Factors Affecting The Stability Of Zirconia Based All-ceramic Crowns Materials:META Analysis And Doping Experiments

Objective:Many clinical failures of ZrO₂ dental crowns can be found in long-term clinical observations such as the cracking?chipping?of veneering porcelain and the low temperature degradation of zirconia.Studies have shown that zirconia all-ceramic crown restoration in the high temperature sintering process of cooling will produce residual stress on the surface of the material and will affect the porcelain and zirconia porcelain enamel bond strength,resulting in porcelain cracking.The problem of low temperature degradation is that the intraoral water molecules can destroy the zirconium-oxygen bond of zirconia,which decreases the stability of the zirconia-based crown.Therefore,this study mainly focuses on the stability of zirconia all-ceramic crowns.In the first part,we studied the stability of veneering porcelain of the all-ceramic crown restoration.In detail,this study investigated the effect of sandblasting surface treatment on the bonding strength between veneer porcelain and crown by meta-analysis.In the second part,we studied the stability of the crown of the zirconia-based all-ceramic crown restoration.The effect of doping on the low temperature degradation was studied by doping yttrium and cerium into zirconia.Methods:In the first part of the study,we searched the related articles from the Medline database for literature review,and then evaluated the quality of the literature,and screened and excluded the literature.Finally,the data was extracted and analyzed through Review Manager soft-ware.In the second part,pure zirconia,yttrium-doped zirconia and yttrium-doped cerium oxide were prepared by a home-made preparation method called complexing-hydrothermal method.Specifically,the reactors were weighted and mixed together.Then different additives such as EDTA and glycerol were added into the solution.During the mixing process additives,we adjusted the pH value by dropping ammonia,followed by putting the mixed solution into hydrothermal reaction kettle for hydrothermal reaction.Finally,zirconia-based samples could be obtained through centrifugal washing.X-ray diffractometry was used to examine the effect of additives EDTA and glycerol,as well as doping yttrium and cerium,on the phase and crystal size of the samples derived.In addition,the effect of doping on the stabilities of samples was studied by aging experiments.Results:The first part of the analysis shows that there is no bias from the results of the literature published,but there is obvious heterogeneity.Furthermore we exclude the literature with obviously different with otuers and carried out META analysis again,the result still has large heterogeneity.The second part of the analysis showed that the addition of EDTA can decrease the grain size,but cannot improve the tetragonal phase purity;in contrast,the addition of glycerol can improve the tetragonal phase purit,but has little effect on the grain size.Conclusion:1.The sandblasting treatment cannot be considered to increase the bonding strength of the zirconia-based all-ceramic crown.2.The doping of yttrium and cerium stabilizes into the zirconia crystals can stabilize the tetragonal phase and improve the properties of to resist the low temperature degradation.