Laser Raman Micro-spectroscope Observation for the Analysis of Resin-dentin Interdiffusion Zone

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Adhesion of resin composites to tooth substrate is currently believed to rely on the infiltration of bonding resin into the porous zone, establishing micro-mechanical retention to etched surface. If adhesive resin does not penetrate the demineralized tooth substrate, then the porous layer within this layer will be exposed to oral fluids and vulnerable to degradation. The purpose of this study was to investigate the effect of self-etching primer application duration on resin penetration into dentin and dentin bond strength. After making bonded specimens, sectioned through the bonded interface. The sectioned surfaces were then polished with diamond pastes down to 1.0 μm particle size. Raman spectra were successively recorded along a line perpendicular to the tooth/resin interface. The sample stage was moved in steps of 0.2 μm on a computer controlled X-Y precision table. Additional spectra from samples of tooth and cured bonding resins were recorded for reference. The relative amounts of the hydroxyapatite (960cm-1,P-O), bonding agent (640cm-1,aromatic ring), and alkyl group (1450cm-1,C-H) in the enamel/resin bonding area were calculated. From the Raman spectroscopy, the widths of demineralized dentin increased with prolonged treatment time. The patterns of gradual transition of components were different among the groups. Furthermore, the tooth/resin interface represents a gradual transition of bonding agent from resin side to tooth side. From the results of this study, nonuniform resin infiltration into the etched enamel was detected and the degree of resin infiltration was different among the bonding systems used.