Purpose: In order to clarify the relation between blood flow and masseter muscular activities, two types of blood flow measuring device having a difference in the depth of measurement were used to measure surface blood flow and intramuscular blood flow of the masseter muscle during clenching, and the results were analyzed in conjunction with heart rate.
Methods: The heart rate, and intramuscular and surface blood flows of the masseter muscle, during medium clenching by 20 healthy subjects, were measured prior to clenching, at 10 to 50 seconds into clenching, at 10 to 50 seconds after clenching, and at 1 to 5 minutes after clenching, and the changes in blood flow before, during, and after clenching were investigated.
Results: The relative percentage of surface blood flow increased steadily upon clenching and reached a maximum value at 50 seconds into clenching (p<0.01); it decreased steadily upon ceasing clenching, and returned to its initial value at 1 minute after ceasing clenching. On the other hand, the relative percentage of intramuscular blood flow decreased upon clenching (p<0.01); it increased dramatically at 10 seconds after ceasing clenching, decreased thereafter, and returned to its initial value at 3 minutes after ceasing clenching. At about 40 to 50 seconds into clenching, the blood flow increased steadily, though only slightly. The relative percentage of heart rate increased during clenching (p<0.01), showed a maximum value at 50 seconds into clenching, decreased quickly thereafter, and returned to its original value at 20 seconds after ceasing clenching. During clenching the heart rate showed a tendency to steadily increase, though only slightly.
Conclusions: It was concluded that, though both the surface blood flow and intramuscular blood flow of the masseter muscle during clenching were caused by an increase in the heart rate and a surge in blood flow into masseter muscle, they differ in the way their flow changes.

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Purpose: This study investigated the relation between magnetic resonance imaging (MRI) findings and occlusal condition of the intercuspal position in temporomandibular disorders (TMD) patients.
Methods: Thirty TMD patients, and 29 control subjects, were selected for this study. Occlusal contacts and occlusal bite force in the intercuspal position were determined with occlusal registration strips, black silicon (bite checker), and Dental Prescale 50 H type R (pressure sensitive sheet), respectively. The subjects were divided into three groups based on MRI assessments: disk displacement with reduction (DDWR), disk displacement without reduction (DDWOR), and normal subjects.
Results: The number of teeth with occlusal contact in the intercuspal position of the DDWOR TMD patients group was lower than in the normal control group. The number of teeth with occlusal contact on the anterior teeth showed a similar tendency. The total occlusal bite force in the intercuspal position in the DDWOR TMD patients group was lower than in the DDWR control group and the normal control group. The occlusal bite force on anterior teeth in the intercuspal position showed a similar tendency. The ratio between anterior teeth and molars occlusal bite force in the intercuspal position in the DDWOR TMD patients group was lower than in the normal control group.
Conclusions: There is some relation between MRI findings and occlusal condition of the intercuspal position in TMD patients.

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Purpose: In this study, the stick-biting test was applied to temporomandibular disorders (TMD) patients, and the responses were compared with disc conditions combined with pain at clinical examination. The purpose of this study was to clarify the diagnostic accuracy of this test for diagnosing disc displacement with pain at clinical examination.
Methods: Subjects were selected from patients who visited either the prosthetic or the oral and maxillofacial departments at Tsurumi University Dental Hospital and were diagnosed as having TMD. They were asked to clench unilaterally on a plastic stick (about 9mm thick) placed at the most posterior portion on the dentition. Then, the site and amount of evoked pain were recorded. Those findings were related to MRI findings combined with pain at clinical examination; that is, no disc displacement (N), disc displacement without pain (NP-Dis), and disc displacement with pain (PDis).
Results: Pain on the non-clenching side was mostly evoked at the TMJ region, and their disc conditions were chiefly in P-Dis. The diagnostic accuracy of this test for this phenomenon was: efficiency, 83%; sensitivity, 71%; specificity, 89%; positive predictive value, 76%, and negative predictive value, 86%.
Conclusions: It was suggested that pain in the contralateral-side TMJ region during the stick-biting test was useful to clinically identify painful disc displacement at clinical examination with high diagnostic accuracy.

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Purpose: To develop an objective and quantitative method of evaluating the characteristics of masticatory laterality.
Methods: Seven test foods (chewing gum, boiled fish paste, gummy jelly, pickled radish, dried cuttlefish, peanut, giant corn) were used. Ten subjects with normal occlusion were asked to chew the test food freely for 20 seconds. The mandibular incisal point was recorded by theSirognathograph Analyzing System III. The number of chewing strokes (on either side) was counted, and the asymmetry index (AI) was calculated. This test was carried out three times. The median and the range of the Al in the three trials were also calculated.
Results:(1) Masticatory laterality was represented quantitatively by calculatingthe AI.(2) Subjects were classified into three types: unilateral type (U type), omnilateral type (O type), and variabletype (V type), by the median and range of AI.(3) Masticatory laterality tends to be influenced by the hardness rather than the property of the test food.
Conclusions: The method of objective and quantitative evaluation of masticatory laterality was discussed using several foods. The results suggested that this method was objective and quantitative, that each subject showed a characteristic pattern of masticatory laterality, and that masticatory laterality was influenced by the hardness of the test food.

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Purpose: Tissue conditioners contain various types of phthalic esters as plasticizers. A recent study reported that these phthalic esters would have estrogenicity. The aim of this study was to identify and quantify the leached plasticizers from tissue conditioners.
Methods: Three different tissue conditioners were immersed in distilled water and artificial saliva for up to 14 days. Cumulative plasticizer leaching in each immersion medium was measured at days 1, 3, 5, 7, and 14. Following each storage period, leached plasticizer was extracted with hexane and analyzed by high-performance liquid chromatography (HPLC).
Results: Leaching of plasticizer increased with longer immersion durations for up to 14 days. There was a significant difference between the leaching rate on first day and those of following immersion periods. The total amount of leached plasticizer in artificial saliva (15.1-39.4mg/g) was higher than that in distilled water (11.8-30.7mg/g). Benzyl benzoate showed the highest value of the amount of leached plasticizer, and butyl phthalyl butyl glycolate showed the lowest value, under both immersing conditions. Based on the total amount of leached plasticizer for 14 days, the daily amount of leached plasticizer was calculated as benzyl benzoate, 2.19; dibuty phthalate, 1.60; and butyl phthalyl butyl glycolate, 0.84mg/g/day, in distilled water; and benzyl benzoate, 2.81; dibutyl phthalate, 1.76; and butyl phthalyl butyl glycolate, 1.08mg/g/day, in artificial saliva.
Conclusions: The results of this study suggested that the amount of leached plasticizer was dependent on the type of plasticizer (molecular weight and chemical structure). The daily amount of leached dibutyl phthalate would be 20 times greater than food uptake.

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