THERMALLY INDUCED CHANGES IN DENTAL PORCELAIN EXPANSION

拟议研究的总体目标是确定机制 负责热诱导的热传导系数的变化 牙科陶瓷所经历的扩张，并使用 从而获得了开发更耐这种陶瓷的理解 变化 这种热稳定陶瓷的发展将 大大减少牙齿开裂和龟裂的倾向， 在陶瓷熔结金属陶瓷冷却过程中， 从而减少了成本、不便和再治疗创伤， 接受这种修复的牙科患者。 第一 具体目标是完成多个影响的测量 烧结，等温热处理，以及不同的冷却速率， 各种牙科陶瓷的热膨胀系数。 这些测量将在传统的差分中完成 牙科材料部开发的激光硬度计 格鲁吉亚医学院实验室。 第二个具体目标 是为了确定陶瓷膨胀的机制 在各种热处理过程中发生变化。 将使用的方法 区分可能的机制是：定量X射线 衍射法，高温x射线衍射法，热台 扫描电子显微镜和跨中挠度测量 陶瓷-金属双材料带材的高速红外弯曲 在牙科材料实验室开发的光束粘度计， 格鲁吉亚医学院。 在目前的赠款期间， 定量X射线衍射法被证明是一种合适的工具， 晶体热膨胀系数的测量 在玻璃瓷基质中原位的牙科瓷的成分。 这项技术将大大有助于确定的机制 与牙科陶瓷的热不稳定性有关。 可能 牙科陶瓷的热不稳定性的机制包括 白榴石的结晶或溶解，白榴石转化为 透长石，白榴石颗粒在玻璃基质中的保留， 微裂纹和烧结，以及捕获各种程度的过量 由于不同的冷却速率，玻璃基质中的体积。 的 提高陶瓷热稳定性方法的研究进展 frits是拟议工作的第三个具体目标。 的战略 用于开发改进的陶瓷熔块的方法包括减少或消除 白榴石耦合/去耦，稳定白榴石部分， 避免了在冷却时的亚稳立方白榴石滞留， 陶瓷烧成温度，并尽量减少影响，由于 玻璃基质的结构松弛。

The overall goal of the proposed research is to determine the mechanisms responsible for the thermally induced changes in coefficient of thermal expansion that are experienced by dental porcelains and to use the understanding thus gained to develop porcelains more resistant to such changes. The development of such thermally stable porcelains would greatly reduce the tendency for cracking and checking of the dental porcelains during cooling of porcelain-fused-to-metal restorations, with consequent reductions in cost, inconvenience, and re-treatment trauma to the dental patient receiving this type of restoration. The first specific aim is to complete the measurement of the effects of multiple firings, isothermal heat treatments, and different cooling rates on the coefficients of thermal expansion for a variety of dental porcelains. These measurements will be accomplished in a conventional differential dilatometer and in a laser dilatometer developed in the Dental Materials Laboratory at the Medical College of Georgia. The second specific aim is to determine the mechanisms responsible for porcelain expansion changes during various heat treatments. The methods which will be used to discriminate among the possible mechanisms are: quantitative x-ray diffractometry, high-temperature x-ray diffractometry, hot-stage scannign electron microscopy, and measurement of the mid-span deflection of bimaterial porcelain-metal strips in a high rate infrared bending beam viscometer developed at the Dental Materials Laboratory at the Medical College of Georgia. During the present grant period, quantitative x-ray diffractometry was shown to be a suitable tool for the measurement of the thermal expansion coefficients of the crystalline components of dental porcelains in situ in the glassy porcelain matrix. This technique will greatly aid in the determination of the mechanisms involved in the thermal instability of dental porcelains. Possible mechanisms for thermal instability of dental porcelains involve the crystallization or dissolution of leucite, the conversion of leucite to sanidine, the retention of leucite particles in the glass matrix via microcracking and sintering, and trapping of various levels of excess volume in the glass matrix owing to different cooling rates. The development of methods for improving the thermal stability of porcelain frits is the third specific aim of the proposed work. The strategies for developing improved porcelain frits involve reduction or elimination of leucite coupling/decoupling, stabilization of the leucite fraction, avoidance of metastable cubic leucite retention upon cooling from the porcelain firing temperature, and minimization of the effects due to structural relaxation of the glass matrix.