title: Fracture mechanics analyses of ceramic/veneer interface under mixed-mode loading.
abstract: Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive stresses in the veneer.
authors.affiliation: Key Laboratory of High Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, PR China.
authors.forename: Gaoqi
authors.initials: G
authors.lastname: Wang
authors.affiliation: Key Laboratory of High Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, PR China. Electronic address: zhangsong@sdu.edu.cn.
authors.forename: Song
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Prosthodontics, Qilu Hospital of Shandong University, Jinan 250012, PR China.
authors.forename: Cuirong
authors.initials: C
authors.lastname: Bian
authors.affiliation: Department of Prosthodontics, Qilu Hospital of Shandong University, Jinan 250012, PR China.
authors.forename: Hui
authors.initials: H
authors.lastname: Kong
mesh_terms: D002138:Calibration; D002516:Ceramics; D019245:Compressive Strength; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D004867:Equipment Design; D020342:Finite Element Analysis; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide
keywords: Bi-materials; Dental ceramics; Fracture criterion; Interface toughness; Mixed-mode