Making endodontic access through a crown and repairing the access opening in lieu of making a new crown is problematic. In my empirical opinion and experience, the vast majority of crowns that I have accessed, either for first time treatment and/or retreatment, using the LA Axxess kit (SybronEndo, Orange, CA), have shown some measure of coronal microleakage, even when the crown may appear to be clinically and radiographically sound. Upon access, even in such radiographically acceptable crowns, it is common to find cracks of all types, caries, and unset restorative materials amongst many possible events that previously were not visualized. In addition, especially in crowns that cover the entire chamber and furca of the tooth, it is not at all uncommon to find previously unidentified small posts and previous endodontic access (including the presence of cotton pellets and obturation materials that may have washed out or been radiolucent). In short, it is unwise to make assumptions about the integrity of any crown and/or simply assume that every endodontic access through a crown (that initially looks sound) can be repaired with a filling.
As might be expected, judging a radiograph on the quality of crown margin integrity is challenging. Radiographs that show excellent crown margins or do not show caries may be grossly deficient depending on radiograph angulation and/or quality of development. While often not practical (mostly for financial reasons more than any other single consideration), the ideal endodontic access is one made after a previous crown has been removed and the tooth carefully examined under a surgical microscope for all of the issues mentioned above, even if the crown is new. Placing a coronal filling risks leaving undiagnosed caries, existing leakage and creates more linear margin to seal and maintain. It might be considered a long-term temporary filling.
It is challenging when the patient may have recently had a crown placed and the patient now has symptoms of irreversible pulpitis or necrosis and access is indicated. Ideally, at the time of the crown preparation, the clinician will take multiple radiographs from various angles and a complete history (medical, dental and of the tooth) and evaluate pulpal status. Such evaluation would include evaluating the tooth to percussion, palpation, mobility and probings as well as to cold. Any unusual finding that is not within normal limits must be carefully evaluated so as to identify those teeth that may either need root canal therapy at that time or are likely to need treatment if they are manipulated for a crown. In essence, by carefully anticipating the pulpal status and the nature of the patient’s chief complaint as to why they need the crown, often times the future need for a root canal can be anticipated and addressed to avoid the difficult situation where a patient has just paid for a new crown and now either needs a new one or to have access made through it.
In addition, the above notwithstanding, if it is not possible to make a new crown, and a coronal filling must be placed into the patient’s tooth, the greatest level of visualization and magnification that can be used to visually inspect the inside of the tooth is optimal. Such an inspection should seek to identify any areas where the crown is inadequate (especially when such marginal discrepancies are not visualized outside the tooth) as well as a visual inspection for all manner of unfavourable events (caries, crack lines, unset restoratives, etc). I welcome your questions and feedback.
Dr. Richard Mounce is in private endodontic practice in Portland, OR, USA. Dr. Mounce is the author of a comprehensive DVD on cleansing, shaping and packing the root canal system for the general practitioner.
