Understanding and Improving On the Balanced Force Technique

The manual balanced force technique employing stainless steel K-files with a non-cutting tip, developed by James Roane in 1985 was rightfully considered a major breakthrough in the instrumentation of curved canals. The implementation of this technique gives the dentists the means to instrument curved canals without inducing varying degrees of canal transportations including ledging and frank perforations. It has special significance because it was introduced before the advent of NiTi rotary instrumentation.?

The technique consists of the following steps: A thin K-file with a non-cutting tip is introduced into the canal and is rotated clockwise about 90o with light apical pressure causing the flutes to engage and embed into the canal walls. This step is followed by the application of significant apical pressure as the K-file is now rotated counterclockwise any where from 180o to 360o. By applying apical pressure during the counterclockwise motion, instead of withdrawing from the canal, the flutes cleave off the engaged dentin and are now reading for a subsequent clockwise/counterclockwise cycle in advancing the instrument to the apex in a non-distorted fashion. An initial precaution is to avoid excessive apical pressure during engagement lest the non-cutting tip embed to deeply into the canal wall creating a ledge and deviating from the original canal anatomy.?

The balanced force technique is done manually and consequently is time consuming and hand fatiguing. Considering the fact that this technique was developed prior to rotary NiTi, hand fatigue was simply part of endodontic instrumentation regardless of the techniques employed at that time and was considered entirely normal and not something to be avoided. Without considering any comparison between the manual balanced force technique and our approach of engine-driven 30o oscillations of K-reamers both unrelieved and relieved when we first introduced this approach, it becomes evident that the latter approach has several advantages over the original balanced force technique.

One of the main advantages is the complete elimination hand fatigue. The oscillating handpiece generates a 30o arc of motion at a frequency of 3000-4000 cycles per minute. The 30o arc of motion is one third the arc of rotation used in balanced force to engage the dentin and consequently engages less and embeds less. The counterclockwise arc of motion also 30o is anywhere from 1/6 to 1/12 that generated by the balanced force technique. Given the shorter arcs of motion in both directions, every complete cycle generated in 30o oscillations removes less dentin, a reduced task per cycle that keeps the instruments centered with even less potential to deviate from the original canal anatomy. The shorter 30o cycle puts less stress on both the instruments and the teeth being cleansed and shaped.??

Given the minimal arcs of motion generated in 30o oscillation one might conclude that the smaller amount of dentin being removed per cycle makes 30o oscillation less efficient. To compensate for the small amount of dentin removed per stroke with oscillation, however, is the high frequency of the cycles generally about 3600 per minute. The arc of motion in balanced force is on average about 6-8 times greater considering the clockwise and counterclockwise coupling removing significantly more dentin per stroke, but the number of strokes generated by the oscillating handpiece is conservatively estimated at about 36 times more than the manual balanced force technique more than compensating for the shorter arcs of motion in terms of dentin removal. From a point of efficiency short arcs of motion coupled to high frequencies are vastly more efficient than longer arcs of motion coupled to a much lower frequency. The short arcs of motion induce less stress in the instruments and the teeth virtually eliminating instrument separation and the dentinal micro-cracks that are associated with techniques that induce instrument breakage.?In short, the smaller the arc of motion the more control the dentist has over its actions.

Another significant difference between balanced force and the engine-generated??30o oscillation technique is the substitution of K-reamers both unrelieved and relieved for the non-cutting tipped K-files. One unique feature of the balanced force technique was finding a way to remove dentin from the canal walls without using a pull stroke where K-files conventionally shave the engaged dentin away from the canal walls. The advantage of this approach was less distortion, a reduced incidence of impacting debris apically and losing length during the instrumentation process. By employing stainless steel reamers, instruments incorporating half the number of flutes along a similar working length of 16 mm and having a vertical orientation twice that of the flutes along the length of the K-file, the oscillating reamers encounter less resistance along length with the vertically oriented flutes immediately shaving dentin away from the canal walls with the first 30o clockwise arc of motion. The result is the more rapid advancement of the reamers to the apex and less force being applied giving the dentist a better tactile perception of what the tip of the instrument is encountering.?

K-reamers are more flexible than comparably sized K-files and with the incorporation of a flat along the entire working length of the K-reamers starting with a 15/02 they are even more flexible allowing them to adapt to highly curved canal configurations more readily. In both the balanced force technique and the 30o engine-driven oscillation technique it is the short arcs of motion that prevent the distortions that arise from full repetitive rotations that can occur even with rotary in highly curved canals. A common sense conclusion, and one validated by the many cases I have shown of apparent non-distortion in highly curved situations, is that a shorter arc of motion is safer and more predictable than a larger one. That is the reason the manual balanced force technique was more predictable than the full rotations of stainless steel K-files. 30o oscillation of K-reamers uses an even shorter arc of motion coupled to a much higher frequency and is significantly safer and more efficient than the balanced force technique. Engine-driven, if conducted properly will always be an advantage over the manual employment of instruments.

Knowing many endodontists, particularly of my vintage, have an almost religious fervor and loyalty regarding the manual balanced force technique, please look at the results posted below that we attained by only using the oscillating stainless steel reamers in the entire preparation of the canals. These results were attained with no need for concern regarding instrument separation and their vigorous application to oval canal spaces producing three-dimensional cleansing and sonic activation of the irrigants.

The insight that let me understand why 30o oscillations stay true to the canal anatomy came from the mechanics that were first applied to the balanced force technique. In a sense, one could describe 30o oscillations as “balanced force lite” because it puts less stress on the instruments per full cycle of motion by doing less work, but more than makes up for the lower work per cycle by having many more cycles per minute (say at most 100 manual cycles per minute as compared to 3600 cycles in 30o engine-generated oscillations).

We learn from others, but should not be stymied by the past. At the end of the day, the only things that matter are effective clinical results and the safer and more efficiently we can gain those results represent good standards for measuring progress.?

Regards, Barry