RESUMO
OBJECTIVE: To determine the effect of varying the adhesive pH on the bond strength of an experimental self-etch adhesive system (BISCO, Inc) to dentin with the bonding surface perpendicular (occlusal direction) or parallel (axial direction) to dentin tubules. METHODS: An experimental self-etch adhesive was modified by adding base to increase the pH from 1.1 to 2.7. Shear bond strength (SBS) was measured using an Ultradent jig method with Aelite All-Purpose Body light-cured composite (BISCO, Inc). Human dentin was prepared by exposing the axial and occlusal surface. The self-etch adhesive was applied according to the manufacturer's instructions and cured for 10 seconds@ 500mW using a VIP (BISCO, Inc) halogen curing light. Scanning electron microscope (SEM) examination was used to view both the occlusal- and axial-oriented dentin surfaces that were etched using pH (1.2~3.0) adjusted phosphoric acid solutions. All bond strength data analysis was performed using ANOVA, followed by a Student-Newman-Keuls multiple range test. RESULTS: When the dentin-bonding surface was parallel to the tubule orientation (axial), the bond strength was independent of the pH of the self-etch adhesive (p>0.05). When the bonded surface was perpendicular to the tubule orientation (occlusal), the bond strength numbers were decreased as the pH decreased; the decrease became statistically significant when the pH was lower than 1.8. With a pH higher than 2.3, the bond strength had no difference (p>0.05) between the occlusal and axial positions. When the pH was lower than 1.8, SEM pictures confirmed that the smear layers and smear plugs were completely solubilized by the phosphoric acid solution. Higher pH values (2.02.8) showed smear layers partially solubilized and pH values of 3.0 fully retained the smear layer.