Fracture resistance of bi-layered and translucent zirconia after thermo-mechanical fatigue

Objective: This study aimed to evaluate the fracture resistance of bi-layered and two types of translucent zirconia after thermo-mechanical fatigue. Materials and Methods: first upper premolar sound natural tooth was prepared and duplicated into epoxy resin die. Forty two full coverage crowns were fabricated and divided into three groups' n= 14 according to type of ceramic material; Group (SHT): full contoured super-high translucent multilayer zirconia system were constructed using CAD/CAM. Group (ST): full contoured super translucent multilayer zirconia system were constructed with CAD/CAM. Group (BZ): Bi-layered zirconia: Fourteen copings were constructed using Solid ZI white with CAD/CAM and then were conventionally veneered with Vita Vm9 (feldspathic porcelain). Crowns were cemented using self-adhesive resin cement. All samples were subjected to thermal cycling (5o -55o C/10,000 cycle) then to chewing simulator (240,000 cycles, 50N). All samples were subjected to fracture resistance test. Results: Fracture resistance values all of the tested groups were (1727.19±311.75 N, 1399.75±130.08 N, 1112.70±195.20 N). bi-layered zirconia (BZ) restorations (control group) used in the current study after thermo-mechanical fatigue, showed higher fracture resistance values than the super translucent monolithic zirconia (ST) and super high translucent monolithic zirconia (SHT) group (intervention groups). Conclusions: all the crowns tested obtained high fracture resistance (above 1000 N) and could n successfully withstand the average clinical masticatory force in the premolar region. The group of bilayered crowns recorded higher fracture resistance mean value than the two groups of translucent monolithic crowns.