title: Influence of convergence angle of tooth preparation on the fracture resistance of Y-TZP-based all-ceramic restorations.
abstract: OBJECTIVE
  To investigate the influence of the convergence angle of tooth preparation on the fracture load of Y-TZP-based ceramic (YZ - Vita YZ) substructure (SB) veneered with a feldspathic porcelain (VM9 - Vita VM9).
  
  
  METHODS
  Finite element stress analysis (FEA) was performed to examine the stress distribution of the system. Eighty YZ SB were fabricated using a CAD-CAM system and divided into four groups (n=20), according to the total occlusal convergence (TOC) angle: G6 - 6° TOC; G12 - 12° TOC; G20 - 20° TOC; and G20MOD - 20° TOC with modified SB. All SB were veneered with VM9, cemented in a fiber reinforced epoxy resin die, and loaded to failure. Half of the specimens from each group (n=10) were cyclic fatigued (10(6) cycles) before testing. Failure analysis was performed to determine the fracture origin. Data were statistically analyzed using Anova and Tukey's tests (α=0.05).
  
  
  RESULTS
  The greatest mean load to fracture value was found for the G20MOD, which was predicted by the FEA. Cyclic fatigue did not significantly affect the load of fracture. Catastrophic failure originating from the internal occlusal surface of the SB was the predominant failure mode, except for G20MOD.
  
  
  CONCLUSIONS
  The YZ-VM9 restorations resisted greater compression load than the usual physiological occlusal load, regardless of the TOC angle of preparations. Yet, the G20MOD design produced the best performance among the experimental conditions evaluated.
authors: Department of Dental Materials and Prosthodontics, Sao Paulo State University - UNESP, Sao Jose dos Campos, SP, Brazil.
authors: Pedro Henrique
authors: PH
authors: Corazza
authors: Sabrina Alves
authors: SA
authors: Feitosa
authors: Alexandre Luiz Souto
authors: AL
authors: Borges
authors: Alvaro
authors: A
authors: Della Bona
mesh_terms: D000704:Analysis of Variance; D017076:Computer-Aided Design; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D055119:Elastic Modulus; D020342:Finite Element Analysis; D016012:Poisson Distribution; D019246:Tooth Preparation / Q000379:methods*; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium