IADR Abstract Archives
Low-Temperature Degradation of Dental Zirconia
Objectives: Yttria-stabilized zirconia ceramic has emerged as a popular dental restorative material because of its excellent mechanical properties when in the predominately tetragonal phase. Compared to its use in other industries, zirconia is relatively recent to the field of dentistry, and the long-term performance under oral-conditions is not entirely clear. Dental zirconia with a meta-stable but strong tetragonal atomic arrangement can transform to a weaker monoclinic atomic arrangement at ambient temperature, which is known as low-temperature degradation. The objective of this study was to use Raman spectroscopy to evaluate the low-temperature degradation of various dental zirconia products subjected to accelerated ageing tests.
Methods: Dental zirconia for both posterior and anterior restorations was sourced from multiple milling blank and raw powder vendors. The materials were sintered at 1580oC in a SintraPlus furnace, and the specimens were aged in a Lancer autoclave at 134oC for a range of time periods. After aging, the specimens were examined using a Raman microscope (Horiba) equipped with a 532nm laser. The amount of tetragonal and monoclinic phases were calculated based on the Raman signals.
Results: The Raman measurements showed that the zirconia products stabilized with 3mol%-yttria were comprised primarily of the tetragonal phase with small amounts of monoclinic phase. After ageing at 134oC for 5 hours, a large amount of the tetragonal phase transformed into monoclinic phase for the 3mol%-yttria products, as shown by the significant increase of the peaks at 178cm-1 and 190cm-1 (FIG.1). Zirconia products stabilized with 5mol%-yttria also exhibited phase transformation to the monoclinic phase, but to a lesser degree compared to the 3mol%-yttria products.
Conclusions: Raman spectroscopy measurements showed that meta-stable tetragonal zirconia underwent transformation into the weaker monoclinic phase as a result of accelerated ageing conditions. It was also shown that the degradation kinetics are sensitive to the amount of yttria doping.
Methods: Dental zirconia for both posterior and anterior restorations was sourced from multiple milling blank and raw powder vendors. The materials were sintered at 1580oC in a SintraPlus furnace, and the specimens were aged in a Lancer autoclave at 134oC for a range of time periods. After aging, the specimens were examined using a Raman microscope (Horiba) equipped with a 532nm laser. The amount of tetragonal and monoclinic phases were calculated based on the Raman signals.
Results: The Raman measurements showed that the zirconia products stabilized with 3mol%-yttria were comprised primarily of the tetragonal phase with small amounts of monoclinic phase. After ageing at 134oC for 5 hours, a large amount of the tetragonal phase transformed into monoclinic phase for the 3mol%-yttria products, as shown by the significant increase of the peaks at 178cm-1 and 190cm-1 (FIG.1). Zirconia products stabilized with 5mol%-yttria also exhibited phase transformation to the monoclinic phase, but to a lesser degree compared to the 3mol%-yttria products.
Conclusions: Raman spectroscopy measurements showed that meta-stable tetragonal zirconia underwent transformation into the weaker monoclinic phase as a result of accelerated ageing conditions. It was also shown that the degradation kinetics are sensitive to the amount of yttria doping.
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