TMJ Disorders: Future Innovations in Diagnostics and Therapeutics

Stribeck Curve Analysis of Temporomandibular Joint Condylar Cartilage and Disc

Temporomandibular joint (TMJ) diseases such as osteoarthritis and disc displacement have no permanent treatment options, but lubrication therapies, used in other joints, could be an effective alternative. However, the healthy TMJ contains fibrocartilage, not hyaline cartilage as is found in other joints. As such, the effect of lubrication therapies in the TMJ is unknown. Additionally, only a few studies have characterized the friction coefficient of the healthy TMJ. Like other cartilaginous tissues, the TMJ condyles and discs are subject to changes in friction coefficient due to fluid pressurization. In addition, the friction coefficient of the TMJ is affected by the sliding direction and anatomic location. However, these previous findings have not been able to identify how all 3 of these parameters (anatomic location, sliding direction, and fluid pressurization) influence changes in friction coefficient. This study used Stribeck curves to identify differences in the friction coefficients of TMJ condyles and discs based on anatomic location, sliding direction, and amount of fluid pressurization (friction mode). Friction coefficients were measured using a cartilage on glass tribometer. Both TMJ condyle and disc friction coefficients were well described by Stribeck curves. These curves changed based on anatomic location, but very few differences in friction coefficients were observed based on sliding direction. TMJ condyles had similar boundary mode and elastoviscous mode friction coefficients to the TMJ disc, and both were lower than hyaline cartilage in other joints. The observed differences here indicate that the surface characteristics of each anatomic region cause differences in friction coefficients.

Prevalence and correlations of temporomandibular disorders in Northern Jordan using diagnostic criteria axis I

AIM

The aim of the present study was to document the prevalence and possible correlations of temporomandibular disorders (TMD) in a sample of participants from Northern Jordan.

METHODS

A total of 368 adult participants were consecutively selected from visitors to a major health facility in Northern Jordan and examined according to the diagnostic criteria (DC) for TMD (DC/TMD) protocol. Patients with conditions that could interfere with TMD diagnosis were excluded. Pearson correlation and analysis of variance statistical tests were applied. Statistical significance was set at P ≤ 0.05, with a 95% confidence interval.

RESULTS

A total of 98 patients (26.7%) had 1 TMD diagnoses; 60 participants (16.3%) had a pain-related TMD diagnosis, 48 (13%) had intra-articular joint disorders (IAD), and 16 had both pain-related TMD and IAD. In addition, six (1.6%) participants were found to have degenerative joint disease. Females were found to have a higher prevalence of pain-related TMD diagnoses (r = 0.111, P = 0.034) and headache (r = 0.129, P = 0.013) than males. Clicking was positively related to both pain-related TMD (r = 0.154, P = 0.003) and IAD (r = 0.576, P = 0.000).

CONCLUSION

The frequency of TMD and related features was reported in a Northern Jordanian population using DC/TMD for the first time, and the results are comparable to other populations in similar study settings.

Impact of Temporomandibular Disorders and Sleep Bruxism on Oral Health-Related Quality of Life of Individuals With Complete Cleft Lip and Palate

The temporomandibular disorders (TMDs) and sleep bruxism (SB) affect the quality of life (QoL) of the individuals in general. However, the literature lacks studies on individuals with cleft lip and palate (CLP). Thus, this study aimed to evaluate the impact of TMD and SB on the oral health-related quality of life (OHRQoL) of individuals with CLP. Thirty-six individuals, both genders, aged between 30 and 50 years, at routine treatment in the Dental Prosthesis Sector of Hospital for Rehabilitation of Craniofacial Anomalies-University of São Paulo were selected and divided into the following groups: G1-unilateral complete CLP (n = 22) and G2-bilateral complete CLP (n = 14). Three questionnaires were applied: Oral Health Impact Profile (OHIP-14), SB self-report and Research Diagnosis Criteria for TMD. Fisher test, Mann-Whitney test, and t test were applied to verify values between TMD, SB, gender, and OHIP-14 (P < 0.05). The mean OHIP-14 score was of 5.80, and females had higher (8.58) OHRQoL than males (3.31). There was association with gender and OHRQoL (t test, P = 0.006), TMD with OHRQoL (Mann-Whitney test, P = 0.036), and TMD and SB (Fisher test, P = 0.006). Temporomandibular disorder was diagnosed in 30% of the individuals. Of these, 16.66% did not present SB, while 13.88% presented it. The association TMD versus SB showed statistically significant differences and 83.33% of the individuals reporting SB also had TMD. Based on this study, the authors can conclude that: TMD impacts OHRQoL in CLP patients, females are more affected in their OHRQoL than males, SB was strongly associated with TMD.

Correlation of Condylar Translation During Maximal Mouth Opening with Presence of Signs of Temporomandibular Joint Disorders in an Asymptomatic Population of 18-25 Years Age Group of Northern India

Objective(s):

The objective of this study was to determine the frequency of “subluxation” and presence of clinical signs of Temporomandibular Joint Disorder (TMD) in asymptomatic individuals and its distribution according to age and sex.

Materials and Methods:

The material investigated comprised of 200 asymptomatic subjects with 400 joints. The subjects were divided into two groups of 18-25 years and 50-60 years of age consisting of equal number of males and females. Clinical examination involved measurement of maximal inter-incisal distance, joint sounds and deviation. For radiological examination, Temporomandibular Joint (TMJ) open mouth close mouth view option (TMJ1/2) was used on a Digital Panoramic Machine. All the radiographs were traced to assess subluxation and anterior translation of the condyle. The statistical analysis was carried out using Statistical Package for Social Sciences (SPSS Inc., Chicago, IL, version 15.0 for Windows).

Results:

The prevalence of the signs of TMDs in the asymptomatic population was found to be very high and more predominant in females as compared to males. Furthermore, the older age group had comparatively less signs of TMDs. It was of interest that the subjects presenting with clinical signs of TMD were significantly less as compared to the subjects presenting with subluxation. The value of anterior translation was found to be more in females in the younger age group as compared to the males. Similarly, it was more in males as compared to females in older age group. But the mean anterior translation difference in females in 18-25 years and 50-60 years showed a statistically significant difference with P-value 0.017.

Conclusion:

Subluxation is a very common feature found in almost all the subjects in this study with a high prevalence. Hence, we may assume that the increased incidence of TMDs could be a direct result of the phenomena of subluxation. The decrease in mandibular length could be the cause of decreased mouth opening and increased subluxation.

Functional anatomy of the equine temporomandibular joint: Histological characteristics of the articular surfaces and underlining tissues

It has been assumed that dental conditions cause disorders of the equine temporomandibular joint (TMJ), due to biomechanical overload or aberrant loading. However, the incidence of published TMJ disorders in horses is low and this leads to the question whether the equine TMJ is adapted well to its biomechanical requirements or is able to remodel its articular surfaces in response to modified loading conditions. The aim of this study was to determine the histological characteristics of healthy equine TMJs. The tissue components of the articular surfaces of 10 TMJs obtained from horses without any clinical history of dental or TMJ disorders were analysed. Apart from the mandibular fossa of the temporal bone, the osseous aspects of the TMJ exhibited a uniform zoning pattern. The articular surfaces were composed of three tissue layers: (1) a superficial cell-rich dense connective tissue layer; (2) a middle fibrocartilage layer; and (3) a deep hyaline-like cartilage layer. The articular disc was composed of an inner core of fibrocartilage and hyaline-like cartilage meshwork covered with both cell-rich dense connective tissue and fibrocartilage at its dorsal and ventral aspects. In contrast, the mandibular fossa was only covered by a dense connective tissue, frequently supplemented by a synovial membrane, suggesting low biomechanical stress. Glycosaminoglycans, which are indicative of compressive loads, were predominantly present within the rostral part of the articular tubercle and the retroarticular process, the dorsal part of articular disc and the entire mandibular head, but were absent within the mandibular fossa. The results of this study suggest the presence of different biomechanical demands in the dorsal and ventral compartment of the equine TMJ.

Effect of a functional variant of tumor necrosis factor-β gene in temporomandibular disorders: A pilot study

BACKGROUND

Temporomandibular disorders (TMD) are a group of conditions that cause chronic orofacial pain. The tumor necrosis factor β (TNF-β) is a proinflammatory cytokine that is involved in the various aspects of the inflammatory process including organization and maintenance, and in the arrangement of cells at the inflammation site. The purpose of this study was to evaluate the correlation between TNF-β +252A/G (rs909253) variant and susceptibility to TMD in a Turkish cohort.

METHODS

The study included 104 patients (26 males, 78 females) with TMD and 126 healthy controls (44 males, 82 females). The TNF-β +252A/G variant analysis was based on Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP).

RESULTS

There was no deviation from HWA for TNF-β +252A/G variant in patient and control groups. There was significant difference in genotype and allele frequencies between patient group and control group in terms of TNF-β +252A/G variant, respectively (P = 0.010, 0.015). A significant increase in the TNF-β +252 AG genotype and G allele frequencies were observed in TMD patients compared to healthy controls. The individuals with GG genotype and G allele had an increased risk of developing TMD. A statistically significant association was observed when the patients were compared with the controls according to AA genotype vs AG+GG genotypes (P = 0.002, OR: 2.23, 95% CI:1.31-3.82). TNF-β +252A/G genotype distribution was associated with chewing problems (P = 0.046).

CONCLUSIONS

In conclusion, our results provided evidence that TNF-β +252A/G variant may contribute to TMD development in a Turkish cohort. Further studies are needed to confirm this observation.

Estrogen Promotes Mandibular Condylar Fibrocartilage Chondrogenesis and Inhibits Degeneration via Estrogen Receptor Alpha in Female Mice

Temporomandibular joint degenerative disease (TMJ-DD) is a chronic form of TMJ disorder that specifically afflicts people over the age of 40 and targets women at a higher rate than men. Prevalence of TMJ-DD in this population suggests that estrogen loss plays a role in the disease pathogenesis. Thus, the goal of the present study was to determine the role of estrogen on chondrogenesis and homeostasis via estrogen receptor alpha (ERα) during growth and maturity of the joint. Young and mature WT and ERαKO female mice were subjected to ovariectomy procedures and then given placebo or estradiol treatment. The effect of estrogen via ERα on fibrocartilage morphology, matrix production, and protease activity was assessed. In the young mice, estrogen via ERα promoted mandibular condylar fibrocartilage chondrogenesis partly by inhibiting the canonical Wnt signaling pathway through upregulation of sclerostin (Sost). In the mature mice, protease activity was partly inhibited with estrogen treatment via the upregulation and activity of protease inhibitor 15 (Pi15) and alpha-2-macroglobulin (A2m). The results from this work provide a mechanistic understanding of estradiol on TMJ growth and homeostasis and can be utilized for development of therapeutic targets to promote regeneration and inhibit degeneration of the mandibular condylar fibrocartilage.

Temporomandibular Joint Disorders in Older Adults

OBJECTIVES

To review the literature and summarize the evidence of temporomandibualar joint (TMJ) disorders (TMDs) in older adults, focusing on clinical manifestations of TMDs in older adults, highlighting the incidence and sexual dimorphism of TMJ degeneration and the role of sex hormones in this process, and providing potential treatment options for TMD in older adults.

DESIGN

Two review authors performed the literature search, study inclusion, and data extraction. PubMed, Embase, and Google scholar were searched for literature until August 2017 (Figure ). We adopted a combination of Medical Subject Headings with related free text words for the search in PubMed and optimized the search in other search engines.

RESULTS

Traditionally, it was believed that TMDs predominantly affected women of childbearing age, but recent large studies in Europe and the United States have shown that the prevalence of TMD peaks after childbearing age (45-64) and then gradually decreases with age, although not much is known about the disease in older adults.

CONCLUSION

Most older adults have TMJ degeneration, which affects women more than men. In most older adults, the symptoms of TMD are mild and self-limiting and can usually be treated with self management.

Comparative Histomorphometric Evaluation of Healthy and Ankylosed Mandibular Condylar Process

Background

Temporomandibular joint (TMJ) ankylosis is one of the most disruptive maladies afflicting the masticatory system. The characteristic feature is the formation of bony mass bridging condyle with glenoid fossa. The exact pathogenesis is, however, not completely understood.

Purpose

To investigate and compare histomorphometric features of ankylosed condylar specimen with normal condylar process.

Materials and Methods

Group I included 17 post-traumatic unilateral TMJ ankylosis patients managed by excision of ankylosed mass and interpositional arthroplasty. Group II included 13 condylar head fracture patients managed by surgical debridement. The bony specimens of both the groups were subjected to histomorphometric examination for assessment of percentage of bone in trabeculae area (%BONE), osteocyte cell density (OSTCD), the presence of inflammation and fibrosis.

Results

The mean %BONE, OSTCD, %inflammation, %fibrosis was 60.4%, 340.9 mm², 52.9 and 58.8% in group I and 29.6%, 202.6 mm², 31 and 0% in group II.  %BONE, OSTCD and fibrosis in cases of TMJ ankylosis were significantly higher than the controls while no significant difference was observed in the presence of inflammation.

Conclusion

The persistence of joint inflammation following condylar head fracture causes aggressive reparative process leading to ankylosis.

Roles of Ihh signaling in chondroprogenitor function in postnatal condylar cartilage

Condylar articular cartilage in mouse temporomandibular joint develops from progenitor cells near the articulating surface that proliferate, undergo chondrogenesis and mature into hypertrophic chondrocytes. However, it remains unclear how these processes are regulated, particularly postnatally. Here we focused on the apical polymorphic layer rich in progenitors and asked whether the phenotype and fate of the cells require signaling by Indian hedgehog (Ihh) previously studied in developing long bones. In condyles in newborn mice, the apical polymorphic/progenitor cell layer was ~10 cell layer-thick and expressed the articular matrix marker Tenascin-C (Tn-C), and the underlying thick cell layer expressed Tn-C as well as the chondrogenic master regulator Sox9. By 1 month, condylar cartilage had gained its full width, but became thinner along its main longitudinal axis and displayed hypertrophic chondrocytes. By 3 months, articular cartilage consisted of a 2-3 cell layer-thick zone of superficial cells and chondroprogenitors expressing both Tn-C and Sox9 and a bottom zone of chondrocytes displaying vertical matrix septa. EdU cell tracing in juvenile mice revealed that conversion of chondroprogenitors into chondrocytes and hypertrophic chondrocytes required about 48 and 72 h, respectively. Notably, EdU injection in 3 month-old mice labeled both progenitors and maturing chondrocytes by 96 h. Conditional ablation of Ihh in juvenile/early adult mice compromised chondroprogenitor organization and function and led to reduced chondroprogenitor and chondrocyte proliferation. The phenotype of mutant condyles worsened over time as indicated by apoptotic chondrocyte incidence, ectopic chondrocyte hypertrophy, chondrocyte column derangement and subchondral bone deterioration. In micromass cultures of condylar apical cells, hedgehog (Hh) treatment stimulated chondrogenesis and alkaline phosphatase (APase) activity, while treatment with HhAntag inhibited both. Our findings indicate that the chondroprogenitor layer is continuously engaged in condylar growth postnatally and its organization and functioning depend on hedgehog signaling.

Temporomandibular Joint Septic Arthritis

Infection of the temporomandibular joint (TMJ) is a rare pediatric condition resulting from the introduction of pathogens into the joint by hematogenous seeding, local extension, or trauma. Early recognition of the typical signs and symptoms including fever, trismus, preauricular swelling, and TMJ region tenderness are critical in order to initiate further evaluation and prevent feared complications of fibrosis, ankylosis, abnormal facial structure, or persistence of symptoms. Contrast-enhanced computed tomography with ancillary laboratory analysis including erythrocyte sedimentation rate, C-reactive protein, and white blood cell count are beneficial in confirming the suspected diagnosis and monitoring response to therapy. Initial intervention should include empiric parenteral antibiotics, early mandibular mobilization, and joint decompression to provide synovial fluid for analysis including cultures. This report describes a case of TMJ bacterial arthritis in a healthy 6-year-old male who was promptly treated nonsurgically with intravenous antibiotics and localized needle joint decompression with return to normal function after completion of oral antibiotics and physical therapy.

Antinociceptive, anti-inflammatory and toxicological evaluation of semi-synthetic molecules obtained from a benzyl-isothiocyanate isolated from Moringa oleifera Lam. in a temporomandibular joint inflammatory hypernociception model in rats

Inflammation is a key component of many clinical conditions that affect the temporomandibular joint (TMJ) and Moringa oleifera Lam. has been used to treat inflammatory diseases. Here, we evaluated the toxicological effects on mice of a naturally-occurring isothiocyanate from M. oleifera and its seven analogue molecules. Further, the anti-nociceptive and anti-inflammatory effects on a rat model of TMJ inflammatory hypernociception were assessed. The systemic toxicological profile was determined in mice over a 14-day period: MC-1 1 μg/kg; MC-D1 1 μg/kg, MC-D3 100 μg/kg, MC-D6 1 μg/kg, MC-D7 1 μg/kg, MC-D8 1 μg/kg, MC-D9 10 μg/kg, and MC-H 1 μg/kg. The safest molecules were assayed for anti-nociceptive efficacy in the formalin (1.5%, 50 μL) and serotonin (255 mg) induced TMJ inflammatory hypernociception tests. The anti-inflammatory effect was evaluated through the vascular permeability assay using Evans blue. Further, the rota-rod test evaluated any motor impairment. Among the tested molecules, MC-D7, MC-D9, and MC-H were not toxic at the survival rate test, biochemical, and hystological analysis. They reduced the formalin-induced TMJ inflammatory hypernociception, but only MC-H decreased the serotonin-induced TMJ inflammation, suggesting an adrenergic receptor-dependent effect. They diminished the plasmatic extravasation, showing anti-inflammatory activity. At the rota-rod test, no difference was observed in comparison with control groups, reinforcing the hypothesis of anti-nociceptive effetc without motor impairment in animals. The analogues MC-D7, MC-D9, and MC-H were safe at the tested doses and efficient in reducing the formalin-induced TMJ hypernociception in rats. Our next steps include determining their mechanisms of anti-nociceptive action.

The secreted protein WNT5A regulates condylar chondrocyte proliferation, hypertrophy and migration

OBJECTIVE

Our previous study showed that WNT5A, a member of the noncanonical WNT pathway, is involved in interleukin-1beta induced matrix metalloproteinase expression in temporomandibular joint (TMJ) condylar chondrocytes. The purpose of this study is to further explore the roles of WNT5A in cartilage biology of the TMJ.

METHODS

An early TMJ osteoarthritis-like rat model was constructed by a mechanical method (steady mouth-opening). The gene and protein levels of WNT5A during the condylar cartilage changes were measured. Effects of WNT5A on chondrocyte proliferation, hypertrophy and migration were analyzed after WNT5A gain or loss of function in vitro. A c-Jun N-terminal kinase (JNK) inhibitor SP600125 was used to evaluate the involvement of JNK pathway in these effects of WNT5A. The expression and transcription activity of cell cycle regulators c-MYC and Cyclin D1 were examined to determine the mechanism behind WNT5A regulation of chondrocyte proliferation.

RESULTS

WNT5A was significantly upregulated in the condylar cartilage of rats in the early TMJ osteoarthritis-like model. Activating WNT5A facilitated condylar chondrocyte proliferation, hypertrophy and migration. Conversely, inhibiting WNT5A activity in chondrocytes decreased their proliferation, hypertrophy and migration. Blockage of the JNK pathway by its inhibitor, SP600125, impaired these effects of WNT5A on chondrocytes. WNT5A regulated both the expression and transcriptional activity of c-MYC and Cyclin D1 in chondrocytes, both of which were upregulated in condylar cartilage of the rat early TMJ osteoarthritis.

CONCLUSION

WNT5A regulates condylar chondrocyte proliferation, hypertrophy and migration. These findings provide new insights into the role of WNT5A signaling in TMJ cartilage biology and its potential in future therapy for TMJ degenerative diseases.

Cognitive behavioral therapy for psychosomatic problems in dental settings

Cognitive behavioral therapy (CBT) has been applied for various problems, including psychiatric diseases such as depression and anxiety, and for physical symptoms such as pain. It has also been applied for dental problems. Although the effect of CBTs on temporomandibular disorders and dental anxiety are well documented, its effectiveness on other types of oral symptoms remain unclear. Little information comparing the different types of CBTs in the dental setting is currently available. Because dental professionals are often expected to conduct CBTs in the dental setting, it is important to develop proper training programs for dental professionals.

In this review article, we demonstrate and discuss the application of CBTs for psychosomatic problems, including temporomandibular disorders, dental anxiety, burning mouth syndrome, and other oral complaints in dental settings.

Distribution of pericellular matrix molecules in the temporomandibular joint and their chondroprotective effects against inflammation

The objectives of this study were to (1) determine the distribution and synthesis of pericellular matrix (PCM) molecules (collagen VI, collagen IV and laminin) in rat temporomandibular joint (TMJ) and (2) investigate the effects of PCM molecules on chondrocytes against inflammation in osteoarthritis. Four zones (fibrous, proliferating, mature and hypertrophic) of condylar cartilage and three bands (anterior, intermediate and posterior) of disc were analysed by immunohistochemistry for the presence of PCM molecules in rat TMJs. Isolated chondrocytes were pre-treated with PCM molecules before being subjected to interleukin (IL)-1β treatment to stimulate inflammation. The responses of the chondrocytes were analysed using gene expression, nitric oxide release and matrix metalloproteinase (MMP)-13 production measures. Histomorphometric analyses revealed that the highest areal deposition of collagen VI (67.4%), collagen IV (45.7%) and laminin (52.4%) was in the proliferating zone of TMJ condylar cartilage. No significant difference in the distribution of PCM molecules was noted among the three bands of the TMJ disc. All three PCM molecules were expressed intracellularly by chondrocytes cultured in the monolayer. Among the PCM molecules, pre-treatment with collagen VI enhanced cellular proliferation, ameliorated IL-1β-induced MMP-3, MMP-9, MMP-13 and inducible nitric oxide synthase gene expression, and attenuated the downregulation of cartilage matrix genes, including collagen I, aggrecan and cartilage oligomeric matrix protein (COMP). Concurrently, collagen VI pretreatment inhibited nitric oxide and MMP-13 production. Our study demonstrates for the first time the distribution and role of PCM molecules, particularly collagen VI, in the protection of chondrocytes against inflammation.

Magnetic Resonance Imaging (MRI) Evaluation for Anterior Disc Displacement of the Temporomandibular Joint

Background

Magnetic resonance imaging (MRI) is the criterion standard imaging technique for visualization of the temporomandibular joint (TMJ) region, and is currently considered the optimum modality for comprehensive evaluation in patients with temporomandibular joint disorder (TMD). This study was aimed at finding the value of MRI in pre-clinical diagnosis of TMJ disc displacement.

Material/Methods

Patients primarily diagnosed as having anterior disc displacement by clinical symptoms and X-ray were selected in the present study. MRI was used to evaluate surrounding anatomical structures and position, as well as morphological and signal intensity change between patients and normal controls.

Results

Posterior band position was significantly different between the patient group and control group. At the maximum opened-mouth position, the location of disc intermediate zone returned to normal. At closed-mouth position, the thickness of anterior and middle, but not posterior, band increased. The motion range of the condyle in the anterior disc displacement without reduction (ADDWR) patient group was significantly less than the value in the anterior disc displacement with reduction (ADDR) patient group and the control group. Whether at closed-mouth position or maximum opened-mouth position, the exudate volume in the patient group was greater than in the normal group.

Conclusions

MRI can be successfully used to evaluate multiple morphological changes at different mouth positions of normal volunteers and patients. The disc-condyle relationship can serve as an important indicator in assessing anterior disc displacement, and can be used to distinguish disc displacement with or without reduction.

Clinical Signs and Subjective Symptoms of Temporomandibular Disorders in Instrumentalists

PURPOSE

Most of the reports on instrumentalists' experiences of temporomandibular disorders (TMD) have been reported not by clinical examinations but by subjective questionnaires. The aim of this study was to investigate the clinical signs and subjective symptoms of TMD in a large number of instrumentalists objectively.

MATERIALS AND METHODS

A total of 739 musicians from a diverse range of instrument groups completed a TMD questionnaire. Among those who reported at least one symptom of TMD, 71 volunteers underwent clinical examinations and radiography for diag-nosis.

RESULTS

Overall, 453 participants (61.3%) reported having one or more symptoms of TMD. The most frequently reported symptom was a clicking or popping sound, followed by temporomandibular joint (TMJ) pain, muscle pain, crepitus, and mouth opening limitations. Compared with lower-string instrumentalists, a clicking or popping sound was about 1.8 and 2 times more frequent in woodwind and brass instrumentalists, respectively. TMJ pain was about 3.2, 2.8, and 3.2 times more frequent in upper-string, woodwind, and brass instrumentalists, respectively. Muscle pain was about 1.5 times more frequent in instrumentalists with an elevated arm position than in those with a neutral arm position. The most frequent diagnosis was myalgia or myofascial pain (MFP), followed by disc displacement with reduction. Myalgia or MFP was 4.6 times more frequent in those practicing for no less than 3.5 hours daily than in those practicing for less than 3.5 hours.

CONCLUSION

The results indicate that playing instruments can play a contributory role in the development of TMD.

3D superimposition and understanding temporomandibular joint arthritis

OBJECTIVES

To investigate the 3D morphological variations in 169 temporomandibular ioint (TMJ) condyles, using novel imaging statistical modeling approaches.

SETTING AND SAMPLE POPULATION

The Department of Orthodontics and Pediatric Dentistry at the University of Michigan. Cone beam CT scans were acquired from 69 subjects with long-term TMJ osteoarthritis (OA, mean age 39.1±15.7 years), 15 subjects at initial consult diagnosis of OA (mean age 44.9±14.8 years), and seven healthy controls (mean age 43±12.4 years).

MATERIALS AND METHODS

3D surface models of the condyles were constructed, and homologous correspondent points on each model were established. The statistical framework included Direction-Projection-Permutation (DiProPerm) for testing statistical significance of the differences between healthy controls and the OA groups determined by clinical and radiographic diagnoses.

RESULTS

Condylar morphology in OA and healthy subjects varied widely with categorization from mild to severe bone degeneration or overgrowth. DiProPerm statistics supported a significant difference between the healthy control group and the initial diagnosis of OA group (t=6.6, empirical p-value=0.006) and between healthy and long-term diagnosis of OA group (t=7.2, empirical p-value=0). Compared with healthy controls, the average condyle in OA subjects was significantly smaller in all dimensions, except its anterior surface, even in subjects with initial diagnosis of OA.

CONCLUSION

This new statistical modeling of condylar morphology allows the development of more targeted classifications of this condition than previously possible.

The incidence of osteoarthritic change on computed tomography of Korean temporomandibular disorder patients diagnosed by RDC/TMD; a retrospective study

Objective Osteoarthritis (OA) of the temporomandibular joint (TMJ) is generally thought to be an age-related disease like those of other joints. This study aims to investigate the incidence of computed tomographic (CT) OA changes in Korean temporomandibular disorder (TMD) patients diagnosed by the Research Diagnostic Criteria for TMD (RDC/TMD). Materials and methods The clinical records and radiographs of 1038 TMD patients (297 men and 741 women with mean age 31.1 ± 17.4 and 34.0 ± 16.2, respectively) diagnosed based on RDC/TMD Axis I in 2010 were reviewed. Results The incidence rate of OA changes in TMD patients is estimated to 27.3%, and higher in women than in men (15.5% in men and 32.0% in women) by 2.3 odds (p < 0.001). It has no correlation with age, showing an almost flat incidence rate throughout the age from the 2nd decade and has no correlation as well with pain or disc displacement diagnosed according to RDC/TMD, while arthrosis/arthritis diagnosis based on RDC/TMD supplemented by plain radiographs shows high risk of OA changes on CT by 38.8 odds (p < 0.05). Conclusions These results imply that the OA changes in young Korean TMD patients are as common as in the old and have no correlation with clinical pain and noise. Considered with high prevalence of TMDs known in the young population, the overall/absolute OA changes in the TMJ can be even higher in the young than in the old population, not like in other joints.

Contemporary management of TMJ involvement in JIA patients and its orofacial consequences

Juvenile idiopathic arthritis is the most common chronic rheumatic condition during childhood. Temporomandibular joint arthritis is frequently asymptomatic. When it takes place during childhood, it may affect condylar growth; therefore, these children are at risk of unfavorable long-term outcomes from the associated joint damage. The etiology is not completely understood, but it is considered as multifactorial with both genetic and environmental factors involved.

The standardized examination and imaging protocols serve important purpose to diagnose temporomandibular joint (TMJ) arthritis not only to establish an early interventional strategy but also to assess craniofacial growth and the progression of signs and symptoms in those patients. Although the treatment of juvenile idiopathic arthritis (JIA) has changed dramatically over the last decades due to new therapeutic options, TMJ arthritis still can develop during the course of the disease. In clinical experience, TMJs appear to respond less well to the standard of care used to treat other joints. More individualized approach to the patient’s treatment serves as the main goal of personalized medicine. It could be achieved by adopting new methods of medical imaging such as conebeam computer tomography as well as developing reliable biomarkers which may assist with predicting disease type, course, or severity and predicting response to medication.

This article provides an overview of current information on orofacial complications in JIA and its management. Based on information provided in this review, more precise diagnosis, proper tools for recognizing people at risk, and more efficient treatment approaches could be implemented. This may lead to more personalized treatment management strategies of TMJ complications of JIA patients.

Disc displacement without reduction: a retrospective study of a clinical diagnostic sign

OBJECTIVE

The purpose of this retrospective study is to evaluate a clinical diagnostic sign for disc displacement without reduction (DDWR), the absence of additional condylar translation during opening compared with protrusion.

METHOD

Thirty-eight electronic axiographic and magnetic resonance imaging (MRI) examinations of the TMJ were analyzed in order to compare the opening/protrusion ratio of condylar translation between non-painful DDWR and non-DDWR.

RESULT

According to the Mann-Whitney U test, the opening/protrusion ratio in non-painful DDWR differs significantly from non-DDWR (p < 0.0001).

DISCUSSION

Among non-painful DDWR, there is no additional condylar translation during opening in comparison with protrusion, and this is probably also the case for DDWR without limited opening, which is a subtype that has not been validated by the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). Comparative condylar palpation can analyze this sign, and therefore, further comparative investigations between MRI and clinical examination are needed to validate the corresponding clinical test.

Comparison of Diagnostic Performance Between Visual and Quantitative Assessment of Bone Scintigraphy Results in Patients With Painful Temporomandibular Disorder

This retrospective clinical study was performed to evaluate whether a visual or quantitative method is more valuable for assessing painful temporomandibular disorder (TMD) using bone scintigraphy results.In total, 230 patients (172 women and 58 men) with TMD were enrolled. All patients were questioned about their temporomandibular joint (TMJ) pain. Bone scintigraphic data were acquired in all patients, and images were analyzed by visual and quantitative methods using the TMJ-to-skull uptake ratio. The diagnostic performances of both bone scintigraphic assessment methods for painful TMD were compared.In total, 241 of 460 TMJs (52.4%) were finally diagnosed with painful TMD. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the visual analysis for diagnosing painful TMD were 62.8%, 59.6%, 58.6%, 63.8%, and 61.1%, respectively. The quantitative assessment showed the ability to diagnose painful TMD with a sensitivity of 58.8% and specificity of 69.3%. The diagnostic ability of the visual analysis for diagnosing painful TMD was not significantly different from that of the quantitative analysis.Visual bone scintigraphic analysis showed a diagnostic utility similar to that of quantitative assessment for the diagnosis of painful TMD.

Jaw disorders in the pediatric population

PURPOSE

This article will review the etiology, risk factors, history, and physical assessment of temporomandibular joint disorders (TMDs). In particular, this article discusses the role of the pediatric provider in diagnosing and beginning the initial treatment of TMDs, as well as the appropriate treatment plans. It also reveals some of the controversies regarding etiology and treatment of TMDs, as well as the paucity of research specific to TMDs in pediatrics.

DATA SOURCES

A computerized search in PubMed and Ovid Medline, from 2006 to 2012, was conducted. A few seminal articles were included that were published before 2006. Hand searching was also performed, which included a few articles between 2012 and 2015.

CONCLUSIONS

Although TMDs are mostly found in adults, it is also a finding in pediatrics, which increases in prevalence during adolescence. More research specific to pediatric patients with TMDs needs to be conducted so that pediatric-specific care can be provided.

IMPLICATIONS FOR PRACTICE

TMD is a condition found in the pediatric population, and it is important for providers to take an adequate history and physical examination that incorporates the temporomandibular joint (TMJ) and muscles of mastication. It is also critical that providers begin initial education and management, followed by appropriate referrals.

Correlation Between Clinical Findings of Temporomandibular Disorders and MRI Characteristics of Disc Displacement

Objectives : Temporomandibular joint (TMJ) dysfunction is a common condition that is best evaluated with magnetic resonance (MR) imaging. The first step in MR imaging of the TMJ is to evaluate the articular disk, or meniscus, in terms of its morphologic features and its location relative to the condyle in both closed- and open-mouth positions. Disk location is of prime importance because the presence of a displaced disk is a critical sign of TMJ dysfunction. However, disk displacement is also frequently seen in asymptomatic volunteers. It is important for the maxillofacial radiologist to detect early MR imaging signs of dysfunction, thereby avoiding the evolution of this condition to its advanced and irreversible phase which is characterized by osteoarthritic changes such as condylar flattening or osteophytes. Further the MR imaging techniques will allow a better understanding of the sources of TMJ pain and of any discrepancy between imaging findings and patient symptoms. Henceforth, the aim of the study was to evaluate whether MRI findings of various degrees of disk displacement could be correlated with the presence or absence of clinical signs and symptoms of temporomandibular disorders in symptomatic and asymptomatic subjects. Materials and Methods : In this clinical study, 44 patients (88 TMJs) were examined clinically and divided into two groups. Group 1 consisted of 22 patients with clinical signs and symptoms of TMDs either unilaterally or bilaterally and considered as study group. Group 2 consisted of 22 patients with no signs and symptoms of TMDs and considered as control group. MRI was done for both the TMJs of each patient. Displacement of the posterior band of articular disc in relation to the condyle was quantified as anterior disc displacement with reduction (ADDR), anterior disc displacement without reduction (ADDWR), posterior disc displacement (PDD). Results : Disk displacement was found in 18 (81.8%) patients of 22 symptomatic subjects in Group 1 on MRI and 4 (18.1%) were diagnosed normal with no disc displacement. In Group 2, 2 (9.1%) of 22 asymptomatic patients were diagnosed with disc displacement while 20 (90.1%) were normal. Sensitivity and Specificity tests were applied in both the groups to correlate clinical findings of TMD and MRI characterstics of disc displacement and results showed Sensitivity of 90% and Specificity of 83.3%. Conclusion : Disk displacement on MRI correlated well with presence or absence of clinical signs and symptoms of temporomandibular disorders with high Sensitivity and Specificity of 90% and 83.3% respectively.

Progenitor Cells of the Mandibular Condylar Cartilage

The secondary cartilage of the mandibular condyle is unique as it undergoes endochondral ossification during growth and robustly remodels in response to changes in its mechanical loading environment. This cartilage is derived from mesenchymal progenitor cells that express markers of early osteoblast differentiation, namely alkaline phosphatase (ALP) and runt-related transcription factor 2 (Runx2). Interestingly, these progenitor cells then differentiate into cartilage with appropriate mechanical loading. Our laboratory has determined that these cells can be labeled by osteoblast progenitor cell markers, including the 3.6 fragment of the rat collagen type 1. However, the role these mesenchymal progenitor cells play in adult mandibular condylar cartilage maintenance and adaptation, as well as the existence of a more potent progenitor cell population within the mandibular condylar cartilage, remain in question. Further characterization of these cells is necessary to determine their potency and regenerative capacity to elucidate their potential for regenerative therapy.

Orthognathic surgery and temporomandibular joint symptoms

The aim of this article is to review temporomandibular joint symptoms as well as the effects of orthognathic surgery(OGS) on temporomandibular joint(TMJ). The causes of temporomandibular joint disease(TMD) are multifactorial, and the symptoms of TMD manifest as a limited range of motion of mandible, pain in masticatory muscles and TMJ, Joint noise (clicking, popping, or crepitus), myofascial pain, and other functional limitations. Treatment must be started based on the proper diagnosis, and almost symptoms could be subsided by reversible options. Minimally invasive options and open arthroplasty are also available following reversible treatment when indicated.

TMD manifesting in a variety of symptoms, also can apply abnormal stress to mandibular condyles and affect its growth pattern of mandible. Thus, adaptive developmental changes on mandibular condyles and post-developmental degenerative changes of mandibular condyles can create alteration on facial skeleton and occlusion. The changes of facial skeleton in DFD patients following OGS have an impact on TMJ, masticatory musculature, and surrounding soft tissues, and the changes of TMJ symptoms. Maxillofacial surgeons must remind that any surgical procedures involving mandibular osteotomy can directly affect TMJ symptoms, thus pre-existing TMJ symptoms and diagnoses should be considered prior to treatment planning and OGS.

Tissue engineering of the temporomandibular joint disc: current status and future trends

INTRODUCTION

Temporomandibular joint disorders are extremely prevalent and there is no ideal treatment clinically for the moment. For severe cases, a discectomy often need to be performed, which will further result in the development of osteoarthritis. In the past thirty years, tissue engineering has provided a promising approach for the effective remedy of severe TMJ disease through the creation of viable, effective, and biological functional implants.

METHODS

Although TMJ disc tissue engineering is still in early stage, unremitting efforts and some achievements have been made over the past decades. In this review, a comprehensive summary of the available literature on the progress and status in tissue engineering of the TMJ disc regarding cell sources, scaffolds, biochemical and biomechanical stimuli, and other prospects relative to this field is provided.

RESULTS AND CONCLUSIONS

Even though research studies in this field are too few compared to other fibrocartilage (e.g., knee meniscus) and numerous, difficult tasks still exist, we believe that our ultimate goal of regenerating a biological implant whose histological, biochemical, and biomechanical properties parallel native TMJ discs for clinical therapy will be achieved in the near future.

Are temporomandibular disorders associated with habitual sleeping body posture or nasal septal deviation?

Numerous factors can be considered for the etiology of temporomandibular disorders (TMD). The aim of the present study was to investigate whether the presence of both nasal septal deviation (NSD) and habitual prone sleeping posture (HPSP) predisposes TMD. We evaluated 200 subjects in 4 groups. Group I (NSD-, HPSP-/control group), Group II (NSD+, HPSP-), Group III (NSD-, HPSP+), Group IV (NSD+, HPSP+). All patients were examined according to the research diagnostic criteria to determine the presence of TMD. Group IV had the highest value for TMD incidence (44 %). Thus, we found that the presence of both NSD and HPSP parameters increased TMD incidence in Group IV compared to the control group (p = 0.000). Additionally, Group IV showed significantly higher values than Group II (p = 0.012) and Group III (p = 0.039). For Group III (NSD-, HPSP+), TMD was determined higher compared to the control group (p = 0.009). A statistically higher value of presence of TMD was determined in Group II (NSD+, HPSP-) than control group (p = 0.029). The incidence of TMD was significantly higher in women than men (p = 0.020). We concluded that one having an unilateral obstructive nasal septal deviation in addition to a habit of sleeping in prone position must be alert for potential TMD.

UTE imaging in the musculoskeletal system

Tissues, such as bone, tendon, and ligaments, contain a high fraction of components with "short" and "ultrashort" transverse relaxation times and therefore have short mean transverse relaxation times. With conventional magnetic resonance imaging (MRI) sequences that employ relatively long echo times (TEs), there is no opportunity to encode the decaying signal of short and ultrashort T2 /T2 * tissues before it has reached zero or near zero. The clinically compatible ultrashort TE (UTE) sequence has been increasingly used to study the musculoskeletal system. This article reviews the UTE sequence as well as various modifications that have been implemented since its introduction. These modifications have been used to improve efficiency or contrast as well as provide quantitative analysis. This article reviews several clinical musculoskeletal applications of UTE.

Lubricin is Required for the Structural Integrity and Post-natal Maintenance of TMJ

The Proteoglycan 4 (Prg4) product lubricin plays essential roles in boundary lubrication and movement in limb synovial joints, but its roles in temporomandibular joint (TMJ) are unclear. Thus, we characterized the TMJ phenotype in wild-type and Prg4(-/-) mouse littermates over age. As early as 2 weeks of age, mutant mice exhibited hyperplasia in the glenoid fossa articular cartilage, articular disc, and synovial membrane. By 1 month of age, there were fewer condylar superficial tenascin-C/Col1-positive cells and more numerous apoptotic condylar apical cells, while chondroprogenitors displayed higher mitotic activity, and Sox9-, Col2-, and ColX-expressing chondrocyte zones were significantly expanded. Mutant subchondral bone contained numerous Catepsin K-expressing osteoclasts at the chondro-osseous junction, increased invasive marrow cavities, and suboptimal subchondral bone. Mutant glenoid fossa, disc, synovial cells, and condyles displayed higher Hyaluronan synthase 2 expression. Mutant discs also lost their characteristic concave shape, exhibited ectopic chondrocyte differentiation, and occasionally adhered to condylar surfaces. A fibrinoid substance of unclear origin often covered the condylar surface. By 6 months of age, mutant condyles displayed osteoarthritic degradation with apical/mid-zone separation. In sum, lubricin exerts multiple essential direct and indirect roles to preserve TMJ structural and cellular integrity over post-natal life.

TMJ degeneration in SAMP8 mice is accompanied by deranged Ihh signaling

The temporomandibular joint (TMJ) functions as a load-bearing diarthrodial joint during mastication, and its continuous use and stress can lead to degeneration over age. Using senescence-accelerated (SAMP8) mice that develop early osteoarthritis-like changes in synovial joints at high frequency, we analyzed possible molecular mechanisms of TMJ degeneration and tested whether and how malocclusion may accelerate it. Condylar articular cartilage in young SAMP8 mice displayed early-onset osteoarthritic changes that included reductions in superficial/chondroprogenitor cell number, proteoglycan/collagen content, and Indian hedgehog (Ihh)-expressing chondrocytes. Following malocclusion induced by tooth milling, the SAMP8 condyles became morphologically defective, displayed even lower proteoglycan levels, and underwent abnormal chondrocyte maturation compared with malocclusion-treated condyles in wild-type mice. Malocclusion also induced faster progression of pathologic changes with increasing age in SAMP8 condyles as indicated by decreased PCNA-positive proliferating chondroprogenitors and increased TUNEL-positive apoptotic cells. These changes were accompanied by steeper reductions in Ihh signaling and by expression of matrix metalloproteinase 13 at the chondro-osseous junction in SAMP8 articular cartilage. In sum, we show for the first time that precocious TMJ degeneration in SAMP8 mice is accompanied by--and possibly attributable to--altered Ihh signaling and that occlusal dysfunction accelerates progression toward degenerative TMJ disease in this model.

[The role of occlusal disorders in development of temporomandibular joint dysfunction]

Currently Temporomandibular joint (TMJ) dysfunction is a very highly discussed topic by both researchers and clinicians. the incidence of the of TMJ is dysfunctions still not very well established because of heterogeneity of the diagnostic criteria used by different authors. This article is dedicated to the analysis of basic theories of the etiology of the aforementioned pathology, including overview of main pathophysiological mechanisms of the TMJ, dysfunctions occlusive disorders in particular. The main problem being analyzed is the use and efficacy of the electronic axiography in successful diagnostic and therapy of the TMJ dysfunction.

Quantitative 3D ultrashort time-to-echo (UTE) MRI and micro-CT (μCT) evaluation of the temporomandibular joint (TMJ) condylar morphology

OBJECTIVE

Temporomandibular dysfunction involves osteoarthritis of the TMJ, including degeneration and morphologic changes of the mandibular condyle. The purpose of this study was to determine the accuracy of novel 3D-UTE MRI versus micro-CT (μCT) for quantitative evaluation of mandibular condyle morphology.

MATERIALS AND METHODS

Nine TMJ condyle specimens were harvested from cadavers (2 M, 3 F; age 85 ± 10 years, mean ± SD). 3D-UTE MRI (TR = 50 ms, TE = 0.05 ms, 104-μm isotropic-voxel) was performed using a 3-T MR scanner and μCT (18-μm isotropic-voxel) was also performed. MR datasets were spatially registered with a μCT dataset. Two observers segmented bony contours of the condyles. Fibrocartilage was segmented on the MR dataset. Using a custom program, bone and fibrocartilage surface coordinates, Gaussian curvature, volume of segmented regions, and fibrocartilage thickness were determined for quantitative evaluation of joint morphology. Agreement between techniques (MRI vs. μCT) and observers (MRI vs. MRI) for Gaussian curvature, mean curvature, and segmented volume of the bone were determined using intraclass correlation coefficient (ICC) analysis.

RESULTS

Between MRI and μCT, the average deviation of surface coordinates was 0.19 ± 0.15 mm, slightly higher than the spatial resolution of MRI. Average deviation of the Gaussian curvature and volume of segmented regions, from MRI to μCT, was 5.7 ± 6.5% and 6.6 ± 6.2%, respectively. ICC coefficients (MRI vs. μCT) for Gaussian curvature, mean curvature, and segmented volumes were 0.892, 0.893, and 0.972, respectively. Between observers (MRI vs. MRI), the ICC coefficients were 0.998, 0.999, and 0.997, respectively. Fibrocartilage thickness was 0.55 ± 0.11 mm, as previously described in the literature for grossly normal TMJ samples.

CONCLUSIONS

3D-UTE MR quantitative evaluation of TMJ condyle morphology ex-vivo, including surface, curvature, and segmented volume, shows high correlation against μCT and between observers. In addition, UTE MRI allows quantitative evaluation of the fibrocartilaginous condylar component.

Increased mandibular condylar growth in mice with estrogen receptor beta deficiency

Temporomandibular joint (TMJ) disorders predominantly afflict women of childbearing age, suggesting a role for female hormones in the disease process. In long bones, estrogen acting via estrogen receptor beta (ERβ) inhibits axial skeletal growth in female mice. However, the role of ERβ in the mandibular condyle is largely unknown. We hypothesize that female ERβ-deficient mice will have increased mandibular condylar growth compared to wild-type (WT) female mice. This study examined female 7-day-old, 49-day-old, and 120-day-old WT and ERβ knockout (KO) mice. There was a significant increase in mandibular condylar cartilage thickness as a result of an increased number of cells, in the 49-day-old and 120-day-old female ERβ KO compared with WT controls. Analysis in 49-day-old female ERβ KO mice revealed a significant increase in collagen type X, parathyroid hormone-related protein (Pthrp), and osteoprotegerin gene expression and a significant decrease in receptor activator for nuclear factor κ B ligand (Rankl) and Indian hedgehog (Ihh) gene expression, compared with WT controls. Subchondral bone analysis revealed a significant increase in total condylar volume and a decrease in the number of osteoclasts in the 49-day-old ERβ KO compared with WT female mice. There was no difference in cell proliferation in condylar cartilage between the genotypes. However, there were differences in the expression of proteins that regulate the cell cycle; we found a decrease in the expression of Tieg1 and p57 in the mandibular condylar cartilage from ERβ KO mice compared with WT mice. Taken together, our results suggest that ERβ deficiency increases condylar growth in female mice by inhibiting the turnover of fibrocartilage.

Endoplasmic reticulum stress regulates rat mandibular cartilage thinning under compressive mechanical stress

Compressive mechanical stress-induced cartilage thinning has been characterized as a key step in the progression of temporomandibular joint diseases, such as osteoarthritis. However, the regulatory mechanisms underlying this loss have not been thoroughly studied. Here, we used an established animal model for loading compressive mechanical stress to induce cartilage thinning in vivo. The mechanically stressed mandibular chondrocytes were then isolated to screen potential candidates using a proteomics approach. A total of 28 proteins were identified that were directly or indirectly associated with endoplasmic reticulum stress, including protein disulfide-isomerase, calreticulin, translationally controlled tumor protein, and peptidyl-prolyl cis/trans-isomerase protein. The altered expression of these candidates was validated at both the mRNA and protein levels. The induction of endoplasmic reticulum stress by mechanical stress loading was confirmed by the activation of endoplasmic reticulum stress markers, the elevation of the cytoplasmic Ca(2+) level, and the expansion of endoplasmic reticulum membranes. More importantly, the use of a selective inhibitor to block endoplasmic reticulum stress in vivo reduced the apoptosis observed at the early stages of mechanical stress loading and inhibited the proliferation observed at the later stages of mechanical stress loading. Accordingly, the use of the inhibitor significantly restored cartilage thinning. Taken together, these results demonstrated that endoplasmic reticulum stress is significantly activated in mechanical stress-induced mandibular cartilage thinning and, more importantly, that endoplasmic reticulum stress inhibition alleviates this loss, suggesting a novel pharmaceutical strategy for the treatment of mechanical stress-induced temporomandibular joint diseases.

Overlap between functional GI disorders and other functional syndromes: what are the underlying mechanisms?

BACKGROUND

Irritable bowel syndrome and other gastrointestinal (GI) and non-GI disorders such as functional dyspepsia, fibromyalgia, temporomandibular joint disorder, interstitial cystitis/painful bladder syndrome, and chronic fatigue syndrome are known as functional pain syndromes. They commonly coexist within the same individual. The pathophysiologic mechanisms of these disorders are not well understood, but it has been hypothesized that they share a common pathogenesis.

PURPOSE

The objective of this review is to discuss the proposed pathophysiologic mechanisms, which have been similarly studied in these conditions. These mechanisms include enhanced pain perception, altered regional brain activation, infectious etiologies, dysregulations in immune and neuroendocrine function, and genetic susceptibility. Studies suggest that these functional disorders are multifactorial, but factors which increase the vulnerability of developing these conditions are shared.

Muenke syndrome mutation, FgfR3P²⁴⁴R, causes TMJ defects

Muenke syndrome is characterized by various craniofacial deformities and is caused by an autosomal-dominant activating mutation in fibroblast growth factor receptor 3 (FGFR3(P250R) ). Here, using mice carrying a corresponding mutation (FgfR3(P244R) ), we determined whether the mutation affects temporomandibular joint (TMJ) development and growth. In situ hybridization showed that FgfR3 was expressed in condylar chondroprogenitors and maturing chondrocytes that also expressed the Indian hedgehog (Ihh) receptor and transcriptional target Patched 1(Ptch1). In FgfR3(P244R) mutants, the condyles displayed reduced levels of Ihh expression, H4C-positive proliferating chondroprogenitors, and collagen type II- and type X-expressing chondrocytes. Primary bone spongiosa formation was also disturbed and was accompanied by increased osteoclastic activity and reduced trabecular bone formation. Treatment of wild-type condylar explants with recombinant FGF2/FGF9 decreased Ptch1 and PTHrP expression in superficial/polymorphic layers and proliferation in chondroprogenitors. We also observed early degenerative changes of condylar articular cartilage, abnormal development of the articular eminence/glenoid fossa in the TMJ, and fusion of the articular disc. Analysis of our data indicates that the activating FgfR3(P244R) mutation disturbs TMJ developmental processes, likely by reducing hedgehog signaling and endochondral ossification. We suggest that a balance between FGF and hedgehog signaling pathways is critical for the integrity of TMJ development and for the maintenance of cellular organization.

Sex differences in chondrocyte maturation in the mandibular condyle from a decreased occlusal loading model

Temporomandibular joint disorders (TMDs) predominantly afflict women of childbearing age. Defects in mechanical loading-induced temporomandibular joint (TMJ) remodeling are believed to be a major etiological factor in the development of TMD. The goal of this study was to determine if there are sex differences in CD-1 and C57BL/6 mice exposed to a decreased occlusal loading TMJ remodeling model. Male and female CD-1 and C57BL/6 mice, 21 days old, were each divided into two groups. They were fed either a normal pellet diet (normal loading) or a soft diet and had their incisors trimmed out of occlusion (decreased occlusal loading) for 4 weeks. The mandibular condylar cartilage was evaluated by histology, and the subchondral bone was evaluated by micro-CT analysis. Gene expression from both was evaluated by real-time PCR analysis. In both strains and sexes of mice, decreased occlusal loading caused similar effects in the subchondral bone, decreases in bone volume and total volume compared with their normal loading controls. However, in both strains, decreased occlusal loading caused a significant decrease in the expression of collagen type II (Col2) and Sox9 only in female mice, but not in male mice, compared with their normal loading controls. Decreased occlusal loading causes decreased bone volume in both sexes and a decrease in early chondrocyte maturation exclusively in female mice.

Murine TMJ loading causes increased proliferation and chondrocyte maturation

The purpose of this study was to examine the effects of forced mouth opening on murine mandibular condylar head remodeling. We hypothesized that forced mouth opening would cause an anabolic response in the mandibular condylar cartilage. Six-week-old female C57BL/6 mice were divided into 3 groups: (1) control, (2) 0.25 N, and (3) 0.50 N of forced mouth opening. Gene expression, micro-CT, and proliferation were analyzed. 0.5 N of forced mouth opening caused a significant increase in mRNA expression of Pthrp, Sox9, and Collagen2a1, a significant increase in proliferation, and a significant increase in trabecular spacing in the subchondral bone, whereas 0.25 N of forced mouth opening did not cause any significant changes in any of the parameters examined. Forced mouth opening causes an increase in the expression of chondrocyte maturation markers and an increase in subchondral trabecular spacing.