Comparative Study On The Adaptation Of Different Spacer Thickness Settings Of Two Kinds Of Implant Supported Zirconia Copings

Objective: The purpose of the research was to evaluate the marginal and internal adaptation between customized abutment and implanted supported zirconia copings fabricated with Cercon and R+ K CAD/CAM system by setting different spacer thickness,so as to provide a better experimental evidence for the selection of the CAD /CAM system and the optimal spacer thickness when manufacturing the zirconium oxide crowns in clinic application.Materials and Methods:A Bego analog(3.75 mm diameter)was implanted on a standard tooth-missing model.Making customized zirconia abutment.Then to design zirconia copings.In the Cercon and R + K CAD / CAM systems,the spacer thickness settings was divided into five groups: 0?m(group 0),20?m(group 20),30?m(group30),45?m(Group),60?m(Group 60),the rest of the design was the same.R + K and Cercon zirconia ceramic blocks were installed in their respectively milling machines,cutting 5 zirconia copings in each group and finally obtaining 50 crowns.The copings were sintering at the temperature required for respective manufacturers,checking the defect-free copings and setting on the same abutment.Two clinicians evaluated copings return rate and marginal fit.Then,each copings was placed in the same abutment,andscanned by Micro-CT,measured the Occlusal Gaps(OG),the Axial Gaps(AG),the Absolute Marginal Discrepancy(AMD),the Marginal Gaps(MG)by Mimics software.The data obtained using SPSS 21.0 software for statistical analysis.Results:(1)Both CAD / CAM systems produce copings that are passively positioned on the same abutment,all with a 100% crown return rate.The adaptation of the copings was evaluated according to the Modified USPHS criteria in the United States.The fitness of the R + K group and the Cercon group reached grade A more than 85%.There was no significant difference in marginal adaptation between the two groups(P> 0.05).(2)The marginal and internal adaptations of each group of zirconia copings and the abutment was measured by Mimics17.0 software.The experimental data show that:(1)The marginal and internal gaps of Cercon system were both less than 150?m;the Marginal Gaps in 30?m group,the Occlusal Gaps and the Axial Gaps in the 60?m group were the lowest.In the Marginal Gaps,groups between the 30?m and 60?m were significantly different(P<0.05).(2)In the R + K system,the internal gaps of the 0?m and 20?m groups were more than 150?m,and the margin and internal fit of the other groups were within the clinically acceptable range.In the AMD,there was no significant difference between each group(P>0.05).Among the Marginal Gaps,there was a significant difference between the 60?m group and the 30?m and 45?m groups(P<0.05).In the Axial Gaps,there was a significant difference between the 30?m group and the 45?m(P =0.045<0.05)and 60?m groups(P<0.05).There was a significant difference in the Occlusal Gaps between 45?m group and 30?m and 60?m groups(P<0.05).(3)There was no significant difference in the Absolute Marginal Discrepancy between the copings of Cercon and R + K in the 30,45 and 60?m groups(P>0.05),but there was a significant difference between the Marginal Gaps,the Axial Gaps and the Occlusal Gaps(P<0.05),and the gaps of the Cercon copings was less than that of the R+ K copings.(4)The Absolute Marginal Discrepancy and the Marginal Gaps of the two system were statistically different(P<0.05).The Absolute Marginal Discrepancy was higher than those of the Marginal Gaps.The values between OG and AG were statistically different(P <0.05),and the values of OG were all higher than those in AG.Conclusion:(1)Under the experimental conditions,the values of all spacer thickness groups in the Cercon system are in a clinically acceptable range;In the Cercon CAD /CAM system,the marginal gaps of 30?m group were significantly superior than the60?m group.(2)The marginal and internal fit of the R + K CAD / CAM system with the spacer thickness of 30,45 and 60 ?m were within the clinically acceptable range.The marginal and internal gaps of the zirconia copings in the 30?m group was superior to that of the 45 and 60 ?m groups.(3)When the spacer thickness was set to 30,45 and60?m,the internal and the marginal gaps of the Cercon copings was obviously better than that of the R + K copings.(4)Cercon and R + K CAD / CAM system marginal and internal fit was not uniform,The fit of the occlusal gaps relative to the axial gaps was less suitable,the marginal gap relative to the absolute marginal discrepancy was better.