الفهرس 
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Abstract
In this in-vitro study, monolithic zirconia and PEEK inlay retained cantilever bridges were constructed. Different preparation designs were done. The measurement of the failure load was carried out after cementation of the IRFDP with self-adhesive resin cement on the prepared natural teeth and after being subjected to thermocycling.
Forty eight recently extracted upper molars were collected and examined under a stereomicroscope for any decay or cracks. The molars were selected upon having a similar bucco-lingual (BL) and mesio-distal (MD) dimensions confirmed with a digital calliper having only 10% deviation from the average. Teeth were sound and extracted for orthodontic or periodontal reasons.
Afterwards the teeth were cleaned using ultrasonic scaler at low power and under copious water coolant to prevent creation of any microcracks. And were stored in distilled water until needed for the study.
The selected teeth were divided into 2 main groups (n=21) according to the type of the fabrication material:
1-group Z: monolithic zirconia.
2- group P: polyetheretherketone (PEEK).
Then each group was sub divided into 3 subgroups (n=7) according to the preparation design
i- Sub group I : occluso-mesial inlay preparation.
ii-Sub group I1: occluso-mesial inlay with palatal wing preparation.
iii-Sub group I2: occluso-mesial inlay with buccal and palatal wing preparations.
Restorations were fabricated from CAD CAM milled zirconia and peek using dry processing, then sintering and finishing of the restorations were carried out. The restorations were surface treated according to manufacturer recommendations, cemented to their corresponding abtments using self adhesive resin cement. After cementation samples were subjected to thermocycling for 5000 cycles, then tested for failure load in a universal testing machine, the load was applied at the center of the pontic. After testing the samples were carefully inspected for determining modes of failure
Failure load was tested using the universal tesing machine showing:
• IRFDP fabricated from PEEK showed higher failure load than those fabricated from zirconia
• Inlay with double wing design of IRFDP showed higher failure load than the other 2 designs.
• No significant difference in fracture load between inlay only and inlay with one wing design and between inlay with one wing and inlay with double wing designs