To evaluate the position of the condylar head in the glenoid fossa (condylar position) in the intercuspal position, various methods have been employed. However, no standard evaluation method has been established. In addition, the correlation between the condylar position and TMJ internal derangement has not been elucidated. We designed a new, simple evaluation method for the condylar position. Furthermore, the correlation between the condylar position and articular disc displacement was examined. Subjects: A total of 160 TMJs of 80 TMD patients examined by tomography and MRI were included in this study. METHODS: Tomogra-phy was used to evaluate the condylar position in the antero-posterior and supero-inferior direc-tions using our evaluation method as follows; (1) Three segments, the anterior (=a), posterior (=b) and superior (=c) joint spaces as shown by tomography were measured . (2) To evaluate the condylar position, 3 acquired values were substituted for 2 numerical expressions. Each antero -posterior and supero-inferior condylar position was expressed in APR and SIR quantitatively.
APR=b-a/b+a× SIR=(a+b/2-c/a+b/2+c)×100
Articular disc positions were evaluated in 3 positions by MRI. The 3 positions were as follows; superior disc position: the articular disc was in the normal position, slightly anterior disc posi-tion: a part of the posterior band of the articular disc was between the articular eminence and condylar head, completely anterior disc position: complete anterior displacement of the articular disc. The differences among the condylar position of the TMJs of the 3 positions were statisti-cally examined. RESULTS: A total of 157 TMJs were quantitatively evaluated in 2 directions. Three TMJs could not be evaluated with this evaluation method. Significant differences were found concerning the anteroposterior direction between the superior disc position and the slight-ly anterior disc position (p=0.021), as well as the superior disc position and the completely anterior disc position (p=0.047). Significant differences were detected in the supero-inferior direction between the superior disc position and the completely anterior disc position (p<0.001), as well as the slightly anterior disc position and the completely anterior disc position (p=0.020). CONCLUSION: A simple and useful method to evaluate the condylar position was designed. A correlation between the condylar position and articular disc displacement was found.

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Occlusal splint therapy is a commonly used conservative treatment for internal derangement of tempor-omandibular joints (TMJs). Among recent imaging techniques to evaluate temporomandibular joint disorders (TMD), MR imaging is most suitable to assess splint therapy. Pseudodynamic MR study may help to confirm recapture of displaced discs after treatment with occlusal splints, but its qualitative nature may limit its application after treatment. The purpose of this study was to assess the feasibility of a newly developed quantitative motion analysis method for the mandibular condyle before and after application of occlusal splints. The subjects were 50 consecutive patients (7 men, 43 women, average 29 years of age, ) with internal derangement. Stabilization type splints were applied in 23 cases (46%), anterior repositioning type in 18 cases (36%) and pivot type in 9 cases (18%). All patients underwent MR imaging with a 1.5-T MR unit with a 3-inch dual surface coil. Pseudodynamic MR study of the opening cycle was obtained using multiplanar GRASS sequence (MPGR). Incremental and decremental sagittal MR images before and after splint application were transferred to the workstation. Software originally developed by Nakasato and Katsuragawa was used to analyze the condylar motion and path. After splint application, normalized position of displaced discs was seen in 11 cases (22%), and occurred most frequently with anterior repositioning type splints. In patients with anterior repositioning type splints, improvement in the condylar motion was most significant. In patients with normalized disc position after application of occlusal splints, abnormal “figure-eight-shaped” condylar paths were corrected in 9 of 10 cases. In the case with normalized disc position after application of anterior repositioning splint, the maximum rotational angle before application of the splint is lager than that of the case without normalized disc position. Rotational function of the condyle in the inferior joint space may be associated with disc recapturing. Conventional pantographic tracing and simplified condylar motion recorders have been advocated to evaluate condylar paths, but inability to trace the disc itself was a major disadvantage. Quantitative analysis of condylar motion after splint application is useful to evaluate slight motion alterations that can not be clearly evaluated on MR images by qualitative analysis alone.

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This study was designed to evaluate the configuration of the articular disc and degree of anterior disc displacement on magnetic resonance (MR) imagings in temporomandibular joints (TMJs) with internal derangement. A total of 363 joints diagnosed as having anterior disc displacement with reduction (ADD w R) and 523 joints diagnosed as having anterior disc displacement without reduction (ADD wo R) by MR imaging were examined. These joints did not show severe osseous changes on the condylar head or glenoid fossa. We assessed the configuration of the articular disc and degree of anterior disc displace-ment. In the ADD w R group, 82.6% of the articular discs showed biconcave configuration; enlargement of the posterior band in 4.6%, biconvex configuration in 0.5%, and others in 10.7%. Moreover 62.5% of the discs showed a slight degree of anterior disc displacement; were 27.2% moderately displaced and were 10.2% severe displaced. The prevalence of slightly displaced discs was higher in the TMJs of cases over 50 years of age than in cases under 30 years in the ADD w R group. On the other hand, in the ADD wo R group 35.9% of the articular discs showed biconcave configuration; enlarge-ment of the posterior band in 12.6%, biconvex configuration in 25.4%, and others in 22.3%. Further-more, 4.4% of the discs were slightly displaced; 43.9% moderately displaced and 51.6% were severely displaced. The prevalence of severely displaced and deformed discs in joints of cases over 40 years of age was high in the ADD wo R group. The prevalence of slightly displaced biconcave discs was higher in the ADD w R group. The other hand, the prevalence of severely displaced deformed discs was higher in the ADD wo R group. MR findings of internal derangement of the TMJ were found to be significantly correlated with age.

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It has been reported that the signal intensity of dense collagen fibers markedly increases in some tissues on MRI, when collagen fibers are oriented at about 55° against the static magnetic field. This angle is sometimes called the magic angle. The magic angle phenomenon is caused by magnetic dipolar-dipolar interaction between water protons. As this phenomenon has been reported to be related to the T2 relaxation rate only, the signal intensity may be influenced by the T2 relaxation rate at the spin echo (SE) sequence if other parameters are fixed. Information regarding the increasing ratio of signal intensity depending on the angle may be clinically important. A bovine tendon was rotated horizontally in a static magnetic field and images were obtained with SE or fast spin echo (FSE) sequences as follows: (a) SE (TR/TE=2000/15, 30, 45, 60), (b) SE (TR/TE=300, 500, 700/14), (c) FSE (TR/TE=3000/15, 105 eff., echo train length 14). By comparing the theoretical curves and data, it was con-firmed that the signal intensity was related to the second power of the local magnetic field strength. The increasing ratio of signal intensity of the bovine tendon at 55° (magic angle) compared with 0° was about 3 times (TE=30). The most influential TE was about 20-40 msec. The increasing ratio of signal intensity did not depend on TR change or the FSE technique.

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Cavernous hemangioma is a common benign tumor in the head and neck region. It is essential to determine the anatomical confinements and blood supplies of hemangiomas to select and plan treatment procedures. Computed tomography and angiography have been employed to diagnose hemangiomas and the use of MRI was recently reported. We report two patients who underwent MRI for diagnosing hemangioma in the buccal region. The signal intensity in these tumors was less than that of subcutaneous fat on T 1-weighted images. On the other hand, T 2-weighted sig-nal intensity on the tumor was greater than that of fat. T 2-weighted images were effective to visualize these cavernous hemangiomas. Two cavernous hemangiomas showed a septation pat-tern that revealed low signal intensity on T 2-weighted images and the T 1 signal of the septum increased in contrast to that of the surrounding area. We report two patients with unique find-ings that might be useful to depict feeding and/or draining vessels in cavernous hemangioma.

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