title: Fractographic analyses of all-ceramic crowns: a study of 27 clinically fractured crowns.
abstract: OBJECTIVE
  The use of all-ceramic restorations has been steadily increasing in the decades since the introduction of high-strength core ceramics as an alternative to metal cores. Even with high-strength ceramic cores, the crowns are susceptible to fractures during clinical function, probably the major concern associated with all-ceramic restorations. The aim of this study was to analyze fracture features of clinically fractured crowns in order to determine crack initiation sites and crack propagation paths.
  
  
  METHODS
  Fractographic methods were used to analyze 27 all-ceramic full coverage crowns with alumina cores and feldspatic veneering ceramic. The fractured crowns were supplied by dentists in private and public practices with information of type of cement and time in function if available.
  
  
  RESULTS
  The fractured crowns comprised 13 incisors, 3 premolars and 11 molars. The results revealed that all fractures initiated in the cervical margin of the crowns and usually from the approximal area close to the most coronally placed curvature of the margin. There was no statistically significant association between the cement used and time in function.
  
  
  CONCLUSIONS
  Fractography of clinically failed all-ceramic crowns can provide information on the fracture modes and design considerations. The findings are in contrast to fracture modes from in vitro tests. The results suggest that more clinically relevant in vitro test methods to study the durability of ceramic crowns should be developed.
authors.affiliation: Department of Clinical Dentistry-Biomaterials, Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway. marit.oilo@iko.uib.no
authors.forename: Marit
authors.initials: M
authors.lastname: Øilo
authors.forename: Nils Roar
authors.initials: NR
authors.lastname: Gjerdet
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003442:Crowns; D003738:Dental Cements / Q000145:classification; D003764:Dental Materials / Q000737:chemistry*; D019232:Dental Restoration Failure; D003801:Dental Veneers; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D008853:Microscopy; D010781:Photography; D011176:Post and Core Technique / Q000295:instrumentation; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D003738:Dental Cements; D003764:Dental Materials; D005899:Glass Ionomer Cements; D017680:Potassium Compounds; D019279:Resin Cements; C016447:feldspar; D015036:Zinc Phosphate Cement; D000537:Aluminum Oxide