Effect of ceramic layering on the fit of cobalt-chromium alloy 3-unit fixed dental prostheses fabricated by additive, soft milling, and casting technologies.

Statement Of Problem: The change in fit after ceramic layering of additively manufactured cobalt-chromium alloy frameworks has not been evaluated extensively.

Purpose: The purpose of this in vitro study was to compare the fit of cobalt-chromium alloy fixed dental prostheses fabricated by different techniques before and after ceramic layering.

Material And Methods: A cobalt-chromium alloy master model was prepared to receive a 3-unit fixed dental prosthesis. Sixty cobalt-chromium alloy frameworks (N=60) were manufactured by using 3 manufacturing techniques (n=20): selective laser melting (Mediloy S-Co), soft milling (Ceramill Sintron), and conventional casting as the control group (Girobond NB). The replica technique was used to measure the marginal and internal discrepancies. The frameworks were then layered with ceramic, and the same fit measuring procedure was repeated. The results were compared before and after ceramic layering within each group. The data were analyzed using the Levene, ANOVA, and paired-samples t tests (α=.05).

Results: A significant difference was found within groups before and after ceramic layering for selective laser melting (P=.006) and soft milling (P=.009) but not for conventional casting (P>.05). No statistical difference was reported in the marginal region for conventional casting group (P=.155) in contrast with the soft milling and selective laser melting groups (P=.003). Soft milling showed increased gap values in the marginal (P=.006) and occlusal regions (P=.004).

Conclusions: Ceramic layering increased the discrepancy of the laser-sintered and milled frameworks, increasing the marginal discrepancy.