Mechanical behavior of yttria-stabilized tetragonal zirconia polycrystal: Effects of different aging regimens

Abstract

This study aimed to characterize and compare the effect of different aging regimens on surface characteristic (topography and roughness), structural stability (phase transformation) and mechanical performance (Weibull analysis) of a Y-TZP ceramic. Discs (15 × 1.2 mm; VITA In-Ceram YZ) were prepared according to ISO 6872-2015 for biaxial flexural strength testing and randomly assigned into five groups (n = 30): as-sintered, no aging treatment (CTRL); 20 h in autoclave at 134°C, 2 bar pressure (AUT); intermittent mechanical loading at 20 Hz/10 6 load pulses (MechLoad); AUT followed by MechLoad (AUT+MechLoad); and storage in distilled water at 37°C, for 1 year (STO). The following analyses were performed: roughness (n = 30), surface topography (n = 2), phase transformation (n = 2) and biaxial flexure strength (n = 30). Phase transformation (increase of m-phase content) was shown to be a spontaneous, unavoidable and time-dependent process, occurring even under ambient conditions (dry storage after 1 year = 6.0% increase), and is considerably accelerated in the presence of moisture (STO = 17.6%; AUT= 63.1%; and AUT+MechLoad = 59.9%). For roughness parameters, only Ra was affected by aging, and the highest values were observed for AUT+MechLoad (0.25 ± 0.07 µm). For Weibull analysis, structural reliability (Weibull moduli) and characteristic strength were not impaired after aging, and some aging conditions led to increased values (highest weibull moduli in AUT, and highest characteristic strength in STO). Phase transformation proves to be a time-dependent spontaneous mechanism that is accelerated in the presence of different stimuli. However, none of the aging regimens had a negative effect on the characteristic strength and structural reliability of Y-TZP ceramic.

A Review on CAD/CAM Yttria-Stabilized Tetragonal Zirconia Polycrystal (Y-TZP) and Polymethyl Methacrylate (PMMA) and Their Biological Behavior

“…This material's high flexibility and other physical alterations in the face of aging procedures have also been tested. This affirmation proves this material's high resistance in an oral environment [41].…”

“…We analyzed yttria-stabilized tetragonal zirconia polycrystal and polymethyl methacrylate from a clinical perspective in two of the selected articles on which we based this research [ 38 , 39 , 40 , 41 , 42 ]. Bagegni A et al presented a complete meta-analysis, examining various implant-fixed restorations (interim or definitive) and their effect on implant survival.…”

Impact of different pretreatments and aging procedures on the flexural strength and phase structure of zirconia ceramics

“…Prior hydrothermal aging led to the highest monoclinic value of 75.27%, which is consistent with the present study. The slightly higher value could be due to the longer aging period in the autoclave of 20 h. A 1-year water storage at 37 °C used by Guilardi et al [47] The type of zirconia used in this study differed in the percentage of aluminum oxide and zirconia with higher aluminum oxide concentrations have been reported to resist the occurrence of monoclinic phase after aging [31]. However, the results of the present study showed comparable values for both zirconia generations, leading to acceptance of the null hypothesis and not supporting the previous study.…”

Evaluation of Marginal/Internal Fit and Fracture Load of Monolithic Zirconia and Zirconia Lithium Silicate (ZLS) CAD/CAM Crown Systems

“…A customized specimen holder device was used to ensure all specimens were placed in the same position for testing. Cemented crown specimens along with their bases were held in position in the loading device and subjected to 500,000 load cycles of 200 ± 50 N at 10 Hz [ 37 , 46 , 48 , 50 , 51 , 52 , 53 ]. The number of cycles used simulated a 2 year functional loading period in the mouth at an estimated rate of 240,000 cycles/year [ 54 , 55 ].…”