Internal and marginal fit of cobalt-chromium fixed dental prostheses fabricated with 3 different techniques

Conventionally, the fabrication method for Co-Cr restorations has been casting by the lost-wax method. Milling and selective laser melting (SLM) are more cost effective and thereby increasingly used. The precision of the different methods regarding internal and marginal fit, however, is not fully known.

The purpose of this in vitro study was to examine and evaluate whether the 3 fabrication methods of conventional casting, milling, and SLM differ in internal and marginal fit for Co-Cr fixed dental prostheses (FDPs).

Thirty Co-Cr metal frameworks for 3-unit FDPs were made with 3 fabrication methods for a model with 2 abutment preparations. Internal fit was measured with the replica method. A white silicone indicator material simulated the cement space. This was measured by light microscopy at ×20 magnification and a digital measurement program. Marginal fit was evaluated with the direct-sight technique at ×4.6 magnification and given a score from 1 to 5. One-way ANOVA and Tukey honest significance tests were used to evaluate differences among groups with regard to internal fit. The Kruskal-Wallis and Mann-Whitney U tests were used to calculate differences among groups with regard to marginal gap. The Pearson r test was used for correlations calculations (α=.05).

Statistically significant differences were found in both internal and marginal fit among the test groups (P<.003). The milled group had the best overall fit, followed by the cast and SLM groups.

SLM restorations had the poorest internal and marginal fit, whereas the milling method had the best results. The SLM technique did not achieve clinically acceptable values for internal fit.