Anticipating canal anatomy: predictable location

Canal location is made predictable by having: 1) All the lighting and magnification possible, while always using a rubber dam.

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Canal location is made predictable by having:

  1. All the lighting and magnification possible, while always using a rubber dam.
  2. A comprehensive understanding of the possible anatomical variations within any particular root.
  3. All the equipment needed (burs, ultrasonic units and tips, etc.) to predictably uncover the canal.
  4. The time and personal desire to locate all anatomy. Early canal enlargement should be conducted in an effort to minimize any risk of iatrogenic outcomes and make canal preparation simple and efficient.

The answer to many endodontic questions is the surgical operating microscope (SOM) (Global Surgical, St. Louis, Mo.). With the SOM, much of the guesswork is taken out of the process of canal location. Whether it's in reading the color, texture, and landmarks of the pulpal floor, or seeing immediately where canals should be and are usually located, the scope is unparalleled for its capabilities to help the clinician locate canals and make negotiation predictable.

If the canal location is suspected but not confirmed, for example, in the ribbon of pulp tissue concealing an MB2 canal, there are several means of identifying a canal. The clinician can put a dye, like methylene blue, into the pulp chamber, or use a caries indicator solution like Seek (Ultradent, South Jordan, Utah) to stain pulpal tissue. Alternatively, sodium hypochlorite can be put into the chamber and the clinician can watch for the bubbles that would be expected to arise from the solution interacting with pulpal tissue.

Canal anatomy is very predictable in how unpredictable its location may be. For example, while a clinician would not routinely expect it, unusual anatomy such as four roots in a lower bicuspid can occur. If a clinician expects that every tooth accessed will have the maximum number of canals, it is axiomatic that they will have the optimal chance to locate all canals. For example, in an upper first bicuspid, realizing that three roots are possible can go a long way toward locating the third root when it is present. Obviously, a careful analysis of the root morphology on the preoperative radiographs is needed from multiple angles to anticipate the anatomy that may be present in a case. Even with ideal preoperative radiographs, it must be assumed that the maximum number of canals is present, even if they are not visible radiographically. Said differently, if you find one canal in a tooth where one or more canals are possible, look for two. If you find two, look for three, etc., they are often there.

Challenging canal location and early enlargement of calcified orifices is made much simpler and safer with ultrasonics. I prefer the Elements Ultrasonic Unit and Red Star tips (both SybronEndo, Orange, Calif.) for uncovering such canals. It is essential that the risk of perforation is always considered when deciding how much dentin to remove and from where in the search for a canal that is not easily located. It is valuable to take radiographs often when removing dentin where perforation is a hazard, in order to redirect oneself toward the true canal. Avoiding heat generation is also a primary concern with ultrasonics, and most often the ultrasonic tips are used with a light water coolant spray.

Aside from these techniques, a risk assessment is always indicated before initiating root canal treatment. Risk assessment in this context means anticipating the challenges that will likely be faced during treatment, and having a plan for managing these challenges. In the context of locating canals, an example is noting whether a crown or the degree to which the canals are calcified obscures the pulp chamber. Accessing a nonvital lower molar with calcified canals in a tooth that is covered by a crown, risks possible perforation or removal of excessive amount of dentin in the attempt to locate the canals. The clinician must remain aware of the access bur's vertical depth of insertion, the horizontal extent of penetration in relation to the occlusal surface, and the pulpal diagnosis. A patient with limited opening, one that is unable to sit still, or one with a thick base metal crown are factors that can further complicate the clinician's ability to easily locate the canal. Removing a crown is often indicated in these cases. Again, the SOM's capabilities are invaluable to locating canals, especially in such complex anatomy.

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 RichardMounce@MounceEndo.com. Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash.

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