Effects of constraint on the oscillatory pattern of endosonic files.

When operated in air, the transverse oscillation of the endosonic file exhibits a series of nodes and antinodes along its length with the greatest displacement amplitude occurring at the unconstrained tip. Endosonic files of varying design, length, and thickness exhibit differences in their oscillation. Preliminary work has revealed that the endosonic file is susceptible to constraint when working within the root canal and a model system was designed to investigate this problem. The constraining influence was found to be greatest when it was applied at those antinodes nearest the tip. This effect was further enhanced if the file was angled. Furthermore, constraint applied at the nodes also influenced the file oscillation. Such results may explain in situ observations on the occasional inefficiency of the system, especially when negotiating the apical third of a curved root canal. Clinical techniques utilizing an endosonic file may require reappraisal in order to minimize such constraint.