The permeability of the dentine and other tissues that are exposed at the tip of a rat incisor

The tissues that form the incisal surface of a rat incisor include dentine, an atubular calcified tissue which lines the last-formed dentine, and calc ified pulp remnants. The permeability of these tissues was investigated in vitro and in vivo using Evans blue dye. The incisal surface was prepared by etching it with acid or removing 1 mm by fracturing or with a diamond disc followed by etching. In some cases, 1.5-3.0 mm was removed to expose the s oft tissue of the pulp. The dye was applied for 30 min, then longitudinal s ections of the crown were cut and examined microscopically to determine the extent to which the dye had diffused into the underlying tissues. In only those teeth in which the dye had been applied direct to the pulpal soft tis sue could any be detected below the exposed tooth surface. In previous expe riments, it was found that both cat and human dentines were freely permeabl e to Evans blue when they were tested in vitro. It is concluded that the de ntine and other tissues that form the incisal surface of a rat incisor are less permeable than cat or human dentine. (C) 2000 Elsevier Science Ltd. Al l rights reserved.