title: The Effects of Margin Curvature on Load at Fracture of Ceramic Crowns.
abstract: OBJECTIVE
  Despite the high fracture strength of modern dental core ceramics, fractures are a common cause of clinical failures. The aim of this study was to use a clinically relevant test method to evaluate the effect of the curvature of the cervical crown margins on load at fracture.
  
  
  METHODS
  Thirty zirconia crowns and 30 glass-ceramic crowns were produced for three premolar preparations with variation in the approximal crown margin curvature: low curvature (r=12 mm), moderate curvature (r=2.5 mm), and high curvature (r=1.5). The crowns were loaded until fracture with a method that mimics clinical fracture modes.
  
  
  RESULTS
  Statistically significant differences were found among both crown margin curvature and material groups (P<.001). Most fractures originated from pre-existing flaws.
  
  
  CONCLUSIONS
  A moderate to low curvature of the crown margins increases crown strength compared with a high curvature.
authors.forename: Marit
authors.initials: M
authors.lastname: Øilo
authors.forename: Ketil
authors.initials: K
authors.lastname: Kvam
authors.forename: Kjetil
authors.initials: K
authors.lastname: Reisegg
authors.forename: Nils Roar
authors.initials: NR
authors.lastname: Gjerdet
mesh_terms: D002516:Ceramics; D003442:Crowns; D019232:Dental Restoration Failure; D006801:Humans