Removal of warm carrier-based products with the Twisted File

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Removal of warm carrier-based products with the Twisted File

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Fig 1a, 1b: Clinical cases treated in the manner described. The Twisted File (SybronEndo, Orange, CA, USA) was used to remove the plastic Thermafil Carriers (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA).
Dr Richard Mounce, USA

By Dr Richard Mounce, USA

Tue. 13 October 2009

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“Does anyone have any advice on how to remove Thermafil with twisted files?” Recently, I received this question via e-mail from a colleague. Thermafil is a warm carrier-based obturation product of Dentsply Tulsa Dental Specialties (Tulsa, OK, USA). The Twisted File (TF) is a product of SybronEndo, (Orange, CA, USA).

It is a fair statement that many of the general dental clinicians who use warm carrier-based obturation in endodontics have never re-treated (removed) them when it is placed in root canal treatment that fails.

Thermafil is a valid obturation technique that is supported in its efficacy by the endodontic scientific literature. The concept most certainly has its advocates and champions.

This said, aside from the cost relative to other options, removal of the carrier can, at times, be challenging. This column was written for the general practitioner to be exposed to and made aware of the basic steps involved in retreatment of warm carrier-based products in which the carrier is plastic and to discuss its removal with the TF. Clinical use of the techniques described would be best learned in a continuing education format using a surgical operating microscope (SOM) (Global Surgical, St. Louis, MO, USA) beginning with practice in extracted teeth.

As mentioned, retreatment of warm carrier-based products can, at time, be problematic. Carriers that have been placed with significant frictional retention into long, narrow and curved canals are more difficult to remove than other such devices. Metal carriers were utilized in early warm carrier-based product versions.

In my clinical experience retreating warm carrier based products, metal carriers have generally been easier to remove than the plastic ones. Whether metal or plastic, techniques for removal varied from the use of solvents, such as chloroform to dissolve out gutta-percha from around the carrier, blended with Hedström files to lift the carriers. For plastic carriers, a rotary nickel titanium (RNT) file spinning counterclockwise, could, in theory, pick up the carrier and propel it out of the canal.

Heat could also be used to melt the plastic carriers to create access into the canal or alongside a plastic carrier. Carrier retention is a function of canal preparation as well as carrier fit. If the canal did not have a continuous taper, frictional retention of the carrier is more likely along more of its length.

Using a carrier that is slightly too large for the prepared canal space can often have the same effect. Plastic Thermafil carriers will not dissolve in solvents, such as chloroform. Up to this point in time, RNT instruments have not been able to predictably machine out the plastic carriers of warm carrier-based obturation techniques. The TF, if used correctly, is the first RNT file that I have used that can do so with predictability.

The TF is never cut across its grain structure in manufacture. The file is twisted in its manufacture while in a crystalline phase structure known as R phase, which is an intermediate phase between austenite and martensite (the resting phase of nickel titanium and the phase present under stress during function, i.e., rotating through a curvature during canal shaping). In addition to twisting, TF manufacture is finalized with a final deoxidation process that maintains the files’ surface hardness and sharpness of the cutting edges.

These properties make the TF very different in its capabilities relative to other RNT instruments that are ground from a nickel titanium wire. One of these functional capabilities is the ability of the TF to grind through plastic carriers. Clinically, depending on the size of the canal to be retreated, usually, either a .08 or .10 TF instrument will be used for this purpose. The TF is used at enhanced rotational speeds for this purpose, usually 900-1200 rpm. It is designed to be used in one canal or one tooth, be that one canal or five canals.

In plastic carrier removal, the TF is advanced passively into the carrier as far as the carrier will allow it. “Passive” is the operative word; if the TF does not want to advance into the plastic carrier slowly and gently, the next smaller TF is used. No gutta-percha solvent is used for this first step; this initial insertion is done dry in the canal, optimally through the surgical operating microscope (SOM) (Global Surgical, St. Louis, MO, USA).

After the initial TF insertion, irrigant can be placed in the canal, if the clinician opts to use irrigant, optimally 2 percent chlorhexidine (CHX). As mentioned, when the first TF inserted will not advance passively through the plastic carrier any further, it is withdrawn, the CHX is added (as and if desired) and the remainder of the carrier removal is performed.

If the same TF taper will allow passive advancement, it can be reinserted; if it will not, the next smaller TF is inserted. It is essential that the clinician be cognizant of two things in the TF’s use for this purpose:

1) taking care not to strip the furcation of the root, in essence to not allow the TF to be pushed toward the furcation and/or preferentially remove dentin toward the furcation. 2) The length of the canal must be kept in mind to prevent the TF from being taken beyond the apical foramen. No RNT system should be used beyond the minor construction of the apical foramen and the TF is no expectation to this rule.

Usually, it will take approximately two TF instruments (or one) to machine a plastic carrier out of the canal. When the carrier has been machined through and the clinician reaches the apex, if a film is taken, usually, the clinician can see small fragments of the carrier at the lateral root walls of the canal.

Use of solvents (most often chloroform) and Hedström files to tug these fragments out of the canal is simple, predictable and can render the entire canal free of any substantial gutta-percha or remnants of the plastic carriers. After carrier removal, optimally, the clinician would gauge the minor constriction of the apical foramen (use a hand K file to determine the initial diameter of the MC) and then finalize the preparation to the master apical diameter.

While it is empirical, it is a common technique to gauge the apex and finalize the canal preparation to three sizes larger than the first file that bound at the MC. Inherent in this recommendation is the awareness that the MC is not being enlarged or transported and that the canal is being shaped up to the MC and not beyond. In essence, the MC that is present is left alone and not moved, enlarged or altered in any way.

A clinically relevant discussion of plastic carrier removal has been provided with the goal of informing general practitioners of common methods of carrier removal using new and innovative technology in the form of the Twisted File.

I welcome your feedback.

About the author

Dr Richard Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, WA, USA. Mounce offers intensive customized endodontic single-day training programs in his office for one to two doctors at a time. For more information, contact Dennis at +1 360 891 9111 or write RichardMounce@MounceEndo.com.

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