Purpose: This study was conducted to evaluate the effect of two different preparation extensions (4mm,6mm) On fracture resistance of endo-crowns restoring Maxillary premolar teeth using Zirconia Reinforced Lithium Disilicate (Vita Suprinity).
Materials and methods: 14 sound premolars were assigned to two groups (n=14), Group A (4 mm extension into the pulp chamber), Group B (6 mm extension intrapulpally). All premolars were decoronated to be 3 mm above the CEJ Proximally. After cementation, fracture resistance test was performed. Data was collected and statistically analyzed..
Results: There was a significant difference between samples regarding different depths of preparation extension were the highest value of fracture resistance was found in samples with 6 mm extension depth (2419.14±733.46) followed by samples with 4 mm depth (1961.71±659.89).
Conclusion: From the results obtained from this study, it could be concluded that endodontically treated premolars can be restored with endocrowns, moreover, the increase of the preparation depth of the endocrowns showed a massive increase in fracture resistance