Abstract: Objective To evaluate the effect of different convergence angles on the fitness of using selective laser melting(SLM) to fabricate the CoCr inner crown, and to compare it with Lostwax(LW) technique. Methods 60 resin base teeth were prepared by CAD/CAM, comprising 3 types of occlusal convergence (6°,8°,12°) and 20 for each; then each type of the specimens was further divided into SLM and LW group (selective laser melting or Lostwax) to fabricate the CoCr inner crown; there are altogether 6 groups with 10 specimens for each group. Each specimen received the treatment of being cleaned, cemented, and cut.The cement thickness of the inner and outer chamfer edge was then measured by scanning electronic microscopy. Analysis of Variance was performed to determine the differences using SPSS 17.0 software package． Results With the convergence angles from 6°,8° to 12°, the cement thicknesses of inner and outer chamfer edge of SLM groups (the outer edge:（59.20±16.14）μm， （46.62± 8.26）μm， （62.66±14.11）μm respectively; inner edge:（59.74±21.44）μm， （47.69±13.53）μm， （73.38±23.03）μm) were smaller than those of the LW groups (outer edge: (63.52±13.97) μm， (61.06±16.12) μm， (65.57±13.85) μm; inner edge: (67.48±23.06) μm， (62.94±18.19) μm， (77.84±17.52) μm); and the difference was statistically significant（P＜0.05）; whatever the crown making method was, the mean cement thickness of inner and outer chamfer edge was as follows: 12°＞6°＞8°group, and the difference was statistically significant（P＜0.05）. Conclusions As the convergence angles are within 12°, the marginal fitness of two different CoCr inner crown making methods are clinically acceptable. The selective laser melting inner crowns result in smaller marginal gaps than Lostwax inner crowns, which shows that the marginal fitness of the selective laser melting inner crowns is better than that of the Lostwax inner crowns.

Key words: selective laser melting, CoCr alloy, marginal fitness, chamfer, cement thickness