A Study of Application of Shape Memory Plastic as Elastic Material in Clinical Dentistry and Orthodontics.

日本开发的形状记忆塑料Polynorbornen的玻璃化转变点为35^ﾟC。一旦环境温度超过临界点，这种塑料就会开始显示出弹性性质，如果变形，就会恢复到原来的形状。我们研究了在聚降冰片弹性阶段产生的力是否可以用来移位人类牙齿。我们发现，直径1 mm的形状记忆塑料丝在50ﾟ℃的温度下伸长到原来长度的2~3倍，以0.5 mm/s的速度施加相对稳定的119-156克的连续光力来移动牙齿。与用于正畸治疗的传统弹性模块相比，这种新材料在37ﾟC的体温下表现出长时间的激光强度退化，并且可以制造成接近所需的牙齿颜色。这些优点使得形状记忆塑料在正畸中的临床应用成为可能。然而，出于实用的目的，与传统金属丝的结合是不可避免的，其临床疗效还有待进一步研究。

Polynorbornen, a shape memory plastic developed in Japan, has a glass transitional point of 35^ﾟC. Once the environmental temperature exceeds the critical point, this plastic will begin to display an elastic property, then return to its original shape, if deformed. We examined whether the force generated during the elastic phase of polynorbornen could be used to displace human teeth. We found that the shape memory plastic wire of 1mm in diameter stretched to two to three times of its original length at a temperature of 50^ﾟC and a speed of 0.5mm/sec would exert a relatively stable continuous light force of 119-156 grams to move the teeth. This new material, compared with conventional elastic modules used in orthodontic therapy, exhibited a laser degree of force degradation at a body temperature of 37^ﾟC for a long period, and can be manufactured to near the tooth color required. These advantages make feasible clinical application of the shape memory plastic in orthodontics. However, a combination with conventional metal wires cannot be avoided for practical purposes, and its clinical efficiency has to be further studied.