Fracture Load and Phase Transformation of Monolithic Zirconia Crowns Submitted to Different Aging Protocols

Abstract

Monolithic zirconia crowns have many favorable properties and may potentially be used to solve dental problems such as chipping. However, monolithic zirconia crown resistance can be affected by its phase transformation when subjected to low temperatures, humidity, and stress. This study evaluated the fracture load and phase transformation of monolithic zirconia crowns submitted to different thermal and mechanical aging tests. Seventy monolithic zirconia crowns were randomly divided into the following five groups: control, no treatment; hydrothermal aging at 122°C, two bar for one hour; thermal fatigue, 10 cycles between 5°C and 55°C, dwell time, 30 seconds; and mechanical fatigue, 10 cycles with a load of 70 N, sliding of 1.5 mm at 1.4 Hz; and combination of mechanical plus thermal fatigue. Fracture load was measured with a universal testing machine. Surface changes and fracture mode and origin were examined with a scanning electron microscope. Monoclinic phase content was evaluated by x-ray diffraction. The fracture load was analyzed using one-way analysis of variance at a level of 5%, and Weibull distribution was performed. No statistically significant differences were observed in the mean fracture load and characteristic fracture load among the groups (p>0.05). The Weibull modulus ranged from 6.2 to 16.6. The failure mode was similar for all groups with the crack origin located at the contact point of the indenter. Phase transformation was shown at different surfaces of the crown in all groups (1.9% to 8.9%). In conclusion, monolithic zirconia crowns possess high fracture load, structural reliability, and low phase transformation.

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

“…18 This study showed Weibull modulus ranging from 10 to 21.43 (Table; Figure 3), which is consistent with the values reported for ceramic crowns. 14,25 We noticed a tendency for Weibull modulus increase after aging, since the groups with higher m-phase content tended to present higher Weibull modulus, which probably can be explained by the toughening mechanism that closes the crack tip, avoiding crack growth. In addition, a small difference in strength between specimens with large flaws and small flaws was observed, probably because of the rising of the toughness curve, which leads to higher toughness for larger flaws and lower toughness for smaller flaws.…”

“…5,6,12,14,23,24 Pereira and collaborators 8 stated that the critical point of m-phase content for a deleterious effect on mechanical performance should be above 50%. Our data show that the AUT+MechLoad group, even with 60% m-phase content, had a statistically higher characteristic strength than the as-sintered condition.…”

Translucency of Zirconia Ceramics before and after Artificial Aging

“…The crystal structure in Y‐TZP may change from tetragonal to monoclinic due to aging or mechanical stress . The amount of monoclinic phase in Y‐TZP increases with aging . With two phases present in Y‐TZP, light scattering might increase .…”

“…23,24,35,36 The amount of monoclinic phase in Y-TZP increases with aging. 24,35,37,38 With two phases present in Y-TZP, light scattering might increase. 18 The monoclinic and tetragonal crystals have different optical properties, which can influence the opacity.…”

The study of aging, fatigue and degradation for the purpose of improving the reliability of dental Zirconia ceramics. A review of articles in world`s journals

“…Фазовый переход наблюдался на всех поверхностях коронки и во всех группах образцов, прошедших термическую, механическую или термомеханическую обработку (от 1,9 до 8,9%). Монолитные коронки обладали очень высокой прочностью разрушения, структурной надежностью и хорошей стабильностью (после любого из циклов испытаний количество моноклинной фазы было незначительным) [6].…”