Analysis of the enamel/adhesive resin interface with laser Raman microscopy

Adhesion of resin composites into enamel is currently believed to rely on infiltration of bonding resin into the porous zone, establishing micromechanical retention to etched enamel. This study investigated the change in chemical composition of the enamel/resin interface using a laser Raman microscopic system (System-2000, Renishaw). Two-step bonding systems, Mac Bond II (Tokuyama Corp), Clearfil Mega Bond and Single Bond (3M/ESPE) were employed. Resin composites were bonded to bovine enamel with bonding systems and sectioned through the bonded interface. The sectioned surfaces were then polished with diamond pastes down to 1.0 microm particle size. Raman spectra were successively recorded along a line perpendicular to the enamel/ resin interface. The sample stage was moved in 0.2 microm increments on a computer-controlled X-Y precision table. Additional spectra from samples of enamel 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 Raman spectroscopy, a gradual decrease in hydroxyapatite was observed, and it was estimated to extend 2.2-2.6 microm for Mac Bond II, 1.2-1.6 pm for Clearfil Mega Bond and 5.2-5.6 microm for Single Bond. Furthermore, the enamel/resin interface represents a gradual transition of bonding agent from the resin to tooth side. Evidence of poor saturation of adhesive resin in etched enamel with Single Bond was detected. From the results of this study, non-uniform resin infiltration into etched enamel was detected and the degree of resin infiltration was found to be different among the bonding systems used.