title: Clinically relevant fracture testing of all-ceramic crowns.
abstract: OBJECTIVE
  Fracture strength measured in vitro indicates that most all-ceramic crowns should be able to withstand mastication forces. Nevertheless, fractures are one of the major clinical problems with all-ceramic restorations. Furthermore, the fracture mode of all-ceramic crowns observed in clinical use differs from that found in conventional fracture strength tests. The aim of the present study was to develop and investigate a method that simulates clinical fracture behavior in vitro.
  
  
  METHODS
  30 crowns with alumina cores were made to fit a cylindrical model with a molar-like preparation design. These crowns were randomly allocated to 3 tests groups (n=10). The crowns in group 1 were cemented to abutment models of epoxy and subsequently fractured by occlusal loading without contact damage. The crowns in group 2 were fractured by cementation with expanding cement. The crowns in group 3 were cemented on an abutment model of epoxy split almost in two and fractured by increasing the diameter of the model in the bucco-lingual direction. The fractured crowns were analyzed by fractographic methods and compared to a reference group of 10 crowns fractured in clinical use.
  
  
  RESULTS
  The fracture modes of all the in vitro crowns were similar to clinical fracture modes. The fracture modes in group 1 were most closely matched to the clinical fractures. These crowns also fractured at clinically relevant loads.
  
  
  CONCLUSIONS
  Laboratory tests that induce a distortion of the abutment model during occlusal loading without occlusal contact damage can simulate clinical fractures of all-ceramic crowns.
authors.affiliation: Department of Clinical Dentistry - Biomaterials, Faculty of Medicine and Dentistry, University of Bergen, Norway. marit.oilo@iko.uib.no
authors.forename: Marit
authors.initials: M
authors.lastname: Øilo
authors.forename: Ketil
authors.initials: K
authors.lastname: Kvam
authors.forename: John E
authors.initials: JE
authors.lastname: Tibballs
authors.forename: Nils Roar
authors.initials: NR
authors.lastname: Gjerdet
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D001732:Bite Force; D002484:Cementation / Q000379:methods; D002516:Ceramics / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D003442:Crowns; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003801:Dental Veneers; D020724:Elastomers / Q000737:chemistry; D004853:Epoxy Resins / Q000737:chemistry; D005030:Ethylenes / Q000737:chemistry; D006801:Humans; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods; D016876:Metal Ceramic Alloys / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014025:Titanium / Q000737:chemistry; D019231:Tooth Preparation, Prosthodontic / Q000379:methods; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: C105314:AllCeram; D003764:Dental Materials; D020724:Elastomers; D004853:Epoxy Resins; D005030:Ethylenes; D016876:Metal Ceramic Alloys; C077451:Procera; C505585:ethylene-propylene-diene-monomer; D014867:Water; D003776:Dental Porcelain; C048399:brass; D015036:Zinc Phosphate Cement; D003300:Copper; D014025:Titanium; D015032:Zinc; D000537:Aluminum Oxide
keywords: Alumina; Ceramic; Dental crowns; Failure analysis; Fracture strength