5.3 Irreversible Errors

Irreversible errors often are the product of reversible errors that were ignored or unidentified, compromising the endodontic treatment outcomes. Some of these errors can have greater impact than others depending on the magnitude, location, and stage at which they were introduced into the procedure. Errors discussed in this section include ledging, zipping, transportation, gouging, over-instrumentation, damage to the periapical tissues, and flare-ups.

5.3.1 Transportation

Transportation of the canal can be defined as “the initial deviation of the original root canal pathway by the removal of dentinal wall on the outer curve and may result in creation of a new canal pathway” (Fig. 5.2). Rotary files vary in the cutting efficiency at their tip. The more aggressive the tip is, the more likely it is to start creating its own path or “transport” the canal. Excessive pressure during rotary instrumentation of introducing larger files in smaller canals can result in aggressive cutting at the tip and loss of the flexibility of the file to be able to follow the original path of the canal. Files with a radial land behind the cutting edge are referred to as “landed files” and that geometric feature can help in keeping the file centered within the root canal system and preventing the file from deviating from the canal curvature to some degree. Holding rotary files at rotation short of the working length results in excessive grinding on the outer walls as the file tries to resolve to its original linear shape, especially files with less flexibility. If undetected, transportation may lead to hedging, zipping, gouging, or even perforation of the root canal wall.

5.3.2 Ledge

Canal ledge can be defined as “an iatrogenic error created during instrumentation of the root canal system resulting in an irregularity in the surface of the root canal system—often times the outer wall of the curvature – that result in the creation of an artificial step within the root canal wall that prevents file placement beyond the irregularity” (Fig. 5.3). Continuous instrumentation short of the working length can force the file tip to start deviating from the original canal anatomy and start creating its own path, which starts with a ledge. This will create a “step” within the root canal system which makes it difficult to bypass into the remainder of the canal especially with rotary files that cannot be precurved to bypass the ledge (Fig. 5.4). A ledge can be removed by successive enlargement of the canal to eliminate irregularities, but it depends largely on the size of the ledge. Ledges usually occur on the outer curvature of the canal walls where the file tip tends to straighten the canal and may result in the file abruptly stopping short of the working length since it’s hitting the step created every time the file glides through the canal. If unidentified, ledges can proceed into a larger gouging or elbow and eventually into apical perforation into the outer canal wall.

5.3.3 Zipping

A zip can be defined as an “iatrogenic error created during instrumentation of the root canal system resulting in a tear-drop irregularity in the outer wall of the apical third of a curved root canal system, it’s basically a transportation of the outer wall that results in a reverse-taper at the apical third.” The term “apical zip” was first introduced by Weine and Kelly in 1975 [17]. Zipping can result from introducing large size files to the working length and keeping the rotary file rotating around the curve close to or at the apex resulting in excessive grinding into the outer canal walls. Over-instrumentation of a curved canal beyond the apical foramen can also result in zipping since the file tip has no guidance within the inner walls of the canals, creating its own path by straightening the canal. Zipping the canal poses a challenge in establishing an apical stop at the working length and preventing extrusion of the materials beyond the apex. Precautions should be taken to prevent pushing obturation materials beyond the apex, and sometimes apexification with the creation of an artificial stop at the apical third of the canal should be considered to avoid overextension of obturation materials, especially if thermo-plasticized obturation techniques are to be used.

5.3.4 Gouging/Elbow

Gouging the root canal walls can happen at any level beyond the orifice and can be the result of forcing rotary instruments such as Gates-Glidden burs beyond the resistance level. Canal elbows are “the area of the root canal system immediately coronal to the transported or zipped irregular area.” The curved canal morphology shows an hourglass appearance.

5.3.5 Damage to the Periapical Tissues/Flare-ups

Defined by American Association of Endodontists [18], flare-up is the acute exacerbation of an asymptomatic pulpal and/or periradicular pathosis after the initiation or continuation of root canal treatment. The term has been generously used for situations not only limited to the abovementioned but also any significant additional development of symptoms or signs after procedure, whether it was initially symptomatic or asymptomatic and whether the treatment was still in progress or completed.

Flare-up complicates the treatment course. It is an undesired situation that makes the patient suffer both physically and psychologically. Although mostly minor to moderate [11], flare-up may turn into more severe and systemic complication, such as acute alveolar abscess and cellulitis. With the positive expectation after treatment, patient usually is frustrated and anxious when they experience flare-up. Patient may question the validity of the treatment and the competency of the practitioner. Practitioner, on the other hand, needs to arrange the unscheduled emergency, to repair the potentially undermined patient-doctor relationship and to manage the adverse clinical situation.

The frequency of flare-up varies from as low as 1.58% [12] to an average 8.4% by meta-analysis between 1966 and 2007 [19]. The older studies tend to have higher incidence, while the more recent ones generally have lower number with modern approach. The unclear definition of flare-up and different inclusion/exclusion criteria explain part of the variation. Risk factors such as sex, age, systemic diseases, preoperative pulp and periapical conditions, treatment modalities, inter-appointment medicament, and one- or multiple-visit treatment were widely investigated [11]. Among those, patient factors, such as necrotic pulp, symptomatic apical periodontitis, and acute apical abscess [20], and treatment factors, such as retreatment, over-instrumentation, and hyper-occlusion, have been associated with higher incidence of flare-up.

The etiologies of flare-up can be categorized into mechanical, chemical, and microbial [10]. A flare-up incident can be contributed to any one or a combination of any other two reasons. If not performed in a controlled manner, the mechanically insulted tissue would have increased but not reduced inflammation after procedure. The direct injury to the periapical tissue by extending instrumentation beyond apical foramen is a common reason for the development of postoperative pain. Once the inflammation is initiated, it takes 24–48 h before it subsides if without sustaining factors. In vital cases, the incidence of postoperative flare-up is similar between pulpotomy and incomplete/complete cleaning and shaping [11]. Hyper-occlusion directly challenges the periapical area and worsens the existing condition. Chemical agents including irrigation solutions, inter-appointment medicament, and obturation material bring significant inflammation to the periapical tissue if overextended. Both the mechanical and chemical insults usually result in immediate development of postoperative pain and/or swelling. The lack of continuing sustaining factors usually renders this situation self-limiting.

Microbial cause, however, requires close attention as it has greater association with flare-ups that develop into abscess and more. The microbial cause includes both the microorganisms and their by-products [21]. The changes of both the quality and quantity of microbial composition in root canal system and the periapical tissue after procedure, the increase of microbial loading by extruded infected debris, and the introduction of secondary infection from procedure or coronal leakage all account for flare-ups of microbial cause. Once active infection is established, it triggers a complex immune/inflammatory cascade locally and/or systemically, which turns into pain, swelling, abscess, or cellulitis depending upon host susceptibility [22].

The preventive measures should focus on minimizing mechanical, chemical, and microbial factors. Preoperative radiographs need to be of diagnostic quality with distinct contrast and correct proportion at different angles for anatomy assessment. Working length verification requires both radiographs and electronic apex locator for better accuracy [23]. Within the confine of root canal system and being passive, effective irrigation needs working concentration above threshold and sufficient volume, frequency, and adjunct effort such as mechanical or ultrasonic agitation to ensure and enhance its efficiency and efficacy [24, 25]. Early introduction and constant irrigation into root canal system, along with coronally directed instrumentation, minimize debris buildup and extrusion [26]. The dispensing of inter-appointment medicament prefers to have maximal contact area reaching full working length but not to be extruded to damage apical tissue [27]. The choice and design of the temporary restoration are based on the clinical situation for the protection of the integrity of the tooth structure and the prevention of secondary coronal infection before the tooth is permanently restored.

Contrary to the common practice [28], antibiotic prophylaxis has been shown to have no value to decrease the incidence of flare-ups [29]. However, pretreatment 30 minutes to 1 h before procedure and posttreatment for 24–48 h of NSAID (nonsteroidal anti-inflammatory drugs) or acetaminophen have been proven to reduce the incidence and intensity of postoperative pain significantly [30–32]. Long-lasting anesthesia such as bupivacaine block anesthesia also showed significant relief from central sensitization and decreased incidence and intensity of postoperative pain [33]. Occlusion reduction only helps if there were preexisting periapical symptoms [34].

As all the treatment risk and options, the best moment to inform and communicate with the patient is before the procedure. The potential incident of flare-up and its management should always be an essential part of postoperative instruction. Patient can therefore make an informed decision with full disclosure and mentally be prepared in the infrequent event of a flare-up. Once occurred, being suffered from the discomfort and distressed from the disruption of the recovery course, it is important to reassure the patient with genuine empathy, availability of timely care, reiteration of etiology and treatment outcome, and adequate effective management.

It is critical that whenever there is persistent, worsening, or additional symptom and/or sign, a differential diagnosis needs to be reestablished to rule out other offending source. A major part of the management has to do with the identification of infection in addition to inflammation. In the case of vital pulps, whether debrided completely or not, it is mostly inflammation by nature at least initially. Strategy to reduce inflammation is the goal. Pharmacological management such as the use of NSAID or intra-canal/systemic steroid has shown significant results [35, 36]. If incompletely debrided at the first place, a thorough pulpectomy should be considered to remove the remaining inflamed tissue. If completely debrided already, reentering the root canal system may not address the periapical inflammation unless there is drainage needed. Other identifiable factors such as history of overextended irrigants, inter-appointment medicament, and obturation materials share similar approach. Hyper-occlusion of the temporary restoration is another common irritating factor.

Cases that are initially vital when treated but without follow-up treatments or challenged by secondary infection because of inappropriate or overdue temporary restorations are susceptible to apical infection as in the necrotic cases. The clinical presentation includes typical signs of infection which include locally with significant exudation, swelling, abscess, and cellulitis or systemically with fever, chill, malaise, etc. This may require incision and drainage, drainage through the tooth, and antibiotic treatment.

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