Comparative microtensile bond strength and SEM analysis of bonding to wet and dry dentin

Purpose: To compare bond strengths of resins to acid-etched wet vs. dry dentin. Materials and Methods: Human third molars were bonded with One-Step (OS), Single Bond (SB) or Clearfil PhotoBond (PB) under control moist or air-dried (5 s air blast) conditions. Tensile bond strengths were tested using the microtensile bond testing method. Scanning electron microscopy was done to evaluate the quality and thickness of the hybrid layers following polishing and acid plus NaOCl-challenge. Results: The tensile bond strengths of OS, SB and PB were significantly (P< 0.01) lower (8-19 MPa) to air-dried dentin than to moist dentin (39-50 MPa). No hybrid layers were seen in the air-dried specimens bonded with OS or SB, while relatively thin hybrid layers were produced by PB. In contrast, moist dentin produced high bond strengths with all bonding systems and created thicker, acid/NaOCl-resistant hybrid layers. These results support the predictions of a previously published morphologic model and offer a morphologic explanation for the differences in bond strengths between wet vs. dry bonds.