Morphology and function are closely related to each other in many parts of the human body. In this study, we attempted to find out the mechanism to control this relationship between form and function of the temporomandibular joint region from the biomechanical point of view, using the twodimensional finite element model. In this report, we analyzed factors influencing stress distribution in the condyle region and obtained following results.
1) Muscle vectors (direction and magnitude) of temporalis and lateral pterygoid greatly altered the stress distribution in the condyle area.
2) Morphological changes in the condyle head and mandibular fossa altered the stress distribution.
3) Changes in the occlusal support location, with corresponding amount of activity of each muscle, maintained the stress distribution pattern.
With the above mentioned results, we posit the existence of a mechanism for maintaining and changing condyle morphology with regard to the stress distribution in that area.

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This study observed the three dimensional mandibular positions of TMJ-sound in the area of mandibular border movements, the amplitude of TMJ-sound which occurred during opening closing movements of the mandibular, and the change of TMJ-sound by using an anterior repositioning splint for three months. The subjects were 14 patients with TMJ-sound.
1. The means of the TMJ-sound positions, of the extent of TMJ-sound positions, and of the amplitude of TMJ-sound were larger in the opening phase than in the closing phase in all patients. After three months all of the means decreased.
2. The sound amplitude of many patients during the early phase of opening decreased or disappeared. And even in the subject whose sound did not disappear, the sound position, extension and amplitude decreased.
3. The sound of all patients whose sound occurred in the late phase of opening did not disappear or decrease in amplitude. Further sound positions of these patients did not change as in the early phase.
4. As a result, there is a particular relationship between the sound position and the change of the TMJ-sound when using an anterior repositioning splint. This suggests a relationship between the sound positions and the effect of splint therapy.

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Recent studies have revealed that the biomechanical aspect of the temporomandibular joint has a critical influence on the occurence of temporomandibular joint disorders. Therefore, the configuration of joint components is expected to have a considerable effect on the displacement of the articular disk. The purpose of this investigation was to study the relationship between the disk displacement and the configuration of the condyle and the mandibular fossa. Out of 54 temporomandibular joints from Japanese cadavers aged 45 to 93 years, 18 joints without any gross sign of degenerative change were examined macroscopically. The 18 joints were divided into two groups according to their disk position, one group consisting of 10 normal joints and the other of 8 anteriorly diskdisplaced joints. The mean ages of the groups were 64.0 yrs, and 72.1 yrs respectively. The size of the condyle and the mandibular fossa, the angulation of the posterior slope of the eminence and the disk position were measured on the 3 sagittal sections, i.e, lateral, central, medial. In addition, sellanasion length was measured as a standard to estimate the relative joint size over the cranium size.
The following results were drawn:
1. No significant correlation was found between sella-nasion length and joint size.
2. The condyle of the anteriorly disk-displaced group was smaller than that of the normal group in the antero-posterior direction, whereas no difference was found between the two groups regarding the latero-medial condylar length.
3. The fossa of the anteriorly disk diplaced group was deeper and longer in the antero-posterior direction than that of the normal group. The anteriorly disk-displaced group had a larger angle of the posterior slope of the eminence. A significant correlation was found between the angle of the posterior slope of the eminence and the amount of the disk displacement in the lateral and central sagittal sections.
These results suggest that the condyle which has a small antero-posterior length and/or high and steep eminence has an increased risk of the articular disk slipping off the condyle.

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Our Previous study concluded that patients with unilateral TMJ disorder showed a characteristic two peaks of the velocity of the incisal point movement during chewing movement (the velocity of chewing movement) in the opening phase when they chewed on their normal TMJ side, while normal subjects showed only one peak in the opening phase. The purpose of this study was to investigate the mechanism of this characteristic of the velocity of chewing movement.
5 normal subjects and 5 patients with unilateral anterior disk displacement with reduction were selected for this study. Movements of the incisal point and condyles during chewing movement were recorded simultaneously using the Sirognathograph Analyzing System and the cineradiofluoroscopic system.
The results were as follows;
1) In normal subjects, the non-working condyle showed its maximum velocity corresponding to the peak of the velocity of chewing movement, while the velocity of the working condyle reached its peak in the initial phase of opening.
2) In 5 patients with TMJ disorder, a decrease of the velocity of the non-working condyle was observed in 2 patients corresponding to the decrease of the velocity of the chewing movement.
3) In 5 patients with TMJ disorder, an increase of the velocity of the non-working condyle was observed in 3 patients and that of the working condyle was observed in 4 patients corresponding to the increase of the velocity of chewing movement, which occurred after its decrease.
These results indicate that the characteristic two peaks of the velocity of chewing movement has a close relationship with the velocity of condylar movement.

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A case of severe facial asymmetry with double headed mandibular condyle in a 15-year-old girl was reported at the first medical examination.
Clinical observation for about 30 months after the initial consultation did not disclose any alteration in the TMJ.
Because the patient demonstrated TMJ dysfunction, supplemental mandibualr condyle was excised with the aid of CT scan and other methods.
Prior to the surgery, severe malocclusion and facial asymmetry was improved so as to allow satisfactory jaw movement following the TMJ surgery.
In the TMJ surgery, the disc was shaped closely in the normal posture.
The patient's progress following the operation was favorable and steady.
In the treatment of double headed mandibular condyle it proved useful to examine not only TMJ function but also to use CT scan and bone scintigraphy.
In the surgery for double headed mandibular condyle, it was important for satisfactory postoperative training of mandibular movement both to preserve the original condyle with disc and to establish a harmonious occlusion.

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In is known that posterior open bite has come about the reduction of the articular disk in the closed locking temporomandibular joint. However, there are few reports about the orthodontic reconstruction of this posterior open bite.
This clinical report indicates that dento-alveolar compensation resulting from orthodontic treatment is very effective in the reconstruction of the posterior open bite caused by the disk recapture of the TMJ.
Furthermore, in this long progressed closed lock of the TMJ, fibrous adhesion of the superior articular cavity was identified by double contrast CT. Also, arthroscopic surgery using Nd: YAG laser is effective in tearing off the fibrous adhesion.

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A case of a chronic bilateral anterior dislocation of the TMJ is presented. A 67-year-old male patient was referred to our department for further evaluation. On palpation, both condyles were fixed anteriorly and could perform only hinge movements. There was no tenderness of the TMJ. Roentgenograms showed forward dislocation of bilateral condyles, but no other significant abnormality. General examination did not reveal any systemic disorder, except for a slight mental deficiency. The patient underwent an operation for an intestinal obstruction 6 months prior to referral. It was suspected that the dislocation was caused by excessive opening of the mouth during intubation.
Treatment by manual repositioning with and wituout anesthesia was tried, but in vain. Use of intermaxillary elastic traction was also ineffective. A surgical repositioning following Fink's method was also attempted without success. Since all of the treatment procedures mentioned did not produce good results, a condylectomy was finally carried out. After reduction, a chin cap was applied to position the jaw normally for 11 days. Mouth exercises were done and the patient was able to attain a 3cm opening between anterior alveolar processes. New dentures were then made which fitted very well. About a year after the operation, satisfactory occlusion and good masticatory function were achieved.

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By focusing attention on the psychological aspects of patients with Myofascial Pain Dysfunction (MPD) Syndrome treated in this department, we have encountered many instances of chronic fatigue due to excessive adaptation in daily life. When these patients obey instructions to chew well, to enjoy leisurely meals, and to allow for sufficient sleep, improvement in the symptoms of stiffness and tenderness of the masticatory muscles and an increased incisal opening occurs in a majority of patients.
In order to evaluate eating habits as risk factors in MPD syndrome, guidance for changing habits was provided with reference to the masticatory patterns, time spent for meals, and ideal amounts of sleep. The results of the data gathered were used to study changes in habits and the corresponding reduction in MPD symptoms. 150 patients, 42 male and 108 female, were observed in this study. In patients with improvement in habits, there was an increased improvement in MPD symptoms, as compared to those who failed to change their habits. When studying the individual habit changes, we noted a higher frequency of MPD symptom improvement in those patients who displayed an improved masticatory pattern. In 26 males (84%) and 61 females (73%), there was an improvement in MPD symptoms 2 weeks after the frequency of mastication improved.
MPD symptoms decreased in 15 males (71%) and 33 females (55%) who had increased eating time for 2 weeks.
In 10 males (82%) and 45 females (63%) MPD symptoms improve for those patients who increased their sleep time for a period of 2 weeks.
In patients with MPD syndrome, the presence of risk factors, especially poor eating habits, is strongly suspected to be contributory.

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TMJ X-ray findings have become very important in the diagnosis of TMJ patients. Although detailed information of the TMJ region has been provided by arthrotomogram, a convenient way of taking an image at the first consultation with a view to making an initial diagnosis is needed.
Consequently, the authors have been using the Anatomic X-ray Aliner (AXA). To examine the usefulness of the AXA, we took TMJ photographs of 120 subjects at inter cuspal position, rest position, and maximum opening position with the AXA and investigated their clinical symptoms such as mandibular movements and TMJ sounds. Then the usefulness of AXA for diagnosis of TMJ was analyzed.
Condyle displacement appeared in most of the subjects who had TMJ sounds. No special abnormalities were found in the subjects who had only muscle pains or opening disturbances.
TMJ disorders were found in 21 subjects by questionnaire, in 62 subjects by mandibular function analysis, and in 46 subjects by AXA analysis. More TMJ disorders were found by AXA analysis than by mandibular function analysis.
These results indicate that the X-ray findings with the AXA are very useful for diagnosis at the first consultation.

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Acupuncture at the meridian point of “Gekan” was used to treat the patients' inferior articulator. Instead of using a needle, the authors irradiated the inferior articultor several times with a low power laser (Nd: YAG at 350mW). This relieved the pain somewhat. However, since the effectiveness of the treatment was decided by the patients' subjective judgment alone, the authors made an objective evaluation of the symptomatic change using thermography.
Furthermore, by combinig the use of the visual image mixing apparatus and thermography, we obtained a compound image made of both thermal and visul images. Also, we were able to find more objectively which portions of the masticatory muscle were affected by a locaizd and continuous deterioration of muscle tone. Metabolic disturbance caused by localized anemia causes pain. This pain, in turn, causes neuralgic dynfunction and abnormal jaw movement.
Finally, we also compared the treatment period when soft laser irradiation was used with that needed in the case of the myomonitor.

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