الفهرس 
ABSTRACTOnly 14 pages are availabe for public view
 |  | from | 151 |  |  |
| | | from | 151 | | |
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.