endodontics feature

The Clinical Challenge inEndodontic Retreatment

by Richard E. Mounce, DDS & Gary Glassman, DDS, FRCD(C)

With the advent of implants, at a general dental and special-ist level, endodontics has been challenged to optimize results. Asan alternative to implants, to the greatest degree possible,endodontics must offer patients predictable retention of naturalteeth with failed root canal therapy and those with strategicvalue. Endodontic retreatment is predictable, economical, moreconvenient and far less invasive than implants. Literature-basedsuccess rates for endodontic treatment and retreatment are vir-tually identical to implant therapy.

It is our empirical bias that the clinical challenge in retreat-ment is not primarily the mechanical removal of posts, separatedfiles and repair of perforations, etc., but rather the treatmentplanning skills required to appreciate which teeth should beretreated and which should be extracted. In essence to 1.Appreciate why the treatment failed, 2. Assess the risk factorspresent, 3. Identify solutions that can repair existing iatrogenicevents, 4. Accomplish the above without creating new iatrogenicissues and 5. Give the patient a realistic expectation of pre-dictable clinical success. This challenges the clinician to identifyvertical fractures and non-restorable teeth. In addition, the cli-nician should optimally be able to identify teeth that even if notfractured now, are likely to fracture with time and/or for whichit is not possible to create a proper coronal or apical seal. It is ourbias that in the vast majority of cases it is possible to clearly iden-tify the existing risk factors and provide the patient with a real-istic expectation of long-term clinical success.

Non-surgical endodontic retreatment (NSER) should bethought of as a means to revise failed endodontic results andbring these teeth back into function. Doing so requires that theclinician revise the aspect of treatment that was deficient, repairexisting defects, and create a coronal and apical seal. NSER hasseveral key principles and requirements. These are:

1. It is imperative that the clinician uses a surgical operatingmicroscope (SOM) (Global Surgical, St. Louis, Missouri). Thevisual and tactile control available with its use cannot be dupli-cated by other means. In a practical manner, many of the chal-lenges that clinicians encounter are easily diagnosed andmanaged through the visual information provided by the SOM.For example, if a mid-root perforation has occurred, it is a sim-ple matter to know where the perforation has occurred and have

a much better concept of what retreatment strategies will berequired for its repair. Sources of clinical root canal failure arealmost always immediately evident once looking under theSOM at the particular clinical defect that has caused the failure.Given the relative lack of adaptation of the SOM by the generaldental community, approximately five percent versus the pene-tration rates in the endodontic specialist community (more than90 percent), has led to a entirely different perception of the clin-ical reality of root canal therapy, be that first time treatment orNSER. In short, while loupes are helpful, they are not a substi-tute for the visual and tactile acuity that is possible using theSOM. For example, in attempting to locate an MB2 canal in afailed upper first molar, using the SOM it is often possible to usea bur over the MB2 to uncover the canal in lieu of ultrasonicsand in the process both save time and create exactly the samedesired result as using ultrasonics. For those clinicians not usingthe SOM at higher powers, using a bur on the pulpal floor atany time would be strictly contraindicated.

2. Radiographically, it is essential to have at least two andoften three angles of a failed root canal prior to starting.Starting with one radiographic angle, even if it is digital is likelyto exclude important information that would otherwise be vis-ible. These angles should be straight on, from the mesial andfrom the distal. Radiographic evaluation should be comprehen-sive in that many visual clues to the source of failure can beobtained and will be easily missed if diligent attention to detailis not given. For example, radiolucency in the chamber isindicative of a lack of coronal seal. Small fragments of rotarynickel titanium (RNT) files might remain after cleansing andshaping procedures and the clinician might not appreciate thesefragments. A careful evaluation of the entire canal space canoften identity these file shards (which at times can be entirelysurrounded by obturation material and only recognized by theirincreased opacity relative to the material that surrounds them).Similarly, small fragments of hand K files, such as #6, #8 and#10 sizes can separate which can be almost barely visible, yetduring canal negotiation can frustrate the clinician when thecanal is not negotiable.

Appreciating these subtle radiographic findings will makeinterpretation of the clinical case much easier and lead to

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improved long-term success rather than misinterpreting theexisting signs that would otherwise guide the clinician.

3. In assessing the source of the failed root canal, it shouldbe appreciated that root canals fail for the following reasons:(On the causes of persistent apical periodontitis: a review NairPN Int Endod J 2006; 39:249-81.) “...six biological factors leadto asymptomatic radiolucencies persisting after root canal treat-ment. These are: (i) intraradicular infection persisting in thecomplex apical root canal system; (ii) extraradicular infection,generally in the form of periapical actinomycosis; (iii) extrudedroot canal filling or other exogenous materials that cause a for-eign body reaction; (iv) accumulation of endogenous cholesterolcrystals that irritate periapical tissues; (v) true cystic lesions, and(vi) scar tissue healing of the lesion.” For the vast majority offailed cases in clinical endodontic practice the source of failureis related to intradicular infection in the form of uncleaned andunfilled space and a lack of coronal seal that leads to persistentbacterial contamination of the root canal space (Figure 1). Withregard to expectations of retreatment, the practical matter intreatment becomes trying to sort out what has allowed the bac-teria to gain entry into the tooth or what defect in the treatmenthas led to the bacteria that remain. As a practical matter, forexample, a common finding is canals that have not been located,poor irrigation, canals that have not been prepared to the correcttaper, working length and/or master apical diameter (or workingwidth to use a different term to describe the master apical diam-eter) and a lack of coronal seal, even if the tooth has been oth-erwise well-treated.

As an important and directly related aside, it is a commonobservation that the source of much failure in endodontics is alack of diligent negotiation of canals with small hand files toachieve patency. In essence, at no time in the process did the cli-nician intentionally and with patience use #6, #8 and #10 handK files to discover the curvature, calcification and anatomicalvariations that were always present within the root. As a result,lacking the correct tactile knowledge of the root anatomy, poorly

matched RNT file sequences are used which often lead to iatro-genic outcomes.

The steps in retreatment are universal irrespective of the typeof failure and clinical challenges. These steps are:

1. Achievement of straight-line access. Many times thesource of endodontic failure can be determined easily once theaccess is made. Often the previous access was far too small forthe given canal anatomy. This is especially true in the pursuit ofthe MB2 canal of upper molar teeth. The MB root of upper firstmolars is the root that fails most commonly. The MB2 lies off astraight line between the MB1 and the palatal canal. Most oftenit has not been located because the correct lateral wall accessextension has not been made to uncover the MB2. The exactsequence of files to negotiate the MB2 is detailed below. It isimportant to realize that the exploration of the MB2 in retreat-ment and first time orthograde endodontic treatment is exactlythe same.

In NSER, retaining the crown is always of secondary impor-tance relative to achieving unrestricted canal access. The coronalrestoration can always be remade, but compromising the apicalcleansing and shaping to preserve the crown will compromise thelong-term result and is to be avoided at all costs. While not allcrowns must be removed, most do. Crown removal will exposemany fractures, unset restoratives, missed canals, caries and otherissues that if left undetected represent compromises to the clean-ing, shaping and obturation quality that would otherwise be pos-sible. Crowns are made to fit the existing occlusion, they areirrelevant to the apical location of canals. As a result, it is oftennecessary to expand access to well beyond what would appearnecessarily just looking at the occlusal surface of the tooth.

2. The cervical dentinal triangle must be removed. This is doneprior to attempting to remove gutta percha be this in the carrierbase or master cone based form. Using a RNT file rotated at higherspeeds up and away from the furcation to remove the CDT is ideal.This motion will minimize any chances of furcal perforation.

3. The orifice shape should be ideal before moving apically.It is contraindicated to attempt to remove gutta percha withouthaving an ideal visual and tactile command over the orifice andcanal below.

4. Gutta percha removal is passive, gentle and sequential. Asa first step, heat should be used to remove as much gutta perchaas possible using a downpack motion similar to the downpack ofobturation materials in the SystemB technique. An excellentsource of heat for this purpose is the Elements Obturation Unit*and its accompanying SystemB heat tips. The Fine or FineMedium heat tip can be used in the SystemB downpack motionto great effect. This action alone can often clear approximatelyhalf of the gutta percha from the canal.

Figure 1: Gross

coronal leakage

that led to the

failure of this

root canal.

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Subsequently, a RNT can be used to clear the remainingbulk of gutta percha. Insertion of the RNT is passive and gentleand done at enhanced speeds. In practice the RNT is rotated atbetween 900 and 1500 rpm. Insertion is highly controlled. TheRNT is never allowed to drop into the canal without advancingthe file by intention. When undue resistance is encountered theclinician should back the file out of the canal. If the cliniciankeeps an awareness of the expected true working length anddoes not keep pushing to move the RNT apically when it willnot advance easily, a host of iatrogenic issues can be avoided(canal transportation, file separation, perforation, etc.) In purelyclinical terms, if the clinician is advancing a RNT file at 18mminto a canal which gives resistance to file advancement and theexpected true working length is 21mm, the clinician should stopthe attempted advancement and switch to the third tier ofstrategies for gutta percha evacuation, the use of chloroform.

Chloroform is inserted one drop at a time to create a slurryin the canal and soften the apical remnants of the previous rootcanal filling. The hand K files used to create the slurry should beprecurved and their length and diameter matched to the partic-ular indication. Specifically, if the gutta percha that should bedissolved is at 18-21mm, the hand K file should be 21mm andprecurved to negotiate any canal curvatures present. For an aver-age canal, if patency can be achieved easily, the gutta percha soft-ens easily and a minimal number of successive single drops ofchloroform are needed. It has value to use paper points to soakup excessive gutta percha that will form in the resulting slurry.At all costs, the gutta percha slurry should be kept within thetooth and prevented from being extruded beyond the apical tis-sues. This can be accomplished by carefully monitoring howdeep the files are within the roots at all times and preventingexcessive amounts of chloroform (more than one drop at a time)being placed in the canal. Use of the SOM makes this easy tomonitor and accomplish.

In such canals, the clinicians would never place a RNT fileto the apical extent of the negotiation without assuring them-selves that they had both achieved apical patency and had a con-firmed true working length. In the clinical scenario describedhere, the clinician would monitor when they reach the estimatedworking length and attempt to feel for a tangible “pop” withhand K files. Once the “pop” is felt the clinician would thenplace an electronic apex locator onto the hand K file after dry-ing the canal and get an electronic apex locator length.Cleansing and shaping would proceed as per usual at this pointin the process.

5. We use the Twisted File* (TF) for its simplicity, cuttingefficiency, flexibility, fracture resistance and ability to shape thecanal to larger tapers with fewer files than ever before as well as

prepare larger apical diameters as desired (Figure 2). In the clin-ical scenario above once the true working length and patencywere established in the MB2 canal, a final canal taper of .08/25would be prepared. In roots with and without previous guttapercha obturation, the .08 can be most often inserted to the trueworking length in 3-4 insertions and is followed by the .06/30TF, .06/35 TF and the .04/40 if desired. In addition, it is note-worthy that TF is available in a .04/50 variety. The TF sequencedescribed here is the essence of simplicity and efficiency becausein addition to the larger tapered preparation possible with TF,the achievement of larger apical diameters occurs in a singleinsertion of the .06/30 TF, .06/35 TF and higher as needed.

6. After preparation to the enlarged master apical diameterand taper with TF, the canal can be easily obturated with a

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Figure 2: The Twisted

File (SybronEndo, Orange,

California)

Figure 3: RealSeal Bonded

Obturation material shown

in vitro and in vivo to

a statistically significant

degree to reduce coronal

leakage relative to gutta

percha. (SybronEndo)

Figure 4: The M4 Safety

Handpiece (SybronEndo)

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bonded technique such as RealSeal* mastercones with SystemB or the RealSeal Onebonded obturators.* In more than a theoreti-cal way, a bonded obturation material canhelp resist the coronal leakage. Gutta perchahas no ability to prevent the migration of bac-teria, does not bond to sealer, does not bondto dentin and requires the use of a coronalfilling to protect it against bacterial contami-nation. RealSeal has been shown in a numberof in vitro and in vivo studies to resist coronalleakage in a statistically significant mannerrelative to gutta percha, a definite indicator ofimproved long term success relative to casescompleted with a poor coronal seal obturatedwith gutta percha (Figure 3, page 58).

7. In the clinical case example above, toaddress the MB2 canal, once dentin isremoved over the MB2, its initial manage-ment is critical relative to accomplishingthe goals of cleaning and shaping of thisdelicate space. Specifically, it is imperative in the MB2 tobegin the exploration of the canal with a precurved #6 handK file inserted with the most gentle touch possible. At allcosts the clinician must avoid forcing debris apically or com-pacting pulp tissue into the apical regions of the canal. If thehand K file resists advancement, it should be removed andthe canal irrigated and a new #6 hand K file inserted. If thecanal will allow insertion, it should be taken apically. For anaverage MB2 it will take anywhere between one to threepacks of #6 hand K files to gain apical patency. Once the #6hand K file reaches the true working length, a #8 hand file isinserted and the canal enlarged. This sequence of files isrepeated until the canal is open and negotiable to the diame-ter of a #15 hand K file. This enlargement is much simplerand more efficient with the reciprocating M4 Safety

Handpiece.* While a comprehensive discussion of the M4 isoutside the scope of this paper, once the hand K file reachesthe apex, the M4 is placed onto the file under the rubberdam. With M4 reciprocation, an MB2 can be enlarged froma #6-15 hand K file diameter in approximately two minutesor less. Figure 4-6.

Clinical decisions that should be made in treatment plan-ning and revision of failed root canals are presented above.Emphasis on restorability and the source of failure is indicated.Risk assessment in retreatment is essential. Prior to access, a setof clinical solutions is decided upon to deal with the risk factorspresent. Achieving patency, removing obturation materials pas-sively, preparing the correct final taper and master apical diam-eter are all key components of long term retreatment success. Wewelcome your feedback. n

Authors’ Bios

Dr. Richard E. Mounce is the author of the non-fiction book Dead Stuck, “one man’s stories of adventure, parenting, and marriage told without heap-ing platitudes of political correctness.” Pacific Sky Publishing. DeadStuck.com. Dr. Mounce lectures globally and is widely published. He is in privatepractice in Endodontics in Vancouver, WA, USA.

Dr. Gary Glassman graduated from the University of Toronto, Faculty of Dentistry in 1984 and was awarded the James B. Willmott Scholarship, theMosby Scholarship and the George Hare Endodontic Scholarship. A graduate of the Endodontology Program at Temple University in 1987, he receivedthe Louis I. Grossman Study Club Award for academic and clinical proficiency in Endodontics. The author of numerous publications, Dr. Glassman lec-tures globally on endodontics and is on staff at the University of Toronto, Faculty of Dentistry in the graduate department of endodontics. Gary is afellow and endodontic examiner for the Royal College of Dentists of Canada, and the endodontic editor for Oral Health dental journal. He maintainsa private practice, Endodontic Specialists in Toronto, Ontario, Canada. He can be reached through his Web site www.rootcanals.ca.

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Figures 5-6A-B: Failed cases retreated with RealSeal and the Twisted File (SybronEndo).

*SybronEndo, Orange, California

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