In vitro evaluation of the effect of zirconia type on marginal and internal fit, porcelain bond strength and opposing tooth wear in 3-unit fixed partial denture

Abstract

Background and purpose: This study compares monochrome and multilayer zirconia in three areas. The first part of the study determines and compares the marginal and internal fit of multilayer and monochrome zirconia in a three-unit bridge. Material and method: The bridge preparation is the dental mold, then the prepared teeth are scanned 15 times. Each scan is used to make two bridges (one with multilayer zirconia and the other with monochrome). The bridge will be designed with the help of EXOCAD software and milling will be done according to the issued STL file. The bridges made in the previous step are evaluated and compared for internal and marginal fit using the replica method. The second part of the study is related to determining and comparing the bond strength to porcelain in multilayer and monochrome zirconia. 30 blocks of zirconia, 15 of which are multi-layer zirconia and 15 of which are monochrome zirconia with dimensions of 10 * 5 * 5 mm, and then we sinter them and the porcelain is veneered. All samples will enter the thermocycle process. The shear bond strength is evaluated using a universal testing machine. The third part of the study deals with the determination and comparison of antagonist tooth wear by multilayer and monochrome zirconia. We will have two groups of zirconia blocks, one group consisting of 15 multilayer blocks and the other 15 monochrome blocks. For the antagonist tooth, we use 30 healthy premolars. A chewing simulator is used to measure wear. The criterion for assessing the amount of buccal cusp wear is the premolars. Independent t-test will be used for statistical analysis, and Mann-Whitney test will be used if the data distribution is not normal Result: In evaluating the marginal and internal fit, the difference between the average marginal and cervical gaps in monochrome and multilayer zirconia was not statistically significant(P>0.05), and the average gap in monochrome zirconia was less than multilayer zirconia. The difference between the average axial and occlusal gap in monochrome and multilayer zirconia was statistically significant(p<0.05), and the average gap in monochrome zirconia was lower than multilayer zirconia. The average wear of opposite teeth and shear bond strength to porcelain in monochrome zirconia was higher than multi-layer zirconia, but this difference is not statistically significant(p>0.05). Conclusion: Monochrome zirconia restorations show a similar marginal and internal fit compared to restorations made of multilayer zirconia. Although the occlusal and axial gap in multilayer zirconia is more than that of monochrome zirconia, it is within the allowed clinical range. Porcelain-zirconia shear bond strength and opposing tooth wear are similar in monochrome zirconia and multi-layer zirconia. Multilayer zirconia is generally clinically usable.