Fracture strength of porcelain fused to metal crowns made of cast, milled or laser-sintered cobalt-chromium

Aims. 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 degrees 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. Conclusion. 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.