Davis D R, Kennedy M P
Dent Mater. 1990 Jan;6(1):29-34. doi: 10.1016/0109-5641(90)90041-c.
Previous studies of setting expansion of gypsum-bonded investments have not examined how wax patterns expand with time. The purpose of this study was to provide a method of measuring wax patterns during the setting reaction. Ten MOD inlay wax patterns were invested individually in plastic casting rings and imaged at specific intervals on a stage on which both the rings and xeroradiographic cassettes were fixed. Distances between the axiogingival proximal walls, axiopulpal proximal walls, and axial walls were measured at each interval. Reproducibility of measurements of xeroradiographic images was about 0.3%. After setting, the wax was burned out, and the rings were cooled to room temperature and cast in a Bi-Sn alloy that did not shrink upon solidification. The castings were measured and the means compared with the means of xeroradiographic measurements. There was no significant difference between the expansion means of the axiogingival or axiopulpal dimensions measured by casting or xeroradiographically (p greater than 0.05, two-tailed t test). Significant differences (p less than 0.05) were seen between means of the axial expansion measured by castings and xeroradiographically, suggesting the formation of a void at the proviral walls of the wax patterns. All horizontal expansion occurred between two and 22 min from the start of mix.
以往关于石膏结合包埋材料凝固膨胀的研究尚未考察蜡型随时间的膨胀情况。本研究的目的是提供一种在凝固反应过程中测量蜡型的方法。将10个MOD嵌体蜡型分别包埋于塑料铸圈中，并在一个固定了铸圈和干板X线摄影暗盒的平台上，按特定时间间隔进行成像。在每个时间间隔测量轴龈向近中壁、轴髓向近中壁和轴壁之间的距离。干板X线摄影图像测量的重复性约为0.3%。凝固后，将蜡型烧掉，铸圈冷却至室温，然后用一种凝固时不收缩的铋锡合金进行铸造。对铸件进行测量，并将测量均值与干板X线摄影测量均值进行比较。通过铸造测量和干板X线摄影测量的轴龈向或轴髓向尺寸的膨胀均值之间无显著差异（p>0.05，双侧t检验）。铸件测量和干板X线摄影测量的轴向膨胀均值之间存在显著差异（p<0.05），提示蜡型的预成壁处形成了空隙。所有水平膨胀均发生在调拌开始后的2至22分钟之间。
