[A clinical study on the changes in interocclusal contact caused by attrition, especially on the closely occluding area of upper molar region].

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.