الفهرس 
Efficacy of preparation design on fracture resistance of hybrid-ceramic endo-crown on premolars : An In vitro study
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Abstract
Objectives: The present study aims to evaluate the effect of different preparation designs on fracture
resistance and failure mode of hybrid nanoceramic endocrown on premolars.
Methodology: Fourteen endodontically treated maxillary premolars were prepared to receive
endocrown restorations and divided into 2 groups (n=7) samples in each group according to the
preparation designs. (GB): Endocrowns with butt joint design. (GF): Endocrowns with 2mm ferrule
design. All endocrowns manufactured from hybrid nanoceramic (Cerasmart 270) CAD/CAM blocks.
The endocrown restorations were cemented to the prepared teeth using dual cure self adhesive resin
cement. All specimens were subjected to a compressive force 5KN until fracture occurs by using
universal testing machine. The maximum compressive force was recorded for all specimens, then
failure mode of all samples were examined visually and photographically using digital camera, USB
digital microscope and stereomicroscope. All repairable samples were examined for extension of the
cracks using scanning electron microscope. Statistical analysis of the results was performed by
applying Independent T-test for fracture resistance results, and Kruskal-Wallis test for failure mode
results. The significance level was set at P ≤ 0.05.
Results: Endocrowns with ferrule preparation recorded a highly statistically significant difference
with higher mean value of fracture resistance (1911.57 ± 341.29), compared to the endocrowns with
butt joint which recorded the lower mean value of fracture resistance test (1192.70 ±196.04).
Regarding to failure mode endocrowns with ferrule design showed a high percent of catastrophic
failure while butt joint showed more repairable failure Conclusion: Within the limitations of this in-vitro study, it was concluded that:
1- All fracture resistance loads obtained in the two designs were far beyond the maximum masticatory
forces.
2- Endocrowns with ferrule design showed a higher fracture resistance in comparison to endocrown
with butt joint preparation design.
3- Endocrowns with ferrule design showed a high percent of catastrophic failure mode but at loads
larger than the normal masticatory forces.
4-Endocrowns with butt joint design showed mostly repairable mode of failure at loads larger than
the normal masticatory forces.