title: Influence of Core-Veneer Thickness Ratio on the Fracture Load and Failure Mode of Zirconia Crowns.
abstract: OBJECTIVE
  To evaluate the influence of different core-veneer thickness (CVT) ratios on fracture loads and failure modes of zirconia crowns with or without thermomechanical cycling (TC).
  
  
  METHODS
  Forty yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) cores were veneered with a pressable ceramic and divided into four groups (n = 10): group 1 - 1:3 CVT ratio (0.5-mm core, 1.5-mm veneer); group 2 - 1:1 CVT ratio (1.0-mm core, 1.0-mm veneer); groups 3 and 4 - identical to groups 1 and 2, respectively, except that they underwent TC (1,000,000 cycles with an 84-N load applied at a 4-Hz frequency, temperature cycling at 4°C, 37°C, and 55°C - 30 seconds each). Loads were applied axially to the central fossa of the crowns with a 1 mm/min crosshead speed at 200 N until failure.
  
  
  RESULTS
  Two-way ANOVA showed that the crowns with a 1:3 CVT ratio had a lower mean fracture load than crowns with a 1:1 CVT ratio (group 1 = 1666.4 ± 466.4 N; group 2 = 2156.6 ± 472.3 N). TC had no effect on the fracture load for crowns with the same CVT ratio. The failures observed for the crowns in groups 1, 3, and 4 were fractures within the veneering ceramic, which exposed the core. The failure severity of fractures for group 2 was less extensive, characterized by chipping within the ceramic veneer.
  
  
  CONCLUSIONS
  Crowns with a 1:1 CVT ratio had higher fracture load values and more conservative failures. TC had no effect on the fracture load of the ceramic crowns.
authors.affiliation: Department of Restorative Dentistry, Herman Ostrow School of Dentistry of USC, Los Angeles, CA.
authors.forename: Luciana Mara
authors.initials: LM
authors.lastname: Soares
authors.affiliation: Dental Technician, Campinas, São Paulo, Brazil.
authors.forename: Cristiano
authors.initials: C
authors.lastname: Soares
authors.affiliation: Department of Prosthodontics, São Leopoldo Mandic Institute and Dental Research Center, Campinas, São Paulo, Brazil.
authors.forename: Milton Edson
authors.initials: ME
authors.lastname: Miranda
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Dental Research Center, Campinas, São Paulo, Brazil.
authors.forename: Roberta Tarkany
authors.initials: RT
authors.lastname: Basting
mesh_terms: D002516:Ceramics / Q000737:chemistry; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide
keywords: Ceramic crowns; chipping; thermomechanical cycling