Second Opinion: Excessive Coronal Shaping Adversely Affects the Long-term Prognosis of Endodonticall

Second opinions are common in healthcare; whether a doctor is sorting out a difficult case or a patient is not sure what to do next. In the context of our magazine, the first opinion will always belong to the reader. This feature will allow fellow dentists to share their opinions on various topics, providing you with a “Second Opinion.” Perhaps some of these dentists’ observations will change your mind; while others will solidify your position. In the end, our goal is to create discussion and debate to enrich our profession.

–– Thomas Giacobbi,
DDS, FAGD, Dentaltown Editorial Director

By Drs. Dennis Brave and Kenneth Koch

Historically, endodontics has been witness to many fluctuations in terms of clinical technique. Currently, we are seeing many endodontic preparations that are excessively wide in the coronal third of the canals. Consequently, the questions we must ask ourselves are the following. How did this style (of excessive coronal shaping) evolve and is this good for the long-term prognosis of the endodontically treated tooth?

There are two explanations which account for this excessive shaping. The first explanation is a result of file design. The early generations of rotary files had radial lands and, as a result, created a significant amount of resistance and drag when working in a root canal. In order to reduce the engagement of the lands, and the stress to the instruments, variable tapers were introduced as part of a crown-down sequence. Multiple or variable tapers (.12, .10, .08, etc.) were, in fact, introduced to overcome a design feature thought to be necessary to keep rotary files centered in the canal as they worked. The largest tapers in these techniques are generally used in the coronal aspect of the canal and then followed by smaller tapers as the preparation proceeds apically.

The second explanation, and, clearly the most significant in terms of changing the shape of endodontic preparations, has been obturation techniques. As a result of the popularity of thermoplastic obturation and warm vertical condensation, it became obvious that the larger the opening at the top of the canal, the easier it is to move gutta percha down the canal. That’s fine for manipulating gutta percha but the problem is that these larger tapers (.12, .10, .08, etc,) often compromise the integrity of the tooth. The vertical condensation of heated gutta percha remains an excellent obturation technique but, we believe, that it should be performed in preparations no greater than a constant .06 taper to retain the integrity of the endodontically treated tooth.

The excessive canal shaping that we now often see compromises the long-term prognosis of teeth. This is why we see so many fractures in endodontically treated teeth, especially those that have a post and core. Furthermore, as dentists, the problem with having a technique that does not extend the long-term success of the tooth, is that in the future, patients will choose to extract a diseased tooth in favor of an implant. This is particularly evident if they feel the implant will give them a better long-term prognosis. However, we believe in saving the natural dentition (when at all possible) and part of that is not adversely compromising the tooth when doing a root canal procedure.

As more endodontists desire to place implants, Real World Endo wants to concentrate its efforts on saving the natural dentition. One of our goals is to teach endodontic techniques that will ultimately enhance the long-term success of the endodontically treated tooth. Consequently, it must be noted that constant taper preparations are far more conservative in the coronal third of root canals than variable taper techniques. Fully tapered .06 tapers are acceptable but there are many instances where a .04 taper works better. Recent studies have again demonstrated that .04 taper shapes are more than adequate to allow irrigation agents to generate a through cleansing of the root canal.1 In fact, a strong case can be made that the preferred shape should be, when possible, a fully tapered .04 preparation.

The constant taper advocates, of which we are one, feel that the precision, predictability, and reproducibility of a constant taper shape outweighs the benefits of a variable taper sequence.

A constant taper preparation creates a predictable shape that is easy to match with a synchronized master gutta percha cone. A constant taper preparation is also the ideal shape to act as a platform for new sealer–based obturation techniques.

In fact, the EndoSequence file does exactly that. The EndoSequence file is unique because it combines a true reamer design with alternating contact points on an overall constant taper blank. The alternating contact points (which are ground .02 mm less than the outboard flutes) result in the file never being totally engaged. At any point in the canal there may be a three point contact, two point contact, single contact, and a significant portion of the instrument is not contacting anything. The result is a continual disengagement of the file (along its blank) and a corresponding reduction in torque.2 The final shaping result is a continuous .06 or .04 taper from orifice to apex. Therefore, we are getting the best of both worlds with this instrument design.

References:
1.Nguy D, Sedgley C. The Influence of Canal Curvature on the Mechanical Efficacy of Root Canal Irrigation In Vitro Using Real-Time Imaging of Bioluminescent Bacteria. Journal of Endodontics Nov 2006; 32: 1077-1080
2.Koch K, Brave D. Real World EndoSequence File. Dent Clin North Am. 2004; 48:159-182
3.Koch K, Brave D. A New Endodontic Obturation Technique Dentistry Today May 2006; Vol. 25: 5; 102-107
4.Koch K, Brave D. Endodontic Synchronicity Compendium 26 (3): 218-224, 2005

.04 Taper Preparation

Indications for a .04 taper preparation:
    1. Long canals (greater than 25mm in length)
    2. Canals with large apical diameter (particularly maxillary incisors)
    3. Mandibular incisors
    4. Teeth that display very narrow canals on X-ray
    5. Hybrid technique- In cases where .06 file cannot reach apex, use .04
    taper instrument to facilitate apical preparation, then complete shaping with .06 file.
    6. Significantly curved canals

When one considers the cleaning and shaping aspect of endodontics, along with the restorability and long-term prognosis of the tooth, it seems that in many cases the ideal preparation is a continuous .04 taper. What has delayed the acceptance of this rationale has been the lack of an obturation technique(s) that can be successfully accomplished by the majority of dental practitioners. The emergence of sealer-based or mono-cone techniques such as Activ GP, now gives us the ability to shape, clean, and seal the root canal system in such a fashion that we do not have to compromise the long-term restorability of the tooth.3 The concept of Endodontic Synchronicity (the matching of a laser verified cone to a constant taper preparation) will allow you (regardless of the obturation technique employed) to bring endodontic shaping back into the realm of realistic sizes.4 The net result will be an improved long-term prognosis for these endodontically treated teeth and your patients will appreciate having the option of maintaining their natural dentition.

The following cases demonstrate the benefits of a continuous .04 taper preparation.

Case I: This is a relatively narrow canal in a maxillary incisor (I A) that can be handled beautifully with a .04 taper preparation. Notice how the final fill with Activ GP (I B) allows for preservation of tooth structure.

Case II: Pre-operative image (II A) demonstrates the presence of four canals. Post -operative image (II B) clearly shows the benefits of doing this case with .04 tapers. This case was obturated with Activ GP.