Contemporary Endodontics by Dr. Daniel J. Boehne

To oversimplify the complicated, the gist of endodontics is getting bacteria out of teeth and sealing them to prevent bacterial recurrence. Shape, clean, pack—the endodontic triad. Decades of research by smart, thoughtful clinicians and researchers have led us to an understanding of our procedural goals, and completing those goals is believed to lead to our highest possible rates of success.

When we talk about an endodontic shape, we're talking about the hollow shape that we impart in the root by drilling and scraping the walls of the naturally existing canal, making it larger. The evolution of common endodontic shapes is the product of both research and clinical convenience. It's our belief that we must create a certain amount of shape to physically debride the canal walls and to create room for the penetration of irrigants and proper obturation.1–6

The degree to which we enlarge the canal at the apex has been debated among endodontists for decades, but the consensus is that the apical canal should be enlarged at least to some degree, and then the remainder of the canal should be increasingly enlarged coronally to create a continuous taper to the orifice.1,5 This approach allowed better access for irrigants and obturation instruments available at the time, such as spreaders and pluggers, to reach to the apical preparation. Greater taper is also advocated to increase lateral obturation forces with warm vertical compaction of gutta percha. This design was well thoughtout, but doesn't come without risk.

Bacteria are the main cause of endodontic pathosis,7,8 so eliminating them and preventing their recurrence becomes the goal of endodontics. It makes sense to use bacteria removal as a metric in an attempt to predict clinical outcomes. A simple study design used is to inoculate extracted teeth with bacteria, then compare the efficacy of different techniques in their ability of removing the bacteria.3 The conclusions are used to predict that the superior technique will lead to superior success rates, and the technique is adopted clinically.

This type of inference is problematic when we realize that many endodontically treated teeth are lost because of structural failure, not just persistent infection. Root durability doesn't appear to be a significant variable within the relative short scope of our outcome studies, but it may be more important than we realize for long-term success.

One size shouldn't fit all
Our root-canal shaping objectives have evolved based on the results of bacterial removal and irrigation penetration studies, as well as clinical guidelines to facilitate obturation. Many clinicians base their go-to endodontic shapes on this literature, on popular opinion or even on "radiographic aesthetics." Endodontic shapes are less often determined by the root canal anatomy of the individual tooth being treated.

Cookbook recipes are available for standardized root canal shapes. We now have one-file-does-it-all rotary systems that can shape every canal to the perfect universal shape. Shape, clean, pack … done!

But what if the perfect shape is simply not universal or flat-out wrong? Is it necessary to hollow out a root as much as we've been doing to predictably save a tooth? Is it possible that too much shape can be detrimental in some cases—or in all cases? What if there was more than one way to skin a cat, and the cat might live a longer, happier life the other way?

Like most endodontists, my natural reaction is to feel a little offended when my dental colleagues tell me that endodontically treated teeth break easier than non-endodontically treated teeth. Or maybe the feeling I have is guilt, because they are right. In 2014 my practice averaged almost one patient per day for evaluation of an endodontically treated tooth that had a longitudinal root fracture (split tooth or vertical root fracture), while in the same year I saw only four virgin teeth (free of caries or restoration) that had longitudinal root fractures.

It's a common misconception that endodontically treated teeth break more because they become dehydrated and brittle.9,10 One reason they break more is because our endodontic shaping objectives come at the expense of nonreplaceable tooth structure—at the expense of the strength of the tooth.11,12 The reason why these teeth require endodontics in the first place is because they present to us with cracks, fractures, large carious lesions or restorations, so preserving what tooth structure we have remaining becomes imperative.

Is it possible that larger shapes might be more efficient at removing bacteria to potentially increase the observed short-term outcomes, but actually decrease long-term outcomes because of root fractures? I think so. It's also evident that blind one-size-fits-all root preparations can cause immediate iatrogenic failure in certain cases. Fortunately, with cone beam computed tomography (CBCT), we now have technology that enables the planning of sophisticated, customized root shapes for individual cases. We also have irrigation technology that allows us to irrigate to the apex without additional coronal enlargement, and obturation devices and techniques that can adequately fill smaller shapes.

Conclusion
Advocating minimally invasive endodontics should absolutely not be misconstrued as license to be a lazy clinician; in fact, the opposite is true. Using conservative root shapes is a more arduous path to canal disinfection because extra steps need to be taken to supplement instrumentation. By relying less on instrumentation for debridement, extra emphasis must be placed on irrigation or the use of an interappointment medicament to make up for the difference.

Remember, the goal of endodontics is not to get white lines to the apex on a radiograph, or to achieve radiographic aesthetics; it's to eliminate bacteria to cure or prevent apical periodontitis. Advancements in imaging, magnification, instrumentation, irrigation and obturation have made endodontics predictable with conservative shapes … as long as clinicians are willing to properly embrace the technology to thoroughly and thoughtfully treat these teeth.

References
1. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18(4):269-296.
2. Albrecht LJ, Baumgartner JC, Marshall JG: Evaluation of apical debris removal using various size and tapers of ProFile GT files. J Endod 2004; Jun;30(6):425-8.
3. Saunders, Coldero 2002. Reduction in intracanal bacteria during root canal preparation with and without apical enlargement. Int Endod J 2002 May;35(5):437-446
4. Barbizam JV, Pecora JD, et al. Effectiveness of manual and rotary instrumentation techniques for cleaning flattened root canals. J Endod 2002 May ;28(5):365-6
5. Barbizam JV, Pecora JD, et al. Effectiveness of manual and rotary instrumentation techniques for cleaning flattened root canals. J Endod 2002 May ;28(5):365-6
6. Salzgeber RM, Brilliant JD: An in vivo evaluation of the penetration of an irrigating solution in root canals. J Endod 1977;3:394-398.
7. Kakehashi S, Stanley HR, Fitzgerald RJ (1965). The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surf Oral Med Oral Path 1965;20(3):340-349
8. Sundqvist G: Bacteriological studies of necrotic dental pulps. Dissertation. Umea University Odontological Dissertation No. 7.
9. Papa J, Cain C, Messer HH. Moisture content of vital vs. endodontically treated teeth. Endod Dent Traumatol 1994 Apr;10(2):91-93.
10. Sedgley CM, Messer HH. Are endodontically treated teeth more brittle? J Endod 1992 July;18(7):332-335.
11. Gaikwad A, Pandit V. In vitro evaluation of the strength of endodontically treated teeth treated after preservation of soffit and pericervical dentin. Indian Journal of Conservative and Endodontics, October-December, 2016; 1(3):93-96.
12. Zandbiglari T, Davids H, Schafer E. Influence of instrument taper on the resistance to fracture of endodontically treated roots. Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics 2006;101(1):126-131.

Check out Dr. Boehne's award-winning practice!
This issue's Office Visit feature gives readers a peek at Dr. Daniel J. Boehne's endodontics practice in Dana Point, California, which won a national design competition. Take your tour, starting on page 38.