Development of new phosphate-bonded investment witout harmful gas and dust

众所周知，牙科投资是由细粉末组成的。但是，如果实验室工作人员在打开包装、称重和最初混合时误吸，则可能导致呼吸道疾病。此外，磷酸盐结合的投资可能会释放对人体有害的氨气。本研究的目的是生产无氨的糊状磷酸盐键合投资。试验前制备了两种浆料（代号：paste1 &， paste2）。粉饼是方石英（平均尺寸9.2μm， Tatsumori公司）和磷酸盐（磷酸二氢镁，Yoneyama化学公司）用20cc蒸馏水液化的混合物。Paste2是由油性化合物凝固的MgO（氧化镁#220，Tateho chem.）。设计了四种（A-D）实验性磷酸盐键合投资(pastel (g)/paste2(g) = A: 79.6/25.5, B: 82/22.5, C: 84.4/19.5, D:86.8/16.5)，并评估了它们的基本性能。Paste2能有效地硬化模具，缩短凝固时间。A的抗压强度为生坯强度8.65±1.55MPa，烧结强度7.60±0.62MPa。A在实验模具中明显最强。这些强度值按字母顺序依次变小，经单因素方差分析，A-D组间差异有统计学意义（p<0.05）。另一方面，A的凝固时间约为8分钟，比B-D短。D在混合约13分钟后凝固。热膨胀取决于结晶器中方石的含量。在本研究中，含有较多粉状物质的D有利于热膨胀。900℃时膨胀率约为1.8%。这些结果表明，由于具有完全无尘和牙科铸造模具的可用性，实验性的糊状磷键合投资对操作人员是有用的。因此，我们需要探索更适合牙科铸造模具的膏体/膏体比例或评估从中获得的铸件。

It is well-known that dental investments are composed of fine powders. However, they may cause a respiratory disease if laboratory workers absorb them by mistake when opening the package, weighing and initially mixing at work. Moreover, phosphate-bonded investments may release harmful ammonia gas for human body. The objective of this research was to produce the paste-like phosphate-bonded investments without ammonia. Two pastes (Code: paste1 &, paste2) were prepared prior to test. Pastel was a mixture of cristobalite (average size; 9.2μm, Tatsumori Cor.) and the phosphate (Magnesium dihydrogenphosphate; Yoneyama chem.) liquefied with distilled water of 20cc. Paste2 was MgO (Magnesium oxide #220, Tateho chem.) coagulated by oily compounds. Four (A-D) experimental phosphate-bonded investments (pastel (g)/paste2(g) = A: 79.6/25.5, B: 82/22.5, C: 84.4/19.5, D:86.8/16.5) were designed and their fundamental properties were evaluated. Paste2 was effective to harden the mold and shorten setting time. Compressive strength of A showed 8.65±1.55MPa as green strength and 7.60±0.62MPa as fired strength. A was obviously strongest in the experimental molds. These strength values became smaller alphabetically, and there were significantly differences among A-D by One-way ANOVA (p<0.05). On the other hand, setting time of A was about 8 minutes and shorter than those of B-D. D was found to set after about 13 minutes from mixing. Thermal expansion is depended on the amount of cristobalite including in the mold. In this study, D containing more pastel was advantageous on thermal expansion. The expansion rate was about 1.8% at 900℃. These results suggest that experimental paste-like phosphaie-bonded investments are useful for operators because of complete dust-free and usable properties as dental casting molds. Hence, we need to explore more suitable paste/paste ratio for dental casting molds or evaluate castings obtained from them.