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Early orifice enlargement, finding the canal path

May 1, 2010
The tooth pictured in Fig. 1 was referred recently for completion of a previously accessed root canal treatment.

For more on this topic, go to and search using the following key words: mesial root, early orifice enlargement, canal path, Dr. Richard Mounce, Endo File.

Fig. 1: Clinical case with over-enlargement of the mesial root orifices making the tooth susceptible to strip perforation and/or long-term vertical root fracture.

The tooth pictured in Fig. 1 was referred recently for completion of a previously accessed root canal treatment. In the shaping of the coronal aspect of the mesial root, the clinician used Gates Glidden (GG) drills to remove pulp from the orifice. It appears that a No. 5 GG drill (or its equivalent) was taken to 4-5 mm below the pulpal floor, removing far more tooth structure at this canal level than otherwise necessary. In taking this action, the clinician did not consider that he wanted (or needed) to prepare a continuous taper from the orifice to the apex.

Given the amount of dentin removed, it became virtually impossible to subsequently provide a continuous taper because to do so would remove virtually the entire root. This action also made the root more susceptible to strip perforation and long-term vertical root fracture. An alternative and clinically relevant strategy for the management of the orifice of the mesial roots is presented in this column.

Shaping of root canal systems is undertaken, in part, to allow irrigants access to the apical regions of the canal. Removing coronal dentin allows an irrigant flow that flushes pulp tissue and gives these bactericidal solutions access to otherwise inaccessible apical canal ramifications. A continuously tapering preparation also allows efficient and predictable placement of a biocompatible obturation material that ideally seals the canal off from the movement of bacteria and prevents canal reinfection. To achieve this purpose relative to gutta percha, RealSeal* bonded obturation material has been found, in vitro and in vivo, in the master cone or obturator variety (RealSeal One Bonded obturators), to reduce microleakage.

It is imperative for the clinician to decide the anticipated final prepared canal taper before starting the case. In this root the final taper, using the Twisted File*, is ideally a .08 taper. This taper, from orifice to apex, will provide unrestricted access of irrigants to the apex as well as make the efficient subsequent preparation of an enhanced master apical diameter possible. This taper is larger than tapers created in average roots with other file systems that are manufactured primarily through a grinding process.

Great care should be taken not to overprepare the orifice or work through too small of an opening and risk apical blockage and ledging. All of the successive steps should occur in the presence of copious irrigation. Once the initial orifice size is enlarged several millimeters below the orifice with the .08 Twisted File, the clinician should insert No. 6 and/or No. 8 hand K files to the apex in the presence of a bactericidal irrigant such as sodium hypochlorite. While other clinicians may have their preferred methods, in my hands it is unnecessary to use a viscous EDTA gel below the orifice for lubrication. If the case pictured is managed correctly with hand K files as described here, there is virtually no risk of canal blockage. In any event, once a hand K file (No. 6, 8, or 10) reaches the estimated working length, the canal can be subsequently enlarged to the size of a No. 15 hand K file. Rather than performing this enlargement by hand, the task is much easier using the M4 safety reciprocating handpiece attachment.*

After this glide path creation, the .08 Twisted File should be taken in successive insertions to the apex assuming that the file will move apically with a minimal pressure in a continuous and controlled motion. If the .08 Twisted File will not advance passively and gently to length in approximately three to four insertions, the .06/25 Twisted File should be used and a tandem of .06 and .08 Twisted files employed. This sequence can be used to achieve the basic taper before the enhanced master apical diameter is prepared. It is a relatively simple task to prepare the master apical diameter with a .06/30, .06/35, and .04/40 sequence after the .08/25 has been taken to the apex.

In summary, one of the primary goals of canal preparation is to provide a continuously tapering final shape. A lack of continuous taper is problematic. Using the tooth shown in Fig. 1 as an example, this tooth is at long-term risk of vertical fracture and short-term risk of perforation during treatment. Fortunately, this iatrogenic risk is entirely preventable with a careful preoperative assessment of the expected ideal taper and use of the correct rotary nickel titanium file sequence. I welcome your feedback.

*SybronEndo (Orange, Calif.)

Dr. Mounce is the author of the nonfiction book Dead Stuck, “one man’s stories of adventure, parenting, and marriage told without heaping platitudes of political correctness,” available at Pacific Sky Publishing or Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash.

Fig. 1: Clinical case with over-enlargement of the mesial root orifices making the tooth susceptible to strip perforation and/or long-term vertical root fracture.

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