الفهرس 
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Abstract
Keywords: CAD:CAM systems, marginal adaptation , marginal accuracy, vertical marginal gap,3D printed dies, CEREC, Ceramill, digital microscope Introduction: The importance of precise marginal fit have been confirmed in many studies, Increased marginal gap may lead to many unwanted side effects as micro-leakage, periodontitis , recurrent caries which affects fixed prosthodontics longevity and underling tooth integrity so several studies have investigated the effect of scanning and milling process of CAD/CAM and its relation to the marginal adaptation of resulting restorations. Aim of the work: The aim of this in vitro study is to evaluate the Marginal Accuracy of Lithium Di-Silicate Monolithic Veneers when they are milled By Different CAD:CAM Systems Materials and Methods: a maxillary ready-made scanable model containing central incisor tooth with laminate veneer preparation was used to generate the design of the virtual master die from which 24 dies were 3D printed and one die was scanned using CEREC InEos scanner and the final design of the laminate veneer restoration was made using CEREC in lab software and then this design was exported to the 2 tested milling machines MCX5 and Ceramill motion 2, the milled monolithic lithium di-silicate veneers was then cemented to their crossponding 3D printed dies and was examined under Digital microscope for values of vertical marginal gap Results: the highest mean ±SD value was recorded in Ceramill group II with mean value 68.847.62, While the least mean ±SD value was recorded in Cerec group I with mean value 63.507.91 and There was statistical significant difference between gaps in the two studied groups (P < 0.05). Conclusion :all veneers produced by both milling machines were with clinically acceptable marginal adaptation >120 μm , However There was statistically significant difference in the vertical marginal gap values of the produced veneer between the two test groups CEREC MCX5 and Amangerbach Ceramill Motion 2, with CEREC MCX5 milling machine having the advantage of milling veneer restoration with better marginal adaptation and less vertical marginal gap values.