title: Fracture strength of porcelain fused to metal crowns made of cast, milled or laser-sintered cobalt-chromium.
abstract: OBJECTIVE
  The aim was to compare the fracture strength of porcelain fused to metal crowns with copings fabricated in Co-Cr using different manufacturing techniques (casting, milling and laser-sintering) with crowns manufactured in a high-gold alloy.
  
  
  METHODS
  A total of 50 identical crowns were fabricated and sub-divided into five groups; cast Co-Cr, milled Co-Cr, two groups of laser-sintered Co-Cr and a control group cast in a high-gold alloy. After thermocycling (5000 cycles, 5-55°C) and pre-load (30-300 N, 10,000 cycles) the crowns were loaded until fracture. Load (N) and fracture mode were recorded.
  
  
  RESULTS
  There was a significant difference (p < 0.05) in fracture strength between the control group and one of the laser-sintered groups. The mean values (N) for the groups were as follows: cast Co-Cr, 1560 ± 274; milled Co-Cr, 1643 ± 153; laser-sintered Co-Cr 1, 1448 ± 168; laser-sintered Co-Cr 2, 1562 ± 72; control group, 1725 ± 220.
  
  
  CONCLUSIONS
  There is no difference in strength between Co-Cr crowns produced using the different production technologies: casting, milling or laser-sintering. Metal ceramic crowns made with copings fabricated in a high-gold alloy present numerically higher fracture strength than crowns made with copings fabricated in Co-Cr alloys. The difference is confirmed when analyzing the fracture surfaces, but the difference in fracture strength value is limited and is only significant with regard to one of the two laser-sintered groups.
authors: Department of Materials Science and Technology, Faculty of Odontology, Malmö University, Malmö, Sweden.
authors: Sozan Hama
authors: SH
authors: Suleiman
authors: Per
authors: P
authors: Vult von Steyern
mesh_terms: D002857:Chromium; D003035:Cobalt; D003442:Crowns; D003776:Dental Porcelain; D007834:Lasers
chemical_list: D002857:Chromium; D003776:Dental Porcelain; D003035:Cobalt