Regaining canal patency in endodontic retreatment - De Vos Endo BV

clinical _ canal patency IRegaining canal patencyin endodontic retreatment:finding the pathAuthor_ Richard Mounce, U.S.A._If there is a common denominator in the challengepresented 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, determinelong-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 retreatmentprocedures along with the safe, efficient andeffective removal of the previous endodontic obturationmaterial, the potential for healing is enhanced. Thisarticle was written to discuss methods to allow the astuteclinician to achieve and maintain patency at all levelsin 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 provided(Figs. 1a, b).Creating a challenge in planning for retreatment isthe fact that most often a clinician may not know preoperativelythat 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 radiographicallyvisible. Lack of patency does not occur in a vacuumand 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 harbingerof 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 retreatment.Fig. 1aFig. 1bFigs. 1a–b_ Badly ledged andblocked canal, after retreatment.roots2_2007I15

I clinical _ canal patencyFig. 2_ The Global Surgical OperatingMicroscope (Global Surgical,St. Louis, MO, U.S.A.).Fig. 3_ File-Eze (Ultradent, SouthJordan, UT, U.S.A.)._These strategies are:_Using an enhancedsource of lighting andmagnification, optimallya surgical operating microscope(SOM) such asthe Global SOM (GlobalSurgical, St. Louis, MO,U.S.A.) (Fig. 2)._Copious irrigation at all stages inthe procedure, ideally after every fileinsertion, 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 especiallyin a vital tooth so that pulp tissuecan be irrigated in a coronal directioninstead of being pushed apically and becomethe nidus of a future blocked canal(Fig. 3)._ Endodontic therapy should always be carried outunder a rubber dam. It is the ethical and legal standardof 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 compliantand comfortable patient possible. A full andcomprehensive pre operative assessment of therisk factors present in the clinical case should alwaysbe undertaken with an eye toward determiningif referral is indicated. Strategies for avoidanceof iatrogenic events should be determined beforestarting._ Access should be straight line in that the straightawaycoronal 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-operativeevaluation is ideal. Multiple angles of radiographcan and should be taken preoperatively tofully map the canal system that will later be negotiated.With these materials and strategies in place guidingthe course of treatment, thechances for lost patency areminimized and futurenegotiationmade more likely._A lack of apical patency is caused inseveral ways:_ Canal debris is pushed apically. Blockage can occuranywhere, but it commonly happens eithermid root in the presence of an abrupt mid root curvatureor 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 occludea canal and create a blockage. Most oftenthese metal obstructions are separated files, silvercones, Gates Glidden drill heads and post fragments.Plastic carriers used in warm carrier basedobturation can also become wedged with frictionalretention and present a significant challengein removal._ Some pastes and cements used as obturation materialscan 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 attained.While management of these pastes is beyondthe 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 challengingevent and almost always indication for referral._ 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 beginningretreatment and attempts to regainapical patency:_ The risk of perforation should always be considered.If the canals are likely to be perforated duringremoval 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 options,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 cliniciansshould always ask themselves, is the toothrestorable? Is the tooth strategically valuable? Do16 Iroots2_2007