Investigation of adhesive-dentin interfaces using Raman microspectroscopy and small angle X-ray scattering

Human dentin specimens were treated with two different etch-and-rinse adhesives, Single Bond 2 (SB2) and Prime & Bond NT (PBNT), and two composite resins, TPH and P60. Cross-sectional samples, approximately 1 mm thick, were analyzed with Raman line mapping and imaging across the dentin-adhesive- composite interface. The integrated intensities of selected bands associated with adhesive, organic material, composite and hydroxyapatite of dentin were calculated to determine the distribution of adhesive infiltration into demineralized dentin. The results were compared with the enamel-adhesive composite interface. The demineralized zone was smaller in the enamel-adhesive interface than in the dentin-adhesive interface. The region of collagen-adhesive crosslinking was wider in the PBNT adhesive than in the SB2 adhesive. However, a gap at the dentin-PBNT composite interface, which was not observed at the dentin-SB2 composite interface, might compromise the dentin-restoration bond. K-means cluster analysis of the Raman images confirmed the findings. The ultrastructure of the dentin-resin interface was studied using scanning electron microscopy. Small-angle X-ray scattering was also applied to reveal and quantify fine-scale structural features. SB2 adhesive was found to diffuse more into demineralized dentin along with greater nanosized aggregations in the hybrid layer.