Flexural Strength Of Y-TZP All-Ceramic Crowns And Precious Metal Ceramic Restorations

Objective：The purpose of this in vtro study was to compare the flexuralstrength of Y-TZP all-ceramic crowns and two other different precious metalsporcelain crowns,so as to know more about the mechanical properties of these repairmaterials.It provides a referenced gist for clinic tooth preparation and chosen ofmaterials.Methods：Preparing fifteen cylinder irons with diameter of10mm and height of20mm.Use the precision lathe to make the master dies resembling a molar crownpreparation with bottom diameter of8.0mm,axial wall length of5.0mm,a total axialtaper of8.5degrees and cervical part of90degrees shoulder with1.0mm width.Allline angles obtuse.The fifteen dies were divided into three groups and each of them isfive,inner crowns are made with Au-Pd alloy,high-noble alloy and ZrO2and thicknessare made in0.5mm.All of them are fused with low temperature porcelain and ensurethat is1.5mm thick.All firing cycles were made according to the manufacturer. Thenorm crowns cemented to the dies with glass ionomer cement under a standardizedload of15kg for5min,and were stored at room temperature.All crowns wereindividually mounted in a universal testing machine. The load was applied with a5-mm diameter stainless-steel ball placed on the occlusal surface of the crowns and ata crosshead speed of0.5mm.min-1.Fracture was defined as occurrence of visiblecracks in combination with load drops and acoustic events or by chipping.The loadsat fracture were registered,and differences between the groups were calculated usingOne-way ANOVA.Results：1,The crowns of Au-Pd had the highest flexural strength with the meanvalue of (3932.0±270.04N),the ZrO2group had the lowest flexural strength with themean value of (2082.0±183.49N),and the crowns of the high-noble group had a meanvalue of (2280.0±200.25N).According to the One-way ANOVA,the mean flexuralstrength of Au-Pd group had a significant difference with the other twogroups(P<0.01), While there's no significant difference between the ZrO2group andhigh-noble group(P>0.05). 2,The group of Au-Pd and group high-noble showed the same fracturemodes．All the failures started from the point of load application on occlusal surfaceand extended to the axial surface.Three crowns in two groups presented a pattern IIfailure(less than half of crown lost),the other two crowns presented a pattern IIIfailure(about half of crown lost).In group ZrO2,two crowns presented a pattern IIfailure(less than half of crown lost),and other two crowns presented a pattern IVfailure(lmore than half of crown lost)and one in five crowns presented a pattern Vfailure(severe fracture oftooth and/or crown).Conclusion:Au-Pd ceramic restorations required significantly greater flexuralstrength than high-noble and ZrO2ceramic restorations.(P<0.01).While there's nosignificant difference between the ZrO2group and high-noble group(P>0.05).All ofthem satisfy the clinical requirements.