title: Influence of cusp inclination and curvature on the in vitro failure and fracture resistance of veneered zirconia crowns.
abstract: OBJECTIVE
  The aim was to investigate the influence of cusp inclinations and curvatures on the failure behaviour and fracture resistance of veneered zirconia crowns.
  
  
  METHODS
  Five groups (n = 8/group) of zirconia-based molar crowns were fabricated by modifying cusp inclination (S, steep = 45°; M, medium = 30°; F, flat = 10°) and curvature (P, pointed; R, round; O, round-oblate). Combinations MP, MR, SP, SR and FO were investigated. All crowns were fixed on polymethylmethacrylate teeth, thermally cycled and mechanically loaded. Failures were monitored and fracture resistance was determined after ageing. Crowns were fractographically analysed with scanning electron microscopy.
  
  
  RESULTS
  Chipping during thermal cycling and mechanical loading (TCML) was observed in groups MR (1×), SP (6×) and SR (3×). Defect sizes varied between 0.12 mm(2) (MR) and 17.28 mm(2) (SP). Failures started from occlusal contacts. Mean fracture varied significantly between 1,354.2 ± 360.0 N (SR) and 3,155.8 ± 444.4 N (FO).
  
  
  CONCLUSIONS
  Cusp inclination and curvature influenced failures during TCML and fracture loads. Crowns with medium cusp inclination and pointed or round curvature are recommended for clinical application as they revealed high resistance to chipping. Steep inclination, especially in combination with pointed curvature, was shown to increase chipping rates and areas and to decrease fracture force.
  
  
  CONCLUSIONS
  The results show the necessity of considering design parameters of the veneer in order to reduce failures of zirconia-based crowns.
authors.affiliation: Department of Prosthetic Dentistry, University Medical Center Regensburg, 93042, Regensburg, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Preis
authors.forename: Thomas
authors.initials: T
authors.lastname: Dowerk
authors.forename: Michael
authors.initials: M
authors.lastname: Behr
authors.forename: Carola
authors.initials: C
authors.lastname: Kolbeck
authors.forename: Martin
authors.initials: M
authors.lastname: Rosentritt
mesh_terms: D003442:Crowns; D003801:Dental Veneers; D066298:In Vitro Techniques; D015040:Zirconium
chemical_list: D015040:Zirconium; C028541:zirconium oxide