We have developed a four-item questionnaire for the screening of patients for temporomandibular disorders (TMD), which showed a highest sensitivity of 0.746 and specificity of 0.811.
Purpose: Using this four-item questionnaire, we screened persons working in the Tokyo metropolis for TMD in 2005 and 2006, in order to determine the prevalence of TMD and the contributory factors.
Methods: We used the secondary data of the Tokyo Dental Association for both 2005 (412 people, 396 effective analysis subjects (96.1%)) and 2006 (795 people, 679 effective analysis subjects (85.4%)).
Results: The prevalence of temporomandibular disorders in males was 19.5% in patients in their 20's, 35.1% in those in their 30's, 27.3% in those in their 40's, 14.3% in those in their 50's, and 3.9% in those in their 60's, thus being predominant in the 30's and 40's age brackets. The prevalence in females was 32.2% in patients in their 20's, 38.3% in those in their 30's, 23.5% in those in their 40's, and 6.1% in those in their 50's, thus being predominant in the 20's and 30's age brackets. A multivariate logistic regression analysis revealed the feeling of fatigue (OR=1.55) in the male TMD group, and of depression (OR=1.37) and feeling of fatigue: (OR=1.30) in the female TMD group as significant factors.
Conclusions: These results were developed from secondary data, therefore, although direct relations cannot be confirmed, the need to investigate, worktime, sleep and its association with the onset of TMD was revealed.

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This report describes a skeletal mandibular protrusion with facial asymmetry treated by orthognathic surgery combined with IVRO and SSRO, which revealed bone remodeling on the shifted-side condyle after the surgery. The patient, a 15-year 6-month-old female, complained of anterior crossbite. At the initial stage, overjet and overbite were -2.5mm and +4.5mm, respectively. The molar relationship was Angle Class III, and she was diagnosed as Skeletal Class III with mandibular protrusion (ANB=-1.5°). After preoperative orthodontic treatment, she underwent orthognathic surgery including SSRO on the right side and IVRO on the left side. The amounts of mandibular setback were 9mm and 5mm on the right and left side of the mandible, respectively. From the tomography taken before surgery, and 3 and 12 months after surgery, the left condyle moved anteroinferiorly immediately after surgery. After 12 months, the posterior surface of the left condyle revealed bone remodeling and the subsequent change of the condylar morphology. From this case report, orthognathic surgery combined with IVRO and SSRO was shown to be an effective treatment for an asymmetrical mandibular protrusion. It was also shown that careful observation for a long time is crucial for long-term stability.

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During mastication of hard and solid food, the occlusal vertical dimension is raised by the food to be crushed between upper and lower molar teeth on the working side. Hence, the upper and lower molar teeth are widely apart on the balancing side, resulting in such unbalanced occlusion that there is no effective vertical stop on the balancing side. This study examined the mechanism of stabilization of the working-side temporomandibular joint during the mastication of hard and solid food. EMG activities of the MSS and lateral pterygoid muscle (LP) were simultaneously recorded with movements of the condyle as well as the incisor point during masticatory-like jaw movement induced by electrical stimulation of the cortical masticatory area of anesthetized rabbits. Movement of the condyle in the sagittal plane was directly video-recorded with a high-speed CCD camera. The functional role of the MSS and LP in the condyle movement was examined by taking account of the time lag that exists between EMG and actual mechanical effects such as bite force or jaw movement. Abnormal condyle movement on the working side was observed in 4 of 8 rabbits by applying an occlusal bite-raising splint on the upper molar on the working side. It was revealed that the unusual condyle movements appear in the period between the maximum mechanical effects of the MS and the LP and that the interval between these maximum mechanical effects was significantly prolonged. In addition, the working-side MSS activity showed little changes in magnitude, while the muscle activity was markedly increased in the other 4 rabbits that showed no abnormal movement of the condyle even when the splint was applied. These findings suggest that unusual condyle movements are closely related to the muscle activities of the MS and LP.

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In the present study, we investigated the prognosis of initial treatment of temporomandibular joint (TMJ) closed lock using the actual range of painful mouth opening (obtained by subtracting the range of painless unassisted mouth opening from the range of painful unassisted mouth opening) as an indicator.
The subjects were 27 patients (4 men, 23 women) among 106 patients diagnosed with TMJ closed lock from a total of 341 patients with TMJ disorders who initially visited our hospital from September 2004 to February 2007 (period: 2 years and 6 months). The mean age was 40.3 years (range: 14 to 74 years). The subjects were classified by the actual range of painful mouth opening into the 6mm group (n=16) and the <6mm group (n=11), and these two groups were compared with regard to lock duration, treatment period, VAS pain score, and maximum range of mouth opening.
The improvement rates, which were calculated as a percentage of improved cases among the subjects in each group, were evaluated by the classification of TMJ dysfunction.
Results: The rate of improvement following treatment was significantly higher (p<0.05) in the 6mm group (94%) compared to the <6mm group (36%), irrespective of the range of unassisted mouth opening at the initial visit. Therefore, the actual range of painful mouth opening was thought to be an important indicator for predicting the effectiveness of initial treatment for TMJ closed lock.

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In current clinical guideline making, we need to adopt the “PICO” acronym: patient (or disease), intervention (a drug or test), comparison (another drug, placebo or test) and outcome of clinical questions (CQ).
Purpose: We carried out a questionnaire survey of dentists in general practice to collate the CQ for the treatment of temporomandibular disorders (TMD).
Subjects and Methods: The Japan Dental Association (JDA) carried out the questionnaire survey, and we analyzed the secondary data, in which personal information had been eliminated. All the subjects were general members of the Japan Dental Association and members and non-members of the JDA working in the participating clinics. One-tenth of the number of general members was extracted in principle for every age group. As for the unification of terms, one of the authors compiled a list of similar terms using the text-mining method.
Results: We sent the questionnaire to 5, 999 dentists, and the response rate was 23.5% (1, 412 dentists). Inadequate and incomplete CQ (353) were excluded from the total analysis set of 4, 423, leaving 4, 070 finally included in the effective analysis set. The main therapies (more than 5%) chosen for main symptoms (more than 3%) were 32 kinds of CQ.
Conclusion: These data and/or combinations should be considered when making the clinical guideline for TMD.

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An investigative joint study to determine the psychological factors contributing to the incidence of temporomandibular disorder (TMD) was conducted on healthy volunteers with no current or past histories of TMD.
Since the TMD population mainly consists of patients in their 20s, 207 dental students (139 males and 68 females, mean age 20.4 years) attending Iwate Medical University were involved in this study. Initially, all subjects were asked to fill out a questionnaire screening mandibular functions as well as a psychological questionnaire regarding Y-G, CMI, SDS, MAS and life events and life changes (LeLc). The incidence of TMD symptoms was evaluated 2.5 years later through a self-reported questionnaire.
Of 171 subjects who completed the whole examination 2.5 years later, 25 patients (15 males and 10 females) reported experiencing pain in the temporomandibular joint and/or masticatory muscle and/or jaw opening limitation at the 2.5-year follow-up survey.
A logistic regression analysis was carried out to determine the basic factors that reveal type B and type E of Y-G, and type I of MAS, respectively. A Mann-Whitney U-test was carried out to determine intrinsic factors that show LeLc. A Kruskal-Wallis test and a Bonferroni correction test were performed, revealing that type B and E of Y-G and type I of MAS had a higher life score than the other types. The results of this study suggest that emotional instability and deep anxiety may be contributing factors that cause TMD, and that patients with TMD suffer greater stress than those who are not physically impaired.

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Chronic joint degenerative changes as osteoarthritis and/or rheumatoid arthritis often exhibit temporomandibular joint (TMJ) involvement accompanied by pain and dysfunction. The pathogenesis of these conditions remains poorly understood, but important insights may be provided by suitable animal models of the degenerative joint diseases. The purpose of this study was to develop and histologically characterize an animal model of type II collagen antigen induced arthritis of the temporomandibular joint (TMJ).
Arthritis was induced with an intra-articular injection of type II collagen with Freund's adjuvant in previously sensitized Sprague-Dauley (S. D. ) rats (n=5). The booster immunization was performed a total of 5 times into the articular cavity including the first time. Sham-treated rats with saline solution injection were used as a control (n=5). The TMJs were retrieved en bloc at 63 days after post-challenge for histological examination.
Type II collagen antigen treated TMJs demonstrated degenerative changes of the articular cartilaginous structure, including thickening of superficial fibrous layer, decrease of proliferative layer, indistinctness of hypertrophic layer, and decrease of the whole thickness of the cartilaginous cover of the mandibular condyle. The size of the bony component of the condyle decreased with atrophic changes.
This animal model will be useful for understanding the pathologic course of degeneration of the cartilaginous structure and bone resorption of the mandibular condyle with chronic arthritis of the TMJ.

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