Fit and Retention of Cobalt-Chromium Removable Partial Denture Frameworks Fabricated with Selective Laser Melting

Purpose: To evaluate fit and retention of cobalt-chromium removable partial denture (RPD) frameworks fabricated with selective laser melting (SLM). Methods: Three types of framework for clasp-retained RPDs were virtually designed and fabricated using SLM (n = 30). For comparison, 30 additional frameworks were produced using conventional lost-wax casting. A biomechanical model was created, incorporating extracted teeth mounted on flexible metal posts. Using this model, horizontal constraint forces resulting from a misfit were measured using strain gauges, while vertical forces were not recorded. The constraint force components and resultant forces were determined for all abutment teeth, and the maximum retention force during RPD removal from the model was also assessed. For statistical evaluation, the two fabrication methods were analyzed by calculating the means and standard deviations. Results: The average horizontal constraint forces showed similar values for both fabrication methods (SLM: 3.5 +/- 1.0 N, casting: 3.4 +/- 1.6 N). The overall scatter of data for cast RPDs was greater compared to those fabricated using SLM, indicating a better reproducibility of the SLM process. With regard to retention, the intended retention force of 5-10 N per abutment tooth was not attained in one of the cast groups, while it was consistently achieved in all SLM groups. Conclusions: This in vitro study found that SLM is a promising option for the manufacture of cobalt-chromium RPD frameworks in terms of fit and retention.