The nature of the hybrid layer(HL)following chemical treatments is not currently understood properly. Objective: Using micro-Raman spectroscopy (mRS) and SEM, this study investigated the effect of chemical treatments on the morphology and composition of polished and unpolished HL. Methods: The occlusal 1/3 of the crown was removed from 9 human 3rd molars. Smear layers were created by abrading the dentin with 600grit SiC and the exposed dentin treated with Single Bond per manufacturer's instructions. Dentin surfaces were sectioned parallel and perpendicular to the bonded surface. For each tooth: one-half was polished with silicon carbide (#600, 1000) and alumina(1, 0.05mm); other half was not polished. Both polished and unpolished specimens from each tooth were randomly selected for treatment with one of the following: a) 5N HCl for 30sec followed by 5%NaOCl for 30min; b) 30min 5%NaOCl; c) 30min 5%NaOCl and 1min sonication; d) 5%NaOCl for 30min followed by 5N HCl for 30sec. Following rinsing, each specimen was analyzed with mRS and SEM. Results: For bleach or HCl-bleach, there was almost no change in the spectrum of the polished specimens as compared to unpolished HL without any treatment. In contrast, bleach or HCl-bleach produced a dramatic decrease in the intensity of collagen bands in the unpolished specimens. Based on SEM analysis, the interface of the polished specimens was largely unchanged by the acid or bleach treatments. Exposure to the same chemical treatments resulted in large interfacial voids in the unpolished specimens. Conclusions: Descriptions of HL quality are commonly based on the acid reactivity of polished specimens. The results of this study indicate that polishing dramatically alters the native composition, increasing its acid-resistance and thus, this procedure could give false conclusions about the HL quality. Supported in part by USPHS DE12487.

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