الفهرس 
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Abstract
The aim of this current study was to compare the fracture resistance under cyclic loading of lithium disilicate (IPS e. max CAD) vonlays versus (Rosetta ® SM CAD) vonlays restoring premolars.Methodology: A natural maxillary premolar tooth was prepared according to regular dimensions of all ceramic restorations preparation guidelines, the prepared naturalpremolar tooth was then duplicated into twenty epoxy resin dies, each die was scanned by Medit i500 scanner extra oral scanner and then milled by Sirona MCX5 milling machine using IPS e. max CAD blocks and Rosetta ® SM CAD blocks. A total sample size of 20 will be selected then divided into two equal groups 10 sample each according to the material type used, group (A) ten vonlay samples (n=10) fabricated of IPS e.max CAD blocks, group (B) ten vonlays samples (n=10) fabricated of Rosetta®SM CAD /CAM blocks. Load to fracture was tested.
Result: IPS e.max CAD group recorded statistically non-significant higher fracture resistance mean value (502.39 ±102.89 N) than Rosettagroup (468.76 ± 67.54 N) as described by unpaired t- test (P = 0.5006 > 0.05) Conclusion: (Rosetta SM CAD) and (IPS e.max CAD) restorations have clinically acceptable fracture resistance values and could be used safely in the premolar area.Keywords: onlay, vonlay, veneer, fracture strength, fracture resistance, cyclic loading, E.max CAD and Rosetta®SM CAD