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This observation was carried out to investigate the inorganic constituents of dental calculus of varying locations and different ages. Supragingival calculus was obtained from 540 patients with the periodontal disease. The results were as follows : 1. The weight loss rate in ashing by aging was the highest in the 2nd decade (63.7%) and followed in order by 3rd decade (60.8%), seventh decade 959.8%), fourth decade (55.9%), sixth decade (52.6%) and fifth decade (43.2%). 2. The weight loss rate by ashing was more prominent in the buccal surfaces of the upper posterior teeth (62.0%) than in the lingual surface of the lower anterior teeth (59.7%). 3. The difference in contents of the inorganic constituents by sex was not remarkable. (male, Ca:373.0 P:333.9, female, Ca: 380.2, P: 339.6 ㎍/mg dry weight) 4. In the dry calulus, contents of the inorganic constituents were as follows: Ca:325.8 P:269.10 Mg:1.21 Na:8.44 K:1.32, Zn:0.67 ㎍/mg. 5. The Ca/P ratio was the lowest in the upper anterior region (1.11) and the highest in the lower posterior region (1.29) and the average was 1.20.
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