الفهرس 
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Abstract
Aim: The aim of this study was to measure the fracture resistance of endodontically treated maxillary premolar teeth restored with lithium disilicate crowns retained with fiber posts and cores compared to lithium disilicate and PEEK endocrowns.
Methodology: Thirty-three extracted maxillary premolars were randomly divided into 3 groups (n=11).
Root canal treatment was performed on all of them. Teeth were mounted in epoxy resin blocks, 2 mm
below the cemento enamel junction then randomly assigned to groups; group A: Premolars with 2 mm
ferrule restored with glass fiber post, core build up then full coverage lithium disilicate
(IPS e.max CAD) crowns. group B: Premolars with 2 mm butt margin restored with lithium disilicate (IPS e.max CAD) endocrowns. group C: Premolars with 2mm butt margin restored with PEEK
(Bre.CAM BioHPP) endocrown restorations. All teeth were scanned using CEREC primescan and designed on CEREC software. All designed restorations were milled using inLab MCX5. PEEK endocrowns were designed and milled with cutback then veneered with composite according to the manufacturer’s instructions. Restorations were surface treated then cemented using dual cured resin cement. Samples were subject to fracture resistance testing under compressible load parallel to the long axis of the tooth. Universal testing machine with a mounted rounded tip rod was used to apply vertical force while touching both cusp inclines. The testing machine had a load cell of 5 kilo newton and moved at a crosshead speed of 0.5mm/min. Data was collected and statistically analyzed. Mode of failure was examined and evaluated.
Results: Numerical data was explored for normality by checking the distribution of data and using tests of normality (Kolmogorov-Smirnov and Shapiro-Wilk tests). One-way ANOVA test was used to
compare between the three groups. The significance level was set at P ≤ 0.05. group A had mean value
of 1690 ± 389 N, group B was 1636 ± 432 N and group C was 1582 ± 352 N. There was no statistically
significant difference between mean fracture resistance values in the three groups (P-value = 0.845,
Effect size = 0.012).
Conclusion: All fracture resistance values were higher than the maximum masticatory force recorded
for the premolar region. Endocrowns had fracture resistance similar to those of traditional post, core and crown restorations. PEEK endocrowns were found to have similar fracture resistance to lithium disilicate endocrowns and so are considered a good option for endocrowns.