the effects on dentin permeabilityof burnishing NaF, kaolin, or glycerin, alone and in various combinations, were determined using anin vitrosystem. The results indicate that the important variable was not any of the constituents of the paste but the burnishing process itself. Burnishing dentin creates a partial smear layer on the dentin surface, thereby occluding the orifices of dentinal tubules sufficiently to reduce fluid movement across dentin 50 to 80%.