A Deeper Understanding of the Balanced Force Technique and Beyond

Having been told by my critic that I do not understand the principles of the balanced force technique in endodontic instrumentation and am consequently misleading (lying) when I write about its application with relieved twisted reamers in the 30o oscillating handpiece, I looked up the definition of the balanced force technique as proposed by Dr. James Roane. The definition is as follows:

“The "balanced force" technique was introduced in 1985 and it was reported that the resistance of the dentin, as it circumferentially contacted the flutes of a file in a curved root canal, would be sufficient to override and mask any tendency of the file to straighten during rotational instrumentation.”

The key words here are “the resistance of dentin” stating that its resistance overrides the straightening potential of an instrument that is rotating within the canal. It should be noted that the word rotational should be weighed carefully. Full rotations have been shown to distort canals to the outer wall and is in fact?the reason larger-sized stainless steel instruments should not be used with full rotations in canals of increasing curvature. Dr. Roane recognized this limitation on rotations and confined his arc of motions to no more than 180o clockwise and 120o or greater counterclockwise. Within those confines he was able to negotiate K-type files to the apex without any apparent signs of distortion.?

He stated his reasons for using a K-type file is the cutting edges’ identical rake and clearance angles regardless of the direction of movement. The method of advancing the K-type files to the apex is first one of clockwise stroke not exceeding 180o followed by a counterclockwise rotation of 120o or greater. Please note that the arcs of motion are horizontally applied atypical of the vertical strokes that are generally used with?K-files. Here the K-type files are being applied with a reaming motion.

He notes that the balanced force concept was developed by trial and error experimentation over 12 years. Interestingly, several insights came to our minds in terms of making the balanced force technique more efficient. The first was the recognition that since the K-type of files were being used with a reaming motion might it not be an improvement to use K-type reamers. I had known for years that K-reamers offered less resistance in advancing apically in a canal. The fewer more vertical flutes along the length of the shaft engage the canal walls less than comparably sized K-type files. Less engagement means less resistance allowing the instruments to advance more apically with the same short horizontal manual stroke shaving some amount of dentin from the canal walls while engaging a small amount of dentin at the end of the stroke, dentin that would then be cleaved from the canal walls when the counterclockwise stroke was applied.?

Because only a small amount of dentin is engaged in the clockwise motion, it takes less apical pressure and a smaller arc of motion to cleave off that dentin. Now manually this is a slow process, but we experimented with the 30o oscillating handpiece at a frequency between 3000-4000 cycles per minute and found that the process of reaching the apex in this manner became very time efficient. It worked fine negotiating curved canals without any apparent distortion. There was no reason for it not to work in this manner. The basis principle of the dentin along the length of the canal walls is that it offers more resistance to deformation than the instruments as noted in Dr. Roane’s original paper. Their use in the 30o oscillating handpiece offers significantly shorter arcs of motion that further reduce the stresses generated to both the instruments and the canal walls making them even more adaptable to the canal anatomy.

It was only after the publication of his original article using K-type files that the concept of a non-cutting batt tip was introduced to further aid in the negotiation of curved canals using the balanced force technique, noting that a rounded tip would be more likely to deviate from embedding itself into the canal wall potentially creating a ledge. By confining the reamers we were employing to the high frequency 30o arcs of motion both clockwise and counterclockwise we noted that despite having a cutting tip they followed the path of least resistance namely the patency of the canal. Where in full rotations a cutting tip could penetrate dentin, confined to 30o arcs of motion the instruments unable to penetrate dentin were directed by the higher resistance of the canal wall to conform to the canal anatomy they were negotiating through.

The fact that we could employ instruments with a cutting tip further reduces the extrusion of debris apically. A cutting tip pierces any tissue and debris that is in the way of its path to the apex. A non-cutting tip has a greater potential to impact debris and with further apical force applied in reaching the apex to extrude it apically. So this is where we sit today. We use the 30o oscillating handpiece (M4) at high frequencies (3000-4000 cycles per minute) with relatively light apical forces applied. I have shown many cases here on linkedin of significantly curved canals being instrument without any apparent signs of distortion. The relieved stainless steel twisted reamers are more flexible than customary stainless steel instruments and confined to the short arcs of motion are more than flexible enough to conform to highly curved canals at least through sizes of 60/02 as confirmed in the endodontic literature with stiffer unrelieved K-files.

While all systems produce some degree of apical extrusion, numerous studies have found that the balanced force technique tends to produce less with common sense telling us that an instrument with a cutting tip and predominantly vertical flute orientation?being the only differences should further reduce the extrusion of apical debris. Just to reiterate the benefits of reamers over files I have included two studies below that emphasize their advantages. Finally, perhaps the most valuable addition the 30o oscillating handpiece brings to the table is a method of using the relieved twisted reamers in a way that virtually eliminates any chance of instrument separation giving the dentist the confidence to apply them aggressively against all the walls of even highly oval canals as well as isthmus-like configurations that are often present between canals.

Dr. Roane said it best. His accomplishments and insight were a product of trial and error over many years. With full recognition of his innovative thinking, we have simply tried taking it to the next level where hand fatigue is practically eliminated, debris extrusion is reduced and more rapid three-dimensional cleansing is a reality.

Regards, Barry