Chris J. Lampert, DMD Printer Friendly Version

The Art of Patency
by Chris J. Lampert, D.M.D

The most important objective of endodontic instrumentation is the removal of all pulp tissue, debris, and bacteria from the root canal system. The only way to achieve this fundamental endodontic principle is to establish patency from the canal orifice to the canal terminus. This principal is true regardless of your philosophy on where the obturation material should end. If you cannot achieve patency (finding the main portal of exit), then you cannot clean the entire canal space. There are no exceptions.

Reaching patency allows other endodontic objectives to be achieved. Gauging the apex, creating a continuous tapered canal shape, proper cone fitting, and using an electronic apex locator for length determination all require a patent canal. The two objectives of this article are to explain why negotiation files fail to reach the canal terminus and to describe solutions to the most common problems associated with patency.

There are two main reasons that file advancement stops during canal negotiation. Recognizing the cause will allow you to employ the proper solution. A file either meets binding resistance along its length, called longitudinal binding, or an impediment at its tip. An impediment at the file tip can either be a ledge, a curve, a ledge and a curve, a blockage, compacted pulp tissue, or a bifurcation. The best way to determine why a file will not advance is to use the “smaller file test.” If you started with a size 10 file (which is the preferred negotiating file) and the 10 file no longer advances, decrease in file size to an 08 file. If the 08 file advances further than the 10 file, then the file was binding along its length and not at its tip. If the 08 file will not advance any further than the 10 file, then both files are being impeded at the tip.

Overcoming Longitudinal Binding
The solution to longitudinal binding is to open up the canal by using larger files to increase the canal diameter. This is accomplished by using two or three larger files alternating with a 10 file. For example, use a 15 file to where it goes, then a 10 file, then a 20 file to where it goes, then a 10 file, then a 25 file to where it goes, then a 10 file. This method is continued until the 10 file is patent or until the 10 file reaches a tip impediment. This file sequence increases the canal diameter and allows the 10 file to advance further with each alternating use. Using a 10 file in between the larger files helps prevent ledge formation and clears debris. Use caution not to force the larger files because this will lead to a ledge. In that case, you will have two things working against you.

A second option for overcoming longitudinal binding is to use a small tip sized .04 tapered rotary instrument to enlarge the coronal part of the canal. I prefer to use a 20/04 rotary instrument inserted until it meets resistance. This is much faster than using the hand file method described above.

Overcoming A Tip Impediment
This is probably the most important clinical skill needed to consistently negotiate canals to their terminus. To negotiate a tip impediment, a 10 file with a curved tip (the last 1-2 mm) is used in a circumferential “tip walking” motion until the tip slips past the impediment. Circumferential “tip walking” involves the repeated motion of inserting the file until it stops, slightly withdrawing the file, rotating a few degrees, and reinserting the file. At some point the file tip will align with the canal opening and slip past the impediment. This process could take many attempts and require curving the file tip multiple times, but it is successful at overcoming a tip impediment.

Once patency is established, great care must be taken to maintain it. This is accomplished by passing a patency file (10 file) out the apex by .5 to 1.0 mm.  Using a patency file after every 2-3 instruments will ensure the canal path is clear of debris and the canal terminus is patent. Achieving patency on every canal takes patience and persistence, but it will greatly improve the success of your endodontic treatment.

Chris J. Lampert, DMD maintains a fulltime Endodontic practice in Portland, Oregon, and is involved with research, testing, and development of new endodontic products. Dr. Lampert received his DMD from Oregon Health and Sciences University and his Endodontic post-graduate degree from Boston University. 

Dr. Lampert can be reached at drlampert@thedentistsnetwork.net

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