Real Time and Accelerated Aging of Different Types of Zirconia
Objectives: To evaluate the accelerated and real time aging effect on microstructure and mechanical properties of different types of translucent zirconia with various surface treatments.
Methods: In this study 830 discs were prepared from four Y-TZP based materials. TZ-3YSB-E, ZPex®, ZPex®Smile (Tosoh Corporation, Japan), and Cercon®xt extra-translucent zirconia (Dentsply-Sirona). Final dimensions of each specimen were 15 mm diameter and 1.5 mm thick. Accelerated aging of 5, 24, and 168 hours in steam at 134°C under a pressure of 0.3 MPa was applied to the specimens. Real time aging involved 1 year in normal saline solution at 37°C in an incubator. Sandblasting was performed using a PrepStar®system with Al2O3 50μm particle size at pressure of 60psi, rate 4.2 gram/minute. Grinding with a Buehler AutoMet250 was performed using a 240μm diamond disc with a 0.0034 kg/mm2 load and speed of 120 rpm for two minutes. XRD spectrum was done with a Bruker D8 advance diffractometer under standard parameters. Biaxial flexural strength was determined using a ball-on-three-balls configuration with Instron Model5566A at a crosshead speed of 1 mm/min. Scanning Electron Microscopy (SEM) was used to examine topography and grain size.
Results: Overall zirconia with smaller grain size had higher flexural strength (p-value<.0001, R2=0.72). Sandblasting and grinding treatment increases flexural strength of TZ-3YSB-E and ZPex® (p-value<.0001, R2=0.88). XRD analysis shows that TZ-3YSB-E at room temperature does not have any monoclinic phase before surface treatment and it increased after aging, sandblasting, and grinding. Cercon®xt has the highest amount of cubic phase and it increases with surface treatment (mean 44%, R2=0.59, p-value=0.0004).
Conclusions: Sandblasting and grinding has variable effects on strength depending upon zirconia type. Overall there were no statistical differences in flexural strength, grain size, phase transformation between 5, 24, and 168 hours accelerated and 1-year real time aging process.