The function of the lateral pterygoid muscle, which plays a most important role in jaw movements, has been studied from many points of views, including physiological and functional anatomical ones. In this study, muscle fiber bundles were classified according to the attachment morphology in the insertion area, in addition to the classification based on concepts of the superior and inferior heads. Properties of the muscle fibers in each muscle fiber bundle were evaluated.
By naked eye observation, three types of muscle fiber bundles were classified in the insertion area of the lateral pterygoid muscle. The muscle fiber bundle inserted in the articular disk without changing a tendon (type I), which was observed in all specimens, was derived from the superior head. On the other hand, most of the muscle fiber bundles inserted in the 1/5 exterior area of the pterygoid pit with tendinous attachment (type II), and in the inside of the pterygoid pit with periosteal attachment (type III) were both derived from inferior head. Immunostaining showed that the ratio of slow-type muscle fibers was highest in type I (78.5%), second highest in type III (60.8%), and lowest in type II (40.1%). It is ascertained in this study that the type II muscle fiber bundle, which works to pull the mandible forward, contains many fast-type muscle fibers and has a strong tendinous attachment, whereas the type III muscle fiber bundle, for pulling it sideways, contains abundant slow-type muscle fibers and has a weak periosteal attachment. These findings suggest that type I and type III muscle fiber bundles control the jaw movement with continuous weak forces.

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In a previous report, we assessed the adult population of Yokohama city regarding their knowledge and experience of TMD, and which doctors they thought they should consult. The results indicated that people were less aware of both the name and symptoms of TMD than we had supposed.
On the other hand, examination for TMD was introduced into the medical examinations at schools in 1995, based on a revision of the Law of Students' Health. This introduction might possibly improve students' knowledge of TMD.
In addition, recently, the number of high school students suffering from TMD and visiting dentists, has seemed to be greatly increasing.
In this study, we surveyed 1, 184 high school students in Yokohama city, using the same questionnaire about TMD that was given to the adult population.
As a result, it was concluded that they had less knowledge of this disease than adults, though many of them had suffered from it, and very few students recognized that they should consult a dentist in that situation.

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A double-headed condyle is a well-known anomaly of the mandibular condyle.
Congenital double-headed condyle is caused by interference of blood vessel in the fetal period.
We report a case of an anomaly of a mandibular triple-headed condyle.
The patient was a 22-year-old female. The range of mouth opening was 34mm at the interincisors. She had clicking sounds on her right TMJ without pain. The panoramic radiograph of both TMJs showed broad groove appearance. CT revealed that each side (internal and external) of the condyler head had a small process, and furthermore another small process anterior to the articular tubercle. This anomaly was shown at both TMJs. We diagnosed this case as a triple-headed condyle.

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We recorded EMG activity from the masseter, temporalis, sternocleidomastoid, and gastrocnemius muscles in a TMD patient who had remarkable spasms in jaw-closing muscles during the resting state. Self-sustained discharges were observed in jaw-closing muscles. This result does not seem to fit the “pain-adaptation model.” Self-sustained discharges were cut-off during and after electrical stimulation at an amplitude under sensory threshold. After a silent state was maintained for about 20 sec, EMG discharges returned. When short-term stimulation of Ia-afferents was applied by means of chin vibration, discharges were induced rapidly, and self-sustained discharges were observed after termination of stimulation. These effects are similar to the experiment in which on and off switching of self-sustained motor discharges, or “bistability” of motoneurons, has been observed in the decerebrate cat. “Bistability” is known to be produced by a short-lasting synaptic excitation and inhibitory stimulus. Further, the same effects as ours have been reported on subjects who are suffering from chronic muscle cramps and spasms of a limb or hand. Therefore, it was suggested that a common system: the property of motoneuronal membrane, with limb and hand muscles, is involved in self-sustained discharges in jaw-closing muscles.

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The aim of this study was to evaluate the effect of two consecutive arthrocenteses and NSAIDs administration as a primary treatment for temporomandibular joint disk displacement with reduction and with pain.
Seventeen patients with moderate and severe TMJ dysfunction were selected from a consecutive series of new patients who were seen in TMD clinic at Aichi-Gakuin University Hospital during a one-year period. The patients that had unilateral TMJ symptoms were diagnosed as having TMJ disk displacement with reduction by MR imaging.
Arthrocentesis was performed twice at an interval of 2 weeks. In addition, the NSAIDs, COX-2 inhibiter was given daily, orally, until the each patient's symptoms improved during follow-up for 12 weeks. Postoperatively, the patients were seen every 2 weeks, for 12 weeks. This therapy was continued for a maximum of 12 weeks unless TMJ symptoms were improved. The patients who resulted in no or slight disturbance in TMJ dysfunction were classified as improved. Similarly, the patients who resulted in moderate or severe disturbance were classified as not improved.
The improvement rates were 35%, 59%, 65%, 65%, 65%, and 71% after 2, 4, 6, 8, 10, and 12 weeks, respectively.
The combination therapy appears to be effective for temporomandibular joint disk displacement with reduction and with pain.

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