Effect of aluminum oxide and sodium bicarbonate on smear layer

Objectives: The purpose of this study was to analyze and compare the effect of the use of aluminum oxide and sodium bicarbonate air abrasion systems on the smear layer of human dentin. Methods: Twelve sound molars were selected and the smear layer was created with the use of a 2057 diamond bur. The teeth were split in 3 groups: I. Smear + aluminum oxide treatment; II. Smear + sodium bicarbonate treatment; III. Control (only smear layer). The treatments were made for 15 seconds, with lateral movements of the air abrasion handpiece. The surfaces were washed with a water stream and dried. The specimens were put in Karnovsky solution for 1 hour, dehydrated in alcohol solutions, dried until the critical point (CPD030, Balzers), attached to stubs and metalized with gold (MED010, Balzers) for SEM analysis and photography, in magnifications of 500 and 5000x. Results: The group II presented a standard smear layer with irregularities, where parallel marks, suggesting the bur use, could be observed. In the group I, the smear layer was partially removed in a very unorganized way, without the bur parallel marks, and with some dentinal tubules exposed. The group II, showed a more uniform surface, with the removal of the entire smear layer and maintenance of some smear plugs. In this group, many dentinal tubules were exposed. Conclusions: The sodium bicarbonate was more efficient in removing the smear layer, exposing many dentinal tubules. The aluminum oxide removed only partially the smear layer.