Nonsurgical root canal therapy has become a routine procedure in modern dentistry. Technical and scientific advances in endodontics have resulted in the retention of millions of teeth that would otherwise be lost. Even as advances in surgical and prosthetic restorative care have made tooth replacement less onerous than in the past, it is universally accepted that a natural tooth with a good prognosis is a superior choice to loss and replacement.
Unfortunately, not all treatments result in optimum long-term healing. Given the large numbers of treatments performed, the very small rate of unsuccessful outcomes translates into relatively large numbers of patients requiring further treatment. Dental clinicians should be able to diagnose persistent or reintroduced endodontic disease and be aware of the options for treatment. If they wish to approach treating these teeth, they should have the appropriate armamentarium and be capable of performing these specialized techniques at the highest level ( Fig. 8-1 ). Also, clinicians must always have a scientifically sound, evidence-based rationale for every treatment decision that is made so that they may best serve the patients who entrust them with their care. The purpose of this chapter is to provide information to allow the reader to maximize the likelihood of success in the treatment of persistent endodontic disease.
Etiology of Posttreatment Disease
In the past, undesirable outcomes of endodontic therapy were described as failures. Clinicians quote failure rates based on published success/failure studies. Using the words success and failure may be a holdover from a time when clinicians felt they needed to congratulate themselves on their successes and blame themselves for the failures of their treatment endeavors. This thought process does not reflect reality and can be potentially destructive. There are many instances in which treatments performed at the highest level of clinical competence result in an undesirable outcome, and there are other instances in which a procedure is performed well below a scientifically acceptable standard and yet provides long-term success. We must begin to dissect the science from emotion and ego, and this separation may start with nomenclature. Friedman stated that “most patients can relate to the concept of disease-treatment-healing, whereas failure, apart from being a negative and relative term, does not imply the necessity to pursue treatment.” He has suggested using the term posttreatment disease to describe those cases that would previously have been referred to as treatment failures. This will be the term used in the remainder of this chapter to describe persistent or reintroduced endodontic disease.
Almost 16 million root canal procedures were performed in 1999, and, with success rates varying between 86% and 98%, it has been shown to be a reliable treatment option. Conversely, the incidence of posttreatment disease, although small, translates into a large number of cases where further treatment is needed. When faced with such a situation, the clinician must determine the etiology of the persistent pathosis and devise a rationale and strategy for treatment.
There are many causes for “failure” of initial endodontic therapy that have been described in the endodontic literature ( Fig. 8-2 ). These include iatrogenic procedural errors such as poor access cavity design, untreated canals (both major and accessory), canals that are poorly cleaned and obturated, complications of instrumentation (ledges, perforations, or separated instruments), and overextensions of root-filling materials. Coronal leakage has also been blamed for posttreatment disease, as has persistent intracanal and extracanal infection and radicular cysts. These etiologies may be obvious at the time of diagnosing the diseased, root-filled tooth, or they may remain uncertain until the completion of successful therapy. Occasionally, the cause of posttreatment disease may take years to become discernible or may ultimately never be known. The most important causative factors for the clinician, however, are those related to treatment planning and determination of prognosis.
To treatment plan effectively, the clinician may place the etiologic factors into four groups ( Fig. 8-3 ):
- 1.
Persistent or reintroduced intraradicular microorganisms
- 2.
Extraradicular infection
- 3.
Foreign body reaction
- 4.
True cysts
Persistent or Reintroduced Intraradicular Microorganisms
When the root canal space and dentinal tubules are contaminated with microorganisms or their by-products and if these pathogens are allowed to contact the periradicular tissues, apical periodontitis ensues. As stated earlier, inadequate cleaning, shaping, obturation, and final restoration of an endodontically diseased tooth can lead to posttreatment disease. If initial endodontic therapy does not render the canal space free of bacteria, if the obturation does not adequately entomb those that may remain, or if new microorganisms are allowed to reenter the cleaned and sealed canal space, then posttreatment disease can and usually does occur. In fact, it has been asserted that persistent or reintroduced microorganisms are the major cause of posttreatment disease. Many iatrogenic treatment complications, such as creation of a ledge or separation of an instrument, result in persistence of bacteria in the canal system. It is not the complication itself, however, that results in persistent disease; rather, it is the inability to remove or entomb the microorganisms present that creates the pathologic state. While infected root canals of endodontically untreated teeth generally contain a polymicrobial, predominantly anaerobic flora, cultures of infected, previously root-filled teeth produce very few or even a single species (see also Chapter 14 ). The infecting flora are predominantly gram positive, not anaerobic, and a commonly isolated species is Enterococcus faecalis, which has been shown to be resistant to canal disinfection regimens. Interestingly, if the previous root canal treatment is done so poorly that the canal space contains no obturating material in the apical half of the root canal space, its flora is more typical of the untreated necrotic infected pulp than that of classic “failed” root canal therapy. Though posttreatment disease has been primarily blamed on bacteria in the root canal system, certain fungi, notably Candida albicans, are found frequently in persistent endodontic infections and may be responsible for the recalcitrant lesion.
Extraradicular Infection
Occasionally bacterial cells can invade the periradicular tissues either by direct spread of infection from the root canal space via contaminated periodontal pockets that communicate with the apical area, extrusion of infected dentin chips, or by contamination with overextended, infected endodontic instruments. Usually, the host response will destroy these organisms, but some microorganisms are able to resist the immune defenses and persist in the periradicular tissues, sometimes by producing an extracellular matrix or protective plaque. It has also been shown that two species of microorganisms, Actinomyces israelii and Propionibacterium propionicum, can exist in the periapical tissues and may prevent healing after root canal therapy.
Foreign Body Reaction
Occasionally, persistent endodontic disease occurs in the absence of discernible microorganisms and has been attributed to the presence of foreign material in the periradicular area. Several materials have been associated with inflammatory responses, including lentil beans and cellulose fibers from paper points. In the seemingly endless debate about which endodontic obturation technique is superior, there has been much discussion about the effect of overextended root canal filling materials upon apical healing. Outcomes assessments generally show that filling material extrusion (root filling flush to the radiographic apex or gross overextension) leads to a lower incidence of healing (see also Chapter 7 ). Many of these cases involved not only overextension but also inadequate canal preparation and compaction of the root filling whereby persistent bacteria remaining in the canal space could leak out. Gutta-percha and sealers are usually well tolerated by the apical tissues, and if the tissues have not been inoculated with microorganisms by vigorous overinstrumentation, then healing in the presence of overextended filling materials can still occur.
True Cysts
Cysts form in the periradicular tissues when nests of epithelial cells, retained from tooth development, begin to proliferate due to the chronic presence of inflammatory mediators. These epithelial cell rests of Malassez are the source of the epithelium that lines cystic walls, and cyst formation may be an attempt to help separate the inflammatory stimulus from the surrounding bone. The incidence of periapical cysts has been reported to be 15% to 42% of all periapical lesions, and determining whether a periapical radiolucency is a cyst or the more common periapical granuloma cannot be done with available radiographic methods. There are two types of periapical cysts: the periapical true cyst and the periapical pocket cyst. True cysts have a contained cavity or lumen within a continuous epithelial lining and are therefore isolated from the tooth, whereas with pocket cysts, the lumen is open to the root canal of the affected tooth. True cysts, due to their self-sustaining nature, probably do not heal following nonsurgical endodontic therapy and usually require surgical enucleation ( Fig. 8-4 ).
When a patient presents with posttreatment disease, clinical decision making depends on determining the cause of the persistent disease and then making an assessment of how best to treat the pathologic condition. The following section presents a rationale and methods for performing endodontic diagnosis that offer the greatest likelihood of a successful outcome.
Diagnosis of Posttreatment Disease
It has been stated that “there may be different ways of treating a disease; however, there can be but one correct diagnosis.” The proper diagnosis is probably the most important portion of any endodontic procedure (see also Chapter 1 ). This is not as bold of a statement as one may first suspect when consideration is given to what the patient may undergo if treatment is performed based on an incorrect diagnosis ( Fig. 8-5 ). To make a correct diagnosis, the clinician must rule out nonodontogenic etiology, perform all of the appropriate tests, properly interpret the patient’s responses to these tests, derive at a definitive diagnosis, and decide on treatment options. When performing a diagnosis in endodontic cases where there is no history of previous endodontic therapy, both a pulpal and periradicular diagnoses are necessary. In cases of persistent disease, the diagnosis may not be as straightforward as the clinician may be dealing with partially treated pulp canals, missed canals, and many other types of problems associated with the previous treatment. These must be included in the diagnostic description for each case.
Endodontic diagnosis was thoroughly discussed in Chapter 1 , and the reader is referred there for further details on these procedures. The diagnostic method requires collecting subjective information, developing objective findings, and using these to arrive at a diagnosis and plan of treatment.
The subjective information is collected by questioning the patient and then actively listening to the responses. Of particular interest in cases of suspected posttreatment disease is whether the patient recalls the use of aseptic techniques during the previous endodontic therapy. If a rubber dam was not used, for example, and this can be confirmed with a call to the previous clinician, nonsurgical retreatment will almost certainly be necessary because the canals can be assumed to be contaminated regardless of how aesthetically pleasing the previously filled case may appear on the radiograph. The diagnostician should be careful to avoid or to minimize communicating to the patient any negative feelings he or she has toward the previous treatment, however bad it may seem. This approach allows the patient to become more comfortable with the current clinician and the proposed corrective treatment. An irate patient is an irate patient, and negativity will color the patient’s emotional state, level of trust, and ability to accept current or future treatment plans. If the patient asks a direct question about the previous treatment, an honest answer is necessary, but avoid the temptation to imply superiority by disparaging the former clinician. To state the situation honestly and correctly without being inflammatory, use a sentence such as “Well, it may be that your previous dentist (endodontist) had some difficulty with that tooth. Let’s see if we can figure out what could have been the problem.”
Following a thorough review of the patient’s health history, the next step is to gather all of the objective information needed to obtain an accurate diagnosis. This information will include the clinical and radiographic examination. The clinical examination should include a visual extraoral and intraoral examination, and a thorough periodontal evaluation. Visual examination is greatly aided by magnification and illumination, which can allow the clinician to identify significant conditions invisible to the naked eye, such as fine fractures on root surfaces ( Fig. 8-6 ). Exposed dentin from recession and narrow based probing defects may be the result of an endodontic infection draining through the sulcus; however, they sometimes indicate vertical root fracture. The presence of occlusal wear facets indicates the presence of occlusal trauma that may complicate diagnosis and treatment outcome by predisposing the tooth to fracture, and it has been associated with posttreatment disease. Further information on diagnosis and management of cracks and fractures is provided in Chapter 21 .
Radiographic assessment is obligatory. Even though radiographs may be a critical aid to the clinician, they should never be the sole support for a conclusive diagnosis. They are only one piece of the puzzle in determining endodontic etiology. In cases with previous endodontic therapy, radiographs are useful in evaluation of caries, defective restorations, periodontal health, the quality of the obturation, existence of missed canals, impediments to instrumentation, periradicular pathosis, perforations, fractures, resorption, and canal anatomy. Radiographs should be properly exposed and have a sharp, clear image. They should include the tooth and surrounding tissues, and multiple angulated films should be used to determine endodontic etiologies using the buccal object moves most rule ( Fig. 8-7 ). Bitewing radiographs are useful for determining periodontal bone height and looking for caries or fractures. All sinus tracts should be traced with a cone of gutta-percha followed by a radiograph to localize their origin.
Cone beam computed tomography (CBCT) has been introduced into endodontics, and its usefulness in the management of endodontic retreatment is unquestioned. It has provided a quantum leap in our ability to determine the causes of posttreatment apical periodontitis by giving the clinician, for the first time, the ability to easily, safely, and inexpensively visualize the tooth and surrounding structures in three dimensions (3D). CBCT use in endodontics is discussed in detail in Chapter 2 , but when faced with a tooth needing retreatment, it is especially helpful. The CBCT allows the clinician to determine the true size, extent, and position of periapical and resorptive lesions and gives added information about tooth fractures, missed canals, root canal anatomy, and the nature of the alveolar bone topography around teeth. CBCT technology has greatly enhanced presurgical diagnosis and treatment planning, because the relationship of adjacent anatomic structures such as the maxillary sinus and inferior alveolar nerve to the root apices can be clearly visualized. This helps the clinician to decide on when to perform endodontic retreatment surgically or nonsurgically. CBCT is more accurate than periapical radiography in the diagnosis of apical periodontitis, and it can reveal the details of the lesions and adjacent structures, thus providing enhanced clinical diagnosis and treatment planning.
There are many manufacturers and brands of CBCT machines on the market today, but the most useful ones for endodontic retreatment are those that produce the clearest image with the highest resolution. These would be the small field of view (FOV) machines that image a small volume and use the smallest picture element (voxel) dimensions available. Radiation exposure to the patient with these machines is in the range of 23 to 488 µSv, which is very small, but the “as low as reasonably achievable” (ALARA) principle applies, so its use in every diagnostic case cannot be encouraged. In a joint position statement in 2010, the American Association of Endodontists and the American Association of Oral and Maxillofacial Radiologists stated that “CBCT should only be used when the question for which imaging is required cannot be answered adequately by lower dose conventional dental radiography or alternate imaging modalities.” When managing posttreatment disease, however, almost every case will benefit from the use of three-dimensional imaging.
One major cause of posttreatment apical periodontitis is untreated canals, and the CBCT gives an unprecedented ability to discover those ( Fig. 8-8 ). In one study, endodontist evaluators failed to identify at least 1 root canal system in approximately 4 of 10 teeth when using images obtained by conventional digital radiography compared with images from cone-beam computed tomography.
Avoiding treatment, which will lead to a predictable failure, is beneficial for both the clinician and the patient. The ability to obtain 3D images of teeth will help the clinician to avoid these mishaps. The diagnosis of root fractures frequently frustrates the clinician, as a definitive diagnosis is often difficult and treating these teeth has a high likelihood of a poor outcome. Although visualizing root fractures in teeth with root fillings is still not predictable using CBCT, the patterns of bone loss indicative of root fracture can sometimes be seen, and this helps the clinician to infer their presence. The prognosis for the treatment of root resorption is directly related to the extent of the resorption, and this usually cannot be determined accurately using conventional radiography. Using small FOV CBCT, however, the extent of the lesions and the prognosis can be determined, usually saving the patient from an exploratory procedure that may be doomed to fail ( Fig. 8-9 ).
Though most clinicians believe that CBCT is not necessary for every patient treated, there are many retreatment situations where the additional information gained (relative to conventional radiography) is extremely valuable. In the future, specific protocols for use will be developed; but for now, the authors recommend that clinicians use their best judgment on when to use this new technology.
Comparative testing is the next procedure performed to collect objective information about the pulpal and periradicular status. Most useful are the periradicular tests that include percussion, bite, and palpation. These allow the diagnostician to begin developing a sense of the status of the periradicular tissues. These tests are of great importance anytime an endodontic diagnosis is needed. However, they are of even greater importance when evaluating teeth that have been previously treated with endodontic therapy due to the lack of significant and consistent evidence that can be gained from pulp vitality tests in these cases. If a tooth exhibits percussion tenderness, it may be due to persistent endodontic disease, but recent trauma or occlusal trauma may also cause this finding, as can periodontal disease.
Pulp vitality tests are often of little value when examining teeth with previous endodontic therapy. However, if the patient’s chief complaint reveals the need for these tests, they must be performed because it is possible that the pain may be referred from a nearby vital tooth and not from the root canal–treated tooth. When there is vital tissue remaining in the canals of a previously root-filled tooth, either by way of a completely missed canal or from an improperly cleaned canal, patients may complain of sensitivity to heat or cold. Pulp vitality tests should then be performed to assess the situation. They are also useful in testing adjacent and opposing nonendodontically treated teeth to rule out those as etiologies for poorly localized pain. Once the tissue is removed from the pulp chamber after root canal therapy, the results of these tests should almost always be negative, even with radicular pulp remaining. Thus, a negative response with previously treated teeth is not necessarily conclusive; whereas a positive response usually means there is responsive pulp tissue remaining in the tooth. Care is always warranted in interpreting pulp test results, however, as false positive and negative results may occur. As with cold tests, the same limits apply to heat tests as far as the reasons for false results and accuracy relative to retreatment cases.
The remaining pulp vitality tests—electric pulp test, test cavity, and direct mechanical dentin stimulation—are of even lesser value than thermal testing when evaluating teeth that have already received endodontic therapy. These are usually precluded by the existing restoration or endodontic therapy.
When all diagnostic information is collected, a diagnosis must be developed. It is important to record the diagnosis in the patient’s record so that anyone reading the record can discern the clinician’s rationale for treatment. The pulpal diagnosis will usually be recorded as previous endodontic treatment, but the periradicular diagnosis will vary depending on the clinical picture presented. In the case of previous endodontic treatment, however, a brief note about the suspected etiology of the persistent disease is warranted.
Treatment Planning
Once the diagnosis is complete, the cause of the persistent disease will usually become apparent. At this point in the clinical process, information must be given to the patient by the clinician as to what treatment options are available and the likely outcomes of each choice. The patient is then allowed to make a decision based on his or her own perceptions of the options, not by the clinician’s opinion as to what is “best” for the patient. The reader is reminded, however, that if the cause of the posttreatment condition remains unknown despite thorough diagnostic workup, then any decision results in an empirical “trial and error” type of treatment. This approach should be avoided if possible, and prior to definitive treatment, consultation with an endodontist or other colleague is in order. This consultation may be as simple as a brief conversation or even referral of the patient, but a second opinion is extremely useful in these situations. In most instances due to the interdisciplinary nature of modern dentistry, consultation with other clinicians who are treating the patient becomes a necessity to enhance the potential for successful treatment outcomes.
Occasionally, a patient will have persistent symptoms that mimic posttreatment disease, but these symptoms are actually the result of nonendodontic conditions such as occlusal trauma, concurrent periodontal disease, or nondental pain conditions. Appropriate diagnostic procedures should allow the clinician to sift through these options and treat accordingly.
The patient harboring true endodontic posttreatment disease has four basic options for treatment, which are as follows:
- 1.
Do nothing
- 2.
Extract the tooth
- 3.
Nonsurgical retreatment
- 4.
Surgical retreatment
The first option is to do nothing with the condition and allow it to take its course ( Fig. 8-10 ). This approach is sometimes a useful, short-term option if the etiology of the condition remains unknown and the clinician feels that another diagnostic sampling would help with diagnosis. Even though most clinicians would find this approach to be a less than desirable long-term course of action, the decision belongs to the patient. The clinician is bound, however, to ensure that the patient has complete information about what will happen if nothing is done. The events in the progression of the disease and a reasonable timeline are necessary, and the conversation needs to be thoroughly documented in the patient record to avoid possible subsequent accusations of abandonment. The question of whether the clinician is required to follow up with the patient or dismiss the patient from the practice is one that each clinician must make based on the clinician’s experience, judgment, and knowledge of the patient.
Extraction of the tooth is usually considered a viable option. Advances in both prosthetic reconstruction techniques and dental implantology have made extraction and replacement a more desirable option in certain cases where previously “heroic” (read “expensive with an unknown prognosis”) methods were needed to “save” the tooth. This alternative, however, provides results that are inferior, more expensive, and much more time consuming than preserving the natural tooth. The average titanium root-form implant restoration can take up to 6 months to finish, not counting preimplant site preparation, which can add months more. Despite published long-term success rates for dental implants, postimplant disease does occur ( Fig. 8-11 ) and can leave the patient with few options. The cost of implant treatment is high and usually not covered under dental benefit plans, so the net financial impact on the patient is large. Implant aesthetics can be inferior to that of natural teeth in the aesthetic zone of the mouth, and some patients are just not candidates for implant procedures. Fixed partial dentures are another replacement alternative with a long history of successful use, but negative outcomes are also possible. Most concerning to the endodontist is the likelihood that retainer fabrication procedures will result in endodontic disease of the abutment teeth, which may potentially occur at a rate of up to 10% ( Fig. 8-12 ). Removable partial dentures are a less desirable option to the patient because they are generally less comfortable, usually require a long period of patient adaptation, and frequently result in damage to adjacent oral tissues (tooth, gingiva, and mucosa) if not meticulously cleaned. Due to these factors, patient compliance with removable dentures is relatively low, and their use is declining. Occasionally, a patient will choose to have a tooth extracted and not pursue replacement. This decision is usually disastrous for the patient, but there are a few situations where this choice is a reasonable alternative. Diseased maxillary second molars with no opposing tooth, or with an opposing tooth in class I or class III occlusion that articulates with another tooth, may be extracted without concern for future inappropriate movement of the remaining teeth, which can be so occlusally and periodontally damaging. In most instances, however, removal of a tooth will result in the need for replacement, and unless the tooth is hopelessly nonrestorable, retaining the tooth with endodontic procedures is better for the patient.
Various situations may render a tooth nonrestorable ( Fig. 8-13 ); however, the line of demarcation between restorable and nonrestorable is a movable one, depending on who is evaluating the tooth. There are several widely agreed upon situations that render a tooth nonrestorable. These include extensive caries or coronal fracture approaching or entering the furcation or the biologic width. This situation may render preprosthetic periodontal procedures ineffective (leaving a furcation involvement or poor crown-to-root ratio, for example) or, worse, removes bone that would otherwise be useful for implant procedures. Terminal periodontal disease (extensive pocketing or mobility) or root fracture generally result in loss of the tooth despite all efforts at treatment. If the patient has a life-threatening endodontic infection with extensive trismus, most oral surgeons are going to extract the tooth rather than allow less aggressive management. Some previously root-filled teeth may have endured procedural complications, such as a nonretrievable separated instrument or irreparable ledge formation. In combination with the proximity to vital anatomic structures, such as the inferior alveolar canal, endodontic retreatment, either surgical or nonsurgical, may not be feasible and extraction may be the only option. These situations are, fortunately, quite rare, and in most instances, teeth presenting with posttreatment disease can be retained with endodontic procedures.
Once the decision has been made to retain the tooth, there are several choices for treatment. These can be grouped together into either nonsurgical or surgical endodontic treatments. The surgical options can be further broken down into periradicular curettage, apical root resection (with or without root filling), root amputation or hemisection, and intentional replantation (extraction/replantation). Occasionally, a situation arises that will require both nonsurgical and surgical types of treatment to effect healing. The American Association of Endodontists has published guidelines that may help the clinician with clinical decision making. However, the choice of which option to undertake will be determined by the clinician’s experience, knowledge, patient considerations, and the preoperative diagnosis. If the etiology of the posttreatment disease can be made known, the choices become more obvious. In a previous section, four basic etiologies were presented. If the suspected etiology is in the first group, which is persistent or reintroduced microorganisms, then several choices are available. However, if the cause of the posttreatment disease is persistent extraradicular infection, foreign body reaction, or the presence of a true cyst, then nonsurgical root canal therapy has little likelihood of allowing healing to occur, and surgical methods should be employed. The problem for the clinician is that in most instances, it cannot be determined which of these etiologies exist, so the treatment becomes more empirical.
The choice of nonsurgical retreatment versus apical surgery becomes the focus of the decision in most instances. Outcomes assessment studies provide some help in making this decision. The reported healing rates of nonsurgical retreatment range between 74% to 98%, but with apical surgery alone, only 59% heal completely. When apical surgery is preceded by orthograde retreatment, however, the incidence of complete healing rises to 80%. In general, nonsurgical retreatment will be the preferred choice, because it seems to provide the most benefit with the lowest risk. It has the greatest likelihood of eliminating the most common cause of posttreatment disease, which is intraradicular infection. Nonsurgical retreatment is usually less invasive than surgery and has a less traumatic postoperative course. There is less likelihood of incurring damage to adjacent vital structures such as nerves, adjacent teeth, and sinus cavities. However, nonsurgical retreatment may be more costly than surgical treatment, especially if large restorations must be sacrificed during disassembly procedures prior to the retreatment. In addition, the amount of time needed for retreatment is usually longer than surgical intervention. There are times when the clinician may not be able to achieve the complete elimination of microorganisms from the canal space, and complete obturation may not be possible. Apical surgery is chosen, therefore, when nonsurgical retreatment is not possible or when the risk-to-benefit ratio of nonsurgical retreatment is outweighed by that of surgery.
There are many factors to consider when deciding whether to retreat surgically or nonsurgically (see also Chapter 9 ). The patient must be fully aware of the proposed treatment and the alternatives, and he or she must be motivated to follow through with all treatment including the final restoration. The patient must have adequate time to undergo the required procedures. If he or she does not, then apical surgery alone may be indicated although the patient must be made aware of the potentially compromised nature of the treatment. Clinicians must be armed with the best equipment and knowledge available, and critical self-evaluation should allow experienced clinicians to know what they can treat and what they cannot. The tooth must be restorable and retreatable. Attempting nonsurgical retreatment on teeth where there is little likelihood of improving the previous treatment provides little benefit to the patient. Thus, in disease situations where there is an apparently adequate root filling and no evidence of coronal leakage, surgery may be indicated. If the previous treatment falls below any acceptable standard and there is no evidence of apical periodontitis, then there is no indication for any treatment unless a new coronal restoration is planned. In that case, conservative retreatment is indicated, and the reported success rates are very high. If there has been a previous procedural complication, such as a ledge that cannot be bypassed or a separated instrument that cannot be removed, then surgery may become a better option. Most times, however, it is still prudent to attempt the retreatment because ledges or separated instruments that appear impenetrable on diagnostic films can frequently be bypassed. Even if they cannot, nonsurgical retreatment can enhance the success of subsequent apical surgery as noted previously. The clinician must be careful not to worsen the situation by overly vigorous attempts to treat the previous complication, as root perforation, worsening of a ledge, or another separated instrument may be the result. Previous failed apical surgery should be retreated nonsurgically and then followed up because many surgical failures are due to poorly cleaned and filled canal systems ( Fig. 8-14 ). In many instances, performing the surgery a second time can be avoided altogether. If there is evidence of root fracture (narrow-based probing defect or a “J”-shaped radiolucency encompassing the root apex and progressing in a coronal direction ( Fig. 8-15 ), then nonsurgical retreatment would be unlikely to improve that situation. Apical exploratory surgery may be necessary, which could result in root resection or even extraction of the tooth.
Each case should be approached as a unique set of considerations that need to be reviewed and interpreted prior to selecting a treatment method. Once the selected option is undertaken, however, the prudent clinician is always watchful, as additional pieces of information can be discovered during treatment that may modify previous decisions.
Nonsurgical Endodontic Retreatment
The primary difference between nonsurgical management of primary endodontic disease and that of posttreatment disease is the need to regain access to the apical area of the root canal space in the previously treated tooth. After that, all of the principles of endodontic therapy apply to the completion of the retreatment case. Coronal access needs to be completed, all previous root-filling materials need to be removed, canal obstructions must be managed, and impediments to achieving full working length must be overcome. Only then can cleaning and shaping procedures be instituted that will allow for effective obturation and case completion. The remainder of this chapter is devoted to these topics in the order that they generally present themselves to the clinician treating the previously root-filled tooth.
Coronal Access Cavity Preparation
Retreatment access has been called coronal disassembly because of the frequent need to take apart or remove the previous coronal and radicular restoration. Following initial endodontic therapy, most teeth require and receive a full coverage restoration, and many times that restoration is supported by a post and core. Coronal-radicular access for retreatment is much more complicated in these cases when compared with endodontically treated teeth that have been minimally restored. The goal of the access preparation is to establish straight-line access to the root canal system while conserving as much tooth structure as possible. The ideal access preparation allows for instruments to enter the canals without being deflected by the access cavity walls. This is reasonably easy to achieve when the tooth is completely intact and a pulp chamber is present, because surface and internal anatomic landmarks can guide the search for the canals. Unfortunately, when endodontic retreatment is necessary, the tooth structure has almost always been altered and is commonly quite misrepresentative of the original anatomy of the tooth.
When presented with a tooth in need of retreatment that has a full coverage restoration, the decision for the clinician becomes whether to attempt to preserve the restoration or to plan its replacement. This decision is made simpler if there is a defect or caries associated with the restoration or if the treatment plan calls for a new crown. The old one is simply removed and replaced later in the treatment sequence ( Fig. 8-16 ). When the crown is considered to be satisfactory, the decision becomes more complex. If the restoration is maintained, the cost for replacement can be avoided, isolation is easier, the occlusion is preserved, and the aesthetics will be minimally changed. Even if the crown requires replacement, the clinician may elect to retain it during the endodontic retreatment to allow for better isolation with the rubber dam. Unfortunately, retreatment may be more difficult with the crown in place, as this could lead to an increased chance for an iatrogenic mishap due to restricted visibility. In addition, removal of canal obstructions, such as posts, will be more difficult, and there is an increased chance the clinician may miss something important such as hidden recurrent caries, a fracture, or an additional canal. To preserve the restoration, two approaches can be taken: access through the crown or crown removal and replacement when retreatment is completed. The simplest choice is to prepare an access cavity through the existing crown, although there is a significant risk of damaging the restoration resulting in the need to replace it. This risk must be communicated to the patient prior to instituting therapy. If the clinician decides to access through the existing restoration, there are several choices of access burs to use, depending on what material the preparation will be cut through. If the access will be primarily cut through metal (amalgam alloy or cast metal) or composite resin, carbide fissure burs such as the #1556 are usually chosen. With many restorations, it is advisable to consider using a combination of burs to achieve access. For example, when a porcelain fused to metal crown is encountered, a round diamond is used to cut through the porcelain layer. Once the metal substructure is encountered an end-cutting bur, such as the Transmetal bur (Dentsply Maillefer, Ballaigues, Switzerland) or the Great White bur (SS White, Piscataway, NJ) can be used to cut through to and remove the core material efficiently. An important consideration for the clinician is the potential for porcelain fracture, which may occur during the preparation or possibly at a later date after completion of the treatment. This damage is especially common with porcelain jacket crowns. Restorations fabricated completely of porcelain are becoming more and more popular, thus creating added concern due to the increased likelihood of crack formation during access. Porcelain is a glass, and drilling through this material will create many microfractures, which in turn, may weaken the structure of the restoration, making it more prone to future failure. Copious coolant water spray and the use of diamond burs are recommended during access through porcelain to minimize occurrence of this event. In a novel approach, Sabourin and colleagues recently showed that, compared with the use of drills, air abrasion produced almost no defects in the porcelain structure of all ceramic crowns when used for endodontic access. It was, however, significantly more time consuming to access through the crown this way.
If the decision is made to remove the crown for reuse, the visibility is increased, allowing for much easier removal of canal obstructions and a decrease in the potential for operator error; however, rubber dam clamp placement and tooth isolation may become a bigger problem. Also, despite all of the varying techniques and armamentaria available for removal of an existing restoration, the procedure remains unpredictable and many times can also result in damage to the restoration or the inability to remove it at all.
The clinician must decide how to remove the crown. If the crown is of no value, even as a temporary, then the clinician can take the easiest road and simply cut it off. However, if the crown is to be preserved, then a more conservative approach must be used. Two considerations, which may influence the decision about removal of a crown or bridge, are what material the restoration is made of and what is it cemented with. Conservative removal efforts are difficult with traditional, all-metal restorations cemented with nonbonded cements. This situation has been even more of a concern lately due to the increasing popularity of tooth-colored restorations, mainly different types of porcelain or porcelain fused to metal (PFM) restorations, which are being bonded to the tooth. These restorations are less likely to withstand the stresses of removal than those fabricated entirely of metal, and restorations that are bonded are much more difficult to remove due to the adhesive strengths of bonding agents. Each new generation of bonding agent is stronger than the previous, making removal increasingly more difficult as cosmetic dentistry advances.
Many devices have been developed specifically for the conservative removal of crowns. Some of the more commonly used devices are forceps that have been designed specifically for crown removal such as the K.Y. Pliers (GC America, Alsip, IL) ( Fig. 8-17 ), which use small replaceable rubber tips and emery powder to enable a firm grasp of the crown without damaging it. Other instruments of this type include the Wynman Crown Gripper (Integra Miltex, York, PA), the Trial Crown Remover (Hu-Friedy, Chicago, IL), and the Trident Crown Placer/Remover (CK Dental, Orange, CA). Unfortunately, a crown that has been cemented with long-term cement or has been bonded to the tooth will usually not be removed with one of these instruments. There are also forceps designed specifically to engage the margins of the crown while using an adjacent tooth as a fulcrum. Squeezing the handles together will cause the crown to be elevated off of the tooth. The Roydent Bridge Remover (Roydent, Rochester Hills, MI) works in this fashion and can be effective in crown removal, but care must be taken to avoid damage to fine, fragile margins, especially on porcelain crowns. Another type of instrument can be engaged under the margin, and a subsequent impact delivered at this site will dislodge the restoration. The Easy Pneumatic Crown and Bridge Remover (Dent Corp, White Plains, NY) and the Coronaflex (KaVo, Lake Zurich, IL) create this impact from compressed air, whereas the Morrell Remover (Henry Schein, Melville, NY) applies the force manually using a sliding weighted handle. The ATD Automatic Crown & Bridge Remover (J. Morita, Irvine, CA) uses vibrations to break the crown-to-preparation bond, and the Crown-A-Matic (Peerless International, N. Easton MA) delivers a shock impulse to loosen the crown. As mentioned earlier, crown margin damage may result, as can inadvertent extraction of the tooth if the periodontium is compromised ( Fig. 8-17, E ). A different approach to conservative crown removal involves drilling a small hole through the crown to allow a device to thread a screw through the hole. This approach creates a lifting force that separates the crown and the tooth. The instruments that work in this manner are the Metalift (Classic Practice Resources, Baton Rouge, LA), the Kline Crown Remover (Brassler, Savannah, GA), and the Higa Bridge Remover (Higa Manufacturing, West Vancouver, BC, Canada). Although very effective on metal crowns, these instruments may cause damage to porcelain occlusal surfaces on PFM restorations, and their use in both anterior teeth and in all porcelain restorations is generally precluded.
Another interesting technique designed to remove a crown without causing damage is performed using the Richwil Crown & Bridge Remover (Almore, Portland OR). This material is a water-soluble resin, which is softened using warm water ( Fig. 8-18 ). The small block of material is placed on the crown to be removed, and the patient bites into this material until the resin cools and hardens at which point the patient opens his or her mouth, generating enough force to pull the crown off. The clinician must be careful to avoid using this technique when the opposing tooth is extensively restored, because the opposing restoration may inadvertently be removed during the procedure. None of these techniques works in every case, and they may produce damage to the restoration being removed or possibly others. These are, however, methods that are available and may work while permitting reuse of the restoration.
Post Removal
Once the access is prepared, it is common to encounter a post, as posts are frequently used in the restoration of endodontically treated teeth. The clinician may encounter many different types of posts during retreatment ( Fig. 8-19 ). They can be classified into two categories: prefabricated posts and custom cast posts. Historically, cast posts were more commonly used than prefabricated posts; however, since the 1990s, cast posts have become much less popular. The main reason for this decrease is the convenience of placing the prefabricated post immediately after post preparation as opposed to waiting for a laboratory to fabricate the casting. There is also less likelihood of the interappointment contamination that frequently occurs with temporary post/core/crowns that are needed for cast/custom post and core fabrication. Prefabricated posts come in a variety of shapes, designs, and materials. The shapes can be subclassified into two groups: parallel sided or tapered. The design of posts also can be subclassified into active (threaded), passive, vented, fluted, and acid-etched groups. There are also many materials that have been used to fabricate posts, such as stainless steel, gold, titanium, ceramic, zirconium, and fiber-reinforced composite posts. Cast posts, which are fabricated in a laboratory, will always be made up of precious or nonprecious metal alloys. These posts also come in a variety shapes and configurations because they are custom manufactured for each root in which they are placed. Most of these have some degree of taper, and many will be cast in one piece with the core included.
In addition to the shape, design, and material of posts, there are two more very important factors that will have some influence on the clinician’s ability to remove them. These factors are the adhesive material used to cement the post and the location in the arch of the tooth that requires post removal.
The same concerns regarding cements that were discussed in the section on crown removal apply to post removal. The main consideration is whether the post was cemented with traditional cement or bonded with a composite resin and dentin-bonding agent. Several post systems on the market today, such as the ProPost (Dentsply, York, PA), use acid-etched metal posts that are bonded into the canal with cements, such as Panavia (Kuraray America, New York, NY) or C&B Metabond (Parkell, Edgewood, NY). Removal of these posts is extremely difficult and occasionally impossible, regardless of which technique is used. One study has shown that heat generation with ultrasonic vibration may help to decrease retention of resin cemented posts, but concern for heat-generated periodontal ligament damage may preclude this technique.
With regard to location, the more posterior in the arch, the more difficult the post is to remove. This predicament is a result of accessibility. The more accessible the tooth is, the easier the post is to remove because the clinician will have more techniques and instruments available to use. Also, the more anterior the tooth is, the less the opposing occlusion will interfere with post removal.
Post Removal Techniques
After initial access and after the post to be removed has been located, the clinician is faced with the decision of how to remove it. Many techniques have been developed for the sole purpose of post removal. Regardless of which technique is chosen, there is one simple yet extremely important rule to follow: it is not only what is removed but what is left behind that is important. This rule applies to the removal of all intracanal obstructions. The reason for this rule is to make sure that the remaining tooth, after removal of the obstruction, can be restored predictably with a good long-term prognosis. For example, there is little use in successfully removing a post and leaving behind a root that is eggshell thin and prone to fracture ( Fig. 8-20 ).
The first step in post removal is to expose it properly by removing all adjacent restorative materials. With preformed posts, the bulk of the core material around the post and within the chamber can be removed with a high-speed handpiece using cylindrical or tapered carbide or diamond burs. When the majority of the restorative material is removed, a less aggressive instrument, such as a tapered bur in a slow-speed handpiece or a tapered, midsized ultrasonic tip, should be used to remove the last of the embedding core material. This process is greatly facilitated by use of magnification and illumination. Once there is minimal restorative material remaining, a smaller-sized ultrasonic instrument should be used to minimize the risk of removing unnecessary tooth structure or thinning of the post. The more post that is left, the more options for removal, and the more tooth structure that is left, the more options for restoration. At this point, a high-speed bur is too risky to use. When the core is cast in one piece with the post, a high-speed instrument can perform this process to generate a shape that can facilitate removal.
Once the post is well isolated and freed from all restorative materials, the clinician can begin the retrieval process. There are many instruments and kits on the market that can be used to remove posts; however, prior to using one, the retention of the post should be reduced. The clinician can usually continue to use the same medium-sized ultrasonic tip that was used to get to this point. Using this instrument at the interface between the post and the tooth (the cement line) and constantly moving it around the circumference of the post will disrupt the cement structure along the post/canal wall interface and decrease post retention facilitating removal, although the effects of ultrasonic vibration may be minimal in reducing retention of well-fitted, long, large-diameter titanium posts. Titanium has a lower modulus of elasticity than stainless steel, so it may dampen the ultrasonic vibrations, which may decrease the effectiveness of the ultrasonic; however, one study failed to duplicate this effect. Nonetheless, care should be taken not to push the ultrasonic tip against the post with too much force, as this will dampen the ultrasonic wave and actually reduce the effectiveness of this technique. Taking away a small amount of the dentin around the coronal aspect of the post is not critical at this time, as this will aid in the reduction of post retention without unduly weakening the root. If the root is thin, however, and the amount of space between the cement line and the root surface is restricted, the size of the tip that can be used may be limited. Unfortunately, the smaller tips are not only less effective for post removal, but they are also more prone to breakage. At this point, the ultrasonic handpiece should be used with copious air-water spray as a coolant. Due to the heat that can be generated from this procedure, the tip should be removed from the access every 10 to 15 seconds to allow the use of an air/water syringe not only to clean the area of debris but also to reduce the temperature produced that could potentially cause damage to the periradicular tissues. If a rubber dam is in place, the area around the post may be flooded with a solvent such as chloroform prior to activating the ultrasonic instrument, as this will help dissolve the cement around the post. Using a solvent in conjunction with removal of cemented obstructions may prove beneficial because the ultrasonic energy produced will set up shock waves in the solvent and make it penetrate deeper into the canal space, exerting a faster solvent action on the cement.
Using an ultrasonic instrument in this fashion is not simply helpful in reducing post retention; this may also prove to be all that is needed to remove the post. Many times, after judicious use of the ultrasonic instrument, the post will loosen and actually spin out of the preparation, completing post removal ( Fig. 8-21 ). In addition, if post removal cannot be accomplished in this manner, the resulting post exposure will be very beneficial in contributing to the predictable use of other techniques, as many of the instruments to be discussed involve using a trephine bur to shape the coronal end of the post. Ultrasonic exposure will facilitate this process. Another instrument to consider for exposing and loosening a post is the Roto-Pro bur (Ellman International, Hicksville, NY) ( Fig. 8-22 ). There are three shapes available, all of which are six-sided, noncutting tapered burs that are used in a high-speed handpiece around the circumference of the post. The vibrations created when the noncutting flutes come in contact with the post decrease the retention of the post, facilitating its removal.
If retention reduction does not remove the post, some form of vice is needed to pull the post from its preparation. Many post removal kits are available on the market today with varying degrees of effectiveness. One such device is the Gonon Post Removing System (Thomas Extracteur De Pivots, FFDM-Pneumat, Bourge, France), which is a very effective instrument for removing parallel or tapered, nonactive preformed posts. This kit utilizes a hollow trephine bur that is aligned with the long axis of the post and placed over its newly exposed end. The trephine then cuts in an apical direction, shaving off the post’s outer layer not only to remove tooth structure adjacent to the post but also to reduce the circumference of the post to a specific size and shape. This procedure is necessary to allow a specific, matched-size extraction mandrel to create or tap a thread onto the exposed milled portion of the post. Once the extraction mandrel with its associated washer/bumpers ( Fig. 8-23 ) is attached to the post, the extraction forceps or vice is applied to the tooth and post. Turning the screw on the handle of the vice applies a coronal force in a similar fashion as a corkscrew removes a cork from a bottle of wine. This method is effective because all the force is applied to the bond between the tooth and the post, ideally in the long axis of the root. The main problem with this technique is the size of the vice that can make access in the molar region and between crowded lower incisors difficult. Also, if the extraction force applied is not directed in the long axis of the root, root fracture may occur.
The Thomas Screw Post Removal Kit (Thomas Extracteur De Pivots, FFDM-Pneumat) ( Fig. 8-24 ) is an instrument designed specifically for the removal of active or screw posts. The trephine burs are identical to those used with the Gonon Post Removal System, although the extraction mandrels are threaded in the opposite direction. The mandrels are reverse threaded to enable them to tap onto the screw post in a counterclockwise direction so that continued torquing force while creating the thread will unscrew the post.
The Ruddle Post Removal System (Sybron Dental Specialties) ( Fig. 8-25 ) and the Universal Post Remover (Thomas Extracteur De Pivots, FFDM-Pneumat) were designed to combine the properties of both the Gonon and Thomas kits. Both of these very similar kits are useful not only for removing parallel or tapered passive types of posts but also for removing screw posts. They can even be adapted to remove large separated instruments in the coronal straight portion of a large canal. These kits also use a trephine bur to machine the post to a specific size that will dictate which mandrel to use. These mandrels tap in the counterclockwise direction so that the same taps can be used for both passive and active posts. Once the mandrel is tapped onto the post, the extraction jaws, or vice, can be applied and activated, enabling removal of passive posts, or the tap is continuously rotated counterclockwise to unthread screw-type posts.
Another device that works in a similar fashion as the Gonon and the Ruddle Post Removal System is the JS Post Extractor (Roydent Dental Products). The biggest advantage of this kit is the size, as this is the smallest of the kits that work using a pulling action, which may help in cases where access is difficult. However, this kit does have one disadvantage: it does not have as large of a variety of trephine burs and extraction mandrels as some of the others. Therefore, the size of the post may be a limiting factor.
Another post removal device is the Post Puller, also known as the Eggler Post Remover (Automaton-Vertriebs-Gesellschaft, Germany) ( Fig. 8-26 ). This device works in a similar manner as some of the others; however, there are no trephine burs or extraction mandrels. The design of this instrument enables it to be used more efficiently with the crown removed. In addition, the design also allows this instrument to be used for cases in which the post and core are cast as one unit. This device consists of two sets of jaws that work independently of one another. With this device, both the post and the tooth are reduced to allow attachment of the post puller. Because there are no trephine burs, this reduction is done with a high-speed handpiece and bur. Next, the first set of jaws are attached to the post while the second set of jaws push away from the tooth in line with the long axis of the tooth removing the post from the canal. Care must be taken to align the pulling forces of this instrument with the long axis of the root to prevent fracture, and also, this technique is not recommended for the removal of screw posts. In a survey of the Australian and New Zealand Academy of Endodontists, this was the most commonly used technique for post removal. However, in a survey of the American Association of Endodontists, this was one of the least used techniques. Clearly, techniques that are common in one country are not always that common in another.
The increased popularity of cosmetic dentistry has created an impetus toward the use of tooth-colored posts that are fabricated from ceramic, zirconium, or various types of fiber-reinforced composite. Unfortunately, as with all posts, cosmetic posts also will need to be removed periodically. Neither the use of the Gonon Kit nor ultrasonic instruments allows for removal of fiber posts, whereas the use of a high-speed bur to channel down through the post may result in a high rate of root perforation. The use of the Largo Bur (Dentsply) and the Peeso drill to remove these posts has been advocated, and most of the post manufacturers have removal burs in the kit. These manufacturers’ removal kits have been shown to be more efficient at removing their own fiber posts than the use of diamond burs and ultrasonics. In addition, a new bur, the GyroTip (MTI Precision Products, Lakewood, NJ), has been designed for the specific purpose of removing fiber-reinforced composite posts ( Fig. 8-27 ). These drills consist of a heat-generating tip designed to soften the matrix that binds the fibers within the fiber-reinforced post. The fibers within the post are parallel, which assists the axial travel of the drill through the center of the post. The fluted zone of the drill allows the fibers to be safely removed, creating access to the root canal filling. Above the fluted zone, a layer of plasma-bonded silica carbide reduces the heat generation that would otherwise occur if a smooth carbide surface were rotating in contact with enamel or dentin. This abrasive zone also provides for a straight-line access preparation and facilitates the placement of a new post. Ceramic and zirconium posts are usually impossible to retrieve. They are more fragile than metal posts, and though ceramic posts may be removed by grinding them away with a bur (a procedure with a high risk of root perforation), zirconium has a hardness approaching that of diamond and cannot be removed by this method.
Regardless of the post type or retrieval method used, once the post has been removed, the final step in exposing the underlying root filling material is to ensure that none of the post cement remains in the apical extent of the post space. This step can be easily accomplished by visualizing the cement using magnification and illumination and then using a straight ultrasonic tip to expose the underlying canal filling.
Potential Complications of Post Removal
As with many dental procedures, post removal has risks. These risks include fracture of the tooth, leaving the tooth nonrestorable, root perforation, post breakage, and inability to remove the post. An additional concern is ultrasonically generated heat damage to the periodontium.
Even though there may still be some who feel posts strengthen teeth, it is widely accepted that they do not. Actually, it has been shown that post preparation alone weakens teeth. Therefore, it seems obvious that any additional work, which may require removal of further tooth structure, will further weaken the tooth, increasing the likelihood of fracture. An in vitro study showed that cracks can form in radicular dentin during post removal using both the Gonon Kit and ultrasonics, but there was no significant difference between these two groups, and teeth with posts that were not removed. The authors speculated that the potential for vertical root fracture might increase; however, the clinical significance of this remains unknown. A more recent study, however, concluded that the incidence of root fracture during post removal was extremely low and that with good case selection, post removal is, in fact, a predictable procedure. If, however, post removal would also leave the remaining tooth structure in a state that may not be predictably restored with a good prognosis and if this situation can be predicted ahead of time, surgery may be the preferred treatment option.
Perforation is an additional possible complication that can happen during post removal, especially if the post is removed by simply attempting to drill it out with high-speed burs. If perforation occurs, the clinician should repair it immediately, as the prognosis will worsen as the time between perforation and repair lengthens. Once a perforation occurs, the clinician must reconsider the prognosis and determine whether the tooth should be salvaged. Terminating the procedure and pursuing a different treatment option could be considered at this point. Extraction and replacement with an implant or a fixed prosthesis was a treatment option prior to initiating the retreatment, and some may consider this treatment the best option once a perforation has occurred. However, with the development of mineral trioxide aggregate (Pro-Root MTA, Dentsply, York, PA), perforations can be repaired with a favorable prognosis. The techniques and materials for perforation repair will be discussed in detail in a later section of this chapter.
Another complication is separation of the post, causing removal of the coronal segment leaving a small portion of the post with even less accessibility. This separation will decrease the likelihood of removal and occurs more frequently when attempting to retrieve titanium posts.
The use of ultrasonic energy for prolonged periods of time can generate excessive amounts of heat. The heat generated can cause damage to the surrounding periodontium. This damage may be as serious as both tooth and permanent bone loss ( Fig. 8-28 ). For this reason, stopping periodically to cool off the area with a water spray is necessary. This will be discussed in detail in a later section.
If the clinician is unable to remove the post, he or she will be faced with a decision of what to do. This decision is based on whether the post is being removed for restorative purposes or due to the persistence of disease. If the reason is for restorative purposes and the clinician can adequately restore the tooth with the existing post or post segment, then he or she should do so. If the tooth cannot be properly restored without removal of the post and placement of a new post, then extraction and replacement with an implant or fixed prosthesis will be needed. If the reason for post removal is the persistence of disease, the tooth should be treated surgically and restored as well as possible.
Regaining Access to the Apical Area
Once the coronal-radicular access is made and all posts and obstructing restorations have been removed, then the clinician must regain access to the apical area by removing the previous root-filling materials ( Fig. 8-29 ). This part of nonsurgical retreatment is complicated by the large variety of types of root fillings used. Today, the majority of root fillings are performed using gutta-percha in various forms; however, many other materials have been and are still being used. Silver points were popular until the 1970s and various types of pastes are, unfortunately, still in use. The authors have seen cases of definitive root filling with phenol-soaked paper points and sometimes no root filling at all. New materials, such as Resilon (Resilon Research LLC), a soft polyester material that is bonded into the canal space, are coming on the market all the time. Though all root-filling materials have their advocates and their critics, the only certainty is that all will have some incidence of persistent disease and will need retreatment.
During the diagnostic phase, it is important to ascertain the nature of the root filling to minimize surprises when attempting retreatment. Sometimes this is readily apparent, but, in other instances, this determination may require contacting the previous clinician to discover what type of root filling was used. Occasionally, this information cannot be determined until canal entry, so extreme caution should be used when performing access so as not to possibly remove parts of the root filling that may be useful in its removal, such as the core material in solid core obturators.
Gutta-Percha Removal
One of the great advantages of using gutta-percha for root filling is its relative ease of removal. When the canal contains gutta-percha and sealer or a chloropercha filling, it is relatively easy to remove this material using a combination of heat, solvents, and mechanical instrumentation. Upon access, it is usually relatively easy to find the treated canal orifices with the visible pink gutta-percha material inside. Initial probing with an endodontic explorer into the material can help rule out the possibility that there is a solid core carrier. If there is a plastic carrier, then heat should not be used to remove the coronal gutta-percha (more on this later). If there is no carrier, heat is applied using an endodontic heat carrier that has been heated to a cherry red glow in a torch. Unfortunately, the carrier begins to cool upon removal from the flame, so many endodontists are now using a heat source, such as the Touch ‘n Heat (SybronEndo, Orange, CA) ( Fig. 8-30, A ), to provide constant, consistent heat application to soften the gutta-percha in the coronal portion of the canal. Care must be exercised, however, not to overheat the root, which can cause damage to the periodontal ligament. Thus, the heat should be applied in a short burst to allow the instrument to penetrate the gutta-percha mass, followed by cooling, which will cause the material to adhere to the heat carrier facilitating its removal ( Fig. 8-30, B ). After removing as much gutta-percha as possible with the heated instrument, then remove any remaining coronal material with small Gates-Glidden drills, taking care not to over enlarge the cervical portion of the canal. However, because the previously treated tooth may have had an under-prepared cervical third of the canals, these drills can also be used to flare the coronal aspect in an anticurvature direction to facilitate enhanced straight line access to the apical one third of the canal and to create a reservoir for potential solvent use. Again, probe the canal, this time using a #10 or #15 K-file. It is sometimes possible to remove or bypass the existing cones of gutta-percha if the canal has been poorly obturated, thus eliminating the need for solvents. If that is not possible, then a gutta-percha solvent must be used to remove the remaining material in the apical portion of the canal.
Several solvents have been recommended to dissolve and remove gutta-percha for retreatment ( Fig. 8-31 ) including chloroform, methylchloroform, eucalyptol, halothane, rectified turpentine, and xylene. All of the solvents have some level of toxicity, so their use should be avoided if possible; however, a solvent is usually needed to remove well-condensed gutta-percha. The most popular solvent is chloroform because it dissolves the gutta-percha rapidly and has a long history of clinical use. In 1976, the U.S. Food and Drug Administration (FDA) banned the use of chloroform in drugs and cosmetics due to a report of suspected carcinogenicity. There was no associated ban on its use in dentistry ; however, the report did result in the search for alternatives, some of which are listed earlier. When used carefully, chloroform is regarded as a safe and effective endodontic solvent. All of the others generally have been reported to be less effective or have some other drawback that limits their use. Xylene and eucalyptol dissolve gutta-percha slowly and only approach the effectiveness of chloroform when heated. Rectified turpentine has a higher level of toxicity than chloroform, and it produces a very pungent odor in the operatory. Halothane has been shown to be as effective a solvent as chloroform in several studies, but a more recent study indicated that the time for removal of the root filling was longer than when using chloroform. The increased cost and volatility of halothane and the potential for idiosyncratic hepatic necrosis make it less desirable to use as a gutta-percha solvent. Although methylchloroform is less toxic than chloroform, it is also less effective as a solvent for gutta-percha. Both halothane and chloroform have been shown to affect the chemical composition of dentin and may affect bonding strengths of adhesive cements to the altered dentin. The clinical significance of these effects remains unknown, however. The evidence for the carcinogenicity of chloroform in humans is suspect, but with careful use, its toxicity may be eliminated as a risk factor to both the patient and the personnel in the operatory. As such, its continued use as a gutta-percha solvent is recommended.
Using an irrigating syringe, the selected solvent is introduced into the coronal portions of the canals, which will then act as a reservoir for the solvent. Then, small hand files (sizes #15 and 20) are used to penetrate the remaining root filling and increase the surface area of the gutta-percha to enhance its dissolution. This procedure can be facilitated by using precurved, rigid files such as the C+ file (Dentsply Maillefer) ( Fig. 8-32 ), which can penetrate the gutta-percha mass more efficiently than the more flexible types of K-files. The newly introduced C+ file is a stainless steel, end-cutting hand file that is twisted from a square blank. The secret to its stiffness is that the taper varies along the shaft, giving it the rigidity and strength to cut through well-condensed gutta-percha efficiently. The gutta-percha must be removed carefully, however, to avoid overextending the resultant mixture of gutta-percha and solvent beyond the confines of the canal to minimize the risk of severe postoperative pain. Electronic apex locators are accurate in treatment and nonretreatment situations ; however, they seem to misread the working length frequently when gutta-percha is initially being removed. This clinical observation may be due to the file being covered with chloropercha that may affect its conductivity. It has been shown that apex locators may be less accurate in retreatment situations ; however, in this study the error was that readings indicated a working length that was too short. In a more recent study, an apex locator built into a rotary handpiece indicated working lengths that were too long in simulated retreatment situations. It is recommended that a radiograph be made to gain a preliminary measurement when the estimated length is approached in order to avoid overextending root-filling materials into the periodontium. Well into the retreatment, after the root fillings have been thoroughly removed, the apex locator will regain its accuracy if a clean file is used. Once the working length is reached, progressively larger diameter hand files are rotated in a passive, nonbinding, clockwise reaming fashion to remove the bulk of the remaining gutta-percha until the files come out of the canal clean (i.e., with no pink material on them). The solvent should be replenished frequently, and when the last loose fitting instrument is removed clean, the canal is flooded with the solvent, which then acts as an irrigant. The solvent is then removed with paper points. The wicking action of the absorbent points will remove much of the remaining film of gutta-percha and sealer that remains adhered to the canal walls and in the irregularities of the canal system. Verification of the cleanliness of canals after gutta-percha removal is not improved by merely using a microscope ; however, using kinked small files, the clinician should probe the canal wall looking for irregularities that may harbor the last remnants of gutta-percha. These irregularities can usually be felt rather than seen and should be cleaned using this method.
It should be noted that there exists a glass ionomer based endodontic sealer (Ketac-Endo, ESPE, Seefeld, Germany) that is used in conjunction with gutta-per cha. This sealer is virtually insoluble in both chloroform and halothane, and it must be retreated by removing the gutta-percha and then by using ultrasonics to debride the canal walls. Canal cleanliness can approach that of other gutta-percha retreatment cases, but it is difficult and time consuming to achieve this result.
Overextended gutta-percha removal can be attempted by inserting a new Hedstrom file into the extruded apical fragment of root filling using a gentle clockwise rotation to a depth of 0.5 to 1 mm beyond the apical constriction, which may engage the overextended obturation. The file is then slowly and firmly withdrawn with no rotation, removing the overextended material ( Fig. 8-33 ). This technique works frequently, but care must be taken not to force the instrument apically, which furthers the extrusion of the gutta-percha; in addition, the file may separate. The overextended apical fragment should not be softened with solvent, as this application can decrease the likelihood of the Hedstrom file getting a solid purchase of the apical extrusion.
Using rotary systems to remove gutta-percha in the canals has been advocated due to enhanced efficiency and effectiveness in removing gutta-percha from treated root canals. This has generally been borne out in the literature. Several types of mechanical rotary systems are available for gutta-percha removal, including rotary file systems such as the ProFile (Dentsply) ( Fig. 8-34 ), a mechanical push-pull, quarter-turn file system; the Canal Finder (Endo Technique Co., Tustin CA); and dedicated gutta-percha removal instruments, such as the GPX (Brasseler USA), the ProTaper Universal retreatment files (Dentsply) ( Fig. 8-35 ), and the Mtwo R (Sweden and Martina, Due Carrare, Italy). These engine-driven instruments mechanically chop up the gutta-percha and sealer while thermoplasticizing the root filling mass via frictional heat to aid in removal. A survey of Australian dentists showed that 54% of the respondents who perform endodontic retreatment used rotary instrumentation to remove gutta-percha either always (15%) or sometimes (39%) with an increased likelihood of rotary gutta-percha removal if the clinician had more experience with the use of these instruments. In vitro studies have generally shown these systems to be efficient in that they typically need less time to remove the bulk of the gutta-percha filling material than is needed for hand removal, although in two studies, they were slower to remove the root filling than hand filing Assessments of canal cleanliness and extruded apical debris generally indicated that there were no overall differences between hand and mechanical gutta-percha removal. In one study using Quantec SC instruments (Kyocera Tycom Corporation, Irvine, CA), however, it was found that hand files with solvent cleaned canals more effectively. This finding has been repeated using the ProTaper retreatment files ; however, in another study in the same journal issue, ProTaper retreatment files were found to leave canals cleaner than hand files. Clearly, this is an area where further research is warranted. It is recommended that after rotary gutta-percha removal, subsequent hand instrumentation is needed to remove the residual obturating materials completely from the canal. In several studies of mechanical gutta-percha removal, either the mechanical instruments or the tooth root fractured. However, this result was reported to occur less frequently when the instrument rotary speed was increased from 350 to 1500 rpm, and one study showed no separation or other canal defects when using dedicated retreatment files, the ProTaper Universal and Mtwo R instruments. The dedicated retreatment files have end-cutting tips to enhance penetration and removal of the root filling mass, thus increasing their efficiency ( Fig. 8-35, B ). This, in combination with flute design and techniques advocated, may be the reason for the potential reduced risk of separation. Although the mechanical gutta-percha removal systems may provide an enhanced efficiency, the increased risk of instrument separation, further complicating retreatment, may outweigh this benefit. Dedicated retreatment files may reduce this risk.
Engine-driven instruments can also help with the removal of residual root-filling materials after the bulk of the gutta-percha has been removed. A new instrument, the Self-Adjusting File (SAF; ReDent, Ra’anana, Israel), has been recommended for removal of the root-filling residue that remains after root-filling removal. When the Self-Adjusting Files were used after rotary retreatment files, reduction of canal residues were 66%, 68%, and 81% in the coronal, apical, and middle thirds of the canal, respectively, when compared with using ProTaper Universal retreatment files alone. Another study compared the use of ProTaper Retreatment files followed by F1 and F2 ProTaper instruments with the use of a #25 .06 Profile followed by the Self-Adjusting File for their effectiveness in removing gutta-percha-based root fillings. With the use of high-resolution micro-CT and an arbitrarily selected threshold of less than 0.5% residue remaining as effectively cleaned, none of the ProTaper group cases met this threshold, whereas 57% of the cases in the ProFile/SAF group met the threshold. Unfortunately, in both of the previously mentioned studies, none of the retreatment methods rendered all of the treated canals completely free of all root-filling residue.
Use of the Nd:YAG laser to remove gutta-percha from root-filled teeth has been investigated in vitro. The time taken to remove the gutta-percha was within the range of other studies of mechanical gutta-percha removal, and the addition of solvents did not improve the performance of the laser. As in most other studies, gutta-percha, in varying amounts, was left in the canals after laser removal. Root surface temperatures did increase, however, and without further investigation proving safety and efficacy, laser gutta-percha removal cannot be recommended at this time.
Resilon (Resilon Research LLC) ( Fig. 8-36 ) is a thermoplastic polyester polymer that is bonded into the canal space using an unfilled resin bonding system (Epiphany, SybroEndo, Orange, CA). It is also marketed as RealSeal (SybroEndo). It has been advocated as a root canal obturating material to replace traditional gutta-percha and sealer due to its apparent, enhanced sealing ability and potential to strengthen root resistance to fracture as a result of internal bonding. Resin-bonded obturation systems have been advocated in the past ; however, the difficulty to retreat canals filled with this obturating material has prevented its widespread use. The Resilon polymer itself is reported by the manufacturer to be soluble in chloroform and may be removed by heat application, a behavior that is similar to gutta-percha. Studies have shown that the polycaprolactone polymer of the Resilon is removed easily and leaves canal walls cleaner than removal of gutta-percha and AH+ sealer, although this finding has been disputed. Hassanloo and colleagues found that there was less residue on the walls when removing gutta-percha/AH+ if the materials were allowed to set for a longer period. This finding has been corroborated and indicates that there may be a temporal effect, which introduces a methodological bias in these studies. There may also be a problem with removal of the unfilled Epiphany resin sealer, especially because the sealer tags have been shown to penetrate deep into dentinal tubules and presumably also into anatomic ramifications of the canal that need cleaning during retreatment. More research into this interesting material and technique is warranted, especially to determine the best technique for retreatment. After the Resilon core has been removed using heat and chloroform, the authors would recommend the use of a resin solvent such as Endosolv-R (Septodont, Paris, France) ( Fig. 8-37 ) to attempt elimination of the unfilled resin sealer prior to instrumentation.
