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Dimensional changes related to ordering in an AuCu-3wt%Ga alloy at intraoral temperature
I Watanabe1, M Atsuta, K Yasuda
1Department of Fixed Prosthodontics and Department of Dental Materials Science, Nagasaki University, School of Dentistry, Japan.
Objectives:
The purpose of this study was to evaluate the distortion behavior of a gold alloy with age-hardening ability at intraoral temperature induced by phase transformations.
Methods:
Bridge-type specimens were prepared using AuCu-3wt%Ga alloy with age-hardening ability at 37 degrees C. Dimensional changes, hardness and surface roughness were measured. Transmission electron microscopy observation was carried out using AuCu-3wt%Ga discs aged at 37 degrees C for 30 d.
Results:
Hardening was brought about rapidly in the initial stage of aging at 37 degrees C owing to ordering. The ordering was attributed to the formation of AuCu I and AuCu II superlattices. A linear contraction of 0.04% was induced by aging at 37 degrees C for 3 d. Distortion of the bridge-type specimen was brought about by a combination of linear contractions. The surface roughness increased in the initial stage of aging due to the surface relief effect of internal coherency strain caused by tetragonality.
Significance:
The mode of distortion may be more advantageous for use in crown-type rather than inlay-type restorations, and the amount of contraction may not produce any problems in clinical use.