title: Tensile strength of bilayered ceramics and corresponding glass veneers.
abstract: OBJECTIVE
  To investigate the microtensile bond strength between two all-ceramic systems; lithium disilicate glass ceramic and zirconia core ceramics bonded with their corresponding glass veneers.
  
  
  METHODS
  Blocks of core ceramics (IPS e.max® Press and Lava™ Frame) were fabricated and veneered with their corresponding glass veneers. The bilayered blocks were cut into microbars; 8 mm in length and 1 mm(2) in cross-sectional area (n = 30/group). Additionally, monolithic microbars of these two veneers (IPS e.max® Ceram and Lava™ Ceram; n = 30/group) were also prepared. The obtained microbars were tested in tension until fracture, and the fracture surfaces of the microbars were examined with fluorescent black light and scanning electron microscope (SEM) to identify the mode of failure. One-way ANOVA and the Dunnett's T3 test were performed to determine significant differences of the mean microtensile bond strength at a significance level of 0.05.
  
  
  RESULTS
  The mean microtensile bond strength of IPS e.max® Press/IPS e.max® Ceram (43.40 ± 5.51 MPa) was significantly greater than that of Lava™ Frame/Lava™ Ceram (31.71 ± 7.03 MPa)(P<.001). Fluorescent black light and SEM analysis showed that most of the tested microbars failed cohesively in the veneer layer. Furthermore, the bond strength of Lava™ Frame/Lava™ Ceram was comparable to the tensile strength of monolithic glass veneer of Lava™ Ceram, while the bond strength of bilayered IPS e.max® Press/IPS e.max® Ceram was significantly greater than tensile strength of monolithic IPS e.max® Ceram.
  
  
  CONCLUSIONS
  Because fracture site occurred mostly in the glass veneer and most failures were away from the interfacial zone, microtensile bond test may not be a suitable test for bonding integrity. Fracture mechanics approach such as fracture toughness of the interface may be more appropriate to represent the bonding quality between two materials.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
authors.forename: Chuchai
authors.initials: C
authors.lastname: Anunmana
authors.affiliation: Department of Advanced General Dentistry, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
authors.forename: Tharee
authors.initials: T
authors.lastname: Champirat
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
authors.forename: Bundhit
authors.initials: B
authors.lastname: Jirajariyavej
keywords: Bond strength; Ceramic; Glass-ceramic; Lithium disilicate; Microtensile; Zirconia