Experimental Study The Effect Different Optical Impression Methods And Ceramic Materials On Marginal And Internal Fit Of All-ceramic Crowns

Objective Study the effect different optical impression methods and different ceramic materials on marginal and internal fits of all-ceramic crowns in Cerec 3D/inlab MC XL system, and provide an experimental basis for their clinical application.Methods A right mandibular first molar in the standard model was prepared and replicated into sixty-four plaster casts, eight of them were selected randomly for direct acquisition optical impression, and then obtain eight Cerec Blocs all-ceramic crowns; twenty-four of them were selected randomly for indirect acquisition optical impression, and then fabricate eight Cerec Blocs, Incoris AL,and In-ceram YZ crowns respectively. Residual thirty-two plaster casts were used for bonding crowns, and then evaluation of fits of Cerec Blocs all-ceramic crowns in direct and indirect methods with modified United States Public Health Service( USPHS) criteria and Scanning electron microscope(SEM) imaging, and the fit of different Ceramic material crowns in indirect methods were evaluated by SEM. Finally, the data were statistically analyzed with SAS9.1 software. Results Clinically acceptable rate is 87.5% among marginal measurement sites according to USPHS criteria and there was no statistically significant difference in marginal fits Comparison between the groups. With SEM imaging, the marginal fits were less than 120μm in all the groups ,and there was statistically significant (P<0.01) between Incoris Al group(65.1±28.2μm) and In-ceram YZ groups(43.4±13.6μm),Cerec Blocs groups (43.2±15.0μm, 38.3±19.3μm)in direct and indirect method ,and no significant difference was found between this latter three groups. Moreover, no significant difference was found in average of internal fits between Cerec Blocs groups (119.1±60.6μm, 112.4±45.0μm), But there was statistically significant difference(P<0.01) between mesial surface (85.9±32.0μm) and distal surface (171.3±61.9μm) in direct method; Cerec Blocs group was superior to Incoris AL group (139.8±44.9μm)and In-ceram YZ group(141.9±40.9μm)in indirect method,But there was no statistically significant(P> 0.05)between Incoris AL group and In-ceram YZ group . The fits of occlucal surface(range 187.2 to 289.8μm)was relatively poor in the four groups.Conclusion Under the conditions of this study, (1) The Optical impression methods had no significant effect on marginal and internal fits of Cerec Blocs crowns,while distal shadow Phenomenon exists in direct method acquisition optical impression. (2) Ceramic materials had certain effect on marginal and internal fits of crowns. (3) each group ' marginal fits were clinically acceptable,while the fits of occlucal surface need to further improve.