Retention of magnetic keepers in cast noble metal alloy

Objectives: This in vitro study investigated the effect of burn-out temperature on the retention of a Magfit EX keeper in cast gold alloy dowel and the thickness of the oxide layer at the keeper-alloy interface. Methods: One-hundred-and-five Magfit EX keepers were cast with gold alloy at three different burnout temperatures: 500°C, 600°C, 700°C. Sixty samples were tested in an Instron universal testing machine (UTM) until catastrophic tensile failure; forty-five samples were sectioned and the interface evaluated under a scanning electron microscope (SEM). Results: Retention of the keepers was significantly higher at lower burnout temperatures (p<.05). The retention of the keepers became unpredictable and immediate failures were observed at a burnout temperature of 700°C. Oxide formation at the keeper-alloy interface was significantly less at lower burnout temperatures (p<.05). Conclusion: High burn-out temperature for casting Magfit keepers with type IV gold alloy may lead to early loss of the keepers. The burnout temperature is recommended to be set at 500°C.