Low-temperature degradation and real time aging of multi-layer translucent zirconia
Embargo Date
2027-07-29
OA Version
Citation
Abstract
OBJECTIVES: This study aimed to evaluate the effects of low-temperature degradation (LTD) and real-time aging on the mechanical, microstructural, and optical properties of various multilayer translucent zirconia materials featuring chroma and/or yttria gradients. Given the increasing use of multilayer zirconia in dental restorations, understanding how these materials perform under hydrothermal conditions is critical for long-term clinical success.
METHODS: A total of 360 bar specimens were fabricated from six commercially available multilayer zirconia systems: Cercon xt ML (Dentsply Sirona), IPS e.max ZirCAD Prime (Ivoclar Vivadent), LayZir All Indication (Smart Dentistry Solutions), Origin Beyond+ Hybrid (Origin Zirconia), Katana HTML (Kuraray Noritake), and Vita YZ ST Multicolor (VITA Zahnfabrik). Specimens underwent either artificial aging via steam sterilization at 134°C under 0.2 MPa pressure for 1, 7, or 14 days (LTD), or real-time aging for 1 or 2 years in saline at 37°C. Flexural strength was measured using a 3-point fully articulated test fixture, while surface roughness, warpage, and grain size were analyzed using profilometry and field emission scanning electron microscopy (FE-SEM), respectively. LTD-transformed layer thickness was measured using SEM cross-sectional analysis. Yttria content was quantified using microwave plasma atomic emission spectroscopy (MP-AES). Optical properties were assessed using contrast ratio and color difference measurements per ISO 2471:2008 protocol.
RESULTS: Flexural strength significantly decreased with both LTD and real-time aging (p < 0.001), with the most pronounced reduction observed after 14-day LTD. Warpage increased significantly with aging (p < 0.001), with Cercon xt ML exhibiting the highest dimensional distortion. SEM confirmed LTD-affected subsurface transformation zones up to ~10–15 µm in dentin regions after 14-day LTD. The contrast ratio and translucency demonstrated statistically significant but clinically acceptable changes across materials and aging protocols (ΔCR and ΔE* values remained below perceptibility thresholds).
CONCLUSION: Aging-induced degradation of multilayer zirconia is both material and layer dependent. Mechanical properties such as flexural strength and dimensional stability decline with extended LTD duration, particularly in materials with high tetragonal phase content. ZirCAD and Katana demonstrated greater resistance to LTD, likely due to optimized microstructure and yttria distribution. While translucency changes were statistically significant, they did not surpass esthetic thresholds. These findings highlight the need for careful material selection in high-stress and long-term clinical applications and encourage further studies using dynamic in situ and intraoral simulation models.
Description
2025
License
Attribution-NonCommercial-ShareAlike 4.0 International