Indications for Nonsurgical Endodontic Retreatment

Retreatment is considered the primary procedural option when the tooth exhibits inadequate initial root canal treatment, has palpation and percussion sensitivity, localized swelling, recurrent caries, leaky provisional restorations, and substandard or missing coronal restorations. Radiographic evaluation may show the presence of untreated canals, poor canal obturation with voids, separated instruments, recurrent caries not located during clinical examination, or defective restorations with open margins that can potentially contribute to nonhealing. Any combination of clinical symptoms, radiographic evidence, and other clinical findings may indicate that nonhealing is evident but may also arise without any contribution of the aforementioned conditions.

Contraindications for Nonsurgical Endodontic Retreatment

A major factor to determine the requirement for nonsurgical retreatment is the restorability of the tooth after the necessary removal of preexisting restorative materials. Additional tooth structure may be lost during caries elimination and removal of post and core materials. The restorability decision often requires comprehensive disassembly of preexisting restorations and evaluation of the remaining root canal system. Other factors include the presence of extensive periodontal involvement that weakens tooth support and/or the presence of problematic coronal or radicular fractures. Patients who are not motivated to save the natural tooth are poor candidates for retreatment.

Treatment Planning for Nonsurgical Retreatment

In most instances, nonsurgical root canal retreatment is the first treatment of choice for either overcoming a nonhealing outcome of a previous root canal treatment or correcting a previous inadequate endodontic treatment with no clinical and radiographic signs of failure ( Fig. 19.6 ). ^, Moreover, nonsurgical endodontic retreatment is usually preferred to other treatment options because the procedure is less invasive than surgical endodontics, replantation, transplantation, and extraction and replacement with implant.

Typical cases that need endodontic retreatment because of various reasons. (A and B) The teeth need endodontic retreatment as a result of fracture of their restorations. (C and D) Maxillary left first premolar needs endodontic retreatment as a result of failure of the previous root canal therapy.

In addition to the technical challenge of performing endodontic retreatment, other aspects of the treatment should also be considered. Important factors in this respect include cost-effectiveness of the treatment, periodontal status, the remaining tooth structure after removing all caries and preexisting restorations, restorability of the tooth, the total cost of treatment, the need for crown lengthening in order to place a suitable full-coverage restoration, and esthetic and functional conditions.

Cost-effectiveness of a treatment might affect decision-making when there are different treatment options. Both microsurgical endodontic retreatment or nonsurgical endodontic retreatment with a crown are more cost-effective treatments compared with extraction and placement of an implant.

The practitioner should always evaluate periodontal status, restorability, and function of the tooth during the examination visit. The occlusal contacts of the tooth should also be evaluated, particularly if during the previous treatment the occlusal surface of the tooth has been reduced for a long time ( Fig. 19.7 ).

(A) Occlusal surface of the mandibular right second molar has been reduced after the previous root canal treatment. (B) Occlusal view of the tooth that needs reconstruction. (C) No space for placing a full coverage restoration over the tooth.

An important aid in treatment planning is to order CBCT before commencing endodontic retreatment. Practitioners should only request CBCT after taking relevant courses and gaining experience and knowledge on interpretation of CBCT images and their limitations. The European Academy of DentoMaxilloFacial Radiology has recommended incorporating courses on CBCT into both undergraduate and postgraduate curricula as well as continuing education programs for dentists and endodontists in order to improve their skills in relation to the interpretation of the tomographic images used in their clinical practice.

Although CBCT could be an important aid for the practitioner, it does not mean it should be ordered for all the endodontic retreatment cases. ^, For endodontic retreatment purposes CBCT could be ordered if ^, :

• •

  Conventional two-dimensional radiography (periapical) did not provide enough information regarding the reason(s) for failure in a tooth that previously received endodontic treatment ( Fig. 19.8 ).

  

  (A) Maxillary left second premolar received root canal therapy 2 years ago; however, the patient complained of pain and sensitivity on percussion and palpation since the treatment visit. (B) The CBCT image in coronal view showed apical perforation in the buccal root ( white arrow ).

• •

  Conventional two-dimensional radiography (periapical) shows the possibility of complex root canal anatomy in a tooth with a history of endodontic therapy ( Fig. 19.9 ).

  

  (A and B) Periapical radiography showed possibility of a complex root canal anatomy in mandibular left first molar. (C) CBCT image in axial view showed that the distolingual root had been overlooked (white arrow) . (D) The tooth received endodontic retreatment.

• •

  There is possibility of mishaps and overlooked root canal(s) that are not adequately detected by conventional two-dimensional radiography ( Figs. 19.9 and 19.10 ).

  

  (A) The maxillary right first molar with inadequate root canal therapy showed a possibility of mishap during access cavity preparation. Both CBCT images in coronal (B) and sagittal (C) views showed trifurcation perforation. (D) Maxillary left first and second molars showed the possibility of trifurcation perforation of a previous pulpotomy. No sign of trifurcation perforation was observed on CBCT images in coronal (E) and sagittal (F) views.

Based on standards of care, the dentist should choose whether conventional radiography is sufficient for commencing endodontic retreatment or there is need for more information by ordering CBCT. The practitioner should discuss the risks and benefits of requesting CBCT with the patient and both arrive at a decision either to order the tomography or to only use conventional radiography during treatment planning. Higher radiation dose, higher cost, and lower resolution are disadvantages of CBCT compared with periapical radiography.

There is no unique treatment plan for all the teeth with a history of endodontic therapy and nonhealing periapical lesions. Each case should be evaluated individually and decisions on the treatment plan should be made based on patients’ preference, possibility of rendering ideal treatment, and considering the prognosis. Most patients are interested in being active or collaborative in making a decision when teeth have apical periodontitis. Variables should be discussed with patients and a final shared decision should be made.

Endodontic Retreatment Procedures

Access Through Full-Coverage or Preexisting Restorations

The decision to remove all the existing restorations during endo-dontic retreatment depends on several factors. In most cases, the practitioner should remove all the existing restorations before commencing the endodontic retreatment procedure because of the possibility of leakage and presence of recurrent caries. In addition, it is reasonable to remove a previous restoration as well as caries before performing endodontic retreatment to determine whether future restoration is possible or not. However, in some instances, the patient might have recently received a suitable restoration and removing it would increase the cost of the treatment. In such a case, providing access cavity through the previous restoration might be recommended ( Fig. 19.11 ). Preserving a crown restoration could also help to improve dental dam isolation and maintain occlusion, with the least alteration in esthetics. However, it might restrict the practitioners’ ability to observe cracks, missed root canal(s), and recurrent caries. If a prior restoration of the retreated tooth is amalgam, there would always be a chance of inadvertent pushing of amalgam fragments (induced during access cavity preparation) into the root canal space and blocking the root canal negotiation.

Examples of access cavity preparation with and without preexisting restoration. (A) A maxillary right second premolar with a history of recently placed porcelain fused to metal crown being clinically symptomatic. (B) The access cavity was prepared through the crown. (C) Follow-up radiography 1 year after the treatment showed successful outcome and the tooth was clinically symptom free. (D) Maxillary right first premolar was an abutment of a bridge. Because of suitable marginal adaptation of the bridge and favorable esthetic, endodontic retreatment was performed through the full coverage restoration. (E) The missed root canal was located. (F) Despite unsuccessful effort for removing overextended gutta-percha, periapical radiograph showed that the radiolucent lesion healed 18 months later.

Based on the American Association of Endodontists (AAE) difficulty assessment form, root canal retreatment has been categorized as highly difficult. If the tooth has received a full-coverage crown or is an abutment for a bridge and needs to receive endo-dontic retreatment, it will definitely increase the difficulty, and it may be wiser to refer the patient to an endodontist. For more information on the subject, the reader should refer to Chapter 6 of this book.

If either a prefabricated or a cast post is present even in a tooth that recently received a restoration, removal of all the existing restorations is highly recommended.

Removal of Existing Restorations

Endodontic treatment outcomes may depend more on the marginal adaptation of the restoration than the quality of root canal fillings. ^, Hence, because of the possibility of coronally induced bacterial ingress into the canals, it is essential to remove the preexisting coronal restorations and evaluate the presence of secondary caries and root canal contamination ( Fig. 19.12 ). When a tooth presents with a full coverage restoration, composite resin, or amalgam restoration with recurrent caries, open margins, or loss of marginal integrity, complete removal of the restoration is indicated. In the majority of cases, removal of the full coverage restoration is necessary to see if there is any undetected bacterial contamination. ^{, ,} Disassembly of the preexisting restorations allows inspection for possible recurrent caries and fractures and evaluation of the tooth’s restorability. ^{, ,} If coronally induced bacterial ingress is evident, the entire remaining tooth structure should be inspected, including the canals and the pulpal floor. When the remaining coronal structure is assessed as being inadequate, orthodontic extrusion of the root should be considered (see Chapter 21) .

(A) Preoperative radiograph showing a wide gap between the coronal restoration and the root with a periapical lesion. (B) Intraoral photograph showing poor marginal adaptation of the crown. (C) Coronal view of CBCT imaging shows a wide space between the two root canals and the core with a periapical lesion associated with the root. (D) Sagittal view of CBCT imaging also shows spaces between the two root canals and the coronal. (E) Extensive carious lesions discovered under the coronal restoration. (F) Dentin stained with carious detector dye reveals deep carious lesions into the two canals.

Removal of Canal Obstructions

Canal obstructions usually prevent successful negotiation of the root canal system during nonsurgical root canal treatment. Surgical treatment may need to be included to manage these treatment challenges.

Canal obstructions include posts and cores, calcifications of the root canal system, iatrogenic ledges, dentinal debris in the root canal system, fractured instruments, silver points or metallic debris, and some paste materials. ^{, ,} Removals of canal obstructions are typically complex treatment situations that frequently require extensive operator training and experience to manage. For the benefit of the patient, referral to an endodontist should be considered and offered.

There are basically three approaches to managing intracanal fractured instruments: (1) attempting to remove the instrument nonsurgically or surgically, (2) attempting to bypass the instrument, or (3) preparing and obturating the canal with the fractured instrument.

First, a diagnosis and a treatment plan for instrument retrieval should be made with periapical radiography and CBCT imaging (see Chapter 18).

As discussed in Chapter 18, the majority of nickel-titanium (NiTi) rotary instruments fracture in the apical one third of the canals. When a fractured instrument is lodged beyond the curve and extrudes primarily beyond the apical foramen, a surgical approach should be considered because removal sacrifices less valuable structure compared with the nonsurgical approach. A nonsurgical procedure should be initiated if the amount of tooth structure removal after surgery is expected to be greater than a nonsurgical approach.

Bypassing a fractured instrument may not be as successful as removal with ultrasonics, ^, and attempts to bypass the instrument may lead to iatrogenic accidents such as ledge formation, perforations, and transportations, particularly in curved canals. In general, bypassing a broken instrument is a technique-sensitive procedure requiring experience, tactile sense, and perseverance by the clinician.

When an instrument fractures in the apical one third of the canal in a later stage of canal instrumentation and if an excessive amount of tooth structure must be sacrificed to retrieve it, the separate file should be incorporated as part of the filling material and scheduled for periodic review. The sealing ability of the obturation material is not compromised by the presence of a fractured file or other metallic debris.

The use of ultrasonics can effectively remove a fractured instrument when performed under high magnification and illumination.

Ledge formation during root canal preparations can be analogous to broken instruments because they can also limit instrumentation in an apical direction. Ledges are typically generated on the outer canal wall when preparation of the curved canal is not maintained ( Fig. 19.13 ). These canal problems typically occur when stainless steel files are not properly precurved to match the canal curvature. Traditional stainless steel files have aggressive cutting tips (pyramidal tips) compared with NiTi files and are apt to straighten canals unless properly precurved, resulting in ledge formation. Root canal transportation and ledging can also occur during preparation if debris accumulation is not consistently removed. It is important to keep the canal wet and constantly irrigate the canal with an irrigation needle smaller than the root canal diameter during instrumentation to avoid debris blockage. Recognition and visualization of canal ledges is essential for avoiding perforations and other procedural errors. Studies have shown flexible nonlanded NiTi instruments with noncutting tips produce significantly less apical transportation than landed NiTi instruments or NiTi instruments with cutting tips. ^, For more information regarding the ledge management, readers should refer to Chapter 18 of this book.

(A) Preoperative radiograph showing a ledge formation on the outer canal wall in relation to the canal curvature (white arrow) . (B) Intraoperative radiograph showing a precurved #10 K file in the original pathway after filling the ledged space with MTA (white arrow) . (C) Postoperative radiograph showing the root filling in the original canal beyond the ledge.

Post and Core Removal

Successful removal of posts and cores during retreatment depends on multiple factors. They include the operator’s level of skill, experience, training, and instrumentation selection. Small-diameter long shank carbide burs and ultrasonic systems used in conjunction with the dental operating microscope (DOM) facilitate predictable treatment. Other outcome considerations include the type of core material (cast versus resin or amalgam); the length and diameter of the prefabricated or cast post, post location, post material type (metallic or nonmetallic); and variety of cement or bonding system used to secure the post and core system. ^{, ,} Any number of methods used to remove posts can compromise the existing tooth structure. Some posts may be difficult to remove if they are long, well fitted, or cemented with bonding systems or resin cements ( Fig. 19.14 ). Most posts are essentially straight and can be usually managed using small-diameter long shank carbide burs under the DOM. However, nonmetallic posts such as tooth colored zirconia or fiber posts may be difficult to differentiate from the tooth structure. The small-diameter burs partnered with the DOM allow conservative post removal without sacrificing additional tooth structure (see Fig. 19.14 ).

(A) Preoperative radiograph showing a long cast post placed in the canal of the maxillary right incisor with periapical lesions. (B) Removed cast post showing the metal portion that was in the canal looks intact. (C) Radiograph taken immediately after the removal of the post shows the untouched dentin wall. (D) Twelve-month postoperative radiograph showing periapical healing.

In preparation for post removal, the coronal core material must be carefully sectioned and removed incrementally with diamond, zirconia-diamond, transmetal, or carbide burs, and ultrasonic tips to preserve the portion of the post that extrudes coronally from the root canal to facilitate removal of various core materials. ^{, ,}

This procedure is best performed using illumination and magnification to help preserve adjacent tooth structure during the procedure. After core removal, any visible cement surrounding the post can be circumferentially removed using fine ultrasonic tips or flame-tipped diamond burs. ^, Loosening of the post should be observed as the ultrasonic activation progresses.

Screw posts can usually be loosened with ultrasonics applied to them in a counterclockwise rotation and picked up with various-sized hemostats or small-tipped forceps or pliers. However, this procedure must be executed with caution because it rapidly generates extremely high temperatures without water coolant. In addition, ultrasonic energy should be delivered in different locations around the exposed portion of the post at intervals lasting no longer than 15 seconds. ^{, , ,} Ultrasonic tips used without water coolant and placed in contact with posts generate temperature increases of 10°C within 1 minute on the external root surface. If this threshold temperature is reached, heat generation can cause necrosis of periodontal tissues, with possible loss of the tooth and supporting bone.

Posts cemented with resin cements and fiber posts are difficult to loosen and remove with ultrasonics. Therefore those posts should be ground down with small-diameter carbide burs under the DOM.

After post removal, any excess cement can be removed using a combination of solvents, rotary or hand instruments, or ultrasonic tips (Video 19.2 ). ^{, ,}

Removal of Gutta-Percha

Gutta-percha is the universally and most commonly used obturation material. Therefore it requires removal more frequently during endodontic retreatment than other materials in order to better prepare a root canal space or improve a canal with an inadequate filling during retreatment. Because biofilms are the primary cause of chronic and recurrent endodontic infections, removal of gutta-percha is essential to successfully retreat the root canal system. This can be accomplished using hand and rotary instruments, ultrasonic instruments, heat systems, or solvents and generally requires a combination of these methods.

The use of Gates-Glidden burs should probably be limited to the coronal portion of the canal, and excessive force must not be used because of the possible presence of apical root resorption or poorly adapted gutta-percha root fillings, which may result in the material extrusion ( Fig. 19.15 ). ^, The most efficient way to remove gutta-percha root fillings is to use ultrasonic and hand instruments under the DOM, followed by rotary instruments ( Fig. 19.16 ). Moreover, chloroform has been reported to be capable of reducing the intracanal levels of Enterococcus faecalis, a common microbe detected in endodontic failures. ^, However, if chloroform is used during the early stages of gutta-percha removal, more filling material will most likely remain in the canal and may contribute to excess extrusion beyond the apical foramen. ^, Xylene, halothane, eucalyptol, eucalyptus oil, carbon disulfide, benzene, and orange oil can also be used for this purpose. Even though they have been shown to be less effective at softening gutta-percha than chloroform, the majority of those solvents do not pose a significant health risk to patients. One investigation measured the amount of residual chloroform, halothane, and xylene expressed through the apical foramen during retreatment procedures. It was determined that the amount of each solvent expressed was below the levels that may pose a health concern to patients (Video 19.3 ).

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2. Retreatment
3. Endodontic-periodontic interrelationship
4. Pathogenesis of Pulp and Periapical Diseases
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