Dentin permeability: effects of smear layer removal.

The results of this study permit the following conclusions: 1. The use of dilute (6%) citric acid for very short time intervals permits sequential removal of the smear layer on human dentin. 2. Acid-etching for as little as 5 seconds removes much of the smear layer and exposes the orifices of dentinal tubules. 3. Dentin permeability increased rapidly during acid-etching with 6% citric acid, reaching a maximum value after only 15 seconds of etching. 4. The production of a smear layer on dentin during restorative procedures establishes a protective diffusion barrier. Removal of the smear layer by acid-etching increases the permeability of dentin which, under some conditions, must be regarded as a liability.