Treatment of multiple ceramic alloys before recasting

Abstract

Dental laboratories often reuse dental casting alloys by recasting them, but the processing methods before recasting require further research. The purpose of the study was to determine the treatment methods to remove the surface contamination of the previously melted alloys before recasting. Cobalt-chromium (Co-Cr), commercially pure titanium (CP Ti), palladium-copper-gallium (Pd-Cu-Ga), and gold-platinum (Au-Pt) ceramic alloys were investigated in the present study. Field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy (EDAX), and x-ray photoelectron spectroscopy (XPS) were used to evaluate the changes in the surface structures and compositions of Co-Cr, CP Ti, Pd-Cu-Ga, and Au-Pt ceramic alloys after airborne-particle abrasion and immersion in various chemical solutions for different time periods. The data obtained by EDAX and XPS were statistically analyzed by Kruskal-Wallis and Nemenyi tests (α=.05). By using appropriate mechanical and chemical treatment procedures, the contamination content of previously cast ceramic alloys was found to be below the detection limits of EDAX and XPS. The statistical results showed that, compared to the control group (new alloys after polishing), the impurity element was not detected after being treated with these methods, which was not statistically different to control group. The surface contamination of ceramic alloys was effectively removed by using certain mechanical and/or chemical treatment methods. Within the limitations of the present study, the most appropriate ways to treat ceramic alloys before recasting were as follows: (1) for Co-Cr ceramic alloys: Al2O3 airborne-particle abrasion and immersion in aqua regia for 15 min; (2) for CP Ti ceramic alloys: Al2O3 airborne-particle abrasion and immersion in 65% HNO3 and 40% HF 1:7 (V/V) for 60 min; (3) for Pd-Cu-Ga ceramic alloys: glass bead airborne-particle abrasion and immersion in 40% HF solution for 30 min; and (4) for Au-Pt ceramic alloys: glass bead airborne-particle abrasion.