Sanae Yamada

Effect of occlusal splints on the electromyographic activities of masseter muscles during maximum clenching in patients with myofascial pain-dysfunction syndrome

Integrated EMG activities of masseter muscles during maximum voluntary isometric contraction with and without full-arch maxillary stabilization splints were observed in patients with MPD syndrome having occlusal interferences and in healthy subjects having no occlusal interferences. The masseter muscle activity was more significantly reduced in patients with MPD syndrome during maximum clenching with splints than in those patients without splints. In healthy subjects, such a significant difference could not be observed with and without splints. This finding suggests that the elimination of the occlusal interferences by means of occlusal splints could reduce the degree of sensory information from the periodontal receptors during nocturnal clenching or grinding. This could result in a decrease in masseter muscle activity giving rise to muscular relaxation.

Quantitative electromyographic diagnosis of myofascial pain-dysfunction syndrome

The slopes of the V/T curves of masticatory muscles were determined in patients with MPD syndrome, and the changes in the slopes were observed prior to and during electrical muscle stimulation and splint therapy. The slopes of the V/T curves in patients with MPD syndrome were significantly steeper than those of the healthy subjects. In patients with MPD the slopes were decreased by electrical muscle stimulation of moderate duration and by insertion of the splint. These findings suggest that the most simple procedure for the diagnosis of MPD syndrome is to compare the slopes in MPD patients with those of healthy subjects. The observation of the changes in slopes during electrical muscle stimulation and splint therapy permits a more quantitative diagnosis of MPD syndrome. It also permits a quantitative measurement of improvement of symptoms in patients with MPD syndrome.

Adhesion between copper-plated acrylic tray resin and a polysulfide rubber impression material

The method of copper plating on acrylic resin was developed, and the bond strength to polysulfide rubber was measured in comparison with that of the adhesive coating. The bond strength with copper plating was greater than with adhesive coating. The specimens with adhesive coating failed due to a rupture occurring at the elastomer-adhesive interface, while those with copper plating had cohesive-adhesive failure. The method of copper plating on acrylic resin improved the adhesion between the polysulfide rubber and the custom-built acrylic resin tray.

Casting a gold alloy to embedded precision attachment metals

The technique for casting a gold alloy to embedded attachment metals has been described. The joints of gold alloy cast to commercially available attachment metals were examined with a metallurgic and a scanning electron microscope. The investigation indicated that an uninterrupted gapless joint is possible, and that some diffusion occular along the interfaces with some attachment metals. In view of these findings, it is concluded that this technique can be recommended as a dental laboratory procedure.

Correlation between Chewing Path and Muscle Activity in Chewing Movement. Premature Contact.

This study was performed to determine whether or not malocclusion decreases the interdependent relationship between the chewing path and muscle activity. For experimental premature contact attached to the lower 1st molar on the habitual chewing side, two thicknesses (50 μm and 100μm) of metal foil were used. Chewing movements using a stick of gum were recorded simultaneously as the path and electromyograms. The parameters for the path were the amount of anterior-posterior and right-left movements at 1 mm, 7 mm and lowest point vertically below the intercuspation in the opening-closing path and the maximum amount of mouth opening per stroke, and those for electromyograms were the interval of EMG bursts and the integrated in the central portion of the bilateral masseter muscles and the anterior portion of the bilateral temporal muscles. The presence or absence of premature contact, and changes in the relationship between the chewing path and muscle activity according to the thickness of interference were analyzed in terms of the first canonical correlation coefficient in canonical correlation analysis. Premature contact could be a factor that decreases the first canonical correlation coefficient, but no differences were observed between the two thicknesses.

An Evalution of Relationship between Chewing Cycle and Mastication Muscle Activities.

The present study was to determine the fluctuation patterns in the path and activity of masticatory muscle during chewing masticatory movements in three groups of subjects having different degrees of persistent lateralized mastication (expressed as a lateralized mastication index): group I (mild), group II (intermediate), group III (severe).With regard to the standard deviation of each parameter, N-HM mastication showed a greater variance than HM mastication in all three groups.The difference between the sides of mastication was the smallest in group I and the largest in group II.Furthermore, the number of subjects showing such a relationship was the smallest for most parameters in group I and the largest in group III. Subsequently, the interdependent relationship of the course and masticatory activity was examined by the first canonical correlation coefficient of canonical correlation analysis. In HM mastication, all three groups showed practically equal correlation coefficients of 0.87-0.88.In addition, the subjects in group I showed little or no difference between the two chewing sides, while groups II and III showed a decrease in correlation in N-HM mastication.

The Influence of Continuous Mastication with Non-habitual Chewing Side on Masticatory Movements.

The present study was designed to analyze the influence of the continuous mastication with the nonhabitual chewing side on mastication movements.1. The daily increase in the ratio of one side biased chewing on the nonhabitual chewing side was either rapid or gradual.2. On the habitual chewing side, there were no daily characteristic fluctuations in the 2 variables of area, but other parameters tended to increase. On the other hand, on the nonhabitual chewing side, all parameters tended to decrease daily.3. As a result of a canonical correlation analysis made between the number of chewing strokes and all parameters on the habitual and the nonhabitual sides, the first canonical correlation coefficient was larger on the nonhabitual side than on the habitual side.

Tolerance of Left-right Deviations on the Arrangement of the Upper Middle Artificial Teeth

The present study investigated the tolerance of left-right deviations in the arrangement of the upper middle artificial teeth relative to the median line of the face. For this purpose, the alignment of the maxillary incisor relative to the median line of the face was used as a point of reference.The model photos used for this investigation were prepared by combining 5 photos of both the face and the rows of teeth. In a stimulation series, the center of the row of teeth was displaced either to the left or to the right, and magnitude of this displacement was evaluated by groups of dentists, patients and students, who examined these photos. The results were classified into 5 reaction categories. According to magnitude adaptation level and estimation method, the left-right deviation tolerance was determined by psychological judgement.The results revealed that the lowest average tolerance of measuring 2.586mm was reported by the group of dentists, followed by values of 3.704mm and 4.204mm, which were reported by patients and students, respectively.

1/f Fluctuation on Appearance in Tapping Rhythms.

The present study was made not only to spectro-analyze the fluctuation of the tapping rhythm in subjects with normal masticatory function and to examine its overlapping with 1/f fluctuation as vital responsibility, but also to observe the influence of an experimental object intervened on the occlusal surface.As a result, normal subjects showed 1/f spectrum at each subjects proper rhythm, but not 1/f at a metronome-loading rhythm. In case of an object intervened at proper rhythm, the thickness of the object (100, 400μm) was suggested to make change in spectrum.

Estimate of the Original Gingival Color in Reflection Spectrum Data of Redness Gingiva by Multiple Regression Analysis.

This study was made to examine if original gingival color of an individual patient in healthy condition can be presumed from the observed data on the color of his gingiva having presented pericoronal gingival redness. The subjects were 50 males (aged 23-31) whose gingivae have been identified as clinically healthy. X, y, V, Bl and f values were determined from raw data obtained by the color measurement of 4 gingival spots near the cervical regions of maxillary central and lateral incisors. Multiple regression analysis was made with x, y and V values of the healthy papillary gingiva as objective variable and with each element of the observed data (twenty-dimensional observed value vector) upon the manifestation of gingival redness, which has bi-graded according to the degree of redness (slight redness, redness), as explanatory variable.As a result, the analysis of a bi-graded observed data series according to the degree of gingival redness was confirmed to make it possible to presume the original gingival color of the papillary part in healthy condition, suggesting the usefulness for its clinical application.