Ultrasonics in Endodontics: Precision, Power, and Possibilities

In an ultrasonic instrument the main driver oscillates in a true longitudinal manner and as it moves back and forth a transverse wave is generated along the length of the file with the formation of series of nodes and antinodes along the length of the file. However, in a sonic instrument a circular motion characterized by a single antinode at the tip and a node near the driver is generated. The action of driver imparts both a vertical and lateral component of the action of the file. Thus, when a file is constrained within a root canal, this lateral component is essentially eliminated and a true vertical and longitudinal file movement remains. This difference in the oscillatory pattern between sonic and ultrasonic file pattern may explain the reportedly superior efficiency of sonic instrument during clinical usage. Contrary to earlier reports, it is highly unlikely that a confined area such as a root canal would increase the probability of cavitation inception. Recent research has shown that the hydrodynamic shear stresses caused by the acoustic streaming fields are responsible for many of the beneficial effects attributed to their use in endodontics.