Lees S, Barber F E
Science. 1968 Aug 2;161(3840):477-8. doi: 10.1126/science.161.3840.477.
Ultrasound is readily conducted across a boundary when the specific acoustic impedances of the two media are about equal. The specific acoustic impedance of dental enamel is about that of aluminum. A longitudinal sonic pulse, less than 250 nanoseconds in duration, conducted to the tooth through an aluminum rod, has positively detected the enamel-dentin junction as well as the dentin-pulp interface.
当两种介质的声特性阻抗大致相等时，超声波很容易穿过边界。牙釉质的声特性阻抗与铝的大致相同。通过铝棒传导至牙齿的持续时间小于250纳秒的纵向声脉冲，已确切检测到釉质-牙本质交界处以及牙本质-牙髓界面。
