الفهرس 
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Abstract
An all-ceramic crown is a routine treatment option and poses challenges when root canal therapy is indicated. Ceramics are poor conductors of heat, making it difficult to control heat formation during access opening preparation.
Repair of the access opening presents a challenging clinical situation because replacement may involve discomfort for the patient and increased cost. Chairside repair using composite with different techniques may be a simple alternative method to total replacement of the prosthesis.
This study was designed to evaluate the effect of endodontic access opening performed through all-ceramic IPS e.max Press crowns and to evaluate the fracture resistance of the ceramic crowns after access repair with two different systems (ceramic repair kit) and (direct conventional composite).
A freshly extracted non-carious maxillary first premolar was embedded in acrylic block and prepared to receive an all-ceramic crown. A silicon mold of the prepared tooth with its acrylic block was made, then epoxy resin material was poured to form the master epoxy die that was duplicated to form 24 epoxy dies.
Twenty-four all ceramic crowns were fabricated from IPS e.max Press and then cemented by Variolink II resin cement to their respective epoxy resin dies. The specimens were divided into 3 main groups each of 8 crowns. Group I (intact crowns), Group II (accessed and repaired with conventional composite technique) and Group III (accessed and repaired with ceramic repair kit)
All specimens were exposed to thermal and cyclic loading before access opening preparation to simulate oral cavity conditions.
All samples were loaded to fracture using the universal testing machine to record the fracture resistance of each crown. Data were collected and tabulated.
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Statistical analysis was carried out and results showed that there was a significant difference between the intact and the repaired crowns, where the intact had higher fracture strength than the repaired crowns with both techniques.
The results also showed that there was a significant difference between repairing with ceramic repair kit and that with the conventional composite technique, where the crowns repaired with the ceramic kit had higher fracture resistance than those repaired with the conventional composite technique.
Regarding the mode of failure, the results showed that there was no significant difference (P=0.099) in fracture modes between group I (control) and group III (ceramic repair). While, there was a significant difference between each of them with group II (conventional repair).
Mode V was the most observed failure mode contributed to (37.5%) of all the specimens, while mode II was the least observed one contributed to (12.5%) of all the specimens. Mode I was not observed in this study.