The “Balanced Force” Concept for Instrumentation of Curved Canals

By Roane JB, Sabala CL, Duncanson MG

Date: 01/1985
Journal: JOE



Purpose: to describe the balanced force technique to support its validity, and to make its concepts available so that

others may also examine and test its validity.

Rational :

  • K-files are bidirectional cutting tools, allow the clinician to select any of the four potential cutting approaches (insertion, withdrawal, clockwise, or CCW)
  • Restoring force: applied against the curvature by the file to return to its original straight condition.
  • Restoring force will increase if:

1.Metal mass increase (trianglular vs. square)

2.Radius of curvature decrease

3.Arc of the canal curvature increases

4.Distance from the curve to the file tip is decreased

  • Extending file beyond apex before next larger file (undesirable)
  • Modification of the file tip


  • Clockwise rotation up to 180 degrees, counterclockwise rotation at least 120 degrees with apical pressure.
  • Until the WL is reached. Then a larger size instrument is used in the same manner.
  • Final clockwise cleaning rotation is used to load canal debris into the flutes.
  • If file was over extended, enlarge the apical size by 2 large files to the WL to create apical stop.