by Richard Mounce, DDS
An assessment of the success or failure of previous endodontic therapy should always be undertaken before restorative treatment begins on a given tooth. A recent referral underscores the soundness of this guiding principle.
The patient was referred for evaluation of tooth No. 30. The molar was asymptomatic and without apparent radiographic pathology. The tooth had root canal treatment many years ago with silver cones. The treatment failed and apical surgery subsequently was performed. Recently, the crown placed at the time of the initial root canal had fallen off and led the patient to seek care. Before the referral, the referring doctor determined that the coronal seal was not adequate and placed a new buildup. In the process, the tails of the three silver cones were cut off at the orifice level. All the silver cones were short of the radiographic apex by an average of 4 to 5 mm. There was an untreated second distal canal. After the new buildup, the tooth was prepared for a crown, an impression taken, the crown fabricated, and cementation scheduled. At this stage, referral for evaluation and possible treatment was made.
This clinical scenario - a patient with a crown at the lab with an appointment for cementation who is then referred for endodontic treatment - is not unique. These referrals often are accompanied by a note that asks the endodontist to “keep the access small” and/or to “not touch the crown margins.” Inherent in both of these requests is the belief that such a modification of access size might be possible or even desirable. It is not. Given the clinical indication, access needs to be as big as necessary. Limiting the access size so one does not touch the margins can easily translate into uncleaned and unfilled space apically, a lack of irrigation, as well as a lack of access to the silver cones. In this case, the cones were going to be exceptionally difficult to remove since the tails had been cut off.
Several important lessons can be derived from this clinical case:
First, if the crown fell off - given the time delay - coronal leakage was responsible as confirmed by the referring doctor’s decision to place a new buildup. This leakage virtually guarantees that the already inadequately cleansed, shaped, and obturated canals were contaminated. Ideally, at the time of the initial examination, the tooth would have been referred for evaluation and retreated (for this reason, among others).
Second, virtually all silver cones are corroded to one degree or another, many severely. With the leakage and the short fillings present in this case, the cones described were certain to be corroded. Placing a new buildup, sealing in bacteria and corrosion, is inconsistent with long-term success.
Third, while a comprehensive discussion of the possible retreatment of this tooth is beyond the scope of this column, retreatment was made infinitely more difficult by the clinician cutting off the silver cones. Once these tails were removed, the predictability of silver cone removal diminished considerably.
With the tails gone, methods for removal become significantly more complex and should involve the surgical operating microscope (Global Surgical, St. Louis, Mo.), ultrasonics (MiniEndo II, SybronEndo, Orange, Calif.), and rely heavily on small hand files precurved apically with an EndoBender pliers (SybronEndo). File Eze (Ultradent, South Jordan, Utah) can be used as a lubricant to bypass the silver cones with hand files, and ultimately, attempt to lift them coronally (among other techniques). In addition, removing enough dentin around the orifices of the canals to expose the tails (again) to allow insertion and bypassing with a hand file would increase the long-term risk of root or furcal floor fracture.
One might argue that surgery could always be performed on the tooth at a later time; however, this concept is flawed. Making the roots shorter would not strengthen the tooth, and the prognosis for second apical surgeries is generally guarded to poor. In this case, the retrofill would have to be placed against - at best - a dirty canal space and/or a rusted silver cone.
In summary, addressing all the endodontic needs of the tooth in a restorative context is essential before placement of restoratives. In other words, the correct sequence and foundation for treatment in stages (endodontic assessment and treatment first) to assure the best long-term prognosis is an essential tenet in the restorative endodontic continuum.
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Dr. Mounce has no commercial interest in any of the products mentioned in this article.
Dr. Richard Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash. Among other appointments, he is the endodontic consultant for the Belau National Hospital Dental Clinic in the Republic of Palau, Korror, Palau (Micronesia). He can be reached at firstname.lastname@example.org.