Answering common endodontic questions: Part 1

When presenting lectures globally, especially to general practitioners, three questions predominate:

by Richard Mounce, DDS

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When presenting lectures globally, especially to general practitioners, three questions predominate:

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

These questions will be answered in a clinically relevant manner in this two-part series. Question 1 is answered here, and questions 2 and 3 will be answered in next month's The Endo File.

What is the ideal master apical file (MAF) size?

The endodontic literature conclusively argues that larger MAF sizes create cleaner canals. A No. 50 MAF creates a cleaner canal than a No. 30. A No. 40 MAF creates a cleaner canal than a No. 20. Enhanced apical diameters remove more dentin in the apical third and allow greater volumes of irrigation. A secondary benefit to creating larger MAF sizes is ease of cone fit. Cone fit in a properly tapered canal is simple and efficient. The converse is true.

Traditionally, apical preparations have been smaller than they are now. Several reasons account for this trend. To some degree, the literature basis for making larger apical preparations has been reflected in the treatment regimen of some clinicians. Second, rotary nickel titanium (RNT) files have made canal preparation more predictable and faster, requiring fewer instruments and providing more consistent shape than using hand files and Gates Glidden drills.

In addition, assuming the system is used properly, RNT files are less technique sensitive than previous alternatives. For example, if used correctly, the Twisted File* (TF) can enlarge a canal to an .08 25 preparation with one single file in the majority of roots.

To create larger MAFs clinically, the clinician gauges the apex and prepares the canal to three sizes larger than the first file that binds at the true working length. Finding the hand K file that binds (resists apical displacement) at the minor constriction (MC) of the apical foramen “gauges” the diameter of the canal at the termination point of canal preparation.

After gauging, the canal can be prepared to the larger diameter with any of a variety of file systems, including Lightspeed (Discus Dental, Culver City, Calif.) and K3.* In April of this year, TF will have larger tapers and tip sizes up to a No. 50 .04 taper. It is currently available to a No. 25 tip size in five tapers between .04 and .12.

Irrespective of the file system, the principles employed to create larger apical diameters is straightforward. Much like a small cup fits into a bigger cup, the smaller taper of the enhancing files fit into the larger taper of the prepared canal.

Transferring this concept to the creation of larger apical diameters, if a preparation is made with a .08 TF and 25 tip size, whether it is .02 taper, .04 taper, or .06 taper, this small taper fits inside the large taper and will remove dentin only at the apical 3 mm to 4 mm. As a result, a preparation with a larger MAF will appear slightly parallel in the apical 3 mm to 4 mm relative to a preparation that is not enhanced apically.

Typical follow-up questions

It is common for clinicians to ask two follow-up questions at this stage. How is cone fit attained? If the clinician is using carrier-based obturation, how does he or she know the desirable carrier size for a significant number of cases? I use the RealSeal One Bonded Obturators (RS1).* With RealSeal, either in the master cone form or the obturator form, a bonded obturation that diminishes microleakage across the totality of the canal space relative to gutta percha in a statistically significant way is provided.

In any event, the principle used to fit the obturators relies on a small taper fitting into a large taper. RS1 obturators are .04 taper (less tapered). The smaller taper of the obturator, once heated, is inserted into the larger taper of the preparation, usually .06 or .08 using TF. A polysulphone size verifier is used to determine which obturator is correct.

Alternatively, with master cones, I use the .06 RealSeal No. 20 cone and trim the tip by .5 mm at a time to the MC until tugback is achieved. I do not utilize multiple tapers and tip sizes of master cones. All cone fitting is custom trimmed to the particular preparation.

Questions 2 and 3 will be answered in Part 2.
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 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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