Micro-Raman analysis of the hybrid layer created by three adhesives

Objectives: This study examined quality and morphology of the hybrid layer (HL) created by one-step self-etch adhesives used on smear-layer covered or on etched dentin by means of a micro-Raman analysis. The tested hypothesis was that preliminary etching does not affect degree of conversion. Methods: Adper Easy Bond (AEB, 3M ESPE, 1-step self-etch) and an experimental adhesive formulation (EXL-759, 3M ESPE, 1-step self-etch) were applied on etched dentin (etch-and-rinse mode) or on smear-layer covered dentin (self-etch mode, following manufacturer's instructions) with simulated pulpal pressure. Prime&Bond NT (PB, Dentsply, 2-step etch-and-rinse) was used as control (on etched dentin). Specimens were transversally cut to expose the bonded interfaces to the micro-Raman beam (Renishaw InVia; laser wl 785nm). Peaks associated with mineral dentin components (PO functional group at 960cm-1) and adhesive (phenyl C=C group at 1610cm-1) within the bonded interface were used to detect the hybrid layer (HL) depth, and the ratio between a reaction peak (C=C at 1640cm-1) and a reference peak (phenyl C=C 1610cm-1) was used to calculate the degree of conversion (DC) of the adhesives into the HL. Statistical analysis was performed with one-way ANOVA (p<0.05). Results: the result aare showed in the table below (Different superscript letters indicate statistical differences (p<0.05)). Conclusions: One-step self-etch adhesives showed a higher DC than control (2-step etch-and-rinse). The tested hypothesis was accepted since DC of tested one-step adhesives was irrespective from the substrate (i.e. smear-layer covered vs etched dentin).