A Study Of The Metal-ceramic Bonding Strength Of PFM Made By 3D Printing Technology

Objective: The purpose of this study was to investigate the effect of different technologies(3D printing technology,CAD-CAM cutting and traditional casting technology)on the metal-ceramic bonding strength,involving different metallic alloys(cobalt-chromium alloy and pure titanium).And to evaluate the PFM crown made by 3D printing technology can meet the clinical requirements.Methods :1.Specimen preparation:Using computer software to design a virtual mode of 3mm×25mm×0.6mm size.Through the data conversion,metal powder was separately made into cobalt-chromium alloy,titanium specimens 10 each by using 3D printing equipment;20 specimens(10 of them are cobalt-chromium alloy and the other is titanium)were made by cutting instrument with CAD-CAM system;The wax slices were cut into 25mm×3mm×0.6mm rectangular boxes.In accordance with the traditional casting technology to prepare cobalt-chromium alloy,pure titanium specimens 10 each.All the specimens were polished by sandpaper with vernier caliper for measurement.Finally,60 specimens with size of(25±1)mm×(3±0.1)mm×(0.5±0.05)mm were obtained.2.Specimen grouping:The specimens were divided into 6 groups according to different processing methods and metal materials.Group A1:Cobalt-chromium alloy,3D printing;Group B1:Cobalt-chromium alloy,CAD-CAM cutting;Group C1:Cobalt-chro-mium alloy,casting;Group A2: Pure titanium,3D printing;Group B2:Pure titanium,CAD-CAM cutting;Group C2:Pure titanium,casting;Group A1,B1,C1:Cobalt-chromium alloy;Group A2,B2,C2:pure titanium.3.SEM observation section structure:A sample was randomly selected from each group to observe its section structure by means of SEM.4.Measurement of surface roughness :All specimens were treated with alumina particles on the surface(A1,B1,C1 group with a diameter of 250 ?m Al2O3,A2,B2,C2 group with a diameter of 110 ?m Al2O3),and then measured the surface roughness.5.SEM and EDS observation of metal-ceramic combinational area: Porcelain was applied onto the specimens according to ISO 9693-1:2012(E).Morphological observation on the metal-ceramic combinational area by SEM.The ionic diffusion and the element distribution character were analysis by EDS.6.The three-point bending test:The metal-ceramic bonding strength of specimens was measured by a three point bending test.7.The observation of fracture surface:The metal specimens were observed by naked eye.The specimens of each group were randomly selected to observe the surface and the element exploration by SEM and EDS.Results:1.SEM of the section structure:3D printing group(A1,A2)showed uniform distribution of honeycomb like structure.In the cutting group(B1,B2),there were dense irregular pitting.In addition,the casting group(C1,C2)can not only see the obvious bubbles and micro gaps,but also show the distribution of metal particles inside the tip size.2.Ra:Group A1 and B1 showed no significant difference(P>0.05),Group C1 was significantly higher than that of Group A1 and Group B1(P<0.05);There wasno significant difference between Group A2 and Group B2(P>0.05),Group C2 and Group B2 was significantly higher than that of Group A2(P<0.05).3.SEM and EDS of the metal-ceramic surface:Group A1 and A2 of metal-ceramic surface were irregular wavy,which were closely connected.Group B1 and B2 of metal-ceramic combination,the boundary structures were uneven,and occasionally had wave shaped structure.Group B1 and B2 of metal-ceramic combination were loose with micro cracks,and the boundary had line structures.In the group of A1,B1,A2,B2,the interdiffusion of element was evident in both sides of the bonded interface.But in Group C1 and C2,the element diffusion phenomenon was not obvious.4.?b:The strength of each group was :Group A1 was 36.08 ? 2.90 N,Group B1 was 36.92 ? 2.97 N,Group C1 was28.15 ? 1.91 N.There was no significant difference between Group A1 and Group B1(P>0.05),C1 group was significantly less than A1,B1(P<0.05);Group A2 was 38.24 ? 2.19 N,Group B2 was 38.48 ? 2.22 N,Group C2 was30.16 ? 2.01 N.There was no significant difference between Group A2 and Group B2(P>0.05).Group C2 was significantly less than Group A2,B2(P<0.05).5.SEM and EDS of the fracture surface: Group A1,B1:There were a lot of porcelain in the fracture plane,and the distribution of the porcelain body was uniform,which was closely connected with the metal depression.The uneven structure could be observed on the C1 fracture surface,and there was no obvious residual porcelain body.On the fracture surface of A2,B2 group remained large pieces of porcelain,which was closely connected with metal.A large number of small bubbles with a diameter of 5-10 ?m were seen in theporcelain layer.The uneven distribution of pores could be seen on the fracture surface in Group C2,and no obvious residual porcelain on the metal surface.The elements on fracture surface of Group A1,B1,A2,B2 indicate that the fracture occurs mainly in the ceramic layer and the oxide layer on the metal surface.The fracture surface elements of C1 and C2 suggest that the fracture occurs mainly on the surface of the metal oxide layer.Conclusion:1.The metal-ceramic bonding strength of PFM crown made by 3D printing technology are higher than the minimum requirement of ISO 9693-1:2012(E)(>25MPa).It provided theoretical and experimental basis for clinical application.2.The metal-ceramic bonding strength of PFM crowns by using 3D printing and CAD-CAM cutting technology were significantly higher than the one made by traditional casting technology.