Effect of burn-out temperature on magnetic keepers in cast noble metal alloy posts

Abstract

Statement of problem: Early loss of magnetic keepers in cast gold posts is seen in clinical practice. Purpose: The purpose of this vitro study was to investigate the effect of burn-out temperature on the retention of magnetic keepers in cast gold alloy and on the thickness of the oxide layer at the keeper-alloy interface. Material and methods: One hundred and five keepers (Magfit EX) were cast with gold alloy (Protor 3) at 3 different burn-out temperatures: 500°C, 600°C, or 700°C (n=35). To test for retention of keepers, 60 specimens (n=20) were tested to failure in tension mode in a universal testing machine (UTM); 45 specimens (n=15) were sectioned, and the interface was evaluated under a scanning electron microscope (SEM). Tensile force data were analyzed with 1-way ANOVA, and SEM data were analyzed with 1-way repeated measures ANOVA. Bonferroni multiple comparisons were performed for post hoc analysis (α=.05). Results: Retention of the keepers was significantly higher at lower burn-out temperatures (P<.001). The retention of the keepers became unpredictable and immediate failures were observed at a burn-out temperature of 700°C. Oxide formation at the keeper-alloy interface was significantly less at lower burn-out temperatures (P<.001). Conclusions: A burn-out temperature of 500°C for casting the Magfit EX keeper with type IV high-strength gold alloy is recommended. (J Prosthet Dent 2009;101:66-72). © 2009 The Editorial Council of the Journal of Prosthetic Dentistry.