Dulaimi Suha Fadhil, Kanaan Sabiha Mehdi
Department of Prosthodontics Technologies, College of Health and Medical Technologies, Middle Technical University, Ministry of Higher Education and Scientific Research, Baghdad, Iraq.
Open Dent J. 2018 Jul 31;12:494-500. doi: 10.2174/1874210601812010494. eCollection 2018.
Dental stone cast needs 24 to 48 hours to evaporate excess water and acquire enough strength for manipulation. The microwave oven is used to save time by drying and disinfecting stone casts.
The aim of the present study is to evaluate the effect of microwave oven drying on the compressive strength of Type III and Type IV dental stone in three time intervals-3 hours, 5 hours and 24 hours after pouring.
The study involved 120 samples: 60 samples for each type of dental stone. Thirty samples were subjected to air drying at 3, 5 and 24 hours) and 30 samples were dried in the microwave oven at 2450 MHZ -900 W for 150 seconds (at 3, 5 and 24 hours). The samples were tested by unconfined compression machine, with a 2000 kg proving ring at cross-head speed of 1 mm/min.
For the Type III dental stone drying at 3 hours, microwave radiation causes a significant increase in compressive strength and shows the highest score (mean 125 kg/cm); however, at 5 hours no significant difference was observed. However, at the 24 hour time interval, microwave drying causes significant reduction in the mean (100 kg/cm) <0.01 .For the Type IV dental stone testing at all-time intervals (3,5, 24 hours), a significant reduction (<0.05) in mean values was shown(80,85,87 respectively).
Microwave oven drying increased the compressive strength of Type III dental stone at the 3 hour time interval from pouring, while microwave drying at the 5 hour interval had no significant effect; and at 24 hour the compressive strength of the dental stone was reduced. For the Type IV dental stone microwave drying had a detrimental effect on compressive strength at all-time intervals.
牙科石膏模型需要24至48小时来蒸发多余水分并获得足够强度以便进行操作。微波炉用于通过干燥和消毒石膏模型来节省时间。
本研究的目的是评估微波炉干燥在灌注后3小时、5小时和24小时这三个时间间隔对III型和IV型牙科石膏抗压强度的影响。
该研究涉及120个样本：每种牙科石膏60个样本。30个样本在3小时、5小时和24小时进行空气干燥，30个样本在2450兆赫-900瓦的微波炉中干燥150秒（在3小时、5小时和24小时）。样本通过无侧限压缩试验机进行测试，在十字头速度为1毫米/分钟的情况下使用2000千克的测力环。
对于III型牙科石膏，在3小时干燥时，微波辐射导致抗压强度显著增加，且得分最高（平均125千克/平方厘米）；然而，在5小时时未观察到显著差异。但是，在24小时时间间隔时，微波干燥导致平均值显著降低（100千克/平方厘米）<0.01。对于IV型牙科石膏在所有时间间隔（3小时、5小时、24小时）的测试，平均值均显著降低（<0.05）（分别为80、85、87）。
微波炉干燥在灌注后3小时时间间隔增加了III型牙科石膏的抗压强度，而在5小时时间间隔微波干燥没有显著影响；在24小时时牙科石膏的抗压强度降低。对于IV型牙科石膏，微波干燥在所有时间间隔对抗压强度都有不利影响。
