INTERFACIAL MORPHOLOGY AND STRENGTH OF BONDS MADE TO SUPERFICIAL VERSUS DEEP DENTIN

Purpose: To evaluate the interfacial morphology (SEM) of two bonding s ystems to superficial and deep dentin using a reverse-sandwich techniq ue, coupled with measurement of micro-tensile bond strengths (MTBS). M aterials 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 et ch) were applied to superficial versus deep dentin surfaces and the tw o disks were bonded together into a reverse-sandwich configuration. Re sults: SEM revealed that All-Bond 2 and Imperva Bond applied under tot al 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-Bon d 2 and Imperva Bond applied to unetched dentin formed very thin resin -infiltrated layers (less than 0.5 mu m) on both dentin substrates. MT BS of All-Bond 2 and Imperva Bond were more than 20 MPa irrespective o f dentin depth and were not significantly different. Without acid etch ing, the MTBS of both systems to deep dentin was significantly lower t han to superficial dentin. These results suggested that for the total- etch systems, dentin depth affected the thickness of the resin-infiltr ated layer, but the thickness of the resin-infiltrated layer had no si gnificant relationship with MBTS. The present data also indicated that the acid-etch technique could prevent the decrease of bond strength s een in deep dentin in the absence of etching.