BONDING TO INTACT DENTIN

It has been reported that the presence of a smear layer on dentinal su bstrates can compromise bonding. Typically, smear layers are removed b y acidic agents that selectively extract calcium salts from dentin sur faces to leave a collagen-rich substrate. Acid-conditioned dentin (i.e ., demineralized) is then primed and an adhesive agent applied. In the present study, we removed smear layers by ''polishing'' dentin specim ens with a hydroxyapatite paste and ultrasonication. Bonding procedure s were carried out by means of an aqueous solution of 20% 2-methacrylo yloxyethyl phenyl phosphoric acid (phenyl-P) and 30% 2-hydroxyethyl me thacrylate, referred to as 20P-30H, a ''self-etching primer''. The 20P -30H solution was applied to ''intact'' dentin (i.e., non-demineralize d) for either 30 or 60 s. Control samples received no application (0 s ) of the self-etching primer. Mean tensile bond strengths (10 MPa) wer e similar in both the 30-second- and 60-second-primed groups. The widt hs of formed hybrid layers varied from 0.3 +/- 0.2 mu m at 0 s applica tion (control) to 2.1 +/- 0.3 mu m for the 30-second group and 4.1 +/- 0.2 mu m for the 60-second group. SEM and TEM observations revealed t hat the 20P-30H self-etching primer created diffusion channels into '' intact'', calcium-rich dentin which permitted monomer to infiltrate de ntin substrates. Hybrid layers identified under microscopic examinatio n demonstrated resistance to both HCl and NaOCl treatments, suggesting that the hybrid layer was not defective, and that bonding was stable.