Dentin Interface Characterization of Universal Adhesives by Raman Microscopy

Objectives: Objectives: Aim of this study was to investigate morphology and chemical nature of the dentin interface of an experimental (ADH-XTE, 3M) and a commercial universal adhesive (Scotchbond^TM Universal, SBU, 3M).
Methods: Methods: The labial surface of bovine incisors was ground to expose dentin and treated with ADH-XTE or SBU in total etch (TE) or self-etch (SE) modes according to manufacturers’ instructions. A 1mm thick layer of Filtek^TM Z250 (3M) A3 was placed on the adhesive and cured (Elipar S10, 3M). Samples were ground perpendicular to the bonded surface to expose the interface for confocal Raman microscopy (Witec 300R with a 100X objective, NA 0.9; excitation wavelength 532nm). Bands at 1607cm^-1 (phenyl C=C of adhesive and composite) and 965cm^-1 (P=O of hydroxyapatite) were evaluated for spatially resolved spectra from linescans across the interface (step size 180 nm) at different locations of the samples (n≥4), to determine chemical nature and thickness of hybrid layer (HL) and adhesive layer (AL).
Results: Results: The confocal Raman microscope used allows to record Raman spectra of the interface composite-AL-HL-dentin with high lateral resolution. For each sample, a distinct AL and HL was detected. Raman microscopy revealed full adhesive penetration of the HL. HL and AL thickness in µm is given in the table, with the standard deviation (SD) in parentheses. Data by column were analyzed by ANOVA and multiple comparisons using the Tukey test (p<0.05). Means with the same letters are statistically the same.
Conclusions: Conclusion: HL was significantly thicker for TE vs SE samples. There was no significant difference for HL between ADH-XTE and SBU when used in the same etching mode. ADH-XTE afforded similar AL thickness as SBU in TE mode, and lower AL thickness in TE mode.