الفهرس 
Fracture resistance of endodontically treated teeth restored with lithium disilicate crowns retained with fiber posts compared to lithium disilicate and cerasmart endocrowns :in vitro study
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Abstract
The purpose of the in-vitro study was to evaluated fracture resistance in endodonticallytreated teethrestored with lithium disilicate crowns retained with fiber posts compared to lithium disilicate and CERASMARTendocrowns. Thirty caries free human maxillary premolars were selected for the study Teeth randomly divided in to 3 groups (10 n) samples each group, according to the type of restoration: group 1 (GP):endodontically treated teeth with 2mm ferrule effect restored with glass fiber posts retained lithium disilicate crowns. group 2 (GE): endodontically treated teeth restored with Lithium disilicateendo-crowns with butt joint finish line. group 3 (GS): endodontically treated teeth restored with Hybrid ceramic (CERASMART) endo-crowns with butt joint finish line. To facilitated standardization of the tooth position during endocrown preparation and during test procedure, all teeth were mounted in epoxy resin block were positioned in the center of the block, parallel to its long axis and perpendicular to its base. A specially designed centralizing device was constructed to allow the accurate placement of the teeth during fabrication of the epoxy resin blocks.Teeth were endodontically treated, some teeth prepared with 2mm ferrule circumferential and 1mm shoulder finish line wide, with fiber post and composite core to support conventional crowns, this represent group (GP) and other teeth prepared with butt joint design to receive the endocrown restoration, this represent groups (GE & GS).Teeth scanned with CerecOmincam and restoration design with Cerec software, all design restorations were milled with Cerec MC XL machine. The crowns and endocrowns were seated into the prepared teeth with finger pressure and excess cement was removed with a microbrush. Then, the samples were maintained under a constant pressure of 3 Kg using specially designed loading device to standardize the load applied during bonding procedure