Denry I L, Holloway J A, Rosenstiel S F
The Ohio State University, College of Dentistry, Section of Restorative, Prosthodontics, and Endodontics, Columbus 43210-1241, USA.
J Dent Res. 1998 Apr;77(4):583-8. doi: 10.1177/00220345980770041101.
Leucite (KAlSi2O6) is used as a reinforcing agent in some porcelains for all-ceramic restorations; however, it increases their coefficients of thermal expansion, imposing constraints on the processing of the material. The potassium ions in leucite are exchangeable for rubidium or cesium ions, leading to rubidium leucite or cesium leucite (pollucite). Both rubidium leucite and pollucite exhibit a lower coefficient of thermal expansion and inversion temperature than leucite. The purpose of this study was to evaluate the effects of rubidium and cesium leucites on thermal expansion, microstructure, crack deflection patterns, and flexural strength of a leucite-reinforced porcelain. A dental porcelain powder was mixed with rubidium or cesium nitrate and heat-treated. Porcelain bars (n = 3) and discs (n = 15) were made with the exchanged powders. X-ray diffraction analyses were performed before and after bars were fired. Controls were made of untreated Optec HSP porcelain powder, formed into bars and disks, and baked following manufacturer's recommendations. The density of all specimens was determined by Archimedes' method. The thermal expansion behavior of the materials was measured by dilatometry. The microstructure and Vickers indentation crack patterns were investigated by scanning electron microscopy. X-ray diffraction showed that after ion-exchange and firing, leucite transformed into either tetragonal rubidium leucite or cubic cesium leucite. The mean coefficient of thermal contraction (550 to 50 degrees C) was significantly (p < 0.003) greater for the control material, followed by the rubidium-exchanged material, and lowest for the cesium-exchanged material. Crack pattern analyses revealed that the cesium-exchanged material exhibited a significantly lower number of crack deflections compared with those in the two other materials (p < 0.001). The microstructure of the two exchanged porcelain materials was dense, with well-dispersed small crystals as well as larger rubidium or cesium leucite crystals. The mean flexural strength of the rubidium-exchanged material was significantly higher than those of the other materials, which were not significantly different. It was concluded that the thermal expansion of leucite-reinforced porcelain can be lowered by ion-exchange, which also modifies the microstructure, crack deflection patterns, and flexural strength of the material.
白榴石（KAlSi2O6）在一些用于全瓷修复体的瓷中用作增强剂；然而，它会增加其热膨胀系数，对材料的加工造成限制。白榴石中的钾离子可与铷或铯离子交换，从而形成铷白榴石或铯白榴石（铯榴石）。铷白榴石和铯榴石的热膨胀系数和转变温度均低于白榴石。本研究的目的是评估铷白榴石和铯白榴石对白榴石增强瓷的热膨胀、微观结构、裂纹偏转模式和抗弯强度的影响。将牙科瓷粉与硝酸铷或硝酸铯混合并进行热处理。用交换后的粉末制作瓷条（n = 3）和瓷盘（n = 15）。在瓷条烧制前后进行X射线衍射分析。对照组由未处理的Optec HSP瓷粉制成，制成条和盘，并按照制造商的建议进行烘烤。所有标本的密度通过阿基米德法测定。材料的热膨胀行为通过膨胀仪测量。通过扫描电子显微镜研究微观结构和维氏压痕裂纹模式。X射线衍射表明，经过离子交换和烧制后，白榴石转变为四方晶系的铷白榴石或立方晶系的铯白榴石。对照材料的平均热收缩系数（550至50摄氏度）显著（p < 0.003）更大，其次是铷交换材料，铯交换材料最低。裂纹模式分析表明，与其他两种材料相比，铯交换材料的裂纹偏转数量显著更少（p < 0.001）。两种交换后的瓷材料的微观结构致密，有分散良好的小晶体以及较大的铷或铯白榴石晶体。铷交换材料的平均抗弯强度显著高于其他材料，其他材料之间无显著差异。得出的结论是，通过离子交换可以降低白榴石增强瓷的热膨胀，这也会改变材料的微观结构、裂纹偏转模式和抗弯强度。
