title: Influence of substructure design, veneer application technique, and firing regime on the in vitro performance of molar zirconia crowns.
abstract: OBJECTIVE
  The aim of this in vitro study was to evaluate the influence of substructure design, veneer application technique, and firing regime on the failure and fracture resistance of molar zirconia crowns.
  
  
  METHODS
  Six groups (n=8/group) of zirconia crowns were fabricated in simple core (SC) or anatomically reduced (AR) design, veneered with different feldspathic or glass ceramic materials, and defined according to the application technique and firing regime (LT: layering technique; LT_L: LT with long-term cooling; PT: press technique; DV: digital veneering technique). The following groups were investigated: SCLT, ARLT, SCLT_L, SCPT, ARPT, ARDV. Crowns were adhesively bonded to polymethylmethacrylate abutment teeth and subjected to thermal cycling (TC: 2×3000×5°/55°) and mechanical loading (ML: 1.2×10(6); 50N; 1.6Hz) in a chewing simulator with metal-ceramic molar crowns as antagonists. Failures were monitored and fracture resistance determined after aging. Data were statistically analyzed (one-way analysis of variance, ANOVA; post hoc Bonferroni, α=0.05). Crowns were subjected to scanning electron microscopy for fractographic failure analysis.
  
  
  RESULTS
  Failures (chipping, cracks) during TCML were observed in groups SCLT (2×), ARDV (2×) and SCLT_L (1×). Defect sizes varied between 3.5mm (SCLT: crack) and 30.0mm(2) (SCLT_L: chipping). Mean (SD) fracture forces ranged between 1529.0 (405.2)N for SCPT and 2372.3 (351.8)N for ARDV.
  
  
  CONCLUSIONS
  The failure frequency of veneered zirconia crowns could be reduced by using anatomically reduced substructures, the press veneering technique, and an adapted cooling protocol. Fracture resistance increased with use of anatomically reduced substructures and the digital veneering technique.
authors.affiliation: Department of Prosthetic Dentistry, University Medical Center Regensburg, 93042 Regensburg, Germany. verena.preis@ukr.de
authors.forename: Verena
authors.initials: V
authors.lastname: Preis
authors.forename: Christoph
authors.initials: C
authors.lastname: Letsch
authors.forename: Gerhard
authors.initials: G
authors.lastname: Handel
authors.forename: Michael
authors.initials: M
authors.lastname: Behr
authors.forename: Sibylle
authors.initials: S
authors.lastname: Schneider-Feyrer
authors.forename: Martin
authors.initials: M
authors.lastname: Rosentritt
mesh_terms: D000704:Analysis of Variance; D017076:Computer-Aided Design; D003442:Crowns; D000044:Dental Abutments; D003735:Dental Casting Technique; D003776:Dental Porcelain; D017267:Dental Prosthesis Design / Q000379:methods*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006801:Humans; D016876:Metal Ceramic Alloys; D008963:Molar; D018709:Statistics, Nonparametric; D015019:Yttrium; D015040:Zirconium
chemical_list: D016876:Metal Ceramic Alloys; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide