Comparative evaluation of surface roughness in cobalt–chromium alloy castings fabricated by different manufacturing techniques and influence of positive pressure investment technique on its surface roughness – An in vitro study

AIM: The aim of this study was to assess the surface roughness (Ra) of cobalt-chromium (Co-Cr) metal alloy castings by employing different manufacturing techniques and the influence of positive pressure investment process on conventional casting. SETTING AND DESIGN: The study design was an in vitro scientific research conducted in the Army College of Dental Sciences, Secunderabad, Telangana. MATERIALS AND METHODS: A total of 48 samples of Co-Cr metal alloy in square shape with dimensions 10 mm × 10 mm × 2 mm were fabricated using different manufacturing techniques. There were four groups taken, which represent the techniques followed, in which each group contains 12 samples. Group A represented samples which were fabricated using the conventional lost-wax technique, Group B represented samples which were fabricated using the lost-wax technique in which the investment was done under positive pressure (three bars), and Group C represented samples manufactured using the subtractive technique, while the Group D represented samples manufactured using the additive technique. STATISTICAL ANALYSIS USED: The measurement of Ra was done using a contact-based profilometer. One-way analysis of variance test and post hoc Tukey's test were conducted to do the statistical analysis between all the groups and within the two groups, respectively. RESULTS: There was a significant difference observed between all the groups (P < 0.05), and it was found that samples invested under positive pressure had significantly less Ra when compared with those under normal pressure values. CONCLUSIONS: Co-Cr samples produced using computer-aided design-computer-aided manufacturing (CAD-CAM) milling (subtractive manufacturing) had the smoothest surfaces, followed by those made through the lost-wax technique with increased positive pressure. Whereas, samples fabricated using three dimensional printing (additive manufacturing) exhibited the highest Ra among all methods. The study also highlighted that samples produced under increased pressure had less Ra compared to those fabricated under normal atmospheric pressure using the conventional lost-wax technique.