Secrets to better, safer, easier and far less costly endodontics

The use of K-reamers both unrelieved and relieved, where relieved means the incorporation of a flat along the instrument’s working length rather than the use of K-files (Fig. 1). K-reamers are designed with fewer and more vertically oriented flutes that will simultaneously engage the dentin and immediately shave it away when a watch-winding motion is employed. Because of the fewer number of flutes, there is less engagement with the canal walls, resulting in less resistance to apical negotiation. With the dentin being immediately shaven away with the first clockwise motion, the instrument encounters even less resistance, further easing the way for apical negotiation. Using relieved K-reamers, the initial apical negotiation is far less restrictive, giving the dentist the ability to reach the apex of many more canals more quickly and predictably.

One should use them to appreciate the dramatic difference compared to K-files. The way they are used is as important as the design of the instrument in providing better endodontics. Their motion is confined to either a tight, manual, watch-winding motion or limited to a 30-degree arc of motion when used in a reciprocating handpiece. Used in either manner, the small amplitude of motion reduces both torsional stress and cyclic fatigue to the point where they are incapable of inducing instrument separation, which are factors associated with rotating NiTi that tend to make these instruments used more conservatively.

Given the complex pulpal anatomy that exists, more conservative preparations that limit instrumentation to conical shapes tend to leave a good deal of debris in the extensions of what are often asymmetric, highly oval canals (Fig. 2). Both relieved and unrelieved K-reamers, whether used manually or in a reciprocating handpiece, can be used more aggressively and without fear of breakage against the lateral walls of oval canals, from the thinnest instrument onwards.

The full debridement of the canal can be addressed as they can be used in larger sizes and more aggressively because separation is not an issue. In short, both the design of the reamers and the way they are used give the dentist the ability to produce a superior result in three dimensions.

Safer endodontics

When instruments remain intact while performing their mechanics, the process is a safer one. Instruments confined to such a short arc of motion are highly resistant to breakage. Keeping the instrument predictably intact is the first order of improved safety. When the dentist has confidence that the integrity of the instrument is not procedurally compromised, there is no secondary compromise in the shaping of the canals. Improved shaping leads to superior irrigation and obturation, which are the three components of successful endodontics. Once one gets beyond the basics of keeping instruments intact, superior shaping, irrigation and obturation can be interpreted as the pillars of safer endodontics.

Easier endodontics

Not for one moment do I want to imply that endodontics is easy. Negotiating and fully cleansing the complex anatomy of even what appear to be simple single-rooted teeth can be challenging. Yet, we might agree that removing instrument separation as a risk factor removes procedural stress, and that removal makes us breathe a little easier, which in turn makes the procedure easier. When breakage is no longer a factor of concern, we are comfortable in negotiating highly curved canals in the prescribed manner, knowing that we have eliminated the two factors that produce instrument separation, namely, excessive torsional stress and cyclic fatigue. Once we are no longer discouraged in widening the canals because of the possibility of separation, we discover that irrigation is more effective and obturation becomes much easier.

Even in difficult situations where an abrupt curve may be present, the dentist will appreciate the advantages of a reamer design that significantly improves tactile perception of what the tip of the instrument is encountering, giving him the ability to distinguish between a solid wall and a tight canal. Unlike a tight canal, a solid wall produces no tugback, telling the dentist that he must remove the instrument, bend it at the tip and manually attempt to negotiate around the impediment using short arcs of movement in conjunction with a pecking motion. Employing this technique prevents separation even in these types of difficult situations.

Easier endodontics is intimately bound to safer and better endodontics. Of course, we can denigrate the description “easier” by coupling it to varying degrees of insufficient canal preparation, but that is not our goal. We are always using the word easier in the context of producing the best result we can within the parameters of the systems we are using. By widening the parameters for safety, in effect, we give the dentist a greater ability to produce better and easier results.

Far less costly endodontics

The fact that rotating NiTi instruments are vulnerable to breakage has set up conditions for the use of these instruments. The No. 1 suggestion from the manufacturers is to limit them to a single usage. Being expensive, many dentists will use these instruments more than once in defiance of company suggestions, while knowingly or unknowingly accepting the liability associated with extended use. These instruments are far more expensive than both unrelieved and relieved K-reamers.

Unlike rotating NiTi instruments, even the smallest sizes of K-reamers can be used several times as long as the canal has not grossly distorted them, something that happens more often to the thinnest instruments that first enter the canals and go to length. Rather than separating, the worst that happens to a K-reamer from excessive use in the manner prescribed is dullness, a feature that must be looked at as a luxury compared to the separation of NiTi instruments. I have estimated the savings that occur with the adoption of the reciprocating system compared to the use of most rotary NiTi systems to be in the range of 90 percent. One should understand that 40 years ago, endodontics was the envy of the dental profession because it was considered the least expensive specialty. Today, due to the introduction of a whole array of rotating NiTi systems and the adoption of complex thermoplastic techniques, endodontics is the most expensive of dental specialties.

Other points to consider

We have covered the essentials in describing the benefits that derive from incorporating K-reamers — both unrelieved through a 10 and relieved thereafter — used both manually and engine-driven, and confined to short amplitudes of motion that result in better, safer, easier and far less expensive endodontics.

From the past four years of research, we now know that rotating NiTi instruments has great potential to induce micro-fractures[1–4] that can then propagate under the additional forces of obturation, post placement and normal function, leading to a higher incidence of vertical fracture. We know that the manufacturers are presently marketing single-instrument, reciprocating shaping systems that have clearly been shown to inadequately debride canals. They are doing this to make things easier, safer and less expensive for the dentist. Unlike, the K-reamer system, NiTi systems will not produce a better result, something that should be at the heart of any new system. Safer, easier and less expensive systems that are less expensive than other NiTi systems mean little if they are not compatible with better results.

One should always keep in mind that when we take an X-ray of our results, we are only seeing what we have added, the radiopaque material. What we don’t see is the non-radiopaque material we have left behind. The fact that we have created and filled a conically shaped space may have little bearing on the actual degree of debridement that took place. The best time to address the myriad of thin isthmuses that may be present is with the thinnest instruments designed to engage the least while shaving dentin away most efficiently. The crown-down techniques used with rotating NiTi instruments emphasize centered preparations, where deviation from the center is fraught with the possibility of instrument separation. Used most cautiously, these instruments are not designed to explore the many off-centered tissue inclusion (nooks and crannies) that may exist along the length of the canal.

It has taken me many years to appreciate the simplicity that is necessary to produce superior results. We have been fed a continuous amount of dogma on the benefits of so many vulnerable rotating NiTi systems that it appears our only decision is to decide which NiTi system to use. Yet, for me at least, it is the exclusion of this entire avenue of endodontic shaping that has given our practice the ability to tackle all our cases with the freedom that comes from knowing separation is not an issue, and from that basic understanding all the other benefits follow in its wake.

Figures 3 through 8 are examples of several of the more complex cases we have shaped using relieved and unrelieved K-reamers both manually and in the 30-degree reciprocating system. We are cleansing these canals to a greater extent because the imposition of breakage does not apply. We are purposely working all the walls of highly oval canals because centering is not a requirement for safe usage. Greater preparation of canals assures superior irrigation and its activation by using the 30-degree reciprocating handpiece as a sonic source of energy accomplishing two tasks at the same time.

As time goes on, this relatively simple message is gaining momentum and is open to anyone who is willing to go off the beaten path of marketing that the big companies do so well.

Editorial note: This article was published in Endo Tribune U.S. Edition, Vol. 8 No. 3, March 2013 issue. A complete list of references is available from the publisher.