April 1, 2005
by Richard Mounce, DDS
While this question could fill a small book, its answer has huge implications for the long-term success of endodontic therapy. In the most general terms, the greater the amount of uncleaned and unfilled canal space that remains after a root canal procedure, the greater failure rate. Conversely, if the endodontic procedure mimics extraction, the greater the chance of healing. Extraction works because the entire pulp is removed from the patient. The challenge for clinicians is to decide to what point endodontic obturation should be directed in the given procedure. As mentioned above, the level of canal obturation is relevant to long-term success. Cleaning, shaping and obturating less than the entire root canal space has the potential to or certainly could leave uncleaned and unfilled space, especially if the root is obturated to levels determined by arbitrary anatomic averages and not the true apical foramen.
Apical anatomy is relevant as an opening into this question as the apical foramen is diverse in its complexity and at times a true foramen or minor constriction may not be present. As a result, knowing where clinically the root canal filling should be terminated in the given procedure may not always be easy to determine. For example, radiographs can be inaccurate due to angulation errors or their development, electronic apex locators can (in some conditions be less than completely reliable), etc. Complicating matters further, there is disagreement in the endodontic community as to the optimal level of obturation. Some believe that achievement and maintenance of apical patency is desirable and others do not (and advocate filling to some arbitrary point short of the radiographic apex of the tooth).
In general terms, the desirable termination of endodontic procedures is the minor constriction of the apical foramen and all filling material (gutta percha or bonded soft core obturation material (Resilon, Resilon Research, Madison, CT or RealSeal, SybronEndo, Orange, CA) should ideally be contained above this level. The true debate about what level to obturate to lies more in how to determine this point reproducibly and maximize long term success while diminish extrusion of obturating materials and iatrogenic potential.
With this goal in mind, during early exploration of a canal, it may or may not be possible to feel, by tactile sensation, a ‘pop’ at the apical foramen. The canal may be patent, may be severely calcified or the foramen may exit at any angle possible from the main canal not appear to be patent at all. This underscores the importance of precurving the files that are used to explore the apical third as well as to use copious irrigation and recapitulation to make sure that the canal is continuously negotiable throughout the process. The apical foramen is, on average, located 0.26-0.99 mm from the anatomic root end apex (references available). The implications of short filling will be addressed in more detail in part II of this column (May, Oral Health). I welcome your questions and feedback. OH
Dr. Mounce is in private endodontic practice in Portland, OR andis the endodontic contributing consultant for Oral Health.