by Richard Mounce, DDS
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I recently received this e-mail from a reader: “Rich, thanks so much for your column. I start with Nos. 8, 10, and 15 K files with RC Prep and NaOCl to the TWL (apex locator). I start with the TF (Twisted Files*).08, then .06, then the .04 at around 600 rpm, and what seems to occur is the .08 grabs the canal as soon as it hits the wall and seems like it will get bound. Should I start with the .10 and at a higher speed?
Finally, I hear that if you clean, shape, and disinfect adequately, you can fill the canals with dog doo and have success. I question the value of RealSeal. Does it really bond to the canals, and if so, how can it be removed easily? If I bond composite to dentin or root it is a bear to remove with a drill, so I don't think this really bonds well. Besides, if you seal the canals with a plug of etched and primed composite, anything that gets past that will surely leak past the RealSeal. Is this right or am I missing the point?”
Answer: First, access should be straight line and the cervical dentinal triangle should be removed. Hand K file (HKF) or rotary nickel titanium (RNT) insertion without first achieving this access is problematic due to what will be inevitable challenges in the early negotiation of canals in the coronal third, especially in calcified canals or those which meet the pulpal floor at an acute angle.
Second, vital teeth require NaOCl, but in nonvital teeth a case could be made to use 2.0% chlorhexidine as an irrigant in place of NaOCl. Also in nonvital cases, it could be argued that RC Prep is not essential. The primary function of RC Prep is to hold pulpal material in suspension after access and keep it from being propelled down the canal until it is removed.
Third, orifice shaping should be ideal in the coronal third after the clinician is certain that the coronal third is patent. Placing hand files directly into the canal intending to get to the apex without these steps (straight line access, cervical dentinal triangle removal, and coronal third shaping) risks ledging, blockage, and iatrogenic events of all types. In other words, negotiation and early enlargement of the middle and apical third should take place ideally after the first three steps listed above are achieved.
Fourth, the Twisted File* is used crown down for the bulk shaping of the canal. Using TF, large canals such as the palatal canal of an upper molar generally have a final taper of .10. More intermediate canals, such as the mesial root of a lower molar, generally have a final taper of .08. Complex canals such as a highly curved or calcified canal generally have a final taper of .06. I use the Twisted File at 900 rpm. That said, 600 rpm is also an adequate speed. Rpm is a matter of personal preference.
RNTs that cut efficiently will feel to the clinician as though they are pulling him or her into the canal. The problem is not with the RNT, but inserting the RNT properly is a skill that should be mastered by the clinician. In essence, the clinician must “boss” the file. I do not experience the same sensation as the writer of the question because I keep a firm but flexible grip on the handpiece to keep it from advancing into the canal where I don't want it to go.
A two to three second continuous and controlled insertion, after which the canal is irrigated and recapitulated, can go far toward avoiding blockage. Once the RNT file has been advanced to the desired level in the canal, the next RNT file in the sequence is used until the desired taper and tip size reaches the apex. The RNT is not pumped up and down in the canal.
Regarding the bonding question, the evidence for bonding in the endodontic literature is clear despite skeptics. As shown in in vitro and in vivo studies, RealSeal diminishes coronal leakage to a statistically significant degree relative to gutta percha when leakage is measured across the totality of the canal. In clinical case studies, it has been shown to be at least as effective as gutta percha. I have used RealSeal on every case except one since January 2004. I would never return to gutta percha, a material with known defects that include proven clinical degradation and an inability to bond to sealer or dentin.
Gutta percha needs a coronal seal for it to provide predictable clinical success when used as an endodontic obturation material. RealSeal bonds to dentin and it has, as one component of its chemistry, bioactive glass, a substance that promotes remineralization if the RealSeal were to be theoretically degraded. RealSeal is re-treated with the same techniques as gutta percha. I welcome your feedback.
*SybronEndo, Orange, Calif.
Dr. Richard Mounce offers intensive customized endodontic single-day training programs 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.