Answering common endodontic questions: Part 2

May 1, 2009
Question No. 1 was answered in Part 1 of this two-part series, and was published in last month's Endo File.

by Richard Mounce, DDS

For more on this topic, go to and search using the following key words: common endodontic questions, manage an open apex, manage MB2 canal, manage an open apex, Dr. Richard Mounce, The Endo File.

Question No. 1 was answered in Part 1 of this two-part series, and was published in last month's Endo File. These are the three most common inquires that I receive from general practitioners in my lectures across the globe. Questions two and three are answered here in a concise but clinically relevant manner. For all practical purposes, the answers are identical.

  1. What is the ideal master apical file (MAF) size? (See April 2009 issue of DE)
  2. How do you find and manage calcified canals?
  3. How do you find and manage the MB2 canal?

2) How do you find and manage calcified canals?3) How do you find the MB2 canal?

Visualization through the SOM cannot be overstated in its importance in all phases in the location and management of calcified and MB2 canals. Straight-line access is a necessity. Ideally, all restorations should be removed if they are complicating identification of the canal.

While a comprehensive discussion of ultrasonics is beyond the scope of this column, using ultrasonic tips with rounded ends such as the RS2 tip* can selectively remove dentin over an MB2 or create a flat surface from which to more easily locate a calcified canal.

Prior to starting the negotiation, the clinician should determine from the initial radiographs an estimated working length (EWL). This gives the clinician some rough idea of how long the root is, and at what stage of the negotiation to expect a popping sensation as the hand file exits the minor constriction (MC) of the apical foramen.

Once the canal is located, the series of steps taken to negotiate the canal is very similar, whether it's a calcified canal or an MB2. At all costs, the canal should be prevented from becoming blocked. Irrigant should always be placed in the chamber before hand K file insertion.

All hand K files used for canal exploration should be pre curved in the apical 3 mm to 4 mm. They should be inserted with gentle but intentional pressure toward the apex. If the canal resists their advancement, the file should be withdrawn, irrigation performed, and a new pre curved hand K file inserted.

Progress in the canal is made possible through the diligent insertion of the hand K file. The hand K file should not be forced to any predetermined length. It may need to be inserted in many different orientations until a pathway is found to the EWL.

In any event, when the No. 6 reaches the EWL, the clinician should take an electronic apex locator reading to determine the true working length (TWL). After the TWL is determined, a minimal enlargement of the canal can be undertaken to make it ready for the RNT files. The No. 6 hand K file initial negotiation should be followed up with a No. 8 and then a No. 10 hand K file, etc. After each insertion of a No. 6, No. 8, No. 10 or No. 15 hand K file, the canal should be irrigated and recapitulated.

I generally insert a No. 6 hand K file first into virtually all canals, no matter how open or calcified. If the No. 6 goes rapidly to length, the clinician knows that the canal was initially open, patent, and negotiable. If patency is subsequently lost, the clinician will further know that he or she lost the patency instead of the canal never having been negotiable. This is valuable to know. If the canal was once negotiable and its patency was lost, the chances for regaining it improve if the right steps are taken.

The use of mechanical reciprocation with a reciprocating handpiece attachment is very efficient for performing this enlargement from a No. 6 to No. 15 hand K file. Reciprocating handpieces such as the M4 Safety Handpiece* use non-rotational movement. For the M4, this is a 30-degree clockwise and 30-degree counterclockwise reciprocation.

Using the M4, the clinician can rapidly take a canal from the diameter of a No. 6 hand K file to a No. 15 hand K file. Once a No. 15 hand K file can spin freely in the canal, the canal is ready for rotary nickel titanium (RNT) canal preparation. This minimal diameter of a No. 15 hand K file is known as a “glide path.” Use of a reciprocating handpiece attachment can save significant time and hand fatigue relative to manual filing.

Four of the most common questions I hear in lectures have been answered in this two-part series of the Endo File. I welcome your questions and feedback.

* SybronEndo, Orange, Calif.

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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