Determination of residual double bonds in resin–dentin interface by Raman spectroscopy

Objectives: The quality of the hybrid layer is believed to be more important than the thickness of this layer. The purpose of this study was to investigate a method to analyze the percentage of adhesive resin residual double bonds in the dentin–resin interface using laser Raman spectroscopy. Methods: Bovine dentin was treated with dentin adhesives and resin composite was bonded according to the manufacturersʹ instructions. The specimens were sectioned parallel to dentinal tubules and the surfaces were then polished to 1 μm diamond pastes. Raman spectra were recorded along a line perpendicular to the dentin–resin interface in steps of 0.2 μm. The measurement of residual C=C bond was made on a relative basis by comparing the C=C unpolymerized methacrylate stretching vibration (1638 cm−1) against the C=O stretching mode of the ester group (1719 cm−1). The percentage of residual double bonds including pendant and monomeric double bonds was calculated by comparing the obtained ratio with that of uncured adhesive resin. Results: The amount of residual double bonds in the hybrid layer varied from 10 to 25% compared to the uncured adhesives, a relatively higher percentage was detected for Fluoro Bond (12.3–23.6%) and Single Bond (9.5–21.8%), and lower for Mac Bond II (10.6–18.0%) and Mega Bond (10.7–16.3%). No relationship was seen between the percentage of remaining double bonds and the location within the resin–dentin interface. Significance: Laser Raman microscopy used was a useful tool for measuring the residual double bonds in the dentin–resin interface.