THERMALLY INDUCED CHANGES IN DENTAL PORCELAIN EXPANSION

描述：拟议研究的总体目标是 确定引起热诱导变化的机制 出现在牙科瓷器的热膨胀系数中 由于多次点火、缓慢冷却和后焊接 行动。瓷器热膨胀的这些变化是 在烤瓷金属修复体中有害并产生裂纹 (Pfm)在开火后不久或之后的某个时间。任一事件 导致额外的费用，并可能给患者带来额外的创伤。 有六个具体目标。第一个是解释热 白榴石和闪锌矿基瓷的膨胀行为 体积分数、微裂纹密度、白榴石颗粒表面 区域。二是确定局部冷却速度的影响 牙科烤瓷在不同温度下的热稳定性差异 多次烧成、冷却和等温退火热处理。三是 确定H2O作为玻璃改性剂在牙科瓷器中的作用 特别是在白榴石和闪锌矿的结晶中。第四次 是为各种瓷-金属系统制定烧成时间表，以 最大限度地减少热引起的微结构变化，导致 热膨胀变化。五是对瓷器进行改性处理 它们对热膨胀变化的抵抗力更强。第六个要发展 求解热膨胀问题的原型专家系统计算机程序 不匹配问题。实现这些目标所使用的技术包括 X射线定量衍射、扫描电子显微镜能谱分析 色散X射线光谱学、定量体视学和常规 和激光扩张术。

DESCRIPTION: The overall objective of the proposed research is to determine the mechanisms responsible for the thermally induced changes that occur in the coefficients of thermal expansion of dental porcelains as a result of multiple firings, slow cooling and post-soldering operations. These changes in porcelain thermal expansion are detrimental and produce cracks in porcelain fused to metal restorations (PFM) either shortly after firing or sometime later. Either event causes additional costs and possibly additional trauma to the patient. There are six Specific Aims. The first is to explain the thermal expansion behavior of porcelains on the basis of leucite and sanidine volume fractions, microcrack densities, an leucite particle surface areas. The second is to determine the effect of localized cooling rate differences on the thermal instability of dental porcelain during multiple firing, cooling, and isothermal anneals. The third is to determine the role of H2O as a glass modifier in dental porcelain and specifically in the crystallization of leucite and sanidine. The fourth is to develop firing schedules for various porcelain-metal systems to minimize the thermally induced microstructural changes that lead to thermal expansion changes.The fifth is to modify porcelains to render them more resistant to thermal expansion changes. The sixth to develop a prototype expert system computer program for solving thermal expansion mismatch problems. Techniques used in pursuit of these aims include quantitative X-Ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, quantitative stereology, and conventional and laser dilatometry.