الفهرس 
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Abstract
Repairing the full anatomical crowns after endodontic access cavity simulation has proven itself to be a very promising and successful option of treatment rather than complete replacement of the restoration & the repaired crowns are considered clinically serviceable. This study was conducted to evaluate the marginal integrity of the repaired access cavity after TML, also to evaluate the effect of repairing the endodontic access cavity simulation on the fracture resistance of full anatomical CAD/CAM crowns of three different ceramic materials.
A total of 60 resin typodonts with full anatomical crowns were prepared for marginal integrity and fracture resistance testing. Specimens were divided into 3 groups (20 specimens each); group Z: UTML zirconia group, group L: lithium disilicate group, group P: PICN group. Then each group was further subdivided into 2 subgroups (10 specimens each); Subgroup U: Stands for unaccessed, Subgroup R: Stands for repaired where an endodontic access cavity was performed and then repaired. all the 60 specimens were tested for fracture resistance & only the repaired specimens were tested for marginal integrity of the repaired access after TML. Fracture resistance was assessed using Universal testing machine. Mean and Standard deviation values for each subgroup were calculated. Mode of fracture was evaluated under light stereomicroscope at 5x. Whereas marginal integrity was evaluated under scanning electron microscope 6,69 ( SEM) (Model FEI Quanta 3D 200i) attached with EDX Unit (Energy Dispersive X-ray Analyses / thermofisher pathfinder) at x3569 & x200 magnification. Frequency and percentage values for each subgroup were calculated. The significance level was set at p ≤0.05 within all tests. Statistical analysis was performed using R statistical analysis software version 4.1.3 for Windows.
The results revealed the following:
1- There was no statistically significant difference between the fracture resistance of intact and repaired samples of all groups (p>0.05).
2- There was a statistically significant difference between groups in the percentage of intact margin (p<0.001). Subgroup LR had the highest percentage of intact margins followed by Subgroup PR and Subgroup ZR had the lowest values.
3- There was a significant difference between different materials in mode of fracture (p=0.021). The majority of Both Subgroups LR and PR had macro-fractures while most of Subgroup ZR had catastrophic fractures.