Corrosion Resistance And Clasp Retention Of Removable Partial Denture Frameworks Made Of Cobalt Chrome Alloy Using SLM Technique

Objective:This study explored the corrosion resistance and clasp retention of removable partial denture frameworks made of cobalt chrome alloy using selective laser melting（SLM）technique,compared with traditional lost wax casting method.Methods:The cobalt chromium metal framework specimens were fabricated by SLM technology and traditional lost wax casting method,using the same computer aided design（CAD）data.SEM,EDS and XPS was used to analysis the microscopic characteristics and chemical composition of two alloys.The corrosion resistance of two alloys was studied using electrochemical impedance spectroscopy tests and potentiodynamic polarization tests in an artificial saliva solution with different concentrations of lipopolysaccharides（LPS）.The fitness accuracy and retentive force was measured before and after the 5 years’simulation of insertion/removal cycles for clasps.Results:A regular cellular structure was showed in SLM alloys,but the cast alloys exhibited a matrix phase and a heavy second phase in a typical dendritic arrangement.The XPS results showed that the chemical compositions on the surface of the two alloys were similar.There was no significant difference in corrosion parameters between the two alloys in the artificial saliva alone（P>0.05）.At 150μg/m L LPS concentration,the R_p value of both alloys decreased significantly and the I_corr value increased significantly,but the R_p value of SLM alloy was larger than that of casting alloy and the I_corr value was smaller（P<0.05）.SLM and cast clasps had no statistical difference in the fitness accuracy and retentive force before the fatigue cycles.After7200 fatigue cycles,the fitness and retentive force of the two kinds of clasps decreased significantly（P<0.05）,but the decline of SLM clasp was less than the cast clasp（P<0.05）.Conclusion:The microstructure of SLM cobalt chromium metal framework was more homogeneous than the cast specimens,while the chemical composition on the surface of two alloys was similar.LPS can reduce the corrosion resistance of both cobalt-chromium alloy,but the effect of LPS on corrosion resistance of SLM cobalt chromium alloy was smaller than that of cast alloy.The fitness and retentive force of SLM clasp and cast clasp were similar,but the retentive force of SLM clasp was higher than cast clasp,and it can meet the clinical requirements after the 5 years’simulation of insertion/removal cycles for clasps.