RÉSUMÉ
BACKGROUND:At present, the confrontation of CAD/CAM systems and the lost wax casting method for marginal adaptation has been widely concerned, but the results are controversial. OBJECTIVE:To compare the marginal adaptation of single cobalt-chromium PFM crowns produced by 3 Shape CAD/CAM systems and the lost wax casting method. METHODS: A maxilary first premolar was prepared according to the standards. 50 resin-generation models were created by bi-color silicone rubber method and randomly divided into two groups: CAD/CAM group (A1-A25) and cast group (B1-B25). Al the models were cast in plaster. In CAD/CAM group, the digital impressions were obtained by optical scanning, then designed through computer and cut directly by NC miling machine. In cast group, metal ceramic crowns were made by the lost wax casting method. When crowns were al seated on the working dies, the marginal gaps were copied with light silicone rubber and then embedded with occlusal silicone rubber. The thickness of crown marginal gap was measured with a stereo microscope. RESULTS AND CONCLUSION:The average vertical clearance was (34.67±7.48)μm of CAD/CAM group, while (53.70±9.64)μm of the cast group; the difference was statisticaly significant between two groups (P < 0.05). The average level clearance was (37.61±7.63)μm of CAD/CAM group, while (53.02±10.65)μm of the cast group, and the difference was statisticaly significant between two groups (P < 0.05). Experimental findings suggest that, the marginal adaptation of single cobalt-chromium PFM crowns cast produced by 3 Shape CAD/CAM systems is clinical acceptable (< 120μm), and CAD/CAM systems of metal casting is obviously better than the lost wax casting in building metal based crowns with adaptable margin.