Effect of the hydration status of the smear layer on the wettability and bond strength of a self-etching primer to dentin

Purpose: To evaluate die microtensile bond strength (MTBS) of a resin-based composite to smear layer-covered dentin using a self-etching primer, Clearfil SE Bond (CSEB), under two different hydration states. Surface roughness and wettability (contact angle measurements) of water and the CSEB primer were also evaluated on this substrate. Methods: Contact angle (CA) measurements were performed on four caries-free extracted human third molars. The specimens were sectioned parallel to the occlusal surface to expose die moderately deep dentin and ground flat (180-grit SiC) under water to provide uniform flat surfaces. In two samples, the smear layer was completely air-dried; in the other two specimens, die smear layer was briefly air-dried. Contact angle measurements were performed to assess wettability of water and CSEB primer using the Axisymmetric Drop Shape Analysis technique. Surface roughness (SR) was determined with a contact profilometer. In another four molars, CSEB was applied to the smear layer-covered dentin with both hydration states. Resin build-ups were performed incrementally with Tetric Ceram. After storage for 24 hours in water at 37°C, the teeth were sectioned to obtain bonded beams with an average cross-sectional area of 1.0 mm ². Each beam was tested in tension in an Instron machine at 0.5 mm/minute. Kolmogorov-Smirnov and Student t-tests were performed at a 95% significance level. Results: Observed water contact angles were lower on die hydrated smear layer but no differences were found between contact angles on completely and briefly air-dried smear layer when the primer was used for CA measurements. SR was similar for both substrates and MTBS was greater when the adhesive was applied on the completely air-dried smear layer.