After reading this chapter, the student should be able to:
Recognize causes of the initial root canal therapy failure that require nonsurgical endodontic retreatment.
Identify if an initial root canal therapy requires additional treatment
Identify the treatment options available for teeth that need endodontic retreatment.
State the indications and contraindications for nonsurgical endodontic retreatment.
Describe how an accurate diagnosis should be made for nonsurgical endodontic retreatment.
Discuss the treatment plans for nonsurgical endodontic retreatment.
Describe the risks and benefits of nonsurgical endodontic retreatment.
Describe techniques and materials used in nonsurgical endodontic retreatment.
Discuss restorative options and follow-up care.
Discuss the prognosis and outcomes for nonsurgical endodontic retreatment.
When providing root canal treatment using today’s techniques the clinician expects excellent success rates. Modern methodologies and materials have demonstrated this in studies looking at maintaining tooth function and retention. , Initial root canal therapy, however, does not always result in healing for a multitude of reasons. Failure to adequately disinfect the root canal system may result in nonhealing. Bacteria may persist after initial treatment as a result of areas that were inaccessible to instrumentation and irrigation. Causes of treatment failure may include lack of tooth isolation; inadequate cleaning, shaping, and irrigation; and incomplete obturation ( Fig. 19.1 ). In addition to complex anatomic variations in the root canal anatomy, root canal obstructions, including calcifications, can also be a problem The reestablishment of root canal infection after initial treatment may also lead to progression of disease. This reintroduction of microorganisms is primarily caused by coronal microleakage and recurrent decay. , , , Furthermore, initial treatment may be compromised by long-term use of temporary materials before placement of definitive restorations.
Nonhealing after initial nonsurgical root canal therapy may also be related to procedural errors or the presence of biofilms. Procedural errors include perforations, canal transportation, fractured instruments, and ledge formations, all of which can negatively affect the treatment outcome. ,
It is also important to recognize that vertical root fractures (VRF) may sometimes appear as nonhealing lesions. These are longitudinal fractures that occur after root canal treatment and may be related to the weakening of roots from excessive dentin removal or simply from the stresses on teeth from normal function ( ).
Causes of Nonhealing of Initial Root Canal Treatment
A significant reduction or elimination of bacteria in the root canal system after initial endodontic treatment should reduce the presence of periapical periodontitis. The causes of the initial endodontic treatment failure can include inability of the procedure to eradicate bacteria, introduced intraradicular microorganism, extraradicular infection, foreign body reaction, accidental procedures, and nonendodontic related events such as VRF, traumatic injuries, and periodontal disease. Most studies on the unfavorable outcomes of endodontic treatment reported that microorganisms in the root canals or periradicular lesions play a major role in the persistence of apical periodontitis ( Fig. 19.2 ). ,
Diagnosis and Retreatment Options
Diagnosis of a tooth in need of endodontic retreatment should be based on clinical signs and symptoms, radiographic and, when necessary, tomographic interpretations.
Periapical radiographs should be taken in two different horizontal angles to evaluate the quality of obturation, crestal bone level, presence of missed root canals, procedural errors, resorptions, and lateral or periapical radiolucent lesions ( Fig.19.3 ).
Introduction of cone beam computed tomography (CBCT) to endodontics has had a considerable and positive effect on the diagnosis and treatment planning. However, CBCT images reveal more periapical lesions compared with the two-dimensional conventional radiographic techniques. , An investigation by Torabinejad et al. showed that 20% of the teeth with a history of root canal therapy that had no visible radiographic periapical lesions exhibited periapical radiolucencies >1 mm in size when evaluated by CBCT. They cautioned clinicians not to consider all these lesions as treatment failures because the radiolucency might be a previous lesion in its healing phase, persistent periapical disease, or even fibrous scar tissue. They recommended further follow-up as well as a work-up of the case to determine the true nature of these radiolucencies ( Fig. 19.4 ).
Both intraradicular and extraradicular infections might result in nonhealing of root canal treatment. If a periapical radiograph shows adequate root canal therapy, presence of extraradicular infection should also be considered as a reason for failure.
The reason a tooth requires endodontic retreatment should always be confirmed. In addition to performing endodontic retreatment for the failed cases, in some instances, as a result of the fracture of the preexisting restoration, leakage, or unacceptable esthetics, endodontic retreatment should be performed for teeth with inadequate root canal therapy despite the absence of clinical signs or symptoms and radiographic pathosis ( Fig. 19.5 ).
In some cases, dental practitioners might not have a similar treatment plan to manage a tooth with previously failed root canal therapy. Factors such as the practitioners’ personal experience, skill, available armamentarium, patients’ attitude, and demands for receiving endodontic retreatment might influence the treatment plan. Therefore a dentist would help patients participate in a shared decision-making process through full description of all the treatment options, their risks and benefits, as well as economic advantages and disadvantages. Patients usually attend a dental office when they are in pain and discomfort, need to repair a preexisting restoration, have fractured or traumatized teeth, or need treatment as a result of dental caries. Occasionally, making decisions may be difficult because of conditions that could be genuinely complicated. It would be wise to precisely evaluate each case by clinical and radiographic examinations and, if necessary, refer the patient to a periodontist or a prosthodontist to make sure that the tooth is restorable and maintainable after endodontic retreatment. It is critically important to describe all information in a simple language that is easily understood by the patients. Therefore patients’ age, first/second language, and educational background should be considered for better communication. ,
The treatment options in endodontics, when previous root canal therapy is showing signs of failure or when the tooth needs a new permanent restoration, would include nonsurgical root canal retreatment, surgical retreatment, replantation, transplantation, and possible extraction followed by placement of an implant.
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.
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 ).
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 ).
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 ).
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 ).
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.
Risks and Benefits of Retreatment
Like any dental treatment, the risks, benefits, alternative treatments, and the subsequent consequences of choices must always be discussed with the patient. This conversation occurs before commencing treatment and includes an explanation of what the treatment entails, expected treatment time, prognosis, and costs.
Nonsurgical root canal retreatment procedures have numerous potential risks. These include fracture of a porcelain crown during the access procedure, fracture of the root during post removal procedures, and dislodgment of the crown, which may necessitate replacement. In addition, iatrogenic challenges may arise such as extensive removal of tooth structure, canal transportation, creation of ledges, or even perforations. , , The separation of an instrument is also possible, which may impede the ability to completely remove obturation materials. These complications potentially affect the retreatment outcome. The benefits of retreatment include the preservation and retention of the patient’s natural tooth and the avoidance of more extensive clinical treatment and costs.
Nonhealing of root canal therapy may be caused by:
Inadequate tooth isolation
All of the above
Radiographic “apical lesions” after root canal therapy may be a result of:
Nonhealing after treatment
Reestablishment of disease
Vertical root fracture
All of the above
When should risks benefits and alternatives to treatment be given to a patient?
Which of the following describes a disadvantage of CBCT compared with the conventional radiography?
Higher radiation dose
All of the above
Which of the following is a contraindication for endodontic retreatment?
Absence of coronal restoration
A history of soft tissue swelling
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.
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) .
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.
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 ).
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 ( ). , ,
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 ( ).