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 极大地降低了牙体开裂和检查的倾向 烤瓷熔附金属修复体冷却过程中的瓷器 随之而来的成本、不便和再治疗创伤 接受这种修复体的牙科病人。第一 具体目标是完成对多个因素影响的测量 烧成，等温热处理，以及不同的冷却速度 不同牙科陶瓷的热膨胀系数。 这些测量将在常规差动中完成 牙科材料中的膨胀计和激光膨胀仪 佐治亚医学院的实验室。第二个具体目标 是为了确定瓷器膨胀的机制 在各种热处理过程中的变化。将使用的方法 区分可能的机制有：定量x射线 高温x射线衍射法，热台 扫描电子显微镜和跨中挠度的测量 双材料陶瓷-金属带在高速红外弯曲中的应用 密歇根大学牙科材料实验室研制的光束粘度计 乔治亚医学院。在本批款期内， 定量x射线衍射仪被证明是一种合适的工具 晶体热膨胀系数的测量 牙科陶瓷的成分在玻璃瓷基质中原位存在。 这项技术将极大地帮助确定机制。 与牙科瓷器的热不稳定性有关。可能的 牙科陶瓷热不稳定性的机理包括 白榴石的结晶或溶解，白榴石转化为 闪锌矿，白榴石颗粒在玻璃基质中的滞留 微裂化和烧结，以及捕获不同程度的过剩 由于冷却速度的不同，玻璃基质中的体积。这个 提高瓷器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。策略 对于开发改进的瓷砖，涉及减少或淘汰 白榴石偶联/去偶联，白榴石组分的稳定， 避免亚稳立方白榴石在冷却时的滞留 瓷器烧成温度，并将影响降至最低 玻璃基质的结构弛豫。

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.