In Vitro Experimental Study On Adaptation And Internal Uniformity Of Three CAD/CAM All-ceramic Crowns

Objective The aim of this in vitro study was to evaluate the adaptation and internal uniformity of three-dimensional gel deposited zirconia(named as self-glazed zirconia),milled zirconia and milled lithium disilicate crowns and finally provide theoretical basises for the selection of clinical restorations.Method Ten identical PMMA abutment dies were fabricated by scanning and milling with one prepared human mandibular first molar as the master model.Then ten self-glazed zirconia crowns(SGZ),ten milled zirconia crowns(MZ),and ten milled lithium disilicate crowns(MLD)were fabricated through a digital workflow.Non-destructive direct measurement technique(DT),weight technique(WT)and replica technique(RT)were used to measure the marginal and(or)internal discrepancy values,individually.The uniformity index(UI)was calculated to describe the uniformity of internal space based on the internal discrepancy results measured by RT.The results were analyzed using One-way ANOVA and Kruskal-Wallis statistical tests.Level of significance was set at 0.05.Result The result of DT showed that the mean marginal discrepancy of MLD crowns exhibited the highest value among three groups of all-ceramic crowns with statistical significance(p<0.05),the mean marginal discrepancy of two groups of zirconia crowns were similar without statistical significance(p>0.05).The result of WT showed the mean overall discrepancy value of MZ crowns was the highest with statistical significance(p<0.05),while the mean overall discrepancy values of other two groups of all-ceramic crowns were comparable(p>0.05).In the results of RT,the mean marginal discrepancy of three groups of all-ceramic crowns were similar without statistical significance(p>0.05).The SGZ crowns had lower mean value than MLD crowns at the occlusal region and than MZ crowns at all measured locations with statistical significance(p<0.05).Compared to the MZ crowns,the MLD crowns had lower axial discrepancy value(p<0.05)and comparable occlusal and axio-occlusal transition discrepancy values(p>0.05).As to internal space,the three groups of all-ceramic crowns showed good uniformity without statistical significance(p>0.05).Conclusion Three kinds of all-ceramic crowns have adaptation within clinically requirements and comparable internal uniformity.Two kinds of zirconia crowns have better marginal adaptation than milled lithium disilicate crowns.Compared to the crowns fabricated by subtractive milling,zirconia crowns which were fabricated by additive 3D gel deposition can achieve better internal adaptation.