JOURNAL OF PROSTHETIC DENTISTRY THE

Vol. 101 No. 1      January - 2009

ISSN: 0022-3913      UBIC: 171

SUMMARY

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=1 5) 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 oF700°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)

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