Failure of Nonsurgical Root Canal Treatment or Persistent Apical Radiolucencies

Several etiologies have been identified for persistent periapical pathosis following nonsurgical root canal treatment.* Of all factors identified, the only one for which nonsurgical revision would have a predictably high chance for success is the case of inadequate initial root canal treatment in which there are no iatrogenic alterations of the canal morphology^8,19 (Fig. 16-1). If the apical 2 to 3 mm of canal space was cleaned and shaped minimally in the original treatment or left completely uncleaned, the procedures of revision would not differ significantly from routine root canal treatment of any similar tooth.³ The prognosis for healing would be correspondingly very good (Fig. 16-2).

FIGURE 16-1 A, Maxillary lateral incisor with inadequate root canal treatment. Note that the apical canal anatomy has not been altered during the root canal. B, Mandibular molar with inadequate root canal treatment and persistent apical pathosis. There has been no alteration of the apical canal morphology, owing to complete lack of apical preparation.

FIGURE 16-2 A, Persistent periapical pathosis on a tooth with inadequate root canal treatment. B, Following removal of the crown and post, routine root canal procedures were used in revision. Reevaluation at 8 months indicating normal healing.

Inadequate nonsurgical root canal treatment in teeth with significant alteration of the root canal morphology is not unusual in cases with recurrent or persistent apical pathosis (Fig. 16-3). A poor healing response would be expected after nonsurgical revision owing to the increased difficulty or impossibility of cleaning, disinfecting, and obturating the altered apical canal anatomy. While the level of success with nonsurgical revision is below that of initial treatment,^32,74,75 nonsurgical revision is still indicated in most cases as the primary approach, since healing may be possible despite the diminished prognosis (Fig. 16-4). After a suitable period of healing time, usually 6 to 12 months, apical surgery would become the treatment of choice for those that fail to heal. In all cases of nonsurgical revision, the patient should be informed that healing may be delayed and surgical revision may yet be necessary.

FIGURE 16-3 A, Inadequate root canal treatment with significant alteration of the canal morphology. It appears that the apical foramen was grossly enlarged. B, Inadequate root canal treatment with perforation of the apical foramen. C, Inadequate root canal treatment with alteration of the canal morphology. Periapical surgery would be required to treat all three of these cases.

FIGURE 16-4 A, Recurrent periapical pathosis on a mandibular molar with inadequate root canal treatment. B, Working length measurement radiograph indicating significant alteration of the apical canal morphology from the original treatment. C, Reevaluation at 8 months indicating excellent periapical and furcation healing.

Four causes of persistent periapical pathosis that are unlikely to be identified or differentiated by clinical or radiographic means^41,42,74,75 are infection located in inaccessible spaces in the root canal system^{16,30,47–49,71} (Figs. 16-5 and 16-6), infection located outside the root canal in the apical lesion itself^47–49 (Fig. 16-7), true cysts or tumors (Fig. 16-8), and vertical root fracture (see Fig. 4-12, B). The chief clinical presentation is a nonhealing periapical lesion after acceptable root canal treatment. The specific etiology is usually not identifiable preoperatively and is confirmed either at the time of surgery by direct observation or later by histologic examination.^41,42

FIGURE 16-5 Demineralized tooth demonstrating inaccessible canal spaces at the apex along with the presence of silver cone corrosion product that contributed to persistent periapical pathosis.

FIGURE 16-6 A, 6-month reevaluation after root canal treatment of a mandibular left central incisor indicating the lesion had failed to heal. B, Postsurgical treatment radiograph. During surgery, multiple accessory canals were observed as the apical bevel was prepared. The canal had been well filled.

FIGURE 16-7 A, Large radiolucency around maxillary right incisors. Root canal treatment had no impact on the course of the acute infection. Infection gradually involved the bone of adjacent vital teeth. B, Surgical exposure and curettage 1 week after root canal treatment. The infection continued. The central and lateral incisors were ultimately extracted, after which healing progressed uneventfully.

FIGURE 16-8 A, Large radiolucency associated with a failed root canal with silver cones. B, Reevaluation after 6 months indicating radiographic resolution of the lesion. Histologic examination confirmed a true cyst.

Residual bacteria located in inaccessible parts of the root canal system have been the subject of considerable research. Histologic studies of resected root tips and microbiologic studies of bacteria sampled from root canals have identified that the majority of root canal treated teeth with asymptomatic periapical periodontitis harbored persistent bacteria in the apical portion of the complex root canal system.^{42,48,49,71,74} From a clinical standpoint, there is no available method to detect such spaces, but knowledge of their possible presence should serve to increase the thoroughness of canal preparation during routine treatment (Fig. 16-9).

FIGURE 16-9 A, Histologic section of a resected root apex from the mesial buccal root of a maxillary first molar. Note the canal with the arrow was cleaned, shaped, and obturated, but the canal configurations in the rest of the root were not touched during root canal procedures. Tissue debris is still present, and at the end of the root, there is a cyst forming (EP, epithelium). B, Resected root apex from a maxillary lateral incisor demonstrating multiple canal openings and irregularities. Thorough cleaning and disinfecting of these aberrations is all but impossible and may hold the irritants that result in persistent periapical pathosis.

Cases of persistent periapical infection caused by bacteria that persist after adequate root canal treatment are not common. In some cases, these pathogens have established a recalcitrant extraradicular infection that requires surgery.^61–63 The identification of pathogens implicated in this process is usually based on postsurgical histologic examination of the resected tissues.^15,61,62 Like true cysts or periapical pocket cysts (bay cysts),^41,42,53 the clinical diagnosis is usually a nonhealing periapical lesion of indeterminate cause.^61,62

The diagnosis of vertical root fractures was discussed in Chapter 4. Most of these defects will be found to extend through the gingival sulcus, exhibiting a unique periodontal defect that can be probed. In the context of etiology for persistent periapical pathosis, some vertical fractures may not probe or be detectable by radiographic means, such as the case presented in Chapter 18, Fig. 18-17. Occasionally during periapical surgery, a fracture line is observed to originate at the apex and extend coronally. If there is no extension through the attachment, the fracture line may be repaired as part of the root-end filling (Fig. 16-10).

FIGURE 16-10 A, Vertical root fracture extending coronally from the apex. It did not extend through the attachment. B, Repair of the fracture with mineral trioxide aggregate as part of the periapical filling.

Anatomic Obstructions

The standard of care for treatment of teeth with open apices centers around techniques and materials that result in the formation of a calcified apical barrier. Apical surgery would be indicated in cases that fail to develop the barrier or in which the canal anatomy prevents using the technique. Fig. 16-17 illustrates a case in which an early radiograph indicated the formation of a dens in dente in a maxillary lateral incisor.

FIGURE 16-17 A, Dens in dente formation in developing lateral incisor. B, Five–year reevaluation indicating an apical lesion and incomplete apex formation. The patient presented on emergency with an acute apical abscess. C, A 19-month postsurgical reevaluation indicating excellent healing.

Five years later, the patient developed an acute apical abscess, and the periapical film at the time of emergency treatment confirmed that the apex had not developed. It was judged that nonsurgical access through the dens in dente would be destructive and would in itself diminish the long-term prognosis of the tooth. Apical surgery in this case was the most effective and least invasive option.

One of the most common complications in routine root canal treatment is the presence of calcified material in the root canal space. Chapters 8 and 13 discussed the various techniques for successfully locating and penetrating canals that appear radiographically to be partially or completely closed. Nevertheless, some of these teeth are in reality calcified to the extent that penetration to the apex is not possible (Fig. 16-18). Apical surgery is indicated for any of these teeth with apical lesions or persistent symptoms, since root canal procedures terminating far short of the apical foramen are not likely to have any effect. The difficulty of penetrating calcified canals can lead to aberrant canal preparations that are often observed in cases with persistent periapical pathosis. It is rarely possible to successfully renegotiate the uncleaned canal spaces in these cases (Fig. 16-19).

FIGURE 16-18 Calcification made negotiation to the apex impossible in any canal in this maxillary first molar. Surgery is indicated if symptoms persist or an apical lesion develops in the future.

FIGURE 16-19 Mandibular molar with persistent periapical pathosis. The attempt to negotiate the mesial canals was unsuccessful. Periapical surgery was indicated.

It is almost always appropriate to make a traditional access to the canal space and attempt to locate the canal. Ultimately, if the canal cannot be negotiated, the attempt should be terminated before excessive destruction of coronal tooth structure or a perforation occurs. Subsequently the tooth should be restored and periapical surgery treatment planned (Fig. 16-20).

FIGURE 16-20 A, Severely calcified maxillary left central incisor with periapical pathosis. B, After a nonsurgical attempt to locate the canal, the access was permanently restored and surgery was completed.

Iatrogenic Obstructions

The term iatrogenic refers to adverse complications caused by previous treatment. In the case of obstructions, it would be the presence of irretrievable dental materials or instruments in the canal space that prevent the use of nonsurgical revision techniques (see Chapter 14). The placement of these materials could have been intentional, as in the case of posts, or accidental, as in the case of instrument separation. Chapter 14 describes the usual techniques for removing these materials or obstacles, but at times this is impossible, especially when the blockage is in the apical third or located in a curved canal. Periapical surgery is the only effective method to resolve the periapical pathosis and retain the tooth.

One technique which is particularly difficult to revise nonsurgically is the sectional silver cone that was placed to allow space for an intraradicular post. Fortunately, the use of silver cones is obsolete, but a legacy of cases remain. In the event the silver cone section is not removable nonsurgically, apical surgery is indicated. Fortunately in many cases, it is possible to remove the entire piece of silver cone from the apical direction because many will be found to be loose in the canal following resection. If the silver cone can be removed, apical preparation can proceed in the usual manner without complication.

If the silver cone cannot be removed, the apical preparation (described later in this chapter) becomes much more complicated. The metal will have to be cut back with a very small bur or diamond-coated ultrasonic tip to create a cavity preparation for the root-end filling material (Fig. 16-21). The same problem may be encountered with some paste filling materials that set to a hard consistency.

FIGURE 16-21 A, Root canal completed with a sectional silver cone. A symptomatic lesion is present. B, After an unsuccessful attempt at removal, surgery was completed.

When separated instrument fragments cannot be removed, surgery is indicated to clean and fill the apical portion of the root canal. If the instrument fragment does not extend to the apex, it is not necessary to remove it. In fact, the attempt to remove it may excessively destroy root structure. Instrument fragments at the apex or protruding through the apex can frequently be removed during surgery, which greatly facilitates apical preparation and placement of a root-end filling (Fig. 16-22).

FIGURE 16-22 A, Root-treated mandibular first molar with periapical pathosis. Note the separated instrument extending through the apex of the distal root. B, Immediate postsurgical radiograph indicating removal of the instrument fragment before placing the root-end filling.

(Courtesy Dr. Ryan Wynne.)

Intraradicular posts can be problematic in three ways relative to periapical surgery. Like other iatrogenic obstructions, they impede the use of nonsurgical revision techniques. Fortunately, modern technology makes it possible to remove most posts, but it is not always advantageous to do so. On occasion, the remaining tooth structure may be severely weakened, which will diminish the prognosis of the restored tooth even if the revision is successful (Fig. 16-23). Often, periapical surgery is the more conservative approach.

FIGURE 16-23 A, Fractured post in a short root: a treatment planning dilemma. B, Post removal completed. Although necessary for restoration, removal resulted in a very large post preparation and thin dentinal walls.

Secondly, although removal of the post is usually the treatment of choice, it is seldom possible to determine the extent to which a post may be essential to the retention of a restoration. Treatment planning for periapical surgery is sometimes based on the conservation of satisfactory functional or esthetic restorations even if the post could be removed (Fig. 16-24).

FIGURE 16-24

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