THE REMOVAL OF RADICULAR FILLING
MATERIAL OR OBSTRUCTIONS
The following basic principles must be considered as
radicular filling materials are removed:
1. The hardness or consistency of a nonmetallic filling Or the ability to remove an intracanal material cannot be determined radiographically
2. Removal of a previous filling material is usually easier if the root canal treatment is failing because of recurrent
leakage.
3. No canal space is naturally round.
4. Access to the apex and patency are necessary to achieve the root goals of cleaning and shaping the
canal system.
5. The philosophy behind the "crown-down" approach' is most applicable to the removal of radicular
filling materials or obstructions.
6. All preparations increase in size during retreatment. Usually the coronal third demonstrates the greatest
enlargement.9
7. Canals that initially deviate from their natural centerline tend to continue to deviate in the same direction during retreatment. Areas not instrumented during initial treatment are more difficult to contact
during retreatment.
8. Irrigation and disinfection must be emphasized because all canals that are retreated should be considered contaminated with microorganisms.
9. Solvents, while useful, can interfere with debridement.
10. All methods of instrumentation and removal leave debris remaining in the canals.
11. Open canals not being treated should be protected or covered.
12. Patience is a virtue.
The three categories of materials most commonly considered during retreatment are pastes, semisolids with sealers, and solids placed with or without sealers
Removing Gutta-Percha Core Materials
Mechanical and/or solvent dissolution techniques can be used to remove gutta-percha and sealer. The preferred technique is mechanical because it allows for better debris removal. The use of solvents substantially complicates
debridement. When solvents are used to remove gutta-percha or pastes, the dissolved infected debris from these materials is more likely to flow into and coat inaccessible canal irregularities and/or penetrate into the periradicular tissues.
The decision to use one or both techniques hinges on
three factors:
1. The existing condensation quality-Densely filled canals may require a solvent to facilitate penetration.
Poorly condensed fillings can usually be removed mechanically. Usually the coronal aspect of any canal is most densely compacted.
2. The length o f the existing filling material-The use of solvents to dissolve filling materials in the apical third of the canal system risks pushing these materials into
the periradicular tissues. The use of solvents in the apical third with an overextended cone all but ensures that the overextended segment will be severed and remain in the periradicular tissues.
3. The tooth's root morphology, canal shape, size, and curvature-Mechanical techniques remove more dentin than solvent approaches. With a comparatively
straight and substantial root, the clinician may be able to remove all of the gutta-percha using rotary instrumentation. In contrast, a densely filled curved
canal such as the mesiobuccal root of a maxillary first molar may require solvents to reduce the risk of apical transportation or furcal strip perforation.
A mechanical removal technique usually begins with rotary instrumentation (using Gates Glidden drills or nickel-titanium files) to rapidly remove the coronal portion of the gutta-percha. The canal is larger coronally and straight enough to tolerate these procedures.
Minimal pressure is exerted as smaller sizes are used to progress apically in a crown-down manner. The clinician should promptly remove any material adherent to the rotary instrument and carefully cut away from furcal concavities. Alternatively, a heat source with diminishing sizes of heat carriers may be used to remove the gutta-percha.
As the coronal bulk of material is removed, penetration of the apical radicular filling becomes possible. Using an appropriately curved, short ( 21 mm) size 15 or 20 K-file with a repeated reaming action, the clinician should be able to instrument next to the previous filling material.
He or she should not file, force, or push instruments apically. Frequently, the operator will sense that it is possible to almost "screw the file in." If this is feasible, the operator should be careful that the file is not placed so aggressively as to demonstrate "spring-back" when the handle is released. Ideally the entire gutta-percha filling will be bypassed with size 20 or larger K-files. The clinician can use an apex locator to estimate the file position if necessary. Frequent and generous irrigation with NaOCI is indicated.
Old gutta-percha fillings are likely to be brittle. In such situations the gutta-percha will seem to shred and break into small pieces as the path alongside it is created and debris is removed.
After establishing a path, the clinician chooses the next larger Hedstrom file (at least a size 20) and rotates it clockwise alongside the filling material, avoiding springback. Although this file will engage dentin, it will preferentially embed its flutes in the softer gutta-percha.
With controlled force, the clinician removes the Hedstrom file as though it were a corkscrew, turning counterclockwise as necessary if too much resistance is encountered. The entire gutta-percha mass may release, but more often small fragments will be removed each time this process is repeated. The clinician may consider a larger file size if the canal anatomy permits but should be careful not to sever overextended segments. When working close to the estimated working distance, the clinician can take a radiograph with the file in place. Ideally, all apical filling materials should be removed. The value of removing materials that remain in the middle and coronal thirds must be carefully weighed against concerns for
preservation of tooth structure.
Many solvents have been proposed to aid in retreatment of gutta-percha fillings. The authors of this chapter prefer chloroform, but less volatile solvents such as d-limonene (a xylene substitute)" are being investigated and may prove safer.
A solvent dissolution approach usually begins, as does the mechanical approach, with the bulk of materials being removed by rotary instrumentation. This action creates a coronal space or reservoir where the solvent can be deposited. Initially, a 21- mm 15 or 20 K-file can be used to penetrate and remove the dissolving mass of filling material. The instrument flutes should be cleaned after each pass, with the solvent being replenished as it evaporates. As the material further softens, Hedstrom files may be used to expedite removal.
Slowly and without forcing, the clinician can use precurved files to work through the previous filling. Unless it is necessary for visualization, irrigation is not indicated because it will dilute and diminish the solvent's effectiveness. As the apical extent of the filling is approached, the clinician may attempt to complete the process mechanically. If this is not possible, he or she may continue with the solvent while using files with a reaming action to minimize pushing debris apically.
After the file has bypassed or is completely alongside the filling material, he or she can begin irrigating with NaOCI and follow the steps of mechanical removal
REGAINING ACCESS TO THE APEX:
REINSTRUMENTATION, IRRIGATION,
DEBRIDEMENT, AND DISINFECTION
After removing previous filling materials and obstructions, the clinician must re-establish access to the apex along the path of the original canal. It is unusual to find a readily patent and negotiable canal "on the other side."
If this were the case, the operator could proceed with the usual techniques of cleaning and shaping, while placing particular emphasis on irrigation to debride and disinfect. Working length radiographs are essential to evaluate length and preparation. Information provided by electronic measuring devices is complementary to these radiographs.
As the final cleaning and apical shaping continues, the operator must recall that continued preparation naturally tends to deviate from the original centerline of the canal, especially in the coronal third.
If the previous filling materials were under-extended, the goal of apical instrumentation may be complicated by the following canal abnormalities:
1. Blockages with dentinal and/or pulpal debris
2. Dentistogenic complications such as ledges and transportation
3. Calcifications
4. Anatomic complexities
In the worst case scenario, a canal will feel solidly blocked and impenetrable. Recalling basic principles of endodontic instrumentation, the operator should choose a short (21-mm, size .08, .10, or .15) file size, irrigate, and gently feel for a "catch." Usually a small J hook is placed at the instrument's tip and a gradual bend is placed throughout the instrument's length. While exploring the canal, the clinician should resist the natural tendency to push more aggressively, which will only complicate a blockage or ledge.
Frequent irrigation should be employed to remove debris. If no catch is detected, the canal should be dried and irrigated with a chelating agent such as 17% ethylenediaminetetraacetic acid (EDTA) in aqueous solution. As gentle exploration continues, the clinician should curve and recurve the file, while ascertaining that no coronal or radicular access restrictions impede the motion of the file. Irrigation should not be performed with NaOCI because it will neutralize the effect of the chelating agent.
If several canals are being re-entered and the first yields no initial signs of progress, the clinician should leave EDTA in place and proceed to work on another canal. Without rushing, the clinician continues to explore each canal for even the slightest catch and gently pursues it with the smallest file sizes when a catch manifests. This gentle but persistent effort rarely results in perforation, even with EDTA. The clinician should conscientiously discard worn instruments while replenishing the EDTA. After the estimated distance has been achieved, it can be enlarged to a size 15 file and a working radiograph can be taken to confirm length and file position.
If a previously blocked canal continues to resist apical instrumentation, a clipped file approach may carefully be attempted.10 Typically about 1 to 2 mm are clipped from the tip of a 21- mm size 15 file. This procedure leaves the tip with sharp cutting edges that can be used with a back-and-forth, auger-like motion. 13 With this technique the clinician may be able to work through the resistant blockage. Discretion normally dictates that only 1 to 2 mm of length should be attempted in this manner before the clinician gently feels for the natural canal again with a small, unclipped, curved file. Radiographs are essential to monitor the files' progress, especially around curves.
After the original canal has been re-established, hand or rotary instrumentation techniques can be used to finish shaping the preparation.
Considerable emphasis must be placed on debridement, irrigation, and finally disinfection. The retreating dentist must remove as much of the contaminated previous materials as possible, as well as debris created by new instrumentation. Any motion that might push this debris apically should be avoided. As the preparation nears completion, the clinician must undertake a focused search for any additional untreated canals.
The operating microscope offers ideal illumination and v1sibility to accomplish all of these goals. Anatomic grooves and dentin coloration can also guide the operator in locating additional canals. In the apical area, bubble trails and careful tactile exploration with appropriately curved small files may reveal patent apical ramifications. The radiographic file position (centered or not) within the root is also an excellent indicator of
additional canals.
All authors concede that complete debridement of the root canal system is impossible. During retreatment, remnants of previous filling materials will always remain out of reach of reasonable instrumentation.
The operator must assume that these uninstrumented areas and their adjacent dentinal tubules are contaminated with microorganisms. To date, the consensus of most authors suggests that a conscious effort at further canal disinfection must follow cleaning and shaping and precede the filling appointment. At this time, placement of an intracanal dressing such as calcium hydroxide (CaOH)14 or an antibiotic-containing fiber 15 for a period of at least 1 week seems most appropriate. A temporary restoration at least 4 to 5 mm thick is then placed against the sound walls of the access preparation.
FILLING, PROGNOSIS
AND POSTTREATMENT RESPONSIBILITIES
All filling techniques attempt to prevent recurrent leakage and seal in or entomb debris that cannot be removed from the root canal system. The clinical conceptualization of a root canal filling should be that of a maze on a micrometer scale. No ionic or covalent bonds come into play, only physical interfaces among dentin, sealer, and gutta-percha.
All obturation techniques leak. 17 As long as clinicians continue to fill canals in a manner that facilitates nonsurgical retreatment, they will never measurably improve on existing obturation techniques.
The time-honored adage, "It's what you take out, not what you put in," is as true today as it was 100 years ago (see Chapter 7). The reader is left to choose an appropriate filling technique.
The completion of canal obturation leaves the clinician with a sense of prognosis. As part of the ongoing process of consent, treatment outcomes must be conveyed
to the patient. Additional referrals for periodontal or related procedures must be arranged if they were not anticipated preoperatively. For the patient, filling is usually perceived as completion, the end of the root canal treatment. They have survived, and usually their worst fears have passed uneventfully. They are also comfortable and all too frequently complacent, wishing to take a break from treatment. Beyond providing any required postoperative management (e.g., pain and/or infection control), the clinician also has a responsibility to ensure that the patient returns promptly for definitive restorative procedures
. When a specialist provides treatment, this process may begin as a phone call and/or a referral
acknowledgment and a radiograph.
Posttreatment follow-up is as essential as retreatment planning. If any delays in the restorative process are anticipated, a more definitive temporary restoration such as reinforced zinc oxide and eugenol or a light-cured intermediate composite should be placed. Application of an orthodontic band to reduce the possibility of fracture or placement of the core build-up and a temporary crown is frequently indicated. Loss of a temporary restoration requires immediate replacement. Treatment must never be considered complete until the tooth is restored to function.
Endodontic recall examinations should be scheduled at any time if signs or symptoms develop and planned routinely at 1 and 2 or more years.
