Investigations were made of the forces during brushing of the teeth, the patterns of brushing movements, and muscle activities, with and without blockage of sensory perception in the oral cavity, while each subject brushed by the rolling method, scrubbing method, and by his own individual habitual brushing method. We learned from electromyograms that the scrubbing method primarily used the muscles of the palm of the hand and the forearm, while the rolling method cleaned principally by action of the muscles of the upper arm and shoulder. With the rolling method, the rhythmic pattern of the brushing movement and muscle activity were lost when sensory perception in the oral cavity was blocked and, in those subjects who had a low periodontal membrane tactile threshold, the brushing force was greater than when sensory perception was not blocked. However, no effect was observed with blockage of the sensory perception in the oral cavity when the scrubbing method was used. Since brushing movements with the scrubbing method resemble the movements of writing, we also carried out investigations on the relationship between the forces during writing and brushing. As a result we found that with the scrubbing method, the brushing forces were strong for the subjects who had strong writing forces, while they were weak for those with weak writing forces. It was clear from the above results that the force of brushing with the rolling method was affected more by factors relating to oral sensory perception than muscle activity, while with the scrubbing method it was affected more by factors relating to muscle activity of the palm of the hand and forearm than by oral sensory perception. There was a clear difference in the brushing forces, pattern of brushing movements, and muscle activity between experienced and inexperienced subjects with both the scrubbing and rolling methods. Thus we learned that the effect of brushing instructions could be evaluated not only by the efficiency of plaque removal, brushing force or skill of brushing movements, but also by muscle activity. The phenomena observed with the scrubbing and rolling methods were not seen with the subjects' individual habitual brushing method.
The permeability of tight junctions to tracers having different molecular weights was investigated in the submandibular gland of rats stimulated parasympathetically, sympathetically, or both. Lacto-peroxidase (82,000 daltons), horseradish peroxidase (40,000 daltons), and microperoxidase (1,630 daltons) were used as the tracers. The tracers were administered by close arterial infusion via the glandular artery, and their secretion into the saliva was quantified biochemically, and their secretory routes within the gland were determined histochemically at the electron microscopic level. Microperoxidase and horseradish peroxidase passed into the saliva by electrical stimulation of either the chorda or superior cervical ganglion, and the combined stimulation of both caused a larger output of both tracers. No output of lactoperoxidase into the saliva occurred with any type of nerve stimulation. Electron microscopic histochemical observations showed that molecules of molecular weight equal to or lower than that of horseradish peroxidase entered the lumen through the tight junctions between adjacent acinar cells following combined stimulations of chorda and superior cervical ganglion. These findings indicate that electrical stimulation of parasympathetic and sympathetic nerves causes an increase in tight junctional permeability of acinar cells to microperoxidase and horseradish peroxidase. Although the combined stimulation of parasympathetic and sympathetic nerves resulted in increased junctional permeability to these tracers, the junctions remained impermeable to larger molecules, i.e., lactoperoxidase.
The purpose of this study was to estimate the location of the end plate in the masseter muscle, and to decide the appropriate position of surface electrodes for recording electromyograms (EMG) in humans. The subjects were 16 males who had no signs or symptoms of muscular disease. Identical electrode arrays were placed on the masseter muscles on each side. Each subject was asked to clench in the intercuspal position at various levels of maximum EMG amplitude. Eleven amplified EMGs were monitored simultaneously using a linear electrode array consisting of 12 stainless steel contacts. Various values were observed in different regions of the masseter muscle for the root mean square rectified EMG during brief isometric contraction. The superior region of the muscle had lower values than the inferior. The end-plate zone, which is in the center of the lower half of the masseter muscle, showed a lower amplitude than other regions. The propagation of motor unit action potentials was also observed. It was concluded that, aside from the end-plate zone, a position within the lower half of the muscle was most suitable for recording the surface EMG of the masseter muscle.
Glass ionomer cements have the disadvantage of being vulnerable to moisture. We would like to overcome this problem by clinical procedures. Three glass ionomer cements were tested in vitro with the goal of protecting these materials from moisture during clinical operations. To observe the effectiveness of various surface protective measures, we divided each cement sample into six groups, each of which underwent 24-hour surface treatment. The first group was a control where the cement was covered with a glass slab for 24 hours. The remaining five groups were subjected to no treatment or treatment with varnish, cocoa butter, Teethmate-A, or Ketac-Glaze. Two additional groups were prepared for comparison of early finishing with and without water spray. When the Vickers hardness number (HVN) for each sample was measured at 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, and 40 days, it tended to increase after 24 hours, reaching a maximum value at different times with different cements. Analysis of variance revealed that during the first few days the hardness of the control was significantly different from that without treatment or with treatment by varnish or cocoa butter. However, treatment with Teethmate-A or Ketac-Glaze produced results close to those for the control. Significant differences in hardness during the first few days were noted when early finishing was carried out under wet and dry conditions. These findings indicate that a light-cured unfilled resin should be applied to the surface of glass ionomer cement immediately after the initial set to allow complete setting without interference by oral fluids. Also, water spray should be avoided during contouring of the cements if they have not fully hardened.