THERMALLY INDUCED CHANGES IN DENTAL PORCELAIN EXPANSION

拟议研究的总体目标是确定这些机制 对热引起的热系数变化负责 牙科瓷器经历的膨胀，并使用 从而获得了开发更能抵抗这种情况的瓷器的理解 改变。这种热稳定性瓷器的开发将极大地 减少牙科瓷器的开裂和检验倾向 在烤瓷熔附金属修复体的冷却过程中 降低成本，减少不便，并重新治疗牙科创伤 接受这种修复的病人。第一个具体目标是 测量多次点火、等温热处理和 不同降温速率对单晶玻璃热膨胀系数的影响 各种牙科瓷器。这些测量将在一个 传统差动膨胀仪和激光膨胀仪的研制 在佐治亚医学院的牙科材料实验室。这个 第二个具体目标是确定负责 在不同的热处理过程中，瓷器的膨胀会发生变化。这些方法 将用于区分可能的机制的有： 定量x射线衍射仪，高温x射线衍射仪， 热台扫描电子显微镜和跨中的测量 双材料瓷-金属带材在高速红外中的偏转 牙科材料实验室研制的弯曲梁式粘度计 乔治亚医学院。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， 白榴石向闪锌矿的转化及亚稳立方体的保留 白榴石经高温冷却后的脱偶和再脱偶 玻璃基质中的白榴石颗粒通过微裂和烧结， 以及捕获玻璃基质中不同水平的过剩体积 不同的冷却速度。改善环境质量的方法的发展 瓷块的热稳定性是本研究的第三个具体目标。 建议的工作。发展改良型瓷砖的策略 涉及减少或消除白榴石耦合/去耦合， 稳定白榴石部分，避免亚稳立方体 白榴石从瓷器烧成温度冷却后的保留，以及 减小对玻璃基质结构松弛的影响。

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.