Ionizing Irradiation Effect on Mechanical and Optical Properties of Y-PSZ

Objectives: The aim of this study was to evaluate the effect of ionizing irradiation therapy (IIT) on mechanical and optical properties of monolithic yttria- polycrystalline stabilized zirconia (Y-PSZ).
Methods: High and low translucency Y-PSZ were used to prepare 60 bar-shaped specimens (14 mm × 4.0 mm × 1.5 mm) of each material and randomly allocated into four groups (n=30): High-translucency/control (HT/C), high-translucency/irradiated (HT/I), low-translucency/control (LT/C), low-translucency/irradiated (LT/I). Irradiated specimens were submitted to single-dose irradiation of 70 Gray (Gy). Flexural strength (FS) (n=10) using 3-point bending test, fatigue limits (FLs) at 100,000 cycles using staircase approach (n=15), and translucency parameter (TP)(n=5) using a dental spectrometer were determined. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the materials. TP and FS data were analyzed by one-way Analysis of Variance (ANOVA) and Tukey HSD (p=0.64). FLs were analyzed using Dixon and Mood method, and Kaplan-Meier survival analysis.
Results: HT zirconia (HT/C=21.43, HT/I=19.09) presented higher TP values than the LT one (LT/C=13.01 LT/I=12.9) (p < 0.001). IIT affected FS (p<0.05) of LT samples: C - 712.45 MPa ±77.04; I - 588.40 MPa ±143.82; but not the FS (p=0.86) of HT ones: C – 339.8 MPa ±88.08; I – 306.44 MPa ±50.16. Material composition affected FLs (p < 0.001), but IIT did not (p = 0.64). XRD indicated phase transformation on surface of irradiated samples.
Conclusions: IIT may affect some properties of zirconia-based materials. Further studies are needed to estimate to which extent it is recommended to use Y-PSZ for the restoration of teeth that will be subject to IIT.