Adhesion of composite to polished dentin retaining its smear layer

Abstract

This study was designed to measure the adhesion of a composite to the smear layer. An experimental aqueous bonding agent was supplied in the form of two liquids. One contained methacryloyl tyrosine amide (MTYA), glyceryl methacrylate (GM), dimethylaminoethyl methacrylate and benzene sulfinic acid sodium salt, and the other contained glutaraldehyde, succinic acid and 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethy-1-propanaminium chloride (QTX). QTX is a unique water-soluble photo polymerization initiator. The application times and irradiation times of the experimental aqueous bonding agent were varied. The highest mean bond tensile strength was obtained by irradiating the bonding agent for 1 min. A 3 min irradiation decreased the mean bond strength when the bonding agent was applied to the polished dentin surface for 1, 3 or 5 min. The mean values resulting from the application of experimental aqueous bonding agent were higher than those from a commercially available bonding agent which preserved or modified the smear layer. There was a significant decrease in the bond strength after 500 or 2000 thermocycles in specimens with a 5 min application of the bonding agent, but there was no significant decrease in the bond strength when the application time was for 1 or 3 min. SEM observation showed the formation of a hybrid layer with a thickness of approximately 1-1.5 μm. The aqueous bonding agent tested in this investigation was capable of penetrating the smear layer and the bond strength exceeded the values obtained by bonding agents that remove the smear layer.