الفهرس 
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Abstract
Introduction: Marginal and internal fit are critical for the success of dental restorations. All-ceramic CAD/CAM restorations can be fabricated either chair-side or in lab.
Aim of study: To evaluate the fit accuracy of all ceramic restorations fabricated by two different CAD/CAM systems (closed and open systems) using a sectional method.
Material and methods: A lower first molar was prepared for a full coverage restoration, it was laser scanned (Ceramill map 400) and 18 replicas were milled using acrylic CAD/CAM block (Ceramill TEMP). All dies were scanned using CEREC PrimScan. Nine zirconia crowns (group I) were fabricated using a closed system (Cerec In Lab) while the other nine crowns (GroupII) specimens were fabricated using an open system, where the STL files were imported to Ceramill mind CAD software (Amann Girrbach AG, KOBLACH, Austria) for designing and fabrication of zirconia crowns with the same parameters used in group I. Zirconia restorations (Monolithic Katana zirconia) were milled from each system, cemented on their respective dies by self-adhesive resin cement (RelyX™ Unicem) and then were sectioned into four quarters using Buehler Isomet 4000 Linear Precision Saw. A stereomicroscope was used for measurement of the cement space to evaluate the restoration fit accuracy. (n=18).
Results: Statistical analysis revealed that the closed system provided a better marginal and internal fit than the open system and there was no statistical significant difference.
Conclusions: within the limitations of this study, good marginal qualities were achieved using both CAD/CAM systems.
Keywords: CAD/CAM, Open system, closed system, Monolithic zirconia, Marginal adaptation.