogenesis, which is essential for developing and testing novel pharmacologic agents to treat OA.

280 mT static magnetic field promotes the growth of postpartum condylar cartilage.

PURPOSE: Functional appliances made of permanent magnets have been used in jaw orthopedic treatment. However, whether the static magnetic field (SMF) generated by permanent magnets promotes the developmental sequence of condylar cartilage and thus promotes the growth of the mandible remains to be studied. The aim of this study was to investigate the effects of 280 mT SMF on postnatal condylar chondrogenesis and endochondral ossification and the roles of FLRT3, FGF2 and BMP2 signaling in this chondrodevelopmental sequences. METHODS: Forty-eight rats were assigned to two groups (control and SMF). The condyles were collected at the specified time points. The histomorphological changes in the condyle were observed by histological staining. The expression of proteins related to the proliferation and differentiation of the condylar cartilage and the changes in subchondral bone microstructure were analyzed by immunohistochemical staining and micro-CT scanning. FLRT3, FGF2, and BMP2 expression was detected by immunofluorescence staining. RESULTS: Under SMF stimulation, the cartilage of young rats grew longitudinally and laterally, and the thickness of the cartilage became thinner as it grew. The SMF promoted the proliferation and differentiation of condylar chondrocytes and endochondral ossification and increased subchondral bone mineral density, and BMP2 signaling was involved. Moreover, under SMF loading, the increased expression of FGF2 and FLRT3 were involved in regulating cartilage morphogenesis and growth. In late development, the decreased expression of FGF2/FLRT3 and the increased expression of BMP2 promoted endochondral ossification. The SMF accelerated this opposite expression trend. CONCLUSION: FGF2/FLRT3 and BMP2 signals are involved in the regulatory effect of SMF exposure on chondrogenesis and endochondral ossification, which provides a theoretical basis for the clinical use of magnetic appliances to promote condylar growth.

Longitudinal effects of estrogen on mandibular growth and changes in cartilage during the growth period in rats.

Estrogen is a steroid hormone that induces skeletal growth and affects endochondral ossification of the long tubular bone growth plate during the growth period. However, the effects of estrogen on endochondral ossification of the mandibular condylar cartilage are unclear. In this study, ovariectomized Wistar/ST rats were used to investigate the longitudinal effects of estrogen on mandibular growth. The rats were administered different doses of estrogen. Longitudinal micro-computed tomographic scanning, histological staining and ELISA on plasma growth hormone were performed to examine the effects of estrogen on mandibular growth. The results showed that mandibular growth was suppressed throughout the growth period by estrogen in a dose-dependent manner. In addition, long-term administration of a high dose of estrogen to the rats resulted in significant increase in growth hormone throughout the growth period, significant circularization of cell nuclei in the proliferative layer, intensely staining cartilage matrix in the subchondral bone, and significant suppression of estrogen receptor (ER) alpha and beta expression in the mandibular cartilage. However, regardless of estrogen concentration, in the posterior part of the mandibular cartilage, ER expression extended to both the hypertrophic and proliferative layers. These results indicate that estrogen suppresses mandibular growth throughout the growth period. Additionally, it influences endochondral ossification via its effect on ERs.

[Effect of chronic sleep deprivation on condylar cartilage in rats].

PURPOSE: The aim of this study was to investigate the morphological changes of condylar cartilage of temporomandibular joint (TMJ) and the expression changes of IL-1ß,TNF-α,IGF-1 and VEGF in condylar cartilage of TMJ by establishing a chronic sleep deprivation model in rats. METHODS: Sixty rats were randomly divided into experimental group, control group and recovery group. Modified multiple platforms method (MMPM) was used to build chronic sleep deprivation models in experimental and recovery groups. Rats in the recovery group received 1 week of cage feeding after sleep deprivation. H-E staining was used to observe morphological change of the condyle. Immunohistochemical method was performed to detect the changes of IL-1ß, TNF-α, IGF-1 and VEGF. The data was processed by using SPSS 23.0 software package. RESULTS: MMPM can establish chronic sleep deprivation model effectively. H-E staining showed condylar cartilage of the experimental group was split stripped, and the boundaries of cartilage cell layer became blurred. Compared with the control group, the recovery group had less cracks in the fibrous layer or some of the cracks were occupied by fibrous tissue. Immunohistochemistry showed that the positive expression intensity of IL-1ß and TNF-α in the experimental group was significantly higher than in the control group (P＜0.05), the positive expression intensity in the recovery group was significantly lower than in the experimental group(P＜0.05). The positive expression intensity of IGF-1 and VEGF in the experimental group was significantly higher than in the control group(P＜0.05). The expression of IGF-1 and VEGF decreased significantly in the recovery group which received sleep deprivation no more than 3 weeks(P＜0.05). CONCLUSIONS: Chronic sleep deprivation can increase the expression of IL-1ß, TNF-α and VEGF in condylar cartilage and aggravate osteoarthritis. Chronic sleep deprivation can lead to increase of IGF-1 in condylar cartilage tissue, which plays a crucial role in protecting and promoting the reconstruction of condylar cartilage. After chronic sleep deprivation, the expressions of IL-1ß, TNF-α, IGF-1 and VEGF in the condylar cartilage of rats were decreased after 1 week of recovery, and the condylar cartilage underwent restorative reconstruction.

Modificación de la actividad metabólica por medio de un dispositivo intraoral en pacientes con hiperplasia condilar confirmada por SPECT / Metabolic activity modification by means of an intraoral device in patients with condylar hyperplasia confirmed by SPECT

Objetivo: Evaluar los efectos de la aplicación de un dispositivo intraoral de uso permanente en el comportamien- to de los cóndilos con hiperplasia condilar (HC) confirmada por tomografía computarizada de emisión por fotón único (SPECT), estableciendo una comparación con un grupo de pacientes con HC que no utilizó el dispositivo. Materiales y métodos: 30 pacientes con una edad promedio de 21,7 años (+/-5,56) con HC confirmada con SPECT fueron asignados al azar a dos grupos: a los del grupo I (n=18) se les colocó un dispositivo intraoral de uso perma- nente para modificar la posición de la mandíbula, mientras que a los del grupo II (n=12) no se les colocó ningún dispo- sitivo. Se realizaron evaluaciones de dolor, del desvío de la línea media, de la apertura máxima y del disconfort al inicio del estudio y a los 2, 4, 6, 10, 12 y 14 meses. A los 19 meses promedio, la actividad osteoblástica (AO) fue reevaluada me- diante SPECT. Resultados: En el grupo I, la AO en los cortes coro- nales y transversales cesó o disminuyó (p<0,001) respecto a la condición inicial, mientras que en el grupo II la AO au- mentó (p<0,001). Los datos fueron analizados utilizando el test de Wilcoxon de rangos signados. Al ajustar un modelo de ANCOVA robusto utilizando el valor inicial como covariable también se observa que el efecto del grupo fue estadística- mente significativo en ambos cortes (p<0,001). Conclusiones: La aplicación de un dispositivo intrao- ral de uso permanente mejora la evolución de la hiperplasia condilar, lo que lo puede convertir en un tratamiento de uti- lidad para el tiempo que se aguarda para realizar una condi- lectomía alta de cuello de cóndilo, o incluso para evitar este procedimiento (AU)

Objective: To evaluate the effects of the application of an intraoral device for permanent use on the behavior of con- dyles with condylar hyperplasia (CH) confirmed by single photon emission computed tomography (SPECT), establish- ing a comparison with a group of patients with CH that did not use the device. Materials and methods: Thirty patients with an aver- age age of 21.7 years (+/-5.56) with CH confirmed by SPECT were randomly divided into two groups: the ones in group I (n=18) received an intraoral device for permanent use to align the mandible, while those in group II (n=12) did not get any device. Pain, midline shift, maximum opening, and discomfort were evaluated at the beginning of the study and at 2, 4, 6, 10, 12, and 14 months. At an average of 19 months, osteoblastic activity (AO) was reassessed by SPECT. Results: In group I, the AO in the coronal and trans- verse sections ceased or decreased (p<0.001) in comparison to the initial condition, while in group II the AO increased (p<0.001). The data was analyzed by the Wilcoxon signed rank test. Adjusting a robust ANCOVA model using the ini-tial value as a covariate made it possible to observe that the effect of the group was statistically significant in both cuts (p<0.001). Conclusions: The application of an intraoral device for permanent use improves the evolution of condylar hyperpla- sia, which can make it a useful treatment until a high condylectomy of the neck of the condyle is performed, or even to avoid this procedure (AU)

Piezo1 and IFT88 synergistically regulate mandibular condylar chondrocyte differentiation under cyclic tensile strain.

OBJECTIVE(S): Mandibular condyle chondrocytes (MCCs) are exposed to various mechanical environments. Primary cilia, as a carrier for ion channels, can sense mechanical signals. Intraflagellar transport protein 88 (IFT88) is crucial for the assembly and function of primary cilia. Piezo1 is a mechanically activated ion channel that mediates mechanical signal transduction. This study aimed to identify the possible synergistic effect between Piezo1 and IFT88 in MCC differentiation during mechanical conduction. MATERIALS AND METHODS: Confocal immunofluorescence staining was used to reveal the Piezo1 localization. Small interfering RNA (siRNA) technology was used to knock down the expression levels of Piezo1 and IFT88. The chondrogenic differentiation ability of MCCs was evaluated by Alcian blue staining, and the early differentiation ability was evaluated by Western blot of SOX9 and COL2A1. RESULTS: Confocal immunofluorescence results showed that Piezo1 localized in the root of primary cilia. Without cyclic tensile strain (CTS) stimuli, Alcian blue staining showed that Piezo1 knockdown had a marginal effect on the chondrogenic differentiation of MCCs, while IFT88 knockdown inhibited the chondrogenic differentiation. The protein levels of SOX9 and COL2A1 decreased significantly with CTS stimuli. However, these protein levels were restored when Piezo1 was knocked down. In addition, IFT88 knockdown decreased the protein level of Piezo1 with or without CTS. CONCLUSION: Piezo1 and IFT88 might play a synergistic role in regulating MCC differentiation under CTS stimuli.

Experimental functional shift-induced osteoarthritis-like changes at the TMJ and altered integrin expression in a rat model.

Mandibular deviation affects the biomechanical environment of the temporomandibular joint (TMJ) and causes thinning of cartilage on the deviated side. We aimed to evaluate, using a rat model, the effect of mandibular functional deviation on the TMJ in relation to the functional roles of integrin ß family members. The effects of experimental functional deviation on the TMJ of 6-week-old Sprague-Dawley female rats, randomly assigned to control (n = 42) and experimental groups (n = 42), were evaluated at 3 days and 1, 2, 4, and 8 weeks by histological staining, immunofluorescence, real-time quantitative polymerase chain reaction, and micro-computed tomography. The results showed that the experimental functional shift changed the shape of condyles, thinned the cartilage, and increased the proportion of the hypertrophic layer on the deviated sides of condyles. In addition, the extracellular matrix of the condyle cartilage exhibited degradation at 1 week and subchondral trabecular bone was lost at 4 and 8 weeks. Osteoarthritis (OA)-like changes occurred in the left and right condyles of rats in the experimental group and were aggravated over time. Integrin ß family expression, especially integrin ß2 , was altered from week 1, possibly related to the OA-like changes. These data may provide insight into the onset of TMJ OA.

Long-term effect of bilateral anterior elevation of occlusion on the temporomandibular joints.

OBJECTIVE: Incisors tubed prosthesis with bilateral anterior elevation (BAE) relation had been reported to stimulate the proliferative response in the mandibular condylar cartilage of mice, thus the prosthetic occlusion elevation had been proposed to treat cartilage degeneration. Currently, we aimed to detect the long-term effect of BAE on temporomandibular joints (TMJs). MATERIALS AND METHODS: Twelve 6-week-old female mice were assigned to age-matched control and BAE groups (n = 6). Micro-CT images and the macro- and micro-morphology of the mandibular condyles were analyzed at 29 weeks. RESULTS: Compared with the age-matched controls, in BAE group, there were loss of subchondral cortical bone and heavy loss of the subchondral trabecular bone at the superior sites of the TMJ condyles, but hyperostosis at the inferior sites as revealed by micro-CT images and histological slices. In BAE group, cartilage thickness and matrix area were increased with upregulated expression of type II, type X collagen, and Ki67, but the expression of cleaved caspase-3 was downregulated (all, p < 0.05). CONCLUSION: In addition to cartilage thickening, long-term BAE induces loss of the subchondral cortical bone and heavy loss of the underneath subchondral trabecular bone, but hyperostosis further underneath. Using BAE as a treatment remains double-edged.

Changes of the condylar cartilage and subchondral bone in the temporomandibular joints of rats under unilateral mastication and expression of Insulin-like Growth Factor-1.

OBJECTIVES: This study aimed to define changes in the rat condylar cartilage and subchondral bone using the unilateral mastication model. MATERIALS AND METHODS: In this study, forty 4-week-old Wistar rats were randomly divided into experimental (n = 20) and control group (n = 20). In the experimental group, unilateral dental splints were placed on the occlusal surface of left maxillary molars. The rats were sacrificed at 1, 2, 3, and 4 weeks after placement of the splint. Micro-CT scanning and histological staining were performed to observe the changes in the mandibular condylar cartilage and subchondral bone. Levels of insulin-like growth factor-1 (IGF-1) were determined via immunohistochemistry to analyse the occurrence of osteogenic changes. RESULTS: Micro-CT scanning findings demonstrated the occurrence of asymmetric growth of condyle in the experimental group. The condylar cartilage and subchondral bone exhibited degradation on the chewing side of the experimental group and showed decreased bone mineral density, thinner cartilage thickness, and increased degree of degeneration and osteoclast activity. Compared with the control group, the expression of IGF-1 was remarkably higher on the non-chewing side. CONCLUSION: Long-term unilateral mastication can lead to the occurrence of degenerative changes in the condylar cartilage and subchondral bone during growth and development. IGF-1 may play a role in promoting the process of osteogenesis.

Implications of zonal architecture on differential gene expression profiling and altered pathway expressions in mandibular condylar cartilage.

Mandibular condylar cartilage (MCC) is a multi-zonal heterogeneous fibrocartilage containing different types of cells, but the factors/mechanisms governing the phenotypic transition across the zones have not been fully understood. The reliability of molecular studies heavily rely on the procurement of pure cell populations from the heterogeneous tissue. We used a combined laser-capture microdissection and microarray analysis approach which allowed identification of differential zone-specific gene expression profiling and altered pathways in the MCC of 5-week-old rats. The bioinformatics analysis demonstrated that the MCC cells clearly exhibited distinguishable phenotypes from the articular chondrocytes. Additionally, a set of genes has been determined as potential markers to identify each MCC zone individually; Crab1 gene showed the highest enrichment while Clec3a was the most downregulated gene at the superficial layer, which consists of fibrous (FZ) and proliferative zones (PZ). Ingenuity Pathway Analysis revealed numerous altered signaling pathways; Leukocyte extravasation signaling pathway was predicted to be activated at all MCC zones, in particular mature and hypertrophic chondrocytes zones (MZ&HZ), when compared with femoral condylar cartilage (FCC). Whereas Superpathway of Cholesterol Biosynthesis showed predicted activation in both FZ and PZ as compared with deep MCC zones and FCC. Determining novel zone-specific differences of large group of potential genes, upstream regulators and pathways in healthy MCC would improve our understanding of molecular mechanisms on regional (zonal) basis, and provide new insights for future therapeutic strategies.

Primary observation of the role of posttranslational modification of dentin sialophosphoprotein (DSPP) on postnatal development of mandibular condyle in mice.

OBJECTIVES: We aimed to observe the posttranslational role of dentin sialophosphoprotein (DSPP) on postnatal development of mandibular condyle in mice. METHODS: To explore the function of full-length DSPP, four groups of mice were employed: (1) wild type (WT) mice; (2)Dspp knockout (Dspp KO) mice; (3) mice expressing the normal DSPP transgene in the Dspp KO background (Dspp KO/normal Tg); (4) mice expressing the uncleavable full-length DSPP in the Dspp KO background (Dspp KO/D452A Tg). Firstly, Plain X-ray Radiography and Micro-computed Tomography were used to observe the condylar morphology changes of Dspp KO/D452A Tg mice in comparison with the other three groups. Then, Hematoxylin & eosin and toluidine blue staining were applied to uncover the histological changes of mandibular condylar cartilage (MCC) of Dspp KO/D452A Tg mice. To explore the function of the NH2-terminal fragments (i.e. DSP/DSP-PG), three groups of mice were employed: (1) WT mice; (2) Dspp KO mice; (3) mice expressing the NH2-terminal fragments of DSPP in the Dspp-null background (Dspp KO/DSP Tg). The former strategies were utilized to examine the differences of condylar morphology and histological structures changes within three groups of mice. RESULTS: Transgenic full-length DSPP partially maintained mandibular condylar morphology and MCC thickness of Dspp KO mice. Transgenic DSP failed to do so, but led to smaller mandibular condyle and disordered cartilage structure. CONCLUSIONS: Our observations provide insight into the role of posttranslational modification of DSPP in the postnatal development of healthy MCC and maintenance of condylar morphology.

Assessment of bone marrow fat fractions in the mandibular condyle head using the iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL-IQ) method.

The prevalence of temporomandibular joint disorder (TMD) is gradually increasing, and magnetic resonance imaging (MRI) is becoming increasingly common as a modality used to diagnose TMD. Edema and osteonecrosis in the bone marrow of the mandibular condyle have been considered to be precursors of osteoarthritis, but these changes are not evaluated accurately and quantitatively on routine MRI. The iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL-IQ) method, as a cutting-edge MRI technique, can separate fat and water using three asymmetric echo times and the three-point Dixon method. The purpose of this study was to analyze the quantitative fat fraction (FF) in the mandibular condyle head using the IDEAL-IQ method. Seventy-nine people who underwent MRI using IDEAL-IQ were investigated and divided into 1) the control group, without TMD symptoms, and 2) the TMD group, with unilateral temporomandibular joint (TMJ) pain. In both groups, the FF of the condyle head in the TMJ was analyzed by two oral and maxillofacial radiologists. In the TMD group, 29 people underwent cone-beam computed tomography (CBCT) and the presence or absence of bony changes in the condylar head was evaluated. The FF measurements of the condyle head using IDEAL-IQ showed excellent inter-observer and intra-observer agreement. The average FF of the TMD group was significantly lower than that of the control group (p < 0.05). In the TMD group, the average FF values of joints with pain and joints with bony changes were significantly lower than those of joints without pain or bony changes, respectively (p < 0.05). The FF using IDEAL-IQ in the TMJ can be helpful for the quantitative diagnosis of TMD.