الفهرس 
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Abstract
This study has been designed to evaluate the effect of two new hybrid ceramics when they are used as a custom made post and core and cemented with two types of resin cements on fracture resistance of endodontically treated teeth. The two hybrid ceramic materials are Vita-enamic and Cerasmart.They have been cemented by Bisco Duo-Link universal adhesive cementation system and G-cem LinkAce™ self-adhesive cement.
Thirty extracted single canal Premolar were selected. Crowns were sectioned 2mm. shorter to the level of the CEJ. Teeth were root canal treated, obturated using gutta-percha. All teeth were prepared for making one-piece resin post core pattern. This pattern was scanned by CAD.Vita-enamic posts and Cerasmart posts were milled using CAM. All teeth were assigned to one of five groups (N = 5 per group).For group1: cementation of the vita-enamic posts was done using adhesive resin cement system. For group 2 cementation of the vita-enamic hybrid ceramic posts using self-adhesive resin cement. For group 3 cementation of the Cerasmart hybrid ceramic posts using adhesive resin cement system. For group 4 cementation of the Cerasmart hybrid ceramic posts using G self-adhesive resin cement.
Cementation of the fiber posts (easy post - from DENTSPLY) for groups, 5-6 (the control groups) is done: For group 5 adhesive resin cement system. For group 6 self-adhesive resin cement.All restored teeth were tested by in a universal test machine (Lloyd LRX; Lloyd instruments Fareham, Hants, England) to calculate the fracture resistance of each post and cement.
The results revealed that the post materials and cement types had a significant effect on the mean fracture resistance. The highest fracture resistance was achieved in (group 4), followed by (group 2), then (Group3), then (group1) and the lowest value obtained by fiber post (Group6) then (group5).
Custom made hybrid ceramic posts have higher fracture resistance than readymade fiber post in the present study this may be explained by that hybrid nature of the hybrid ceramic post which gather the strength of ceramic and resiliency of composite that is not present in fiber post, customized nature of hybrid ceramic post which lead to decrease thickness of the cement and therefore increase bond strength.
Cerasmart has the highest fracture resistance values, followed by vita-enamic and the lowest Fiberpost. This may be due to the nano ceramic distribution and the equally distributed particles that help in increase the properties of Cerasmart over Vitae-enamic. Self-adhesive resin cement showed a significantly higher value than adhesive resin cement in fracture resistance. This may be due to that the bonding agent need to be light cured in adhesive resin cement and light curing not reach the base of the post space. This makes the bonding of adhesive resin cement less than self-adhesive resin cement as self-adhesive cement needs no bonding agents. The multi steps and sensitivity of technique of application of adhesive resin cement may play a role in decrease of its bond strength.