Study on a Gold Alloy with Age-hardenability at Intraoral Temperature

Abstract

AuCu-3 wt%Ga alloy bridges with age-hardenable characteristics at intraoral temperature were prepared to evaluate the dimensional change, hardness and surface roughness induced by phase transformation. Distortion behavior due to dimensional changes was determined by measuring the clearance formed between the inner surface of a crown and the metal mold. Phase transformation produced remarkable hardening over a few days by annealing at 37°C, and resulted in linear contraction of 0.04% and roughening of the alloy surface. Contraction ceased in about 3 days. Surface roughness was attributed to surface-relief effect relieving the internal coherent strains which originated in the ordering of AuCu. Bond strengths of an adhesive resin to AuCu-3 wt%Ga alloy and a Type IV gold alloy designed for resin-bonded restorations were also investigated in vitro with the use of two different metal primers. Disk specimens were cast in the alloys. The specimens were primed with either a vinyl-thiol primer or a thiophosphate primer, then bonded with an adhesive resin initiated with a tri-n-butyl borane derivative. AuCu-3 wt%Ga alloy exhibited higher bond strength than Type IV gold alloy with the use of metal primers after 20, 000 thermocycles.