title: Effects of core-to-dentin thickness ratio on the biaxial flexural strength, reliability, and fracture mode of bilayered materials of zirconia core (Y-TZP) and veneer indirect composite resins.
abstract: BACKGROUND
  Indirect composite resins (ICR) are promising alternatives as veneering materials for zirconia frameworks. The effects of core-to-dentin thickness ratio (C/Dtr) on the mechanical property of bilayered veneer ICR/yttria-tetragonal zirconia polycrystalline (Y-TZP) core disks have not been previously studied.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to assess the effects of C/Dtr on the biaxial flexural strength, reliability, and fracture mode of bilayered veneer ICR/ Y-TZP core disks.
  
  
  METHODS
  A total of 180 bilayered 0.6-mm-thick composite resin disks in core material and C/Dtr of 2:1, 1:1, and 1:2 were tested with either core material placed up or placed down for piston-on-3-ball biaxial flexural strength. The mean biaxial flexural strength, Weibull modulus, and fracture mode were measured to evaluate the variation trend of the biaxial flexural strength, reliability, and fracture mode of the bilayered disks with various C/Dtr. One-way analysis of variance (ANOVA) and chi-square tests were used to evaluate the variation tendency of fracture mode with the C/Dtr or material placed down during testing (α=.05). Light microscopy was used to identify the fracture mode.
  
  
  RESULTS
  The mean biaxial flexural strength and reliability improved with the increase in C/Dtr when specimens were tested with the core material either up and down, and depended on the materials that were placed down during testing. The rates of delamination, Hertzian cone cracks, subcritical radial cracks, and number of fracture fragments partially depended on the C/Dtr and the materials that were placed down during testing.
  
  
  CONCLUSIONS
  The biaxial flexural strength, reliability, and fracture mode in bilayered structures of Y-TZP core and veneer ICR depend on both the C/Dtr and the material that was placed down during testing.
authors.affiliation: Doctoral student, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
authors.forename: Naichuan
authors.initials: N
authors.lastname: Su
authors.affiliation: Professor, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
authors.forename: Yunmao
authors.initials: Y
authors.lastname: Liao
authors.affiliation: Associate Professor, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, Wash.
authors.forename: Hai
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Associate Professor, Department of Dental Technology, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
authors.forename: Li
authors.initials: L
authors.lastname: Yue
authors.affiliation: Clinical resident, Ningbo Dental Hospital, Ningbo, China.
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Lu
authors.affiliation: Associate Professor, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
authors.forename: Jiefei
authors.initials: J
authors.lastname: Shen
authors.affiliation: Professor, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China. Electronic address: hwang1999@163.com.
authors.forename: Hang
authors.initials: H
authors.lastname: Wang
mesh_terms: D003188:Composite Resins / Q000592:standards / Q000627:therapeutic use*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D003804:Dentin; D006801:Humans; D066298:In Vitro Techniques; D013718:Tensile Strength; D015019:Yttrium / Q000592:standards / Q000627:therapeutic use*; D015040:Zirconium / Q000592:standards / Q000627:therapeutic use*
chemical_list: D003188:Composite Resins; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium