Background: The purpose of this study was to evaluate the morphology and permeability of dentin after brushing with different toothpastes in the presence and absence of smear layers.
Methods: Dentin discs were prepared from extracted third molars. Dentin permeability was measured using a hydraulic pressure apparatus working at 70 cm H2O pressure. Dentin was treated with 0.5 M EDTA for 5 minutes and washed to remove a smear layer and to establish the maximum permeability of each dentin disc, which was expressed as 100%. A new smear layer was then created on the upper surface using a #400 carbide paper under water for 30 seconds. Dentin permeability of the smear layer-covered dentin was measured and expressed as a percentage of the maximum permeability of that specimen, permitting each specimen to serve as its own control. Each sample was then brushed by a mechanical device under water for 3 minutes with constant pressure of 250 g using a medium toothbrush and permeability remeasured. Finally, 1 of 5 different toothpastes was applied on the dentin and brushed for 3 minutes. In another group, the same procedures were performed with the exception of the smear layer production, so it was possible to calculate changes in the permeability of dentin with open tubules following brushing. Scanning electron microscopic (SEM) examination of dentin was obtained before and after treatments with brushing and toothpastes.
Results: Dentin permeability was reduced by brushing procedures when the smear layer was absent, but it was increased when the smear layer was present. Toothpaste application reduced dentin permeability when no smear layer was present on the top of the surface, but modified and increased permeability of samples with smear layers. SEM observations demonstrated the presence of dentifrice particles on dentin surfaces and inside dentinal tubules, and this may be responsible for the observed reductions in permeability. Smear plugs produced during dentin brushing were not removed by the dentifrices.
Conclusions: Dentin permeability and morphology are significantly affected by toothbrushing and by the type of dentifrice used. The presence of smear plugs in the dentin may decrease severity.