Influence Of Different Manufacturing Techniques And Porcelain Firing Cycles On Fit Of Co-Cr PFM Crowns

Objectives:To evaluate the changes of the marginal and internal fit of the cobalt-chromium PFM crowns fabricated with different manufacturing techniques and originated from scanning the prepared tooth,silicone rubber and stone die after porcelain firing cycles.Therefore the influencing factors of the longevity of the restorations can be estimated indirectly to support the choose in clinic.Methods:Five extracted maxillary premolar were selected.According to scanning the prepared tooth,silicone rubber and stone die,which were used by the CAD/CAM and SLM to manufacture Co-Cr alloys the specimens were divided into blank control group(traditional casting),tooth-SLM group,silicone rubber-SLM group,stone die-SLM group,tooth-CAD/CAM group,silicone rubber-CAD/CAM group and stone die-CAD/CAM group.Then all the specimens were fired with the porcelain.Marginal and internal fit were measured by Micro-CT.The results were analyzed by ANOVA and Student's t-test,?=0.05.Results:Compared with the fit before porcelain-fused-metal process,themarginal and internal fit increased after porcelain firing(P<0.05)and had a significant difference.Compared with the control group,SLM group had a smaller marginal fit(91.30±6.70?m,94.9±3.69?m,99.55±11.68?m)than the other groups(P<0.05).The internal fit of CAD/CAM group was smaller(P < 0.05).Compare with the tooth-SLM and stone die-SLM group,silicone rubber-SLM group had the least marginal and internal fit.Conclusion:The crowns fabricated with traditional lost-wax casting were more stable than the SLM and CAD/CAM technology in the porcelain firing process.The porcelain firing caused the increase of different sites of marginal and internal fit.The SLM had a better marginal fit and CAD/CAM had a better internal fit,which they would replace the traditional casting eventually.Silicone rubber had a excellent property.