Effects of the porcelain firing sequence on the bond strengths of cements

Abstract

Bond strengths for the retention of ceramic bonded to metal alloys to the tooth structure involve cavity preparation variables, cement variables and ceramic bonded to metal alloy variables. The aim of this work was to evaluate the retentive strength differences between alloy surfaces, unfired and fired, for porcelain alloys retained with different dental cement compositions. The clinical situation was stimulated by using standardized tooth preparations, extracted teeth and castings cemented with zinc phosphate and polycarboxylate cements, which were debonded on an Instron. Jelenko O, Cameo, Jelstar and Genesis II alloys were compared unfired and fired to simulate porcelain application. Fired Jelenko O casting alloy cemented with polycarboxylate cement produced the greatest bond strengths (6.0 +/- 1.0 MPa). Polycarboxylate cemented castings had greater bond strengths for all alloys whether fired or not. The only effect of firing was an improvement with Jelenko O alloys produced with both cements. All of these differences were statistically significant at the P less than 0.01 level using Tukey's post hoc evaluation. The improvements observed were related to the oxide formation on the internal surfaces of the casting and the ability of polycarboxylate cement to adhere chemically to those layers.