Fracture Strength Evaluation of CAD/CAM Endocrowns After Thermo-Mechanical Aging

Objectives: This in vitro study aimed to evaluate the fracture strength (FS; N) of glass-ceramic, hybrid ceramic, and composite CAD/CAM endocrowns in molars after thermo-mechanical aging.
Methods: 70 human non-carious third molars with similar crown size and shape were randomly divided into seven groups according to the CAD/CAM material used for the fabrication of endocrown restorations. Intact teeth without cavity preparation were used as control (n=10), while 60 teeth were endodontically treated. After endodontic treatment, standardized endocrown preparations were prepared with a 2 mm deep central retention cavity in the pulp chamber, 2mm thick axial walls, and 90⁰ circular butt joint margins. Endocrowns (n=10 in each group) were produced from feldspathic (Cerec Blocks, Sirona, C), glazed (CDG), and milled (CDM) zirconia reinforced lithium silicate (Celtra Duo, Dentsply), leucite-reinforced feldspar ceramic (LRF Initial, GC, LRF), hybrid ceramic (Cerasmart270, GC, CS) and composite (Grandio Blocs, Voco, G) CAD/CAM materials and adhesively luted with a universal adhesive (Futurabond U; VoCo) and dual-cure resin cement (Bifix QM);(Demi Ultra; Kerr). Following thermocycling for 20.000 cycles and 480000 load cycles in a chewing simulator (CS-4.2, SD Mechatronik), FS was evaluated (Instron). Data were analyzed with one-way ANOVA and post hoc Tukey’s tests (p<0.05).
Results: FS was significantly influenced by the CAD/CAM material (p=0.00). CS and CDG had significantly the highest FS, which were not significantly different from the control group (p>0.05), while there were no significant differences between LRF, G, and CDM (p>0.05) that were significantly higher than C (p<0.05). The majority of the failures in CS, CDG, and G groups were repairable, while in C were non-repairable.
Conclusions: Hybrid ceramic and glazed zirconia reinforced lithium silicate glass-ceramic CAD/CAM endocrowns exhibited similar fracture strength as the intact molars. In contrast, feldspathic endocrowns resulted in more irreparable fractures with lower fracture strength.