大気中で熟成させた3Y-TZPの圧痕強度に及ぼすプリエージング温度の影響

Influence of Preaging Temperature on the Indentation Strength of 3Y-TZP Aged in Ambient Atmosphere.

抄録

低温劣化（LTD）に強いAlOを0.25%含むイットリア安定化ジルコニア（3Y-TZP）を、大気中130-220℃で10時間熟成した。その後、老化した試験片をビッカース圧子を用いて9.8～490Nの荷重で圧痕した。LTDの程度とLTDを受けたジルコニア修復物の強度との関係を明らかにするために，予備時効温度が試験片の二軸強度に及ぼす影響を検討した．プリエージング温度を160℃より高くすると，試料の圧痕強度は上昇し，t-ZrO（t）からm-ZrO（m），c-ZrO（c）からr-ZrO（r）への相変態が広範囲で見られた．プリエージング温度が圧痕強度に及ぼす影響は、t→m変態により上昇した残留応力と、圧痕によるエージング試験片表面の引張残留応力の反転により合理的に説明された。その結果，老化した修復物が表面に圧縮残留応力を保持していれば，修復物の寿命は悪化しないことが示唆された．これは，周囲環境におけるt→m相変態の程度が52％未満であることに対応する．

Yttria-stabilized zirconia (3Y-TZP) containing 0.25% AlO, which is resistant to low temperature degradation (LTD), was aged for 10 h at 130-220 °C in air. The aged specimens were subsequently indented at loads ranging from 9.8 to 490 N using a Vickers indenter. The influence of preaging temperature on the biaxial strength of the specimens was investigated to elucidate the relationship between the extent of LTD and the strength of zirconia restorations that underwent LTD. The indented strength of the specimens increased as the preaging temperature was increased higher than 160 °C, which was accompanied by extensive t-ZrO (t) to m-ZrO (m) and c-ZrO (c) to r-ZrO (r) phase transformations. The influence of preaging temperature on the indented strength was rationalized by the residual stresses raised by the t→m transformation and the reversal of tensile residual stress on the aged specimen surface due to the indentation. The results suggested that the longevity of restorations would not be deteriorated if the aged restorations retain compressive residual stress on the surface, which corresponds to the extent of t→m phase transformation less than 52% in ambient environment.