Effect of etchant, etching period, and silane priming on bond strength to porcelain of composite resin.

The purpose of this study was to evaluate the effect of etching and silane priming on bond strength to a feldspathic porcelain (VMK 68) of a composite resin (Clearfil APX). Two hydrofluoric acid etchants (2.5% and 5%) and seven different etching times (0, 30, 60, 90, 120, 150, and 180 seconds) were used to etch the porcelain specimens respectively. A self-curing bonding agent containing a silane coupler (Clearfil Porcelain Bond) was used on both etched and unetched porcelain surfaces. Etched relief patterns were observed by means of a scanning electron microscope, and the bond strengths between the photocured composite resin and the porcelain were determined. Scanning electron micrographs revealed complicated etching patterns with increased etching time periods. Shear testing results showed that the bond strength to the unetched porcelain of the composite resin was very low, and that etching periods for more than 30 seconds effectively enhanced the bond strength. Of the two etching agents applied to the unsilanated porcelain, the buffered 2.5% etchant produced higher bond strengths than the 5% etchant for all etching time periods except for 180 seconds. Silane priming was effective and critical for improving bond strength to the porcelain. Application of the silane bonding agent to the porcelain after hydrofluoric acid etching appeared to be suitable for achieving consistent bonding between the composite resin and the porcelain.