title: A comparative in vitro study of the load at fracture of all-ceramic crowns with various thicknesses of In-Ceram core.
abstract: OBJECTIVE
  The aim of this study was to investigate the influence of three different thicknesses of In-Ceram core on the load at fracture of all-ceramic crowns.
  
  
  METHODS
  Thirty standardized crown-shaped nickel-chromium alloy dies were fabricated using a milling machine. Twenty dies were prepared with a 1 mm shoulder for Groups A and B. The only difference in the ten dies used for Group C was a smaller 0.5 mm lingual shoulder. The thicknesses of In-Ceram were 0.5 mm, 1.5 mm, and 0.75 mm for Groups A, B, and C. All all-ceramic crowns were fabricated in accordance with the manufacturer's instructions. After cementation of the crowns, their fracture resistance was tested with a universal testing machine. The load was directed to a point located 3 mm from the lingual aspect of the incisal edge at 30 degrees to the long axis of each specimen until catastrophic failure occurred.
  
  
  RESULTS
  The mean loads at fracture for Groups A, B, and C were 1117+/-388 N, 2083+/-385 N, and 1439+/-368 N, respectively. No statistically significant difference in load at fracture between Groups A and C was found (p>0.05). However, the differences were statistically significant between Groups A and B (p<0.001) and Groups B and C (p<0.001).
  
  
  CONCLUSIONS
  Under the guidelines of this study, increasing the thickness of the In-Ceram core increased the fracture resistance of the all-ceramic crowns.
  
  
  CONCLUSIONS
  The sufficient thickness of the In-Ceram core of all-ceramic crowns is an important factor in fracture resistance. Therefore, dental practitioners should be careful in patient selection; if the horizontal overlap of a tooth to be restored is too limited, then all-ceramic crowns may not be a feasible option.
authors.affiliation: Department of Prosthetic Dentistry, Dental Sciences Center, Gülhane Military Medical Academy, Ankara, Turkey.
authors.forename: Suat
authors.initials: S
authors.lastname: Gokce
authors.forename: Emine
authors.initials: E
authors.lastname: Celik-Bagci
authors.forename: Ilser
authors.initials: I
authors.lastname: Turkyilmaz
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: C483026:In-Ceram Alumina; C483027:vitadur alpha; D003776:Dental Porcelain; C070870:In-Ceram; D015036:Zinc Phosphate Cement; D000537:Aluminum Oxide