Objectives: The purpose of this study was to evaluate the effect of different investment techniques on the surface roughness and irregularities of castings using a gold palladium alloy and carbon free phosphate investment material. Standardized patterns were invested in 4 different ways .The null hypothesis was that investing patterns utilizing vacuum and positive pressure would produce smoother castings for better fit and finish.

Method: 32 standardized wax patterns were invested in four groups of eight each utilizing four investment techniques as follows Group 1-Vacuum mix and set under atmospheric pressure Group 2-Vacuum mix and set under positive pressure (3 bars) Group 3-Vacuum mix and vacuum invest and set under atmospheric pressure. Group 4-Vacuum mix and vacuum invest and set under positive pressure (3 bars) All the rings were cast using computerized vacuum air pressure induction casting machine to ensure uniformity while casting. They were divested and analyzed for roughness using a profilometer and for irregularities (nodules) using a 10X fiberoptic microscope.

Results: The samples evaluated for surface roughness using one-way ANOVA indicated that the groups were statistically significant (p < .05). Group 3 was smoother than group 1. The samples evaluated for surface irregularities were evaluated using the Kruskal Wallis test and a one-way analysis of variance. Both tests proved to be statistically insignificant.

Conclusions: 1. The surface roughness of castings obtained by different investment techniques showed statistical significance. However from a clinical standpoint, there is no validity of using one technique over the other. 2. The use of positive pressure did not significantly reduce the surface irregularities caused by entrapment of air bubbles during investing.

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