Microtensile bond strength of several adhesive systems to different dentin depths

Purpose: To determine the bond strength of five adhesives systems to either superficial or deep dentin. Methods: Extracted human third molars had their crowns transversally sectioned either next to the occlusal DEJ or next to the pulp, to expose flat, superficial or deep dentin surfaces. The surfaces were bonded with: 1) three two-step, total-etch, self-priming adhesives (Single Bond, Prime&Bond NT, and Excite), 2) a two-step, self-etching primer (Clearfil SE Bond), and 3) a single-step, self-etching all-in-one adhesive (Etch & Prime 3.0) according to manufacturers' directions. Composite build-ups were constructed incrementally with Z250. After storage for 24 hours in water at 37°C, the teeth were sectioned to obtain several bonded beams of 1.0 mm ² cross-sectional area. Each beam was tested in tension in an Instron machine at 0.5 mm/minute. Results were analyzed by two-way ANOVA and post-hoc multiple comparisons (P= 0.05). Bonded interfaces were also examined by TEM. Nanoleakage was examined using a silver-staining technique. Results: Single Bond, Prime&Bond NT and Clearfil SE Bond performed equally when were bonded to superficial dentin; the lowest value was obtained with Etch & Prime 3.0. On deep dentin, the highest bond strengths were attained with Clearfil SE Bond and Prime&Bond NT. The bond strengths of Prime&Bond NT and Excite were significantly higher to deep than to superficial dentin and the rest of the adhesives showed similar bond strength to both dentin depths. Nanoleakage was manifested to variable extent within all hybrid layers examined.