Effect of repeated ceramic firings on the marginal and internal adaptation of metal-ceramic restorations fabricated with different CAD-CAM technologies

Statement of problem. The use of computer-aided design and computer-aided manufacturing (CAD-CAM) for metal-ceramic restorations has increased with advances in the technology. However, little is known about the marginal and internal adaptation of restorations fabricated using laser sintering (LS) and soft milling (SM). Moreover, the effects of repeated ceramic firings on the marginal and internal adaptation of metal-ceramic restorations fabricated with LS and SM is also unknown. Purpose. The purpose of this in vitro study was to investigate the effects of repeated ceramic firings on the marginal and internal adaptation of metal-ceramic copings fabricated using the lost wax (LW), LS, and SM techniques. Material and methods. Ten LW, 10 LS, and 10 SM cobalt-chromium (Co-Cr) copings were fabricated for an artificial tooth (Frasaco GmbH). After the application of veneering ceramic (VITA VMK Master; VITA Zahnfabrik), the marginal and internal discrepancies of these copings were measured with a silicone indicator paste and a stereomicroscope at x100 magnification after the first, second, and third clinical simulated ceramic firing cycles. Repeated measures 2-way ANOVA and the Fisher LSD post hoc test were used to evaluate differences in marginal and internal discrepancies (alpha=.05). Results. Neither fabrication protocol nor repeated ceramic firings had any statistically significant effect on internal discrepancy values (P >.05). Marginal discrepancy values were also statistically unaffected by repeated ceramic firings (P >.05); however, the fabrication protocol had a significant effect on marginal discrepancy values (P <.001), with LW resulting in higher marginal discrepancy values than LS or SM (P <.05). Marginal discrepancy values did not vary between LS and SM (P >.05). Conclusions. All groups demonstrated clinically acceptable marginal adaptation after repeated ceramic firing cycles; however, the LS and SM groups demonstrated better marginal adaptation than that of LW group and may be appropriate clinical alternatives to LW.