by Richard Mounce, DDS
For more on this topic, go to www.dentaleconomics.com and search using the following key words: Twisted File, larger apical diameters, gauging, RNT, Dr. Richard Mounce.
I recently received this e-mail from a reader that asks a common question of clinical relevance.
Q "I've been using the TF system (Twisted File, SybronEndo, Orange, Calif.) for a few weeks now. I really like it. There is one thing at which I would like to become better. The tip size of the TF files is .25. What if I want to open the apex up to .35 or .40? I have a reciprocating handpiece. If I take a .35 (02 taper) stainless steel hand file to TWL and use the TF .06 to the TWL, the apex should be open to a .35. I should then be able to take a .06 RealSeal (SybronEndo) cone and use the Tip Snip at a .35. It should go to length with good tug-back. Problem is, it's not working! Am I missing a step?"
A To address this question, the endodontic literature is very clear that the creation of larger diameters is consistent with the production of cleaner canals. Such larger apical diameters remove more dentin circumferentially in the apical third and allow greater volumes of irrigant to move apically. This clinician's desire to create a larger apical diameter is fundamentally a sound one. This said, the creation of larger tapers and apical diameters must be done in the context of removing dentin safely and efficiently, and in a manner that does not make strip perforation or subsequent vertical root fracture more likely due to overzealous dentin removal. The flexibility, fracture resistance, and cutting ability of TF makes possible .08 (and often .10) tapers to be taken safely into the apical third of all but the most complex root forms.
First, the most common technique for creating a larger apical diameter requires that the apex be gauged. Gauging requires that the clinician use a hand K file to determine the file size that resists displacement through the minor constriction (MC). In other words, if the hand K file does not allow movement beyond the TWL, the clinician has some rough approximation of the initial diameter of the MC.
If a No. 30 hand K file resists displacement through the MC, this tells the clinician that an appropriately enhanced apical diameter might be a .45 or .50, depending on the system that is being used to create the larger apical diameter. Specialists have generally used .02 or .04 tapered K3 (SybronEndo) or LightSpeed (Discus Dental, Culver City, Calif.) to create such larger apical diameters. Clinically, after creating the basic taper as described (to a .06, .08, or .10 TF as indicated), the clinician can gauge and use the K3 or LightSpeed from a 30, 35, 40 and 45, irrigating and recapitulating between each instrument. It is noteworthy that the creation of larger apical diameters, as described here, is a step back in method (not crown down), as the preparation is being made from the apex up.
Clinical opinions vary regarding the value of using reciprocation to the MC as a canal enlarging technique. It is not my favored method. Rotational endodontics with nickel titanium (RNT) has been globally accepted as the preferred method except where cost prohibits its universal adaptation.
One issue that prevents reciprocation from being preferred to RNT is the possible transportation that can occur using stainless steel hand files short or beyond the MC. Used short of the MC, such large stainless steel hand files (above a No. 15) become progressively stiffer and can ledge a canal with a multiplanar curvature. When used past the MC, they can transport the position of the MC, leading to the risk of iatrogenic events including extrusion of sealer, irrigants, and filling materials, as well as leaving the canal with less than optimal cleaning and shaping.
I use the M4 Safety (reciprocating) handpiece (SybronEndo) for early enlargement to create a glide path for the subsequent RNT files (in my hands these are TF). In other words, when the canal will accept a No. 6 or No. 8 hand K file to the MC, the M4 is used to reciprocate the small hand K file at the MC and will create a slightly enlarged canal. (A No. 6 utilized with an M4 can create a canal the size of a No. 8, a No. 8 can prepare a canal to the size of a No. 10 hand K file, and so on.) Such use of reciprocation is highly efficient, very safe, and makes creation of a glide path very predictable before using RNT. It is simple to fit a master cone in a canal that has been prepared to an enhanced apical diameter, regardless of how that master cone might be trimmed.
I welcome your feedback.
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.