Abstract
Studies were made of particle size distribution, ratio Rd/Td etc. of the dust generating through 4 kinds of instruments, Stump bur, Toughron point, Sand cup (coarse) and Sand cup (Fine) under variable load and rotational frequency on 3 kinds of materials, ordinary gypsum, hard plaster and improved hard plaster. The results obtained are as follow : 1) The characteristics of instrument had the greatest influence upon the particle size distribution. 2) Harder material had more constant particle size distribution, and greater distribution for smaller particle diameter. 3) Higher rotational frequency and smaller load had greater ratio Rd/Td, from a fact indicating it might be that, for the same material and instrument, the distribution points to a constant direction over a certain value of condition. 4) Approximate ratio Rd/Td was 1 : 2.5 to 10 for ordinary gypsum, 1 : 2.5 to 7 for hard plaster and 1 : 2 to 8 for improved hard plaster. A part of this study was presented at 31th Annual Meeting of the Japanese Society for Dental Health held in Tokyo, September, 1982.
