2006 Volume 5 Issue 4 Pages 195-202
Purpose: To avoid early fatigue fracture of occlusal rests, the optimum heat treatment condition was sought.
Methods: Each specimen consisted of an occlusal rest (thickness, 0.8 mm), vertical minor connector, and denture base connector. The specimens were conventionally cast, steam cleaned, and finally pickled in a cleaning solution. The heat treatment conditions were classified as as-cast, manufacturer’s instruction, and 800°C solution treatment. Twenty-six specimens were prepared for each of the 3 groups.
A fatigue testing machine was designed so that the occlusal rest component could be deflected by displacing the denture base connector downward. A displacement of 0.46 mm was predetermined from the load-deflection relationship of the specimens. Cyclic load was applied at a frequency of 500 cycles/min until occlusal rest failures occurred or the preset limit of 2 million cycles was reached. Subsequently, Rockwell hardness was tested on the base surface. The results were statistically analyzed.
Results: All the specimens fractured within the preset limit. The heat treatments significantly influenced the fatigue resistance (P<0.003). A significant difference (P<0.05) was detected between the 800°C solution treatment and manufacturer’s instruction groups. The heat treatments significantly influenced the hardness (P<0.001). A significant difference (P<0.05) was observed between the as-cast and manufacturer’s instruction groups and between the 800°C solution treatment and manufacturer’s instruction groups.
Conclusion: The 800°C solution treatment was most favorable for the improvement of fatigue resistance. The heat treatment based on the manufacture’s instruction increased mostly the hardness; however, it was unsuitable for improving the fatigue resistance.
