title: Fracture resistance of three porcelain-layered CAD/CAM zirconia frame designs.
abstract: OBJECTIVE
  Chipping is the most frequent clinical failure of zirconia crowns. Causes of chipping have not been completely understood and different possible reasons have been considered. The study was aimed at evaluating the fracture resistance of 3 different CAD/CAM zirconia frame designs veneered with porcelain.
  
  
  METHODS
  Thirty extracted sound premolars were divided into 3 groups (n=10). Chamfer preparations were performed, impressions were taken. Three zirconia frame designs (Aadva, GC) were realized: reproduction of the abutment contour (flat design, FD); wax-up as for porcelain-fused-to-metal crowns (PFM); anatomically guided, designed to keep constant the thickness of the overlying porcelain veneering (AG). Porcelain veneering was made with pressure layering technique (Initial Zr, GC). Crowns were cemented utilizing a self-adhesive resin cement (G-Cem, GC). After a 24-h water storage at 37°C, using a universal testing machine (1 mm crosshead speed), crowned teeth were loaded in the central fossa in a direction parallel to the longitudinal axis of the tooth. Load at fracture was recorded in Newtons (N). Digital photographs of the specimens were taken in order to assess failure patterns. Between-group differences in fracture strength were statistically analyzed (One-Way Analysis of Variance, Tukey test, p<0.05).
  
  
  RESULTS
  Load at fractures differed significantly among the groups (p=0.004). AG exhibited significantly higher fracture resistance 1721.6 (488.1) N than PFM 1004.6 (321.3) N and FD 1179.5 (536.2) N, that were comparable. Repairable failures occurred in 80% of AG, 70% of PFM, and 50% of FD specimens.
  
  
  CONCLUSIONS
  Anatomically guided zirconia frames resisted significantly higher loads than flat and PFM-like frame designs.
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Italy. Electronic address: ferrarm@gmail.com.
authors.forename: Marco
authors.initials: M
authors.lastname: Ferrari
authors.affiliation: Department of Oral Sciences, Prosthodontics Unit, University "La Sapienza", Roma, Italy.
authors.forename: Agostino
authors.initials: A
authors.lastname: Giovannetti
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Carrabba
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bonadeo
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Rengo
authors.affiliation: Department of Surgery, Faculty of Health and Sport Sciences, University of Zaragoza, Huesca, Spain.
authors.forename: Francesca
authors.initials: F
authors.lastname: Monticelli
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vichi
mesh_terms: D017076:Computer-Aided Design; D003776:Dental Porcelain / Q000737:chemistry*; D003801:Dental Veneers; D008422:Materials Testing; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003776:Dental Porcelain; D015040:Zirconium
keywords: CAD/CAM; Ceramic; Ceramic veneering; Chipping; Fracture load; Framework design; Zirconia