title: Experimental and FE shear-bonding strength at core/veneer interfaces in bilayered ceramics.
abstract: OBJECTIVE
  To compare the bond strength of a ceramic veneer material to two different ceramic core materials using shear strength testing and finite element analysis (FEA).
  
  
  METHODS
  15 blocks of ceramic cores were made of each of IPS e.max ZirCAD (Ivoclar-Vivadent, Schaan, Liechtenstein) (ZirCAD) and lithium disilicate IPS e.max CAD (LS). These were veneered using IPS e.max Ceram (Ceram) according to the manufacturers' instructions. Samples were then mounted, placed inside a shear testing jig and loaded at their core/veneer interfaces with a universal testing machine. Fractured specimens were then examined fractographically at 45×. An independent t-test and a Mann-Whitney U test were used to detect differences in bond strengths and the patterns of failure between the two groups, respectively (p>0.05). Two-dimensional plane stress FE-models were constructed and subjected to shear loading simulating the experimental conditions.
  
  
  RESULTS
  Mean shear stresses (MPa) were 28.8 (9.5) for ZirCAD/Ceram and 29.1 (8.3) for LS/Ceram. Differences were not statistically significant. Fracture patterns were significantly different between the 2 groups as all ZirCAD/Ceram samples broke adhesively at their interface while LS/Ceram samples broke cohesively in the veneer or the core or had mixed adhesive/cohesive failure. Stress distributions in the FEA models were also different, corresponding to the variable fracture patterns in the 2 groups.
  
  
  CONCLUSIONS
  Although shear stresses were similar, fractographic analysis and finite element modeling suggested better bonding between the veneering ceramic and the glass-ceramic than to the zirconia cores. Improved bonding techniques are necessary to prevent clinical delamination of veneered zirconia restorations.
authors.affiliation: Department of Prosthodontics, School of Dentistry, The University of Jordan, Amman, Jordan. nadia_ereifej116@hotmail.com
authors.forename: Nadia
authors.initials: N
authors.lastname: Ereifej
authors.forename: Flávia Pires
authors.initials: FP
authors.lastname: Rodrigues
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D000268:Adhesiveness; D001031:Apatites / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D003198:Computer Simulation; D001840:Dental Bonding; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D020342:Finite Element Analysis; D006801:Humans; D008422:Materials Testing; D011176:Post and Core Technique; D033081:Shear Strength; D013314:Stress, Mechanical; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D001031:Apatites; C520133:IPS e.max CAD LT; C493120:lithia disilicate; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; C023506:Glass ceramics; D015040:Zirconium; C025105:fluorapatite