title: Interfacial toughness of bilayer dental ceramics based on a short-bar, chevron-notch test.
abstract: OBJECTIVE
  The objective of this study was to test the null hypothesis that the interfacial toughness of each of two types of bonded core-veneer bilayer ceramics is not significantly different from the apparent fracture toughness of the control monolithic glass veneer.
  
  
  METHODS
  T-shaped short-bars of a lithia-disilicate glass-ceramic core (LC) and yttria-stabilized polycrystalline zirconia core ceramic (ZC) were prepared according to the manufacturer's recommendations. V-shaped notches were prepared by using 25-mum-thick palladium foil, leaving the chevron-notch area exposed, and the bars were veneered with a thermally compatible glass veneer (LC/GV and ZC/GV). Additionally, we also bonded the glass veneer to itself as a control group (GV/GV). Specimens were kept in distilled water for 30 days before testing in tension. Eight glass veneer bars were prepared for the analysis of fracture toughness test using the indentation-strength technique.
  
  
  RESULTS
  The mean interfacial toughness of the LC/GV group was 0.69 MPam(1/2) (0.11), and did not significantly differ from that of the GV/GV control group, 0.74 MPam(1/2) (0.17) (p>0.05). However, the difference between the mean interfacial toughness of the ZC/GV group, 0.13 MPam(1/2) (0.07), and the LC/GV and the GV/GV groups was statistically significant (p<0.05).
  
  
  CONCLUSIONS
  For bilayer all-ceramic restorations with high-strength core materials, the veneering ceramics are the weakest link in the design of the structure. Since all-ceramic restorations often fail from chipping of veneer layers or crack initiation at the interface, the protective effects of thermal mismatch stresses oral prosthesis design should be investigated.
authors.affiliation: Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville, FL, USA. dtchuchai@staff2.mahidol.ac.th
authors.forename: Chuchai
authors.initials: C
authors.lastname: Anunmana
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Anusavice
authors.forename: John J
authors.initials: JJ
authors.lastname: Mecholsky
mesh_terms: D003776:Dental Porcelain / Q000737:chemistry; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D003801:Dental Veneers; D004055:Differential Thermal Analysis; D055119:Elastic Modulus; D005898:Glass; D008422:Materials Testing / Q000379:methods; D015019:Yttrium; D015040:Zirconium
chemical_list: C493120:lithia disilicate; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium