The Effect of Two Sintering Cycles and Aging on Biaxial Flexural Strength of Strength Gradient Multi-Layered Zirconia (In vitro Study)

Abstract

Objective: Impacts of thermocycling aging and variation in sintering parameters using conventional and speed sintering cycles on biaxial flexural strength (BFS) of IPS e.max ZirCAD Prime and Katana Ultra-Translucent zirconia to be used as a veneer material and comparing them to IPS e.max CAD as a control group. Materials and Methods: Strength gradient multilayered zirconia (IPS e.max ZirCAD Prime) and color gradient multilayered zirconia (Katana UTML) were investigated to be compared to lithium disilicate (IPS e.max CAD). Zirconia Specimens were sintered following speed and conventional sintering protocols. 0.5 mm circular shaped sample of IPS e.max CAD was obtained using a precision sawing machine. Dimensions of the zirconia specimens after sintering were 0.5 mm. it was designed and milled with 20%-25% oversize in order to compensate for the shrinkage that occurs after sintering. Thermocycling was applied for 5000 cycles to simulate 6 months in the oral environment, A universal testing machine was used to measure biaxial flexural strength.Results: In normal cycle, BFS had the highest value in IPS e.max ZirCAD Prime, followed by IPS e.max CAD, while the lowest value was found in Katana UTML Zirconia. In speed cycle, IPS e.max ZirCAD Prime had the highest value, followed by Katana UTML Zirconia, while IPS e.max CAD was the lowest. In both zirconia groups, speed cycle had a higher value than normal cycle, however, the difference wasn’t significant. Conclusion: Biaxial flexural strength wasn’t affected by both sintering cycles after thermocycling aging for both Zirconia groups.