Comparison of the hybrid layer formed by Silorane adhesive, one-step self-etch and etch and rinse systems using confocal micro-Raman spectroscopy and SEM

Abstract 

Objectives

To determine the extent of the hybrid layer (HL) of the novel adhesive system (Silorane, 3M ESPE) compared to one-step and etch and rinse adhesive systems, using 2D confocal micro-Raman spectroscopy and SEM.

Methods

Silorane adhesive system was compared to two one-step self-etch (G Bond, GC; AdheSE One, Ivoclar Vivadent) and etch and rinse (Excite, Ivoclar Vivadent) as controls. Adhesives were applied to human dentine, cured and sections prepared perpendicular to the flat adhesive–dentine surface. Two-dimensional micro-Raman mapping was performed over 20μm×20μm areas across the adhesive–dentine interface. SEM micrographs of the same specimens were obtained. One-way ANOVA (Tukey's post-test) was used to analyse the differences in HL thickness among the four adhesive systems and the paired t-test to compare the results obtained by micro-Raman and SEM for each adhesive.

Results

Silorane adhesive system formed a HL of comparable thickness to methacrylate-based but thicker than the acrylamide-based one-step self-etch adhesives from SEM analysis. A gradual decrease in adhesive penetration was observed in all systems. A 1-μm zone, between the cured primer and bond was identified by Raman but not visualised on SEM. Compared to SEM, HL calculated from Raman data were always greater.

Conclusions

Micro-Raman spectroscopy gives a more precise indication of dentine demineralisation and monomer infiltration and highlights the intermediate zone of ∼1μm between Silorane primer and bond, not visible with SEM at ×10,000 magnification. Giving as it does, a compilation of many linear scans it allows HL mean values to be calculated.

Keywords: Confocal micro-Raman spectroscopy, SEM, Hybrid layer, Self-etch adhesives