Mechanical property and microstructural variations for recast low-gold alloy

Area of Science:

• Materials Science
• Biomaterials Engineering
• Dental Materials

Background:

• Type III gold alloys are widely used in dentistry.
• The impact of repeated casting on the mechanical properties of these alloys is not fully understood.
• Casting defects can compromise the integrity of dental restorations.

Purpose of the Study:

• To investigate the effect of remelting on the mechanical properties of a Type III gold alloy.
• To determine if repeated casting influences yield strength, tensile strength, and percentage elongation.
• To correlate mechanical property changes with the presence of casting defects.

Main Methods:

• Polystyrene patterns meeting ANSI/ADA specification no. 5 were used for casting.
• A Type III gold alloy (46% gold) was cast new and then remelted and recast two, three, and four times.
• Tensile testing was performed on age-hardened specimens at an elongation rate of 0.5 mm/min.
• Statistical analysis (one-way ANOVA, Student-Newman-Keuls) was used to compare mechanical properties.
• Scanning electron microscopy (SEM) was employed to examine casting defects.

Main Results:

• Significant decreases in yield strength (P < .01) and percentage elongation (P < .01) were observed with increasing recasts.
• No significant differences in tensile strength (P > .05) were found between the groups.
• SEM revealed a progressive increase in casting defects with remelting.
• Casting defects were identified as the primary factor influencing the tensile fracture process.

Conclusions:

• Remelting Type III gold alloy leads to a decline in critical mechanical properties like yield strength and elongation.
• The accumulation of casting defects during remelting is the main cause of property degradation.
• Clinicians should be aware of the potential for reduced performance when using repeatedly cast gold alloys.