title: [Fracture reliability of zirconia all-ceramic crown according to zirconia coping design].
abstract: OBJECTIVE
  To study the fracture resistance and characteristics of the bi-layer zirconia all ceramic crowns according to the zirconia coping design using various experimental methods and to compare the results of the in vitro test with the clinical evaluation.
  
  
  METHODS
  The bi-layer zirconia all ceramic crowns were fabricated by the same method as used in clinical practice. Two different coping designs with/without zirconia marginal collar were used. All the samples were cemented onto corresponding resin dies. All the specimens were tested in the 2 groups with/without zirconia collar. The fracture load test was performed on 10 crowns from each group. Fracture strength was tested with a universal testing machine. The fracture modes and features of the failed crowns were observed with an integrated microscope and a field emission scanning electron microscope.
  
  
  RESULTS
  The zirconia collar group showed higher fracture load than the group without zirconia collar. All the zirconia crowns failed with porcelain failure and without zirconia coping broken. The porcelain fracture modes were crack, chipping and delamination. The distribution of the different fracture modes in the groups was the same.
  
  
  CONCLUSIONS
  The bi-layer zirconia crown with 2 mm zirconia marginal collar showed more fracture strength under once load. The fracture modes of the test specimens were the same as the clinical fracture bi-layer zirconia crowns, showing porcelain chipping and delamination.
authors.affiliation: Department of General Dentistry, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Yi-hong
authors.initials: YH
authors.lastname: Liu
authors.affiliation: National Engineering Laboratory for Digital and Material Technology of Stomatology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Dental Technician, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Qing-hui
authors.initials: QH
authors.lastname: Zhang
authors.affiliation: Department of General Dentistry, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Prosthetics, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Hai-lan
authors.initials: HL
authors.lastname: Feng
mesh_terms: D003442:Crowns; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D008422:Materials Testing; D015203:Reproducibility of Results; D014082:Tooth Fractures; D015040:Zirconium
chemical_list: D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide