Changes in the particle size distribution and morphology of abrasives contained in polishing pastes used for professional mechanical tooth cleaning (P. M. T. C. ) were assessed in vitro in 10 different types of polishing pastes currently available on the market, and the following results were obtained:
1) As PP 3, in which the abrasive is diatomaceous earth, was used for polishing, the tendency for the particles of the abrasive to become smaller was found to be more marked than with the other abrasives.
2) The particles of the abrasive in Prophy Paste RDA 250 and Mel-R also tended to become smaller, but only slightly so in comparison with PP 3.
3) No major changes in particle size distribution were observed in PPI, Prophy Paste RDA 170,120, or 40, NEO-PC, NEO-SC, Mel-R, or Mel-F.
4) The edges of the abrasive in PP 3 were much less sharp than the edges of the abrasives in the other polishing pastes, and the particles in PP 3 tended to appear roundish.
5) There were fewer aggregates of abrasive after polishing with PP 3.
Based on the above results, it is inferred that immediately after the start of polishing, the large aggregates of the diatomaceous earth used as the abrasive in PP 3 effectively eliminated the insoluble deposits that had adhered to the surface of the teeth, that the aggregates gradually disintegrated and particle diameter became smaller, and thus that it is possible to clean teeth without severely injuring the polished surfaces, suggesting that diatomaceous earth is an efficacious abrasive in polishing pastes.