الفهرس 
Fracture resistance of lithium disilicate vonlays versus celtra duo vonlays restoring premolars
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Abstract
Statement of problem: Lithium disilicate ceramic has been considered the strongest glass-ceramic with fracture strength ranging from 300 to higher than 400 MPa (IPS e.max CAD).The high number of microstructural, interlocking, needle-like lithium disilicate crystals that are embedded in the glassy matrix gives this type of ceramic higher mechanical properties than other types of glass based ceramic material but mechanical properties limits its use in thin sections in posterior teeth with aload in the premolar region ranging from of 100 N to 300 N, with restriction for patients with bruxism, for which the load values are between 500 N and 800 N Purpose: The aim of the present study was to compare the fracture resistance of lithium disilicate(e-max CAD) vonlays versus CELTRA DUO vonlays restoring premolars.Materials and method:Anatural tooth represent first maxillary premolar was prepared according to regular dimensions of all ceramic restorations preparation guidelines, the prepared naturaltooth was then duplicated into twenty epoxy resin dies, each duplicated epoxy die was scanned by 3 shape D500 extra oral scanner and then milled by Sirona MCX5 milling machine usingE-max blocks and Celtra® Duo CAD blocks. A total of twenty restorations were constructed, the samples were divided into two equal groups, ten samples for each group according to the material type used, group (a)ten vonlay samples (n=10) fabricated oflithium disilicate CAD/CAM blocks, group (b) ten vonlays samples (n=10) fabricated of Celtra® Duo CAD/CAM blocks. Load to fracture was tested