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

Abstract

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±195.20N). bi-layered zirconia (BZ) restorations (control group) used in the current study after thermomechanical 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.