Marginal Accuracy of Crowns Made with Recast High Noble Alloy

Objective: This study characterized the elemental composition of an as-received and recast high noble alloy and to examine the in vitro marginal accuracy of complete cast crowns with 3 different marginal configurations.

Method: Ninety standardized high noble alloy complete crowns were made on epoxy resin dies duplicated from 3 metal master dies with a total convergence of 5-degrees and different margin designs (0.5-mm light chamfer, 1.0-mm deep chamfer, and 1.0-mm shoulder) (n = 30 each). Three casting protocols (n = 10 each) were established in relation to the proportion of as-received and recast gold alloys; the groups included an as-received (100% as-received metal) group, 50% to 50% group (50 wt% new metal, 50 wt% once-recast metal), and recast group (100% once-recast metal). An elemental analysis was determined using x-ray energy-dispersive spectroscopy at 3 sites along the cast crown, and the data were averaged. Marginal accuracy was measured with a microscope before and after cementation. The data were analyzed with 1-way and 2-way analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range test (á=.05).

Result: Elemental composition was significantly different among the casting groups (P<.001). The mean weight percentage values were 72.7% to 75.7% Au, 4.5 to 7.0% Pd, 10.7% to 11.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn. Statistically but not clinically significant differences also were found for marginal accuracy. The lowest value recorded for 100% as-received metal on crowns with 0.5-mm light chamfer (7 ìm), the highest for 100% once-recast metal on crowns with 1.0-mm shoulder (24 ìm), and an intermediate value for 50 wt% new metal, 50 wt% once-recast metal on crowns with 1.0-mm deep chamfer (19 ìm) specimens.

Conclusion: High noble alloy in all casting protocols evaluated may adversely affect the marginal accuracy of complete cast crowns with different marginal configurations.