title: A fractographic study of clinically retrieved zirconia-ceramic and metal-ceramic fixed dental prostheses.
abstract: OBJECTIVE
  A recent 3-year randomized controlled trial (RCT) of tooth supported three- to five-unit zirconia-ceramic and metal-ceramic posterior fixed dental prostheses (FDPs) revealed that veneer chipping and fracture in zirconia-ceramic systems occurred more frequently than those in metal-ceramic systems [1]. This study seeks to elucidate the underlying mechanisms responsible for the fracture phenomena observed in this RCT using a descriptive fractographic analysis.
  
  
  METHODS
  Vinyl-polysiloxane impressions of 12 zirconia-ceramic and 6 metal-ceramic FDPs with veneer fractures were taken from the patients at the end of a mean observation of 40.3±2.8 months. Epoxy replicas were produced from these impressions [1]. All replicas were gold coated, and inspected under the optical microscope and scanning electron microscope (SEM) for descriptive fractography.
  
  
  RESULTS
  Among the 12 zirconia-ceramic FDPs, 2 had small chippings, 9 had large chippings, and 1 exhibited delamination. Out of 6 metal-ceramic FDPs, 5 had small chippings and 1 had large chipping. Descriptive fractographic analysis based on SEM observations revealed that fracture initiated from the wear facet at the occlusal surface in all cases, irrespective of the type of restoration.
  
  
  CONCLUSIONS
  Zirconia-ceramic and metal-ceramic FDPs all fractured from microcracks that emanated from occlusal wear facets. The relatively low fracture toughness and high residual tensile stress in porcelain veneer of zirconia restorations may contribute to the higher chipping rate and larger chip size in zirconia-ceramic FDPs relative to their metal-ceramic counterparts. The low veneer/core interfacial fracture energy of porcelain-veneered zirconia may result in the occurrence of delamination in zirconia-ceramic FDPs.
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY 10010, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Pang
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY 10010, USA.
authors.forename: Asima
authors.initials: A
authors.lastname: Chughtai
authors.affiliation: Division of Fixed Prosthodontics and Occlusion, School of Dental Medicine, University of Geneva, 19 rue Barthélemy-Menn, CH-1205 Geneva, Switzerland.
authors.forename: Irena
authors.initials: I
authors.lastname: Sailer
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY 10010, USA. Electronic address: yz21@nyu.edu.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D003764:Dental Materials / Q000737:chemistry*; D019232:Dental Restoration Failure; D003801:Dental Veneers; D003779:Denture Design; D003830:Denture, Partial, Fixed; D005260:Female; D006801:Humans; D008297:Male; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D013499:Surface Properties
chemical_list: D003764:Dental Materials; D016876:Metal Ceramic Alloys
keywords: Chipping; Delamination; Descriptive fractography; Metal–ceramic FDPs; Occlusal wear facet; Zirconia–ceramic FDPs