商用牙科氧化鋯浸泡醋酸之相變研究

Phase Transformation of Commercial Dental Zirconia in Acetic Acid

廖慧娟(Huei-Jyuan Liao)

指導教授 ： 許學全 ； 吳世經

中臺科技大學/健康科學院/醫學工程暨材料研究所/碩士(2012年)

摘要

釔安定氧化鋯 (Y-TZP) 具有良好的美觀性、生物相容性、以及機械性質，因此被廣泛的應用於牙科領域。然而，氧化鋯在潮濕的環境中使用會有老化現象，也就是低溫衰變 (Low Temperature Degradation, LTD)。此現象會導致機械強度下降、相變化、及離子釋出等等。目前有關氧化鋯的低溫衰變試驗，多以水熱法 (Hydrothermal method) 測試，在134°C的高壓水蒸氣 (Autoclave steam) 中浸泡，測試氧化鋯的衰變情形。本研究擬以浸泡法(Immersion method) 取代水熱法 (Hydrothermal method)，探討牙科用氧化鋯經醋酸浸泡後之相變化，並分析浸泡法與水熱法在動力學上的差異。
本實驗使用三種商業用牙科陶瓷的預燒結瓷塊，分別為：Cercon®(DeguDent)、IPS e.max ZirCAD for inLab®(Ivoclar) 、In-Ceram®2000 YZ CUBES for inLab®(Vita)。瓷塊經 CAD/CAM 切割成寬厚長 5 x 3 x 20 mm 的長方體。依廠商建議的燒結溫度及專用的高溫爐進行緻密燒結。升溫速率、持溫時間、降溫速率均依原廠規範進行。
動力學探討則使用 Y-TZP 粉末，壓錠後，進行 1300°C 至 1550°C 溫度燒結二小時，使用浸泡法溫度 60°C 到 80°C, 4% 醋酸中，以及水熱法溫度 110°C 到 140°C，觀察兩種低溫衰變試驗情形，並由 X 光繞射分析儀 (XRD) 分析相變化。
實驗結果顯示：此三種市售氧化鋯經燒結後均為正方晶相，浸泡醋酸後，單斜晶相逐漸生成。經過 28 天浸泡，e.max® ZirCAD及Vita In-ceram® YZ 的單斜相分率較接近，分別為：22% 和 25%；Cercon® 則僅有 2%。三種商用氧化鋯在浸泡後，微硬度值均會降低，降低的幅度大致相同，並沒有因為相變量的不同而有明顯差異。在動力學方面，將 Y-TZP 以水熱法與浸泡法進行低溫衰變試驗，利用 XRD 分析顯示，燒結溫度愈高之試片，愈容易產生相變。各燒結溫度相變所需活化能，依照 MAJ 方程式計算，也顯示出相同的結果，燒結溫度越高，相變量的活化能就越低。氧化鋯的低溫衰變與晶粒大小有關，當燒結溫度降低，形成的晶粒較小，可以有效抑制相變發生，減少氧化鋯的低溫衰變。

關鍵字

醋酸 ； 釔安定氧化鋯 ； 低溫衰變 ； 動力學

並列摘要

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations are attractive to the dental community due to their superior aesthetics, biocompatibility, and excellent mechanical properties. However, dental applications tend to exhibit the aging of zirconia in wet circumstances, called low temperature degradation (LTD), which is associated with reduced mechanical strength, phase changes, and ion release. Up to now, most of the tests for LTD have used the hydrothermal method or the so-called autoclave method, which involves immersing zirconia in high-pressure steam at 134°C. In this study, the samples were immersed in acetic acid rather than in high-pressure steam. The phase transformations of three commercial Y-TZP blocks were checked after the immersion. In addition, the transformation kinetics was also examined.
Three common commercial brands (Cercon®, Vita In-cream® YZ and e.max® ZirCAD) of Y-TZP dental ceramic blocks were reshaped and then immersed in 4% acetic acid at 80°C for 0, 7, 14, and 28 days. The effects of surface treatments such as blasting and polishing, which are often used in dental prostheses, were also examined.
The Y-TZP powders, which were prepared for the study of transformation kinetics, were pressed uniaxially in a stainless steel mold at a pressure of 100 MPa. The compacted green bodies were then sintered at six temperatures between 1300oC and 1550°C, at intervals of 50°C. The first batch of specimens was immersed in 4% acetic acid at various temperatures from 60°C to 80°C. The second batch of specimens was subjected to the hydrothermal method from 110°C to 140°C. The zirconia phase analysis was determined by X-ray diffraction (XRD).
The results showed that the monoclinic phase increases with immersion time for all three brands of dental zirconia. Cercon® blocks, however, showed the smallest amount of phase transformation, indicating the least degradation after immersion. Blasting and polishing both suppressed the phase transformation. After immersion, the mechanical strength showed a small decrease with time.
The XRD patterns showed that higher sintering temperatures were correlated with greater degrees of phase transformation. For the kinetic aspect, the activation energy was calculated according to MAJ equation; it showed the kinetic energy levels of the samples subjected to the hydrothermal method were 101, 94 and 86 kJ/mol for samples sintered at temperatures of 1450, 1500, and 1550°C, respectively. In addition, the energy levels of samples that had been immersed in 4% acetic acid were 60, 55, 48 and 36 kJ/mol for sintering temperatures of 1400, 1450, 1500, and 1550°C, respectively.
It is evident that different grain sizes caused different degrees of phase transformations. Low sintering temperatures produce small grain sizes and restrain the phase transformations of zirconia, and thus decrease the LTD rate.

並列關鍵字

Kinetics ； LTD ； Acetic Acid ； Y-TZP

參考文獻

[1] T. Kosmac, A. Kocjan, Ageing of dental zirconia ceramic, Journal of European Ceramic Society 32(11), 2012, pp. 2613-2622

[2] C. Piconi, G. Maccauro, Zirconia as a ceramic biomaterial, Biomaterials 20(1), 1999, pp. 1-25

[3] ISO 13356, Implant for surgery-ceramic materials based on yttria stabilized tetragonal zirconia (Y-TZP), International Standardization Organization, 2008

[6] Y. H. Sun, Y. F. Zhang, J. K. Guo, Microstructure and bending strength of 3Y-TZP ceramics by liquid-phase sintering with CAS addition, Ceramics International 29(2), 2003, pp. 229–232

[7] I. Berit Ardlin, Transformation-toughened zirconia for dental inlays, crowns and bridges: chemical stability and effect of low-temperature aging on flexural strength and surface structure, Dental Materials 18(8), 2002, pp. 590–595