[Experimental studies on the transitional characteristics from touch sensation to pressure sensation in the mechanoreceptive sensation of periodontium].

Many studies have made on the physiological significance of the periodontium in relation to oral functions. But, although its importance to oral functions has been pointed out, few investigations have been carried out on the periodontal pressoreceptive information system. To help rectify this situation, as a link in investigations of soft-food textures, the author attempted to determine how a sense of pressure was perceived when loads gradually increasing from very small were applied to the tooth surface. In addition, the author attempted to clarify the way the periodontium discerns differences between initial and secondary loadings in a range of small loads between the touch sensation and the pressure sensation. Subjects were 10 males with sound, natural dentition and no disorders in mandibular functions. In order to eliminate intervention from pressoreceptors in the masticatory muscles and the mandibular joints, the upper first premolar was chosen as the test tooth. Small loads were applied in 2 directions: parallel to the first premolar vertical axis (vertical) and from the lingual to the buccal sides parallel to the occlusal plane (horizontal). For vertical loading, the mesial pit on the occlusal surface was chosen as the loading point. The middle point on the lingual surface was chosen as loading point for horizontal loading. First, loading on the tooth surface was gradually increased to obtain (1) threshold value for touch sensation; that is, minimal load required to incite a touch sensation, and (2) critical value for pressure sensation; that is, minimal load required to incite the pressure sensation subsequent to the touch sensation. Each subject was requested to press a hand switch in the moment he experienced the sensation of being touched and then again when, during increases of load, the touch sensation changed to the pressure sensation. The loading device was built into an electric strain gauge. Loads were increased gradually from 0 g to 60 g, with an increase ratio of about 10 g/sec. Loading wave and switching signal were simultaneously recorded on an oscillograph. Second, in order to determine the ability to discriminate small loads, with the same loading device, initial load was applied to the tooth. This load served as control. As soon as the load was sensed, it was removed. Then the secondary (testing) load was applied. Subjects were requested to say whether the secondary load was larger, smaller than or same as the initial one.(ABSTRACT TRUNCATED AT 400 WORDS)