Evaluating risk factors in endodontic canal enlargement

July 1, 2008
There are two classic scenarios in canal enlargement: the tooth that has had prior endodontic treatment in some various state of completion, and the tooth which is still untouched.

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There are two classic scenarios in canal enlargement: the tooth that has had prior endodontic treatment in some various state of completion, and the tooth which is still untouched. It is generally more challenging to be the second person into a root canal system. Teeth that have been accessed before may have blocked, ledged, transported canal spaces, among many other potential iatrogenic problems. These problems may not be easily visible on radiographs, and patients may not be aware that something untoward has occurred in their tooth. Canals that have never been touched have a decreased probability of iatrogenic potential during their management.

There is usually one prime first chance to prepare a root canal space optimally. For the endododontist, retreatment is common, as is finishing treatment in various stages of completion. For the general practitioner, it is more common to be the second clinician into a tooth where a pulpotomy has been done. The quality of the pulpotomy can influence the risk of a subsequent iatrogenic event. For example, if the coronal third has been overflared, incorrect subsequent enlargement could easily lead to a perforation or put the roots at later risk for vertical fracture.

Considerations in managing teeth that have been previously accessed include:

1) The greater the amount of preoperative imaging that can be gathered from the initial radiographs, the better. Digital radiography from various angles can provide optimal three-dimensional mapping of the canal, short of using cone beam technology.

2) Access may need to be refined so that all overhanging dentin is removed coronally, as is all caries and previous restorations (as clinically appropriate). Before entering the canal, access should be ideal. Ideal access implies that the entire pulp chamber has been unroofed, there is straight-line access, and all canals have been located. Using a surgical operating microscope (SOM) (Global Surgical, St. Louis, Mo.) during access (and all phases of endodontic treatment) can both enhance the result and minimize the chances of making an iatrogenic issue worse. The SOM alerts the clinician as to what may not be ideal in the access, as well as direct initial management of the canal preparation. For example, if a second canal were to branch off the primary canal at the cervical level of a lower second molar, the visualization provided by the SOM would be ideal to see this.

3) If a tooth has been accessed before, initially determining patency is essential. Such a determination includes the use of small-precurved hand files (EndoBender pliers, SybronEndo, Orange, Calif.) throughout the canal to determine patency. If patency is not present and it's at all possible, it should be created. If patency is not easily achieved the clinician should work toward assuring patency before enlarging the rest of the canal space, especially after the orifice has been shaped. To prepare the canal in the presence of an apical blockage is to risk a wide variety of additional iatrogenic events, including instrument fracture, perforation, or severe canal transportation, depending on the treatment materials and methods being used.

It's worthy to mention that if a root canal has been started and remains unfinished, the next clinician must often enlarge the canal from a shape that is partially finished to one that is ideal. To achieve this, the clinician needs to decide what the final taper and tip size will be, where the preparation is adequate, and where it needs enhancement. After a determination of patency throughout the canal, it is generally safest to create a smaller taper initially to the true working length in most roots, and then as clinically indicated, to create a larger diameter as needed.

Coincident to this, an evaluation of the initial size of the orifice must be made to minimize the possibilities of overflaring of the coronal third. Said differently, if the coronal third has been enlarged with an orifice opener and the next clinician immediately inserts additional orifice openers, the risk of unneccessary enlargement in the coronal third, with its attendant complications, is quite high. Indiscriminant use of orifice openers can easily lead to roots that are over- flared and at-risk for subsequent fracture.

This has been a discussion of the implications of being the second clinician into a tooth, with an emphasis on visualization and the creation of apical patency before completing canal enlargement procedures. I welcome your feedback.

Dr. Mounce offers intensive customized endodontic single-day training programs in his office for groups of one to two doctors. For information, contact Dennis at (360) 891-9111 or write [email protected]. Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash.

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