DENTIN BONDING - SEM COMPARISON OF THE RESIN-DENTIN INTERFACE IN PRIMARY AND PERMANENT TEETH

Previous studies have suggested minor differences between primary and permanent teeth in terms of dentin composition and morphology. Other r eports indicated lower bond strengths of resin composites to dentin of primary teeth compared with dentin of permanent teeth; however, no in formation is available regarding differences in the micromorphology of the resin-dentin interface that may explain these lower bond strength s. Therefore, the purpose of the present study was to compare primary and permanent teeth in terms of the thickness of the hybrid layer deve loped with two bonding systems. Our hypothesis was that bonding differ ences previously reported between primary and permanent dentin would b e reflected in hybrid layer differences observable in SEM analyses. Tw enty human extracted and non-carious teeth were divided into 4 groups: 5 primary and 5 permanent teeth restored with All-Bond 2/Bisfil P sys tem; and 5 primary and 5 permanent teeth restored with Scotchbond Mult i-Purpose/Z100. The sample area available on each tooth was divided fo r the two dentin conditioning times (7 and 15 sec). Measurements of hy brid layer thickness were performed by means of SEM at x13,000. The re sults of this study indicated that the hybrid layer produced is signif icantly thicker in primary than in permanent teeth (p = 0.0001), sugge sting that primary tooth dentin is more reactive to acid conditioning. No difference was observed in the hybrid layers produced by the two a dhesive systems (p = 0.7920). The increased thickness of the hybrid la yer in primary teeth (25 to 30%) and the subsequent lack of complete p enetration of adhesive resin into previously demineralized dentin may contribute to the lower band strengths to primary dentin reported in t he literature. If a narrower hybrid layer more uniformly infused with resin is the goal of dentin bonding, it is concluded that a differenti ated protocol for bonding to primary dentin (with shorter time for den tin conditioning) can be used as a means to reproduce the hybrid layer thickness seen in permanent teeth.