Aim: To assess the effect of two CAD/CAM monolithic restorative materials on the fracture resistance of endocrowns subjected to dynamic fatigue loading and surface pre-treatment on microleakage.

Materials and Methods: Twenty-eight freshly extracted human mandibular first molars were endodontically treated and prepared for endocrown restorations. Samples were randomly divided into two groups (n=14) ; lithium disilicate (IPS E-max CAD) and resin hybrid ceramic (SHOFU Block HC). CAD/CAM endocrown restorations were fabricated, surface treated, and cemented with dual-cured adhesive resin cement. Thermocycling was done. Each group was then subdivided into two equal subgroups (n=7) according to the type of test used in the study; dynamic fatigue test and microleakage test.
Results: Shoufu (SH) group recorded a higher significant difference in the mean value of dynamic fatigue failure load and cycles than E.max CAD (LD) group with mean value as indicated by the student t-test (P<0.05). While the LD group recorded a higher significant difference mean value of leakage than the SH group's mean value. There was an inverse correlation between microleakage and dynamic fatigue failure load of the tested groups as indicated by Pearson linear correlation.
Conclusions: Endocrowns made of resin-hybrid ceramic showed higher dynamic fatigue resistance load and lower microleakage compared with that made of lithium disilicate glass-ceramic. Shofu HC Hybrid CAD/CAM blocks can be considered as a promising alternative material to lithium disilicate blocks in the restoration of endocrowns.