Authors: Roane JB, Sabala CL, Duncanson MG Jr.
Title: The "balanced force" concept for instrumentation of curved canals.
Journal: J Endod
Date: May 1985
Citation: 11(5):203-11
Category: Access and Canal Instrumentation
Evidence-based Ranking: 5
Rationale: 1. Important aspect of the technique is the design of the instruments. 2. K- type file w/ triangular cross section and modified tip is instrument of choice for several reasons. a. Cutting edges have identical rake and clearance angles regardless of movement. It is a “bi-directional cutting tool” b. Compared to a square blank, triangular cross section produces reduction in cross sectional mass (by 37.5 %), increase in flute depth, and decrease in restoring force or more flexible (because of the 37.5 decrease in mass) 3. Restoring force is a load which holds the files cutting surface against the curvature in a single direction and it is the load which is responsible for a straightening (creates transportation and ledges) of the curve during preparation. 4. Restoring force is variable and will be decreased by 1. Decrease metal mass (triangular blank) 2. Radius of curvature increases. 3. Arc of curvature decreases. 4. Distance from curve to file tip is increased. 5. Coronal access w/ coronal straightening will increase the radius and decrease the arc, resulting in less restoring force. 6. Modified tips will remove the cutting surfaces expressing the restoring forces and decrease chance of transportation.

Technique: Placement, cutting, and removal of each file should be done with rotary motions only. 1. Placement using clockwise rotation with light inward pressure. 2. Cutting CCW with inward pressure. 3. Removal with one to two CW rotations and slight outward pull. 4. This sequence is repeated until the working depth has been achieved and the canal is fully enlarged. 5. Once the enlargement has been completed, a final clockwise cleaning rotation is used to load canal debris into the flutes and remove debris away from the apical foramen.

Reviewer’s Comments: classic article describing the concept behind the balance force technique.