Interfacial morphology and strength of bonds made to superficial versus deep dentin

Purpose: To evaluate the interfacial morphology (SEM) of two bonding systems to superficial and deep dentin using a reverse-sandwich technique, coupled with measurement of micro-tensile bond strengths (MTBS). Materials and Methods: Superficial and deep dentin disks were prepared from the same tooth in freshly-extracted human third molars. All-Bond 2 (total etch versus no etch) or Imperva Bond (total etch versus no etch) were applied to superficial versus deep dentin surfaces and the two disks were bonded together into a reverse-sandwich configuration. Results: SEM revealed that All-Bond 2 and Imperva Bond applied under total etch conditions formed thicker resin-infiltrated layers (4-8 mu m) on deep dentin than on superficial dentin (2-4 mu m), and that All-Bond 2 and Imperva Bond applied to unetched dentin formed very thin resin-infiltrated layers (less than 0.5 mu m) on both dentin substrates. MTBS of All-Bond 2 and Imperva Bond were more than 20 MPa irrespective of dentin depth and were not significantly different. Without acid etching, the MTBS of both systems to deep dentin was significantly lower than to superficial dentin. These results suggested that for the total-etch systems, dentin depth affected the thickness of the resin-infiltrated layer, but the thickness of the resin-infiltrated layer had no significant relationship with MBTS. The present data also indicated that the acid-etch technique could prevent the decrease of bond strength seen in deep dentin in the absence of etching.