Long-term stability of an injection-molded zirconiabone-level implant: A testing protocol consideringaging kinetics and dynamic fatigue

Objective Separately addressing the fatigue resistance (ISO 14801, evaluation of final product) and aging behavior (ISO 13356, standardized sample) of oral implants made from yttriastabilized zirconia proved to be insufficient in verifying their long-term stability, since (1) implant processing is known to significantly influence transformation kinetics and (2) aging, up from a certain level, is liable to decrease fatigue resistance. Therefore, the aim of thisinvestigation was to apply a new testing protocol considering environmental conditionsadequately inducing aging during dynamic fatigue. Methods. Zirconia implants were dynamically loaded (107cycles), hydrothermally aged(85 degrees 60 days) or subjected to both treatments simultaneously. Subsequent, monoclinicintensity ratios (X-m) were obtained by locally resolved X-ray microdiffraction (mu-XRD2). Transformation propagation was monitored at cross-sections by mu-Raman spectroscopy andscanning electron microscopy (SEM). Finally, implants were statically loaded to fracture. Linear regression models (fracture load) and mixed models (X-m) were used for statisticalanalyses. Results. All treatments resulted in increased fracture load (p <= 0.005), indicating the formation of transformation induced compressive stresses around surface defects duringall treatment modalities. However, only hydrothermal and combinational treatment werefound to increase X-m(p < 0.001). No change in Xmwas observed for solely dynamically loadedsamples (p >= 0.524). Depending on the variable observed, a monoclinic layer thickness of 1-2 mu m (SEM) or 6-8 mu m (Raman spectroscopy) was measured at surfaces exposed to waterduring treatments. Significance. Hydrothermal aging was successfully induced during dynamic fatigue. Therefore, the presented setup might serve as reference protocol for ensuring pre-clinically long-term reliability of zirconia oral implants. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.