I 15

clinical _ canal patency I

roots2_2007

_If there is a common denominator in the chal-lenge presented by endodontic retreatment, it is theachievement of canal patency. More than any othersingle variable, this vexing and problematic issue can,along with the primary need for a coronal seal, deter-mine long-term prognosis. The loss of canal patencycan arise from separated files, canal blockage, canaltransportation of all types, silver cones, carriers used incarrier based obturation, paste fillings that might bechallenging to dissolve, amongst other possiblesources. If patency can be achieved again during re-treatment procedures along with the safe, efficient andeffective removal of the previous endodontic obtura-tion material, the potential for healing is enhanced. Thisarticle was written to discuss methods to allow the as-tute clinician to achieve and maintain patency at all lev-els in the canal in non-surgical retreatment due toblockages by canal debris. A brief description of thecrossover applications for using these methods to aidthe removal of metallic obstructions will also be pro-vided (Figs. 1a, b).

Creating a challenge in planning for retreatment isthe fact that most often a clinician may not know pre-

operatively that the canal is blocked. Many blocked andledged canals are not observable on radiographs. Somevery small metallic obstructions such as the separatedtip of a #6 or #8 hand file may also not be radiograph-ically visible. Lack of patency does not occur in a vac-uum and may only be one of many issues that requireresolution during retreatment procedures. Achievingand maintaining patency of the canal should not occurat the risk of exacerbating and/or creating other andgreater problems. For example, bypassing a blockage ofany sort, especially separated files should not requirethat excessive amounts of tooth structure be removedto make access to the blockage and predispose thetooth to fracture. Sound clinical judgment is called for.

Whether it is in first time treatment or endodonticretreatment, there are common strategies that providepatency and its attendant benefits (cleaner canals andfewer iatrogenic events). Blocked canals are the har-binger of separated files, canal transportations of alltypes, perforations, etc, all of which are deviations fromideal canal preparation. Strategies and materials toprevent blockage become even more vital during re-treatment.

Figs. 1a–b_ Badly ledged and

blocked canal, after retreatment.

Regaining canal patencyin endodontic retreatment:finding the pathAuthor_ Richard Mounce, U.S.A.

Fig. 1a Fig. 1b

16 I

I clinical _ canal patency

_These strategies are:

_Using an enhancedsource of lighting andmagnification, optimallya surgical operating mi-croscope (SOM) such asthe Global SOM (GlobalSurgical, St. Louis, MO,U.S.A.) (Fig. 2).

_Copious irrigation at all stages inthe procedure, ideally after every file

insertion, be they hand or rotary nickeltitanium (RNT) files.

_Use of a viscous EDTA gel like File-Eze(Ultradent, South Jordan, UT, U.S.A.)

to hold the pulp in suspension espe-cially in a vital tooth so that pulp tis-

sue can be irrigated in a coronal direc-tion instead of being pushed apically and be-come the nidus of a future blocked canal

(Fig. 3).

_ Endodontic therapy should always be carried outunder a rubber dam. It is the ethical and legal stan-dard of care in the United States.

_ Anesthesia must be profound. Informed consentmust be comprehensive. Both of these can onlyhelp relax the patient so as to create the most com-pliant and comfortable patient possible. A full andcomprehensive pre operative assessment of therisk factors present in the clinical case should al-ways be undertaken with an eye toward determin-ing if referral is indicated. Strategies for avoidanceof iatrogenic events should be determined beforestarting.

_ Access should be straight line in that the straight-away coronal portion of the canal can be reachedwith hand and RNT files without deflection againsteither a canal wall or the cervical dentinal triangle.

_ Digital radiography (such as DEXIS, DEXIS digitalradiography, Alpharetta, GA, U.S.A.) for pre-opera-tive evaluation is ideal. Multiple angles of radi-ograph can and should be taken preoperatively tofully map the canal system that will later be nego-tiated.

With these materials and strategies in place guid-ing the course of treatment, the

chances for lost patency areminimized and fu-ture negotiationmade more likely.

_A lack of apical patency is caused inseveral ways:

_ Canal debris is pushed apically. Blockage can oc-cur anywhere, but it commonly happens eithermid root in the presence of an abrupt mid root cur-vature or apically in fine canal anatomy that hasbeen occluded with such debris.

_ This debris is most often either pulp and dentinchips but metal obstructions of all types can oc-clude a canal and create a blockage. Most oftenthese metal obstructions are separated files, silvercones, Gates Glidden drill heads and post frag-ments. Plastic carriers used in warm carrier basedobturation can also become wedged with fric-tional retention and present a significant chal-lenge in removal.

_ Some pastes and cements used as obturation ma-terials can be very difficult to dissolve or remove.In the worst-case scenario, there are materialsthat cannot be dissolved with any known solventsand which must be removed with ultrasonics ifstraight-line access to the material can be at-tained. While management of these pastes is be-yond the scope of this article, it may be needed toforce a file beyond the paste if possible withoutcreating a ledge, a process which in some cases ispossible and in others not. In any case, a paste,which cannot be dissolved, is a very clinically chal-lenging event and almost always indication for re-ferral.

_ Transportation of the canal path where a ledge orperforation has been created such that the canalpath cannot be traversed easily, if at all.

_Considerations before beginning retreatment and attempts to regainapical patency:

_ The risk of perforation should always be consid-ered. If the canals are likely to be perforated dur-ing removal of the coronal filling material becausethe existing canal preparation may already beoversized (and leave a canal wall thin), at high riskof vertical fracture, extraction may be the betteroption.

_ Risk versus benefit of extraction relative to the op-tions, most notably bridges and implants. The bestimplant is the natural tooth. When conditionsconspire to make the restorability and long-termprognosis guarded to poor relative to the optionsavailable, extraction should be considered. The cli-nicians should always ask themselves, is the toothrestorable? Is the tooth strategically valuable? Do

Fig. 2_ The Global Surgical Operating

Microscope (Global Surgical,

St. Louis, MO, U.S.A.).

Fig. 3_ File-Eze (Ultradent, South

Jordan, UT, U.S.A.).

roots2_2007

I 17

clinical _ canal patency I

roots2_2007

the risks outweigh the benefit to argue for re-treatment versus the options? These questions arethe cornerstone for a decision to begin retreat-ment procedures.

_ Are there 4 walls to the access preparation so as tohold the irrigants and gutta-percha solvents in thechamber? The benefits of creating these 4 wallsare obvious if they are not already present. Usingcomposite to rebuild the walls of the tooth is a pre-cursor to having a full command over the toothduring all stages of the retreatment in addition tousing a rubber dam and SOM visualization.

_Steps to regain apical patency:

1) After straight-line access is achieved, removal of thecoronal obturation material must be carried outslowly and methodically. Ideally gutta-percha(other than on carrier based products) should be re-moved with heat or a mechanical means and notchemicals, especially if the coronal orifice is openedto approximately a .08 taper or greater. Visualizationand control are enhanced if the chamber is left dryduring coronal removal relative to the alternatives.A heat source such as the SystemB or theElements Obturation unit (SybronEndo, Orange, CA,U.S.A.) is ideal for this purpose. The EOU has theadded advantage of being able to extrude fillingmaterial such as gutta percha or RealSeal bondedobturation material (SybronEndo, Orange, CA,U.S.A.) as well provide the heat source for GP re-moval. Alternatively, an orifice opener can be usedwith the caveat that removal is passive, gentle anddone with control of the insertion forces and speed.Rotations at higher RPM’s such as 1.000-1.500 RPMare most efficient. Great care must be taken to avoidperforation through the thinnest wall present,which is usually the furcal side of a molar root.

2) After there is no additional benefit to removing ob-turation material mechanically, passively and pro-gressively, a cycle of solvent placement and explo-ration with the hand files is undertaken so as tomove the hand file apically to the estimated work-ing length. After the bulk of the gutta-percha is re-moved from the coronal third, with the above

means, 2–3 drops of a gutta-percha and RealSealsolvent such as chloroform can be placed over theorifice. With a small hand K file, usually a #10 or#15, the file can be introduced into the canal tohelp disperse the solvent and dissolve the obtura-tion material passively.

All of the gutta-percha or RealSeal is removedfrom the canal before an attempt is made to bypassthe obstruction to regain patency. Making sure thatall obturation material is removed allows the clinicianto only have one obstacle (the blockage or ledge) tothe apical terminus and allow a more focused controlover the attempted bypass. Obturation material leftin the canal while the trying to regain patency is likelyto cause debris to be further propelled apically. It maybe necessary to apply chloroform and then wick theslurry up with paper points until the entire canal is vis-ibly cleared of gutta-percha. Then and only thenshould negotiation be attempted.

Once the clinician has removed all of the obtura-tion material that is possible with the above meansand an obstructed canal is discovered or confirmed,the clinician is ready to regain patency. Canalanatomy is three dimensional in nature with multi-planar curvature, i.e. buccal to lingual curvature andmesial to distal. The clinical application to this fact isthat simply pushing on a hand file in the same orien-tation repeatedly or with force can oftentimes ac-centuate an existing ledge and/or make the givenblockage worse. RNT files are never used as pathfind-ers or as “ice breakers” in the sense that the RNT is usedto “power through” the blockage. Use of the file in thismanner is the precursor of a rapid separation espe-cially if the tip should become locked and the majordiameter of the file still has the torque to rotate in thecanal.

In tangible practice, these hand K files are alwayspre curved with an instrument like an EndoBender pli-ers (SybronEndo, Orange, CA, U.S.A.). For tactile con-trol, a 21 mm #10 hand file can be snipped with a pairof scissors approximately 2-3 mm above the tip andcreate a smaller and more rigid instrument that ishelpful in pushing through a blockage of debris. Simi-larly a #6 or 8 can also be snipped as well to give the

Fig. 4_ The EndoBender pliers

(SybronEndo, Orange, CA, U.S.A.).

Fig. 5_ Pre curving of a hand file with

the EndoBender pliers.

Fig. 4 Fig. 5

18 I

I clinical _ canal patency

needed diameter and stiffness of the hand file. Suchmodified hand files are invaluable in creating an idealexplorer and pathfinder to allow one the greatest bal-ance between safety and efficiency in passing an ob-struction. Safety, in that the ledge will not be accen-tuated, efficiency in that the blockage can be removedas easily as possible (Figs. 4–6).

3) When encountered, the tactile feel of the obstruc-tion can tell the clinician how best to proceed andcan also allow from the very start for the clinicianto know what the expected chances are for achiev-ing patency. If the hand file reaches a very definitestop and no advance is possible, the chance for a“breakthrough” is diminished. Many times, thistype of blockade means that either a ledge hasbeen created previously or the canal, if it has notbeen transported, is completely occluded.

Alternatively if the obstruction encountered issomewhat soft there is a far better chance of achiev-ing patency. In either event, sodium hypochloriteshould be reapplied copiously after every file inser-tion. Refreshing the surface area of the obstructionwith a tissue dissolving substance along with the

mechanical forces applied can improve the chancesfor progression.

4) Once the blockage is encountered, the curvedhand file is inserted multiple ways within the canalso as to attempt to find or create path through theblockage. Time, patience and ingenuity are re-quired. For example if a #15 hand file will not tra-verse the blockage, a #10 should be attempted andthen a #8 followed by a #6. If the 21 mm variety ofeach of these files will not traverse the blockage,the snipping described above can be used. It is alsopossible to use carbon steel hand files such as thePathfinder CS series, (SybronEndo, Orange, CA,U.S.A.). Carbon steel is harder than stainless steeland this inflexibility is helpful to provide more fo-cused pressure against the blockage.

5) In addition to the above, it may also be possible touse the M4 reciprocating handpiece (SybronEndo,Orange, CA, U.S.A.) with a small hand file (ideallynot modified by snipping). The M4 attachment fitsonto an E-type handpiece attachment. This is nota method that should be employed with a sepa-rated file or metal fragment or if the blockage iscomplete, irrespective of its source. If there is asmall amount of “give” in the blockage, the handfile can be placed against the blockage (at a re-duced setting between 200–300 RPM). If theblockage can be “pierced” and the file attached tothe M4 will advance, it can be taken apically veryslowly. Caution is advised with this concept aseven though reciprocation is very safe, thismethod carries with it an increased risk of fractureof the file tip, especially if the clinician keeps push-ing when the file tip will not advance passively. Ifadvancement is possible, the tactile control of thefile should be short 1–2 mm amplitude apical and

Fig. 6_ Modified hand K files. The file

is snipped at its end in order to give

greater tactile control and stiffness.

Fig. 7_ File sponge, note the number

of hand files at the left of the sponge

ready to be used in gaining patency.

roots2_2007

Fig. 7

Fig. 6

I 19

clinical _ canal patency I

roots2_2007

coronal movement. Ideally, each apical movementwill allow the file to progress further apically. If ad-vancement is not possible, the other methods areemployed and this approached is stopped imme-diately.

In a badly ledged canal, numerous packs of hand Kfiles may be needed. It is not uncommon in a difficultblockage to require 6–10 packs of files. It must be re-membered that new files are sharper and the most ef-ficient. Saving money by using dull files is a falseeconomy as the costs associated with not achievingpatency far greater than the alternatives. (Fig. 7)

In clinical practice, not all obstructions and ledgescan obviously be removed or bypassed. It is a validquestion when one can and should stop attemptingto gain patency. If all the aforementioned strategieshave been employed repeatedly and full and unob-structed access has been created down to the level ofthe blockage, the clinician must weigh the chancesfor a larger iatrogenic event relative to the benefitsof achieving patency. Suffice it to say that when therisks of further attempts will risk the integrity of thetooth for whatever reason, consideration should begiven to completing treatment to the level of theblockage. If healing does not occur, apical surgery isone option going forward.

The above techniques and skills have cross appli-cation with removal and bypassing of several otherobstructions, such as separated files and metallicfragments of all types. For example if a separated RNTfragment is present, it is possible for a tapered RNTfragment to still only occupy a limited volume of thecanal lumen and as such create an opportunity forsmaller hand K files to bypass the fragment. It is cer-tainly possible that a #6 or 8 might be able to traversethe canal alongside the fragment. If the #6 or 8 willeasily and passively bypass the fragment, it is not im-mediately removed from the canal but rather movedvertically with 1–2 mm amplitude until it movesfreely in the canal. Then the next larger hand file isused to bypass the RNT fragment and so on until thecanal is shaped ideally. A RNT file is never insertedinto a canal that already has a RNT fragment as a sec-

ond separation is imminent. Once a RNT separationhas occurred, the canal must be treated by hand forits duration. As much as possible care should be takenso as to assure that enlargement does not dislodgethe RNT fragment into the canal lumen and createblockage. If the fragment is loose in the canal and re-moval is indicated, a Hedstrom file can be used to ob-tain a purchase on the fragment and attempt coro-nal movement and removal of the file. While not en-tirely predictable, this can be effective in some cases(Figs. 8a–c).

In summary, achieving and maintaining apicalpatency in endodontic retreatment is a higher orderskill that is central to the clinician’s access to regionsof the canal that have not been accessed previously.Materials and methods have been described whichcan help the clinician achieve this goal. Amongstother strategies, pre curved hand K files modified bysnipping their tips inserted passively can often allowclinicians to bypass obstructions that otherwisemight not be addressed._

Dr Mounce has no commercial interest in any of theproducts mentioned in this article.

Fig. 8a–c_ Removal of a separated

instrument through bypassing the

canal first with hand K files and its

ultimate retrieval with a Hedstrom file.

Dr Mounce lectures globallyand is widely published. Heis in private practice in En-dodontics in Vancouver,WA, U.S.A. Amongst otherappoint-ents, he is the en-dodontic consultant for theBelau National HospitalDental Clinic in the Republic

of Palau. Korror, Palau (Micronesia).

Richard Mounce, DDSVancouver, WA, U.S.A.E–mail: Lineker@aol.com andRichardMounce@MounceEndo.comwww.MounceEndo.com

_author info roots

Fig. 8a Fig. 8b Fig. 8c