The Effect Of Polishing Methods On Cobalt-chromium Castings Accuracy And Physical Properties

Objective To evaluate the effect of different polishing methods on accuracy and physical properties of cobalt-chromium castings.Method 5 polishing methods were compared: centrifugal barrel polishing, electrical brightening, grinding, grinding + centrifugal barrel polishing and grinding + electrical brightening. 25 upper complete denture bases were cast and divided into 5 groups. The dimensional accuracy between the posterior border of upper complete denture and standardized cast at five different positions were determined by traveling microscope measuring method respectively before and after polishing. 30 specimens sized 30mm×10mm×1.5mm , divided into 6 groups were cast for hardness, surface roughness, flexural strength ,fracture strength and flexural modulus test.Result No difference of the posterior border gaps between the cast base and standardized cast was found(P>0.05) which respectively be 128.08μm,130.32μm before and after polishing. Specimens polished by grinding + centrifugal barrel got the smoothest surface(P<0.01)and highest hardness(P<0.05).There was no difference about flexurai strength ,fracture strength and flexural modulus among 6 groups(P>0.05).Conclusion There is no effect of polishing methods on dimensional accuracy of cast upper base. Base polished by grinding + centrifugal barrel could get the smoothest surface. Castings surface hardness increases after grinding + centrifugal polishing. The flexural strength ,fracture strength and flexural modulus of castings wouldn't change after being polished.