Influence of sintering conditions on low-temperature degradation of dental zirconia.
The effect of sintering conditions and concomitant microstructure of dental zirconia (ZrO2) ceramics on their low-temperature degradation (LTD) behavior remains unclear.


OBJECTIVE
Therefore, their effect on LTD of dental ZrO2 ceramics was investigated.


METHODS
Three commercial pre-sintered yttria-stabilized dental zirconia materials were sintered at three temperatures (1450°C, 1550°C and 1650°C) applying three dwell times (1, 2 and 4h). Grain size measurements and LTD tests were performed on polished sample surfaces. LTD tests were performed at 134°C in an autoclave. The amount of monoclinic ZrO2 on the exposed surface was measured by X-ray diffraction (XRD).


RESULTS
Higher sintering temperatures and elongated dwell times increased the ZrO2 grain size. Simultaneously, a larger fraction of zirconia grains adopted a cubic crystal structure, resulting in a decreased yttria content in the remaining tetragonal grains. Both the larger grain sizes and the lower average stabilizer content made the tetragonal grains more susceptible to LTD. Overall, independent on the commercial dental zirconia grade tested, the specimens sintered at 1450°C for 1h combined good mechanical properties with the best resistance to LTD.


CONCLUSIONS
In general, increased sintering temperatures and times result in a higher sensitivity to low-temperature degradation of Y-TZP ceramics.
KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) & Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium.
Masanao
M
Inokoshi
Department of Metallurgy and Materials Engineering (MTM), KU Leuven (University of Leuven), Kasteelpark Arenberg 44, B-3001 Heverlee (Leuven), Belgium.
Fei
F
Zhang
KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) & Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium.
Jan
J
De Munck
Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8549, Japan.
Shunsuke
S
Minakuchi
KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) & Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium.
Ignace
I
Naert
Department of Metallurgy and Materials Engineering (MTM), KU Leuven (University of Leuven), Kasteelpark Arenberg 44, B-3001 Heverlee (Leuven), Belgium.
Jozef
J
Vleugels
KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) & Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium.
Bart
B
Van Meerbeek
Department of Metallurgy and Materials Engineering (MTM), KU Leuven (University of Leuven), Kasteelpark Arenberg 44, B-3001 Heverlee (Leuven), Belgium. Electronic address: kim.vanmeensel@mtm.kuleuven.be.
Kim
K
Vanmeensel
D003764:Dental Materials; D013696:Temperature; D014961:X-Ray Diffraction; D015040:Zirconium
D003764:Dental Materials; D015040:Zirconium; C028541:zirconium oxide
Aging; Low-temperature degradation; Sintering; Zirconia