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Written by Richard Mounce, DDS Saturday, 01 March 2008 00:00
“I have a patient who had RCT done where the gutta-percha is about 3 to 4 mm overextended. He needs a crown, and I might need to put a post in the root. The tooth is completely asymptomatic, and the x-ray doesn’t show radiolucency at the apex. I am thinking that I should retreat the root canal if I am doing the crown...what are the chances of getting the overextended gutta-percha to come out?”
Recently, I received this question from a good friend (who is a general dentist in a remote foreign location where referral to a specialist is not an option) asking a simple, yet clinically relevant endodontic question. The question has application in treatment planning for both the general dentist who might never retreat failed cases and those who occasionally perform the service. Treatment planning in endodontics and assessing risk are vitally important…in retreatment, doubly so, as there is far less margin for error. The cost and time required to fabricate new restorations demand that the tooth is restorable and retreatment is predictable.
We are taking for granted that there are only 2 untoward clinical findings (defined below) from the comprehensive examination my friend made of the situation. It is important to recall that radiographic assessment of the previous treatment is but one facet of a comprehensive examination, and I was not provided with a radiograph to evaluate along with this question. A detailed discussion of the radiographic interpretation of previous endodontic therapy is beyond the scope of this paper, but it is important to mention briefly that the clinician is primarily looking for 3 things in such a radiographic evaluation:
- That the technical quality be ideal (primarily that narrowing cross-sectional diameters have been prepared and obturated in 3 dimensions amongst other considerations).
- That the coronal seal be intact and that the previous obturation material has not been allowed to come in contact with saliva and its attendant bacteria, ie, there is no radiographic evidence of coronal microleakage.
- The presence of pathology.
In the most general terms, as deficiencies are found in any of these 3 aforementioned parameters, the tooth should be retreated.
Digital radiography is a significant advance for dental imaging, and it is especially useful in endodontics. Three digital radiographs from varying angles (mesial, distal, and buccal) make evaluation of previous endodontic therapy as simple and efficient as possible (DEXIS Digital Radiography [DEXIS]). Multiple radiographic angles allow areas of concern to be visualized that may not appear in one radiographic view.
The 2 untoward findings reported in the history that has been given are the overextension of gutta-percha and the need for a new crown. Of these 2 findings, it is the second that is more clinically significant for reasons that will be addressed.
Several additional underlying questions are folded into my friend’s inquiry. The answers to these questions are multifaceted and interrelated. The underlying questions are as follows:
1. Does the tooth need retreatment?
2. Can the overextension be removed predictably?
3. If it cannot be removed, would leaving it pose any foreseeable problems?
DOES THE TOOTH NEED RETREATMENT?
Figures 1a and 1b. Lack of coronal seal; saliva has a direct route to the obturation material (a). Retreatment of the case (b).
Figure 2. The CORONAflex.
In short, yes. Since the crown needs to be replaced, the safest plan is to retreat the root canal. Long-term success is correlated with excellent coronal seal. The converse is true. Does every root canal have to be retreated if the tooth needs a new crown? While there can be exceptions (and it is difficult to generalize), a significant percentage of the time, after a comprehensive examination, retreatment is in the best interest of the patient, most often for reasons related to coronal microleakage. It is my empirical experience in 16 years of full-time private endodontic practice that virtually every crown accessed for retreatment has, to one extent or another, shown clear evidence of coronal microleakage, especially under the surgical operating microscope (SOM) (Global Surgical; Figures 1a and 1b).
The belief that because there are no symptoms or obvious radiographic pathology with frank or suspected coronal leakage, the tooth can have a new crown placed without retreatment, is simplistic and clinically incorrect. Such a strategy seals bacteria into the root canal system and is a pillar of subsequent failure. The endodontic literature is absolutely clear that coronal leakage is one of the primary reasons for endodontic failure. If saliva has reached the gutta-percha, the root canal needs to be retreated. In one of many studies to illustrate the significance of coronal microleakage, Ray and Trope, et al (1995) found that the placement of an excellent restoration over a less than optimal root canal procedure provided long-term success of approximately 70%, whereas an excellent root canal and a poor restoration provided only 44% success. In short, placing new restorations over contaminated root canal systems is contraindicated.
We do not know if the crown is off the tooth in the clinical history given. If it were not, the CORONAflex (KaVo) is an excellent tool to make crown removal simple and efficient (Figure 2).
To achieve coronal seal, I use PermaFlo applied with a Skini syringe and various tips (all from Ultradent) under the SOM. The placement of PermaFlo is very precise, especially under the SOM, and with use, of course, of the rubber dam. PermaFlo can be placed into the coronal 2 to 3 mm of the canal up to the chamber floor (if my referring doctors want to place the buildup), or alternatively I can bond the entire chamber. In order to bond from the crown to the apex, I join the coronal seal achieved with PermaFlo to a canal bonded with RealSeal obturation material (Sybron-Endo). For more information on bonded obturation, the reader is directed to sybronendo.com or ResilonResearch.com (Resilon [Pentron]).
Figure 3. PermaFlo.
Figure 4. RealSeal.
Relative to gutta-percha, which has no inherent ability to bond to dentin or sealer and no inherent resistance to coronal microleakage, Real-Seal, in a statistically significant manner, has been shown in a number of studies to reduce coronal microleakage relative to gutta-percha. Because of chemical similarity, the core obturation material is bonded to the sealer, which is bonded to the resin impregnated into the tubules. (Figures 3 and 4).
THE SIGNIFICANCE OF EXTRUSION OF SEALER AND OBTURATION MATERIAL
With regard to the extrusion and its possible removal, if a canal is obturated in 3 dimensions from the orifice to the minor constriction (MC), extrusion of sealer or obturation material from the MC is a surplus, and unless there are significant mitigating circumstances, all things being equal, it will not cause harm. Gutta-percha and RealSeal are well tolerated by the body if extruded; this biocompatibility is one of the reasons that both materials are used for endodontic root filling. All common root canal sealers are initially inflammatory to one degree or another in a time dependent manner. Ultimately, most sealer puffs will resorb, irrespective of the sealer used. The presence of a sealer puff is a sign that the MC of the apical foramen was kept open (patent) through-out the procedure. Clinicians who believe in a philosophy of apical patency desire to see a small puff of sealer as a sign that the canal has been kept patent throughout instrumentation procedures and that the entire canal is obturated. In essence, the ideal shape of the final prepared canal with its narrowing cross-sectional diameters would tip off the clinician that the sealer puff was a byproduct of an excellent cone fit and warm obturation.
Assuming that the coronal seal (crown and buildup) shows no sign of leakage or caries; the root canal has been well obturated in 3 dimensions with narrowing cross-sectional diameters from the orifice to the MC, ie, an ideal preparation and obturation; and the absence of any objective or subjective findings that might alert the clinician to the presence of pathology, then the extrusion of sealer or possibly gutta-percha can be watched.
Alternatively, if the canal shows an obvious lack of filling material or sealer and there is coronal leakage, recommendations change and retreatment is indicated.
IS IT POSSIBLE TO GET THE OVEREXTENDED GUTTA-PERCHA BACK THROUGH THE TOOTH INTACT?
With some exceptions, endodontic retreatment is a specialist procedure. This said, knowing how gutta-percha is ideally removed has value for all clinicians. Removal of gutta-percha correctly can minimize the extrusion of a gutta-percha slurry that can occur with improper solvent use (generally chloroform). Proper gutta-percha removal would certainly give this clinical case the best chance for retrieval of the overextended fragment.
To remove gutta-percha, heat and rotary Ni-Ti (RNT) files are favored over chemical means, especially in the coronal and middle thirds of roots. In the apical third, it is sometimes possible to negotiate canals without using gutta-percha solvents, and this will be relevant in answering the clinical questions asked.
In retreatment, 2 cases are relatively common: one in which the canal has been well-prepared and obturated (whose failure usually has its genesis in coronal microleakage) and one in which the canal has been prepared and obturated reasonably in the coronal and middle third but is underprepared or not touched in the apical third. This latter case usually presents itself as a “Coke bottle shape” at the junction of the middle and the apical third. Endodontists often call this phenomenon a lack of “deep body shape.”
Figure 5. Elements Obturation Unit.
Gutta-percha removal in both of these case types is facilitated with the SystemB heat source from a device like the Elements Obturation Unit (SybronEndo). Used in the manner of a SystemB down-pack, segments of gutta-percha can be removed in 3- to 4-mm increments, moving down the canal through the widest portion of the canal preparation. Clinically, a heat tip (the fine medium heat tip is the most universally applicable) is driven through the gutta-percha in approximately 3 seconds but not to its binding point. After pausing a few seconds to allow the tip to cool, the tip is reheated for one second, the clinician pauses for another second, and the gutta-percha to the level of heat tip insertion usually will come out on the end of the heat tip. In this manner, clinicians remove gutta-percha cleanly as they make their way down the canal (Figure 5).
Figure 6. The K3 rotary Ni-Ti system.
Alternatively, the clinician can use heat, as described above, with RNT instrumentation. I use the K3 RNT Shapers (SybronEndo) between 900 to 1,500 rpm with the torque control off for gutta-percha removal. The Shapers come in .12, .10, and .08 tapers, and a fixed No. 25 tip size. The Shapers are used in this application to remove gutta-percha, not to enlarge the canal. Canal enlargement and preparation refinement occur later once the gutta-percha has been removed entirely. The emphasis in removal is on a passive and gentle insertion without forcing the K3 RNT file to any predetermined length. It is possible to create a perforation in a thin furca if a file is inserted with excessive force. The Shapers should remain centered in the canal and be inserted apically only to the extent that they can be placed without undue force. In essence, the Shapers should meet relatively minimal resistance. Upon withdrawal, they are brushed gently against the wall with the greatest bulk of root dentin and away from the thinnest furcal wall. As detailed above, Shapers can remove gutta-percha far more predictably and safely than Gates Glidden drills or Peezo reamers (Figure 6).
In this clinical case, using either heat or mechanical means as described to remove the bulk of the gutta-percha would then be followed initially by gentle exploration with small hand K files Nos. 6 to 10. If the canal is patent with a small hand K-file, a small Hedstrom file might then be placed alongside the extruded master cone. With a little bit of luck, the Hedstrom file should engage the surplus of gutta-percha and pull it up though the canal. A SOM is invaluable in this type of effort, and up to this point no solvents should be used to dissolve the gutta-percha. While it is possible to remove apical surpluses of gutta-percha in the manner described, it is not entirely predictable, even in the most skilled hands.
In the attempted delivery of the overextended gutta-percha, the MC of the apical foramen must be left at its original position and size. This core principle in instrumentation overrides any advantage of removing the over-extended gutta-percha. Forcing Hedstrom files through the apex (or any type of files for that matter) is the harbinger of iatrogenic events (a ripped or torn MC, apical bleeding, extrusion of irrigants and solvents, obturation challenges, etc). If the Hedstrom will easily be accepted (never forced) to or very slightly beyond the MC (1 to 2 mm), it should be allowed to pass to engage the gutta-percha master cone. An apex locator should be able to tell the clinician the exact position of the MC in a patent canal.
Alternatively, it is possible, if the given canal had a significant void in obturation, that neither heat nor RNT files would be needed to deliver the overextension. If such a void existed and the overextended portion of the filling included the original master cone, a Hedstrom file placed into the void alongside the master cone might (and often will) be enough to engage it and deliver it coronally. Again, a SOM is invaluable in any of these various treatment options.
Finally, the clinician should bear in mind that copious irrigation with a solution like 2% chlorhexidine, delivered from a close-ended side-venting needle in the apical third in this clinical situation, might allow the fragment of gutta-percha to be floated coronally if it is loose enough in the canal.
IF THE FRAGMENT HAS TO BE LEFT, WILL IT CAUSE ANY HARM?
If the fragment cannot be removed in the manner described, it can be left and the case completed. The chance of failure from a single 3-mm piece of gutta-percha is relatively remote if the other aspects of the retreatment are carried out diligently, no iatrogenic events occur, and the biologic objectives of endodontic therapy are achieved.
Figures 7a and 7b. Clinical case that was re-treated where the apical fragment of gutta-percha could not be retrieved. In this clinical case, the overextended segment was lost into the sinus and was not found on preliminary scans to facilitate its removal.
A clinical case has been discussed in a clinically relevant manner that stresses the importance of early and effective coronal seal, the clinical implications of extruded gutta-percha, and safe techniques for gutta-percha removal (Figures 7a and 7b).
Disclosure: Dr. Mounce consults for SybronEndo and is on their advisory council. He receives honorarium for some aspects of this position, lecturing for example.
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