Effect of sintering speed of large laboratory furnaces on marginal and internal gaps of CAD-CAM monolithic zirconia crowns

Abstract

Purpose: High-speed sintering protocols have been used to expedite the production of zirconia crowns. However, information on the impact of different sintering speeds on the marginal and internal crown adaptation is sparse and only available for chairside systems. The aim of this study was to assess the impact of different sintering speed protocols on Sintering Speed on Marginal and Internal Gaps of CAD-CAM Monolithic Zirconia Crowns. Material and Methods: This in-vitro study was performed on a total of 45 prefabricated standardized resin tooth preparations for study models. Each preparation received a monolithic zirconia crown designed and milled using a high-end computer-aided design and computer-aided manufacturing (CAD-CAM) system. The crowns were divided in 3 groups of 15 crowns each, according to the sintering protocols available in the system of the laboratory furnace used: conventional (8h), fast (3.5h) or ultra-fast sintering (75 min). Marginal and internal gaps of all crowns were assessed using a high-resolution digital microscope. Statistically significant differences among groups were assessed with the one-way ANOVA test. Results: Regarding marginal gap, conventional sintering (37.83 ± 10.41μm) was slightly outperformed by both fast (30.64 ± 9.32μm) and ultra-fast (24.01 ± 5.62μm) groups (p=.003), with a significant pairwise difference between the first and the latter (p=.006). In addition, there were no statistically significant differences among groups for internal gap measurements (p=.393). Conclusion: All three groups obtained satisfactory marginal and internal gap values. However, the present findings suggest that ultra-fast sintering speed protocols lead to smaller marginal gap of CAD-CAM zirconia crowns, as compared to the conventional counterparts.