Experimental Study Of Cobalt-chromium Metal Crown Compare The Marginal Adaptation Of Different Production Methods

Objective :Two different ways to make mental substrates, lost wax casting process and 3 shape CAD/CAM technology. Compare the fitness of its margin(i.e.the exact degree) to provide theoretical basis for the using of cobalt-chromium ceramic crown.Methods :Prepare an extracted teeth which was chosen from maxillary first premolars according to the preliminary standard of tooth. Then standardize the silicone rubber models, pour gypsum into 50 models, randomly divide them into group a and group b. Number the groups of CAD/CAM from a1 to a25, number the groups of casting from b1 to b25. The two groups manufacture in different ways, but both are based on the model of the original cast. Group a :scan the models with 3shape scanner and transmit the scanned data to computer and then design, then make base crown through mechanical cutting. Group b: make the mental base crown through traditional lost wax casting method. Copy the marginal crevices with silicone rubber on the premise that the base crown and the abutment completely stick together. Measure the size of the marginal crevice of base crown with a stereoscopic microscope, then do some statistical analysis for the experimental data with SPSS 17.0.Result :1. The average vertical clearance of group a : 34.67±7.48 μm, the average vertical clearance of group b : 53.70±9.64μm. The comparison of them showed statistical significance(P<0.05). 2. The average horizontal clearance of group a :37.61±7.63μm, the average horizontal clearance of group b: 53.02±10.65 μm. The comparison of them showed statistical significance(P<0.05)Conclusion :(1) The margin fitness of the base crowns made in two different production methods are all up to the standard of clinic. The tested gap value is within 120μm.(2) The margin fitness(i.e.the exact degree) of cobalt-chromium mental crown made by 3 Shape CAD/CAM system is better than the base crown made by casting process.