Comparison of dimensional accuracy of lithium disilicate CAD/CAM ceramics
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Aim The aim of this in vitro study was to evaluate the geometric accuracy of crowns designed by 3D CAD and fabricated with CAD/CAM system.
Materials and methods Accuracy of geometric crown and milling time were tested using three different ceramic blocks available in the market: GC Initial® LiSi Block (GC Corp) (LS), IPS e.max CAD (Vivoclar) (EM) and Cerec Tessera™ (Dentsply Sirona) (TE). All crowns were fabricated using a CAD/CAM milling machine (Cerec MC XL, Dentsply Sirona) by importing the STL file using a CAM software (inLab CAM SW 20.0.1, Dentsply Sirona). Milling time was recorded. Accuracy of the crowns, defined as the percentage of measurement points satisfying the production repeatability of Cerec MC XL (±25 µm), was assessed after glaze firing process by means of an optical precision measuring machine (ATOS Capsule, GOM) superimposing the fabricated crowns and the original STL file (GOM Inspect, GOM). Data were analyzed with one-way ANOVA and Tukey’s tests. For each material a prismatic specimen was cut and submitted to thermal expansion: the temperature of maximum linear expansion was set as the dynamic softening temperature.
Results LS showed the best accuracy before and after glaze firing process. TE showed the worst accuracy while EM before crystallization process showed no statistically significant difference with LS, whereas after crystallization there was a statistically significant difference. TE showed the longest milling time (19.5 min), EM the shortest (12.0 min) and LS was processed in 14.6 min, with a statistically significant difference from EM.
Conclusion From the results of this in vitro study LS shows high accuracy of margins and acceptable milling time that support its clinical use.
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