Experimental Study Of Accuracy And Fit Of Monolithic Self-glazed Zirconia Crowns

Objective:The aim of this in vitro study was to compare the accuracy and fit of monolithic self-glazed zirconia implant crowns with two monolithic milled zirconia implant crowns.And to compare the fit and uniformity of CAD/CAM monolithic self-glazed zirconia crowns with milled zirconia and lithium disilicate monolithic crowns by a new method.Finally provide a theoretical basis for the selection of all-ceramic crowns.Methods:Part I:A wide-necked prosthetic body at the level of soft tissue was partially embedded in plaster,the model was digitally scanned and designed,10 self-glazed zirconia implant crowns(SGZ),10 milled zirconia implant crowns(WMZ)and 10 milled zirconia implant crowns(UMZ).An intraoral scanner was used to scan the final restorations.The actual data was compared with design data to analyze the accuracy.The marginal fit was measured by the direct method and replica technology,the internal fit was measured by replica technology.Part II:10 identical PMMA abutment dies were fabricated by scanning and milling with one prepared human mandibular first molar as the master model.Then 10 self-glazed zirconia crowns(SGZ),10 milled zirconia crowns(MZ),and 10 milled lithium disilicate crowns(MLD)were fabricated through a digital workflow.Dual-scan protocol was used to assess the fit of crowns.The obtained data were input into SPSS 23.0 software,and the experimental results were analyzed by one-way ANOVA and Kruskal-Wallis test,and the significance level was p<0.05.Results:Part I:There was no significant difference between WMZ and UMZ in the accuracy of implant crowns(p>0.05),SGZ(internal:31.13±3.2μm,external:30.41±4.22μm,total:30.59±3.52pm)had a statistically significant difference in the accuracy of crowns compared with WMZ(internal:52.83±6.57μm,external:52.63±6.49μm,total:52.71±6.49μm)and UMZ(intermal:52.06±5.70μm,external:.50.52±4.57μm,total:51.22±5.14μm).The result of direct method(43.28±10.24μm)and replica technology(45.48±8.63μm)both showed that the marginal fit of SGZ was the best(p<0.05),while the other two groups had no significant difference(p<0.05).The internal fit of SGZ was better than the others(p<0.05).In the occlusal region,the fit of UMZ(197.04±20.47μm)was better than WMZ(209.55±21.57μm)(p<0.05).Part Ⅱ:In the restorations of teeth,mean gap values for the marginal and internal gaps of the 3 groups ranged from 78.07-84.21 μm,and 96.32-120.62 μm.There was no significant difference among the 3 groups regarding the marginal fit(p>0.05).However,the milled zirconia crowns exhibited a significantly greater internal gap than the self-glazed zirconia and milled lithium disilicate crowns(p<0.05).Furthermore,the internal gaps at the axial wall,transition,and occlusal regions of the milled zirconia crowns were significantly greater than those of the self-glazed zirconia crowns(p<0.05 for all)and the milled lithium disilicate crowns(p<0.05).There was no significant difference of uniformity values for marginal and internal gaps among the 3 groups(p>0.05)Conclusion:The accuracy and fit of self-glazed zirconia implant crowns were better than milled zirconia implant crowns,and the fit of implant monolithic crowns met the clinical requirements.For monolithic crowns on natural tooth,self-glazed zirconia had better internal fit than milled zirconia and milled lithium disilicate crowns,and the fit of natural tooth monolithic crowns met the clinical requirements.