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 减少牙科陶瓷开裂和裂纹的倾向 在陶瓷熔附金属陶瓷冷却过程中， 降低了成本、不便和牙科再治疗创伤， 接受这种修复的患者。 第一个具体目标是 测量多次烧制、等温热处理的效果， 不同的冷却速率对热膨胀系数的影响 各种牙科陶瓷。 这些测量将在 传统的差动式流量计和激光流量计 在格鲁吉亚医学院的牙科材料实验室。 的 第二个具体目标是确定负责 在各种热处理过程中，瓷膨胀发生变化。 的方法 将用于区分可能的机制是： 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测量中跨 陶瓷-金属双材料带在高速红外波段的偏转 在牙科材料实验室开发的弯曲梁粘度计， 格鲁吉亚医学院。 热不稳定性的可能机制 牙科瓷器涉及白榴石的结晶或溶解， 白榴石向透长石的转化，介稳立方晶系的保留 白榴石在高温冷却后， 通过微裂和烧结将白榴石颗粒分散在玻璃基质中， 以及在玻璃基质中捕获各种水平的过量体积， 不同的冷却速率。 制定改进方法， 陶瓷熔块的热稳定性是本发明的第三个具体目标， 提议的工作。 提高陶瓷熔块质量的对策 包括减少或消除白榴石偶合/去偶合， 稳定白榴石部分，避免亚稳立方 从瓷器烧制温度冷却后的白榴石保留，和 最小化对玻璃基质的结构弛豫的影响。

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 measure 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 scanning 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. Possible mechanisms for thermal instability of dental porcelains involve the crystallization or dissolution of leucite, the conversion of leucite to sanidine, the retention of metastable cubic leucite upon cooling from high temperatures, the decoupling and recoupling 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 to structural relaxation of the glass matrix.