The effect of different investment techniques on the surface roughness and irregularities of gold palladium alloy castings

Abstract

Surface roughness and irregularities can affect the fit of a restoration. It is unknown whether different investment techniques have an effect on surface roughness and irregularities of gold palladium alloy castings. The purpose of this study was to evaluate the surface roughness and irregularities of gold palladium alloy castings obtained using different investment techniques. Forty disk-shaped wax patterns were prepared and divided into 4 groups. A phosphate-bonded, carbon-free investment was used for the investment procedures. Twenty specimens were invested using a vacuum mixer, while the remainder were invested using a vacuum mixer and investor. The specimens in both broad categories were divided evenly to set in 2 different conditions of pressure. Half were left to set under atmospheric pressure for 1 hour, while the rest were placed in a compression chamber under a pressure of 3 bars for 24 minutes, then allowed to bench set for another 36 minutes. A profilometer was used to evaluate the surface roughness (mum) of the castings. The specimens were also studied under x10 magnification for surface irregularities. Two-way ANOVA was used to examine the relationships among surface roughness, investing, and pressure (alpha=.05). Logistic regression was used to explore the relationships among surface irregularities, investing, and pressure. Two-way ANOVA for surface roughness did not reveal any statistically significant differences. However, there was a trend for the specimens set under atmospheric pressure to present lower values of surface roughness than the specimens set under positive pressure (P=.095). The logistic regression for surface irregularities showed a highly significant impact of pressure. The odds of any surface irregularities for specimens under atmospheric pressure were 9.12 times higher than the odds for specimens under positive pressure (P=.016). Within the limitations of this study, the results suggest that specimens set under atmospheric pressure are much more likely to present surface irregularities than specimens set under positive pressure. The use of pressure can help produce castings with fewer surface irregularities.