Kawara M, Komiyama O, Kimoto S, Kobayashi N, Kobayashi K, Nemoto K
Department of Complete Denture Prosthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
J Dent Res. 1998 Jun;77(6):1446-53. doi: 10.1177/00220345980770060901.
There have been many reports on fatal distortion of heat-activated acrylic denture-base resin which is still widely used in the field of removable prosthodontics. However, these reports have failed to report quantitatively on polymerization and thermal shrinkage factors. In the present study, we attempted to verify that the shrinkage of heat-activated acrylic denture-base resin was caused mainly by thermal contraction after processing. Furthermore, we examined the degree of distortion resulting from long, low-temperature processing, and compared the results with that of the conventional method. The strain gauge and thermo-couple were embedded in a specimen at the time of resin packing. The measurement started from the beginning of processing and continued until the specimen was bench-cooled and immediately before and after it was de-flasked, as well as during seven-day immersion in water at 37 degrees C. The resin expanded when processed by the conventional method. Meanwhile, mild shrinkage, possibly polymerization shrinkage, was observed when the resin was processed by the low-temperature method. This suggested that polymerization shrinkage was compensated for by thermal expansion during processing by the conventional method. Moreover, the shrinkage strains in the period from the completion of processing to immediately after de-flasking, in both the conventional and low-temperature methods, were identical to the theoretical value of thermal shrinkage which we obtained by multiplying the linear coefficients of thermal expansion by temperature differences. The shrinkage strain in the specimen processed by the low-temperature method, measured from the end of processing to immediately after de-flasking, averaged 64% of that in the specimen processed by the conventional method. The results revealed quantitatively that the shrinkage of heat-activated acrylic denture-base resin was mainly thermal shrinkage, and demonstrated the advantage of the low-temperature method in reducing thermal shrinkage.
关于热固化型丙烯酸义齿基托树脂致命变形的报道颇多，该材料在可摘局部义齿领域仍被广泛使用。然而，这些报道均未对聚合和热收缩因素进行定量分析。在本研究中，我们试图验证热固化型丙烯酸义齿基托树脂的收缩主要是由加工后的热收缩引起的。此外，我们研究了长时间低温加工导致的变形程度，并将结果与传统方法进行了比较。在树脂填充时，将应变片和热电偶嵌入试样中。测量从加工开始时启动，一直持续到试样在工作台上冷却、脱模前后，以及在37℃水中浸泡7天的过程中。采用传统方法加工时，树脂会膨胀。同时，采用低温方法加工树脂时，观察到轻微收缩，可能是聚合收缩。这表明在传统方法加工过程中，热膨胀补偿了聚合收缩。此外，在传统方法和低温方法中，从加工完成到脱模后立即测量的收缩应变，均与我们通过热膨胀线性系数乘以温度差得到的热收缩理论值相同。从加工结束到脱模后立即测量，低温方法加工的试样收缩应变平均为传统方法加工试样的64%。结果定量显示，热固化型丙烯酸义齿基托树脂的收缩主要是热收缩，并证明了低温方法在减少热收缩方面的优势。
