Development Of Temporomandibular Joint Disorders Research Articles

Craniomaxillofacial trauma increases the risk of temporomandibular joint disorders and days of work disability—a SWEREG-TMD registry-based study

Although craniomaxillofacial (CMF) trauma is a factor recognized as contributing to the development of temporomandibular joint disorders (TMJD), large population-based research on CMF trauma and subsequent TMJD is lacking. Additionally, it is unknown how previous CMF trauma affects work disability reimbursements for patients with TMJD (pwTMJD). This Swedish registry-based study included 33,315 pwTMJD matched to 333,122 individuals from the general population. Both a case–control design and a cohort design were used in this study to evaluate the association between CMF trauma and TMJD, and to investigate how CMF trauma impacts the number of days on work disability among pwTMJD. The main study finding was that many types of previous CMF trauma were strongly associated with TMJD, with mandibular fractures having the strongest association (adjusted odds ratio 11.4). Furthermore, the strongest association for an increased number of annual days on work disability was found for pwTMJD with a history of CMF trauma. These results suggest that CMF trauma influences the developmental path of TMJD, even in a population-based sample.

Investigating the Relationship Between Orthodontic Treatment and Temporomandibular Joint Disorders in Adolescents

ABSTRACT Background: Orthodontic treatment is widely utilized to correct malocclusions and improve dental aesthetics in adolescents. However, its potential association with the development of temporomandibular joint disorders (TMDs) remains controversial. Materials and Methods: A prospective cohort study was conducted involving 200 adolescents aged 12–18 years undergoing orthodontic treatment. Participants were divided into two groups: those receiving fixed appliances (n = 150) and those undergoing aligner therapy (n = 50). The presence and severity of TMDs were assessed using the Research Diagnostic Criteria for Temporomandibular Disorders at baseline, 6 months, and 12 months post-treatment initiation. Data were analyzed using the Chi-square tests and multivariate logistic regression to identify potential risk factors. Results: At baseline, 10% of the total cohort exhibited mild TMD symptoms. After 12 months, 25% of the fixed appliance group showed an increase in TMD symptoms, compared to 15% in the aligner group. The logistic regression analysis revealed a significant association between the duration of treatment with fixed appliances and the development of TMDs (OR = 2.5; 95% CI: 1.2–5.1; P = 0.02). However, no significant correlation was found between aligner therapy and TMD incidence (OR = 1.1; 95% CI: 0.5–2.3; P = 0.67). Conclusion: The findings suggest that prolonged orthodontic treatment with fixed appliances may increase the risk of developing TMDs in adolescents, whereas aligner therapy appears to have a minimal impact on TMJ function.

Association of Stress with Prevalence of TMJ Dysfunction in Undergraduate Dental Students

Temporomandibular joint disorder (TMD) refers to persistent medical conditions that affect the temporomandibular joint (TMJ) and related structures. Studies showed that stress was closely linked to the development of TMD. Furthermore, healthcare students are particularly susceptible to stress compared to the general population. This can have a negative impact on their quality of life and mental health during their training. The increased prevalence of TMD has also been reported among the same cohort of the population. However, there is a lack of literature published highlighting the prevalence of TMD and their association with increased levels of stress in dental students. This study aims to explore whether increased stress levels are associated with the prevalence of TMD in undergraduate dental students. A total of 218 dental students participated. Two online self-reported questionnaires consisted of structured case history on past medical and dental history with a Fonseca Amnestic Index (FAI) questionnaire used to identify the prevalence of TMD and DESS questionnaire for stress prediction were used. Data were analyzed using SPSS version 22 with a p-value less than 0.05. It was reported that about 48% of students had various TMD with no significant association found between the year of study and gender. However, a significant association was reported between stress gender. A positive correlation was also found between stress and TMD among participants. This study revealed a significant association between stress and the prevalence of TMD in undergraduate dental students. Educational institutions must adopt coping strategies to help trainees manage their psychological stress, which could reduce the incidence of TMD.

Temporomandibular Joint Disorder and Airway in Class II Malocclusion: A Review.

In class II malocclusion, there is an anteroposterior disparity between the upper dentition and the lower dentition, which may or may not be accompanied by a skeletal discrepancy. For orthodontists, this is one of the common malocclusions encountered during clinical practice. This might be due to excess maxillary growth or retarded growth of the mandible or a combination of both. In such types of malocclusion, both the upper and lower airways are affected, the lower one most commonly. Characteristic features seen are a narrow maxillary arch, a proclined upper anterior, and mouth breathing as a developing habit. Also, the position of the condyle in the skeletal type of class II malocclusion plays a vital role in the development of temporomandibular joint disorders. Treating such disparity in a growing individual leads to better results in the long term as well as prevention of malocclusion taking a severe form. Myofunctional appliances are useful for repositioning the mandible as well as the condyle. In adults, extraction of the upper premolars is most commonly done for the correction of class II malocclusion. This provides the patient with a better esthetic appearance.In addition to this, various treatment modalities, such as splint therapy, exercise, and prolotherapy, are beneficial for pain relief and temporomandibular disorder (TMD) correction. This article deals with the characteristics, development, etiology, and comprehensive treatment options of class II malocclusion and its co-relation with the upper and lower airway along with the severity of temporomandibular joint disorders. Repositioning of the condyle in the glenoid fossae is the key to the correction of this disorder.

Temporomandibular Joint Disorder and Biomechanical Simulation of the Replacement: A Literature Review on Various Surgical and Nonsurgical Methods, and Development of the Finite Element Method Approach in the Treatment

Abstract While this study is on the clinical development of temporomandibular joint disorders and understanding various biomechanical approaches through finite element analysis as a panacea, the primary aim is to perform a literature review. Usage of the biomedical prosthesis, over the years, including the initial development and later modernization with image processing and computer simulations, are briefly discussed from 1800 to 2021. Manual data handling was used to select 503 journal papers, of which 116 were further studied in this review. This review explains the complete biomechanical structure of the temporomandibular joint (TMJ), as it disclosed possible reasons for the disorders and shortcomings in the medical treatments. In the Boundary Condition and Discussion sections, the paper discussed the boundary conditions and the results of various studies from 2000 to 2021. It also discussed 36 papers with temporomandibular joint replacement (TMJR) devices, providing important information on the stress–strain distributions in the implant and the mandible-fossa component. Both custom and stock devices are discussed with a finite element method (FEM) approach, with a proper evaluation of multiple software for individual studies. Finally, TMJR devices are considered helpful for treating TMJ disorders. The FEM approach should be considered a precise and valuable biomechanical simulation tool for modifying and improving next-generation prosthetic devices.

Risk factors for temporomandibular disorders in young people

Aim to investigate the prevalence and risk factors for signs and symptoms of temporomandibular joint disorders (TMDs) in young people.
 Material and methods. A clinical examination and questionnaire were randomly administered to 199 students aged 17 to 28 years using a specially designed questionnaire chart. The respondents with identified laterotrusive or mediatrusive occlusal interferences underwent electromyography (4-channel EMG system "Synapsis", Neurotech) of masticatory muscles before and after elimination of occlusal interferences. Psychoemotional state was assessed using the Spielberger Hanin situational and personal anxiety test.
 Results. The results obtained revealed a high prevalence of signs and symptoms of dysfunctional disorders (87.9%), the leading signs of which were pain or stiffness in the head and neck region (52.7%), sounds (squeaks, clicks, crepitus) in one or both temporomandibular joints when chewing and opening the mouth (39.2%), feeling of pressure, stuffiness or noise in the ears (25.1%), pain when opening the mouth (21.6%). The number of such signs and symptoms was greater in persons with postural disorders and respondents after orthodontic treatment.
 Electromyographic study of patients with mediotrusive and laterotrusive contacts showed asynchronous contraction of the masticatory muscles during "protrusion / retrusion" and "opening / closing", increased electrical activity of the temporal muscle on the opposite side in the "right / left mediotrusion" test (111.5 27.1 V) compared with the indices of the subjects after the elimination of occlusal interferences (75 19.3 V; p 0.05). Assessment of the psychoemotional state of the examined patients revealed a moderate level of situational (38.9 points) and personal (38.3 points) anxiety.
 Conclusion. The signs and symptoms of TMDs are a common finding among young people, such as pain, stiffness in the head and neck, sounds in one or both joints when chewing and opening the mouth, a feeling of pressure, stuffiness or noise in the ears. The most significant risk factors for the development of TMDs in this age group are posture disorders, orthodontic treatment and occlusal obstructions, which affect muscle tone and increase the symptoms of TMDs.

Evaluating the role of stress and anxiety with clinical symptoms in TMD patients

Introduction: The etiology of TMD is complex and multifactorial, but it is thought that psychological factors contribute to the etiology and persistence of TMD. Therefore, the aim of this study was to investigate the role of anxiety and depression in the development of temporomandibular joint disorders in patients referred to Tehran University of Medical Sciences, School of Dentistry, International Campus. Materials and Methods: This cross-sectional study was performed on patients referred to Tehran University of Medical Sciences, School of Dentistry, International Campus who had temporomandibular joint disorder. Hence the number of 224 people easily selected at random. They were given 3 questionnaires to assess their anxiety and depression (9-PHQ, 4-PHQ7 and-GAD-7). After collecting data using SPSS software version 22 and considering the error level at 0.50% probability and one-way analysis of variance and frequency analysis were performed. Results: The rate of depression in patients with TMD was 8.83 according to the 9-PHQ questionnaire and 4.72 according to the 4-PHQ questionnaire, and the level of anxiety in patients with TMD according to the 7-GAD questionnaire was equal to 8.95 There was no significant relationship between patients’ gender and their level of anxiety (p<0.50), but there was a significant relationship between patients’ age and their level of anxiety (p>0.50). Conclusion: Age and gender are not significantly associated with temporomandibular joint disorders. Also, anxiety and depression are positively related and there is a significant value achieved with the incidence of TMD in the participants. A reduction in the level of anxiety and depression within people, can have a great impact on the treatment of TMDs in individuals.

Temporomandibular dysfunction in patients with a history of stroke.

Background: The temporomandibular joint (TMJ) is certainly one of the most complex joints in the human body. The American Academy of Orofacial Pain defines temporomandibular joint disorder (TMD) as a set of disorders involving the masticatory muscles, the TMJ, and associated structures. It is pointed as the main cause of non-dental pain in the orofacial region, including head, face and related structures. The most common TMD symptoms involve joint, chewing and face pain. There may also be crackling when opening and closing the mouth, earache, tinnitus, dizziness, dislocations, limitation of movement and painful tenderness to palpation. Stroke causes sequelae in subjects that include motor disorders, speech or language disorders, and swallowing disorders. Approximately 50% of patients with hemiparesis after stroke are known to have facial control deficiency, weakened orofacial and mandibular functions. Objective: To evaluate patients with a history of stroke, seeking a possible relationship with TMD, the pain associated with this change, and the limitations of range of motion related to the presence of hemibody spasticity in patients post stroke. Methods: The sample consisted of 19 patients of both genders, aged 55 to 70 years, who had suffered stroke. It was used the RDC/TMD for TMD diagnosis, Pressure Pain Threshold test, Ashworth scale, and Sanny Fleximeter for cervical ROM evaluation, being the statistical analysis performed by the software Bioestat version 5.3. Results: TMD was diagnosed in 81.8% of the sample, and of these, 45.4% had a diagnosis of disc displacement with reduction. Conclusion: There was an increase in the muscle tone and the pressure pain threshold, and a decrease in cervical spine ROM, related to the affected side and diagnosed with this disorder, observing that the muscle alterations caused by stroke may be predisposing factors to patients, to the development of muscle TMD or even joint TMD.

The association between exposure to childhood maltreatment and the subsequent development of functional somatic and visceral pain syndromes.

Background: Childhood maltreatment is a global public health issue linked to a vast mortality and morbidity burden. This study builds on current literature to explore the risk of developing central sensitivity syndromes (CSS) (consisting of somatic and visceral pain syndromes) subsequent to childhood maltreatment exposure.Methods: A retrospective population based open cohort study using the UK primary care database, ‘The Health Improvement Network,’ between 1st January 1995-31st December 2018. 80,657 adult patients who had experienced childhood maltreatment or maltreatment related concerns (exposed patients) were matched to 161,314 unexposed patients by age and sex. Outcomes of interest were the development of CSS: either somatic (Fibromyalgia, chronic fatigue syndrome, temporomandibular joint disorder, chronic lower back pain, chronic headache, myofascial pain syndrome and restless leg syndrome) or visceral (Interstitial cystitis, vulvodynia, chronic prostatitis and irritable bowel syndrome) in nature. Effect sizes are presented as adjusted incidence rate ratios (aIRR) with confidence intervals (CI). Models were adjusted for the following covariates at cohort entry: age, sex, deprivation, anxiety, depression and serious mental ill health.Results: The average age at cohort entry was 23.4 years and the median follow was 2.2 years. There was an increased risk of developing fibromyalgia (aIRR 2.06; 95% CI 1.71–2.48), chronic fatigue syndrome (1.47; 1.08–2.00), chronic lower back pain (1.99; 1.68–2.35), restless leg syndrome (1.82; 1.41–2.35) and irritable bowel syndrome (1.15; 1.08–1.22) when compared to the unexposed group, whereas no statistical association was seen with the development of temporomandibular joint disorder (1.00; 0.88–1.13), chronic headache (1.04; 0.59–1.86), interstitial cystitis (1.19; 0.51–2.74), vulvodynia (0.65; 0.34–1.26), chronic prostatitis (0.34; 0.07–1.77) and myofascial pain syndrome (0.88; 0.36–2.14). Outcome numbers were low, most likely, due to the rarity of visceral conditions (aside from irritable bowel syndrome). The association between a history of childhood maltreatment and CSS were mainly observed in somatic CSS.Interpretation: The debilitating effects of CSS carry a substantial physical, psychological and economic burden to both the individuals who are diagnosed with them and the health services who serve them. Primary prevention approaches targeting childhood maltreatment as well as secondary preventative approaches should be considered to minimise the associated burden of CSS.

Sex Differences in Estradiol Secretion by Trigeminal Brainstem Neurons.

Estrogen status is a significant risk factor in the development of temporomandibular joint disorders (TMD). Classically, estrogen status is thought to derive mainly from ovarian sources; however, it is well known that estradiol (E2) also is synthesized by neurons in the brain. This study tested the hypothesis that E2 is produced by neurons in trigeminal subnucleus caudalis (Vc), the principal site of termination for sensory afferents that supply the temporomandibular joint (TMJ), to modify evoked responses in a model of TMJ nociception in male and female rats. Intra-TMJ injection of the small fiber excitant, allyl isothiocyanate (AIC), increased the levels of E2 collected from microdialysis probes sites at Vc of ovariectomized (OvX) female rats, ipsilateral to the stimulus, whereas males displayed no change. Dialysate levels of E2 collected from probe sites in the contralateral Vc or cerebellum in OvX rats were not affected by TMJ stimulation. Reverse dialysis of anastrozole, an aromatase (ARO) inhibitor, via the probe reduced perfusate levels of E2 in Vc. Systemic administration of letrozole, a non-steroid ARO inhibitor, for 4 days prevented TMJ-evoked increases in masseter muscle electromyography (MMemg) activity. ARO-positive neurons were distributed mainly in superficial laminae (I-III) at Vc and cell counts revealed no significant difference between OvX and male rats. Intra-TMJ injection of AIC revealed similar numbers of ARO/Fos dual-labeled neurons in OvX and male rats. By contrast, the percentage of ARO neurons co-labeled for glutamic acid decarboxylase (GAD), the biosynthetic enzyme for GABA, was greater in OvX (35%) than male rats (14%). Few ARO-positive neurons were co-labeled for estrogen receptor alpha. These data indicate that E2 is secreted continuously by Vc neurons and that acute stimulation of TMJ nociceptors evokes further secretion in a sex-dependent manner. Reduced TMJ-evoked MMemg activity after ARO inhibition suggests that locally produced E2 by Vc neurons acts via paracrine mechanisms to modify TMJ nociception in female rats.

Intimate partner violence and temporomandibular joint disorder

ObjectiveTo assess the relationship between Intimate partner violence (IPV) (a highly prevalent form of domestic abuse) with the subsequent development of temporomandibular joint disorder (TMD). MethodsA retrospective open cohort study using a UK primary care database was undertaken. 18,547 women exposed to IPV were matched by age to 74,188 unexposed women. Defined through clinical codes the outcome of interest was TMD, and adjusted incidence rates (aIRR) were used to describe the relationship after considering covariates of interest. Results94 individuals in the exposed group were clinically coded with TMD during the study period translating to an incidence rate (IR) or 1.59 per 1000 person years. This was in comparison to 342 outcomes in the unexposed group (IR 1.21 per 1000 person years). The unadjusted IRR was 1.31 (95% CI 1.04–1.65; p < 0.020) and after adjustment for important covariates increased to 1.45 (95% CI 1.14–1.84; p < 0.002). ConclusionOur results suggest that the development of TMD may be associated with exposure to IPV in women. Clinical significanceIn the first cohort to do so, we have identified a moderate association between Intimate partner violence exposure and subsequent development of TMD. This highlights an opportunity for screening of abuse in individuals presenting with TMD.

Incidence and risk factors of the temporomandibular joint disorders in the patients without condylar fractures

To evaluate the incidence and risk factors of the temporomandibular joint disorders (TMD) in the patients suffering from maxillo-facial injury without condylar fractures. sixty patients without condylar fractures were recruited from Feb 2014 to Nov 2015 in the department of stomatology, Lishui people's hospital. The incidence of TMD was recorded at 1, 3, 6, 9 and 12 months after injury through MRI examination. The risk factors for TMD were evaluated by logistic regression analysis. the TMD incidence rates were 25.0%, 30.0%, 35.0%, 41.7% and 48.3% at 1, 3, 6, 9 and 12 months after injury with no statistical difference between male and female (P>0.05). Logistic regression indicated that disorder of occlusal relationship (OR=1.84,95%CI:1.36-2.78) and hemi-mastication (OR=1.56, 95% CI:1.23- 2.24) were independent risk factors for the development of TMD. there was a high incidence of temporomandibular joint disorders in the patients suffering from maxillo-facial injury without condylar fractures. The disorder of occlusal relationship and hemi-mastication were independent risk factors for the development of post-injury TMD.

TMD symptoms and vertical mandibular symmetry in young adult orthodontic patients in North Sumatra, Indonesia: a cross-sectional study.

Background: Temporomandibular joint disorder (TMD) includes symptoms of pain and dysfunction in the muscles of mastication and the temporomandibular joint. Differences in vertical condylar height, observed in the assessment of mandibular asymmetry, is a structural alteration that represents a risk factor for TMD. The study aimed to evaluate the association between TMD symptoms and vertical mandibular symmetry in young adult orthodontic patients in North Sumatra, Indonesia. Methods: The cross-sectional study included 18-25-year-old (mean ± SD, 21.9 ± 2.0 years) old orthodontic patients admitted to the Dental Hospital of Universitas Sumatera Utara, Medan, between June 2016 and March 2017. Vertical mandibular asymmetry was assessed from all 106 subjects using Kjellberg's technique from pre-treatment panoramic radiographs. The TMD symptoms were assessed by structural interviews using modified questionnaires based on Temporomandibular Disorder Diagnostic Index and Fonseca's Anamnestic Index. Results: Of the 106 subjects, 26 (24.5% of the total) with vertical mandibular symmetry and 39 (36.8%) with vertical mandibular asymmetry were positive for TMD symptoms. By contrast, 17 patients (16.0% of the total) with vertical condylar symmetry and 24 patients (22.6%) with vertical mandibular asymmetry were regarded negative for TMD symptoms. There was no significant difference (p=0.520) in TMD symptoms based on vertical mandibular symmetry. Conclusion: The results from this studied Sumatran population indicate that there are common TMD symptoms in young adult orthodontic patients, but there is no significant association between vertical mandibular asymmetry and TMD symptoms. Further study on the development of TMD, mandibular asymmetry and treatment planning for growing patients is suggested, using longitudinal and transitional approaches.

Toll-Like Receptor 4 (TLR4) Stimulates Synovial Injury of Temporomandibular Joint in Rats Through the Activation of p38 Mitogen-Activated Protein Kinase (MAPK) Signaling Pathway.

BackgroundSynovitis is an important disease that cause intractable pain in temporomandibular joint (TMJ), and the inflammation process played a crucial role in the initiation and development of temporomandibular joint disorder. A series of investigations suggested that the increasing expression of interleukin-(IL) 1β secreted by synovial lining cells plays an important role in synovial inflammation and cartilage destruction in TMJ. In this present study, we investigated the signaling pathways which regulate the expression of IL-1β.Material/MethodsThe occlusal interference animal model was created to induce synovial injury. Forty-eight rats were divided into 4 groups: 1) control group, 2) occlusal interference group, 3) TAK-242 (a specific inhibitor targeting the Toll-like receptor (TLR)-4) group, and 4) SB203580 (a specific inhibitor targeting the p38) group. The inflammation changes were observed, and the expression of p38 and IL-1β in the synovial membranes were assayed.ResultsThe results showed that downstream p38 MAPK (mitogen-activated protein kinase) signaling was triggered following the activation of TLR4. Moreover, the injection of SB203580 could inhibit the inflammatory reactions and the increased expression of IL-1β at both mRNA and protein levels.ConclusionsThe results prompted us that TLR4 may stimulates synovial inflammatory reactions and increased expression of IL-1β in rats through the activation of p38 MAPK signaling pathway, p38 was an important mediator in the mechanisms of the initiation and development of synovial injury by regulating the expression of IL-1β in synovial membranes.

TMD symptoms and vertical mandibular symmetry in young adult orthodontic patients in North Sumatra, Indonesia: a cross-sectional study

Background: Temporomandibular joint disorder (TMD) includes symptoms of pain and dysfunction in the muscles of mastication and the temporomandibular joint. Differences in vertical condylar height, observed in the assessment of mandibular asymmetry, is a structural alteration that represents a risk factor for TMD. The study aimed to evaluate the association between TMD symptoms and vertical mandibular symmetry in young adult orthodontic patients in North Sumatra, Indonesia. Methods: The cross-sectional study included 18-25-year-old (mean ± SD, 21.9 ± 2.0 years) old orthodontic patients admitted to the Dental Hospital of Universitas Sumatera Utara, Medan, between June 2016 and March 2017. Vertical mandibular asymmetry was assessed from all 106 subjects using Kjellberg’s technique from pre-treatment panoramic radiographs. The TMD symptoms were assessed by structural interviews using modified questionnaires based on Temporomandibular Disorder Diagnostic Index and Fonseca’s Anamnestic Index. Results: Of the 106 subjects, 26 (24.5% of the total) with vertical mandibular symmetry and 39 (36.8%) with vertical mandibular asymmetry were positive for TMD symptoms. By contrast, 17 patients (16.0% of the total) with vertical condylar symmetry and 24 patients (22.6%) with vertical mandibular asymmetry were regarded negative for TMD symptoms. There was no significant difference (p=0.520) in TMD symptoms based on vertical mandibular symmetry. Conclusion: The results from this studied Sumatran population indicate that there are common TMD symptoms in young adult orthodontic patients, but there is no significant association between vertical mandibular asymmetry and TMD symptoms. Further study on the development of TMD, mandibular asymmetry and treatment planning for growing patients is suggested, using longitudinal and transitional approaches.

TMD symptoms and vertical mandibular symmetry in young adult orthodontic patients in North Sumatra, Indonesia: a cross-sectional study.

Background: Temporomandibular joint disorder (TMD) includes symptoms of pain and dysfunction in the muscles of mastication and the temporomandibular joint. Differences in vertical condylar height, observed in the assessment of mandibular asymmetry, is a structural alteration that represents a risk factor for TMD. The study aimed to evaluate the association between TMD symptoms and vertical mandibular symmetry in young adult orthodontic patients in North Sumatra, Indonesia. Methods: The cross-sectional study included 18-25-year-old (mean ± SD, 21.9 ± 2.0 years) old orthodontic patients admitted to the Dental Hospital of Universitas Sumatera Utara, Medan, between June 2016 and March 2017. Vertical mandibular asymmetry was assessed from all 106 subjects using Kjellberg's technique from pre-treatment panoramic radiographs. The TMD symptoms were assessed by structural interviews using modified questionnaires based on Temporomandibular Disorder Diagnostic Index and Fonseca's Anamnestic Index. Results: Of the 106 subjects, 26 (24.5% of the total) with vertical mandibular symmetry and 39 (36.8%) with vertical mandibular asymmetry were positive for TMD symptoms. By contrast, 17 patients (16.0% of the total) with vertical condylar symmetry and 24 patients (22.6%) with vertical mandibular asymmetry were regarded negative for TMD symptoms. There was no significant difference (p=0.520) in TMD symptoms based on vertical mandibular symmetry. Conclusion: The results from this studied Sumatran population indicate that there are common TMD symptoms in young adult orthodontic patients, but there is no significant association between vertical mandibular asymmetry and TMD symptoms. Further study on the development of TMD, mandibular asymmetry and treatment planning for growing patients is suggested, using longitudinal and transitional approaches.

Involvement of trigeminal astrocyte activation in masseter hyperalgesia under stress

It is commonly accepted that psychological stress contributes to the development of temporomandibular joint disorders, in which chronic orofacial pain is the main symptom. However, the central mechanism underlying the development of these disorders has remained unclear. The current study was performed to determine the involvement of the glia in the trigeminal spinal subnucleus caudalis in stress-induced increases in masseter muscle hyperalgesia in rats. After being subjected to chronic restraint stress, the animals showed decreased body weight gain, behavioral changes and marked masseter allodynia. We also found that astrocytes, but not microglia, in the trigeminal subnucleus caudalis (Vc) were dramatically activated. A further analysis was undertaken to investigate the contribution of the glia; we intrathecally injected l-α-aminoadipate (astrocyte-specific inhibitor) and/or minocycline (microglia-specific inhibitor) into the stressed rats. Our results showed that l-α-aminoadipate (LAA), but not minocycline, could significantly attenuate the mechanical masseter allodynia and behavioral changes induced by restraint stress. In addition, the expression of interleukin-1β (IL-1β) and phosphorylated N-methyl-d-aspartic acid receptor 1 (p-NR1) in the Vc was significantly increased after chronic restraint stress, whereas LAA dramatically inhibited the overexpression of IL-1β and p-NR1. Taken together, these results suggest that activated astrocytes in the Vc may be one of the most important factors in the pathophysiology of masseter hyperalgesia induced by restraint stress and the following overexpression of IL-1β and excessive NMDAR phosphorylation may ultimately contribute to masseter hyperalgesia. Thus, inhibiting spinal astrocytic activation may represent a novel therapeutic strategy for the treatment of orofacial pain induced by stress.

Activation of β-catenin signalling leads to temporomandibular joint defects.

Despite extensive research in knee and hip osteoarthritis (OA), the underlying mechanism of temporomandibular joint (TMJ) disorder remains largely unknown. The purpose of this study was to determine whether the constitutive activation of β-catenin in the middle and deep layers of the articular cartilage can compromise the homeostasis of this tissue in the TMJ. Col2CreERT2 transgenic mice were bred with RosamT/mG reporter mice to determine Cre recombination efficiency. Col2CreERT2 mice were then crossed with β-cateninflox(ex3)+ mice to generate β-catenin conditional activation mice, β-catenin(ex3)Col2ER. TMJ samples were harvested when the mice were 1-, 3- or 6-month-old and evaluated using histology, histomorphometry and immunohistochemistry. β-catenin(ex3)Col2ER mice were further crossed with Mmp13flox/flox and Adamts5-/- mice to generate (β-catenin(ex3)/Mmp13)Col2ER and β-catenin(ex3)Col2ER)/Adamts5-/- double mutant mice to investigate the role of Mmp13 and Adamts5 in the development of TMJ disorder. High levels of Cre-recombination were seen in Col2CreERT2;RosamT/mGmice. Progressive TMJ defects developed in 1-, 3- and 6-month-old β-catenin(ex3)Col2ER mice, as revealed by histology and histomorphometry. Results further demonstrated that the defects observed in β-catenin(ex3)Col2ER mice were significantly decelerated after deletion of the Mmp13 or Adamts5 gene in (β-catenin(ex3)/Mmp13)Col2ER or β-catenin(ex3)Col2ER/Adamts5-/- double mutant mice. In summary, we found that β-catenin is a critical gene in the induction of TMJ cartilage degeneration, and over-expressing β-catenin in TMJ cartilage leads to defects assembling an OA-like phenotype. Deletion of Mmp13 and Adamts5 in β-catenin(ex3)Col2ER mice ameliorates the development of TMJ defects. This study suggests that Mmp13 and Adamts5 could be potential therapeutic targets for the treatment of TMJ disorders.

Psychological stress alters microstructure of the mandibular condyle in rats

Psychological stress plays an important role in the occurrence and development of temporomandibular joint disorder (TMD). The correlation between psychological factors and TMD has been clinically shown, but the influence of psychological stress on the temporomandibular joint (TMJ) structure still lacks direct evidence. Here, we used communication box to establish the rat model of psychological stress. The stress level of animals was estimated by the elevated plus maze (EPM) test and hormonal assays. The histomorphology and three-dimensional microstructure of the rat condyles were observed by hematoxylin–eosin (HE) staining and Micro-CT, respectively. Compared with control rats, the anxious state of the stressed rats was evidenced by higher plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT), as well as lower ratios of open arm entries and time and lower time spent in open arms after 1, 2, 3, 4 and 5week(s) post-exposure to psychological stimuli. HE staining and histomorphometric data analysis showed decreased thicknesses of the central and posterior condylar cartilages in stressed rats at weeks 3, 4 and 5, with the most obvious changes in the posterior part characterized by debonding and thinned fibrous layer, thickened proliferative layer, thinned mature layer and hypertrophic layer. Moreover, Micro-CT scanning revealed local lesion of the subchondral bone in the posterior condylar cartilages of stressed rats at week 5. Our findings indicate that pathologic changes of the histomorphology and three-dimensional microstructure occur in the condyles of stressed rats, hinting us a potential link between psychological factors and the pathogenesis or progression of TMD.

Treatment of Obstructive Sleep Apnea with Oral Appliance

Oral appliances have been considered as effective treatment modality for obstructive sleep apnea (OSA). Especially mandibular advanced device (MAD) showed more effective treatment results compared to other oral appliances. With the accurate diagnosis through polysomnography, clinical examination and radiographic examination, the appropriate application of oral appliances would show promising results for OSA and snoring. However oral appliances can raise the complications such as untoward movement of teeth and development of temporomandibular joint disorders, thus it is highly recommended that the treatment Should be undertaken by skilled dental specialists. Moreover, periodic check-up and adjustment of appliances, if needed, should be performed. Although the assertion that continuous positive airway pressure is superior to MAD physiologically, consensus is not available until now. For optimum treatment for OSA, further researches are necessary for investigation of long-term efficiency, performance, cardiovascular status and objective adaptation. (Ewha Med J 2013;36(2):97101) Received July 22, 2013, Accepted August 7, 2013