Search

Changes caused by attrition in interocclusal contact were investigated in 11 subjects with natural dentition showing no or only slight attrition and 6 subjects with natural dentition showing moderate attrition. Interocclusal spaces in the molar region in the maximally intercuspidated position of each subject were recorded in White Silicone impression material. Light-transmittance measurements of interocclusal records were made to determine differences in interocclusal spaces. Results 1. Mean values of the most closely occluding area in the upper molar region Tooth kind I B II B I M II M Slight-attrition group 0.6 0.9 3.2 2.5 (mm2) Moderate-attrition group 7.2 11.0 30.4 26.8 (mm2) 2. Mean values of ratios between most closely occluding areas and occlusal-surface projecting areas in the upper molar region Tooth kind I B II B I M II M Slight-attrition group 1.1 1.7 3.1 2.7 (%) Moderate-attrition group 13.1 21.0 28.4 27.5 (%) Conclusions 1. Differences in interocclusal spaces between the slight- and moderate-attrition groups were apparent only in the most closely occluding areas. 2. When load on supporting tissues is proportionate to the size of the closely occluding area, the supporting load probably increases as attrition progresses, although the ratio of increasing load changes little among different kinds of teeth.

Recent developments in medical engineering has made it easy to record biological phenomena. Furthermore, the widespread popularity of the personal computer has made data processing system remarkably efficient. In this study, an efficient personal computer system for mandibular movement analysis is investigated, and a data analyzing system for that movement developed. Applying this system to chewing movements in a small number of cases made possible efficient, easy and accurate analysis. The following is an outline of the system and its applicability. 1. Standard measuring coordinate system for mandibular position and designation of mandibular position measuring point An orthogonal coordinate system is used to the standard measuring coordinate system for mandibular position measurement coordinates. The X axis of this orthogonal coordinate system is determined as a straight line connecting two LEDs. The origin point is designated as the center between two LEDs. This connects with the upper dentition or the maxilla. The mandibular position measuring point is designated on the orthogonal coordinate system. The X axis of this orthogonal coordinate system is determined as a straight line connecting two LEDs. The origin point is designated as the center between two LEDs. This connects with the lower dentition or the mandible. The analysis of mandibular position of designated measuring point on the lower dentition or the mandible is performed corresponding to the orthogonal coordinate system on the upper dentition or the maxilla. 2. Calculation of coordinates value [mm] for mandibular position measuring point In the analysis, value [V] for the distance between two LEDs established on the upper jaw is substituted for the already input real distance [mm] between two LEDs. The coordinates value of the mandibular position measuring point is calculated from these substitution value. 3. Data recording Data concerning mandibular movement and myoelectric discharges are recorded by means of a data recorder. Digital data are converted to analogue data from the data recorder by means of a 12-bit A/D converter and they are accumulated in the memory of the personal computer system. Digital data in the memory of the personal computer system can be stored in about 97 seconds for the storage capacity of a floppy disk (2HD) memory area.