Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations

Abstract

Dental laboratories may occasionally recast previously cast dental alloy to produce a prosthesis, but this process may have a negative influence on marginal adaptation. The aim of this study was to evaluate the cervical and internal fit of complete metal crowns that were cast and recast using palladium-silver alloy and 3 different marginal configurations: straight shoulder, 20-degree bevel shoulder, and 45-degree chamfer. Thirty aluminum dies were made, 10 for each marginal configuration. Each group of 10 was further divided into 2 subgroups (n=5), according to the alloy (Pors-on 4) casting history. The dies were waxed using a cylindrical metal matrix to standardize the thickness of the walls. The wax patterns were invested in a phosphate-bonded investment (Deguvest) and cast after heating in an oven (EDG), according to the manufacturer's instruction. The alloy was melted with an oxygen-gas heat source and cooled to room temperature after casting. Afterwards, the specimens were seated on the dies with a static load of 9 kgf for 1 minute. The marginal discrepancy was measured with a metric microscope, using a digital micrometer. All the measurements were done by the same operator. Each crown-die interface was measured 3 times on each of the 4 diametrically opposite points, for a total of 12 measurements for each specimen. Specimens were longitudinally sectioned to obtain 2 hemi-sections for internal discrepancy measurements, measured at 3 points: 1 in the center of the occlusal wall and 2 at each center of each axial wall. Three measurements were made for each point, for a total of 9 measurements per specimen. The results were submitted to parametric statistical 3-way analysis of variance followed by Tukey-Kramer HSD post hoc analysis (alpha=.05). The new alloy provided significantly better adaptation (P<.001) than the recast alloy for both marginal and internal discrepancy measurements. Marginal designs did not shown any statistical differences when the new metal was used. For recast metal, the straight shoulder showed significantly better adaptation (P<.001) than the 20-degree bevel shoulder and the 45-degree chamfered configurations, which were statistically similar to each other. The results of this study suggest that recasting procedures for crown fabrication should not be used with the palladium-silver alloy tested.