Tasaki Y, Ohta M, Yamane M
Shika Rikogaku Zasshi. 1978 Jan;19(45):28-38.
Although many investigations on the thermal expansion of dental investments have already been done, the conditions upon which thermal expansion was measured were not always definitely shown and the phenomena on thermal behavior of dental investments were not reasonably interpreted. In this investigation the effects of W/P ratio of samples, heating rate and furnace atmosphere were studied by "Push Rod" Dilatometer in order to attempt to standardise dilatometry of dental investments. All experiments were designed with two-way layout techniques. The main results were as follows, 1) W/P ratio, heating rate and furnace atmosphere have significant effects on the thermal expansion curves of the gypsum bonded investments. 2) One steep expansion and three stages of shrinkage in heating process of these investments from room temperature to about 900 degrees C were observed. 3) The quantity of the steep expansion, first and second stages of shrinkage and the expansion at 650 degrees C were affected by W/P ratio. 4) The temperature at which the steep expansion or shrinkage occurred were affected by heating rate. 5) Furnace atmosphere affected on both quantity of the steep expansion or shrinkage and their temperature. It also affected on the expansion at 650 degrees C. Then, these factors should be considered in dilatometry of gypsum bonded investments and in dental practice.
尽管已经对牙科包埋材料的热膨胀进行了许多研究，但测量热膨胀的条件并不总是明确显示，并且牙科包埋材料的热行为现象也没有得到合理的解释。在本研究中，通过“推杆”膨胀仪研究了样品的W/P比、加热速率和炉内气氛的影响，以试图规范牙科包埋材料的膨胀测量。所有实验均采用双向布局技术设计。主要结果如下：1）W/P比、加热速率和炉内气氛对石膏结合包埋材料的热膨胀曲线有显著影响。2）观察到这些包埋材料从室温加热到约900摄氏度的过程中有一次急剧膨胀和三个收缩阶段。3）急剧膨胀量、第一和第二收缩阶段以及650摄氏度时的膨胀量受W/P比的影响。4）急剧膨胀或收缩发生的温度受加热速率的影响。5）炉内气氛对急剧膨胀或收缩的量及其温度都有影响。它也影响650摄氏度时的膨胀。因此，在石膏结合包埋材料的膨胀测量和牙科实践中应考虑这些因素。
