Apical Lesions: Diagnostic Considerations

Dr. David A. Beach


“My dentist saw a dark spot on the x-ray.” This statement is commonly heard from patients in endodontic offices on a routine basis. What the patients are referring to is, of course, a possible abscess or some other form of periradicular radiolucency (PRRL). The diagnostic question the practitioner must answer is “What treatment is necessary?” Do all “dark spots” need treatment? The following case reports will highlight some of the diagnostic possibilities for various PRRLs.

The True Dental Abscess

One of the radiographic manifestations of a necrotic tooth can be a PRRL. Not all necrotic teeth will exhibit radiographic changes right away. In order to see a radiolucency on a periapical radiograph, erosion of the cortical plate is necessary. If a lesion is only confined to the cancellous bone, it will not be detected with a standard radiograph.1 The following case is a typical example of a necrotic tooth in need of endodontic therapy. A key point is that pulp vitality testing is important to determine if a tooth is truly necrotic and if any apical lesions seen are related to pulpal pathosis.

A 48-year-old male presented with pain when chewing associated with tooth No. 30. A periapical radiograph revealed a large PRRL (Figure 1a). Vitality testing with a cold stimulus produced a negative response in the tooth. Tooth No. 30 was diagnosed as necrotic with symptomatic apical periodontitis.

After administering local anesthesia, a rubber dam was placed to isolate the tooth, and access was made. The ProTaper Gold SX file (Dentsply Sirona Endodontics) was used to open the canal orifices. A 10 K-file was used to scout the canals, and working length was determined using the Root ZX (J. Morita). An endodontic glidepath was created using 10 and 15 K-files, and 6% sodium hypochlorite was used to flush debris. Following the establishment of a glidepath, the chamber was filled with sodium hypochlorite, and the series of ProTaper Gold instruments S1 through F3 (Dentsply Sirona Endodontics) were used sequentially in all canals. Copious irrigation with sodium hypochlorite was used after each file before proceeding to the next. Stainless steel hand K-files up to size 45 were used to finish the apical preparation of the distal root. Once instrumentation was completed, the smear layer was removed with 17% EDTA, followed by a sodium hypochlorite flush. With the canals and chamber filled with sodium hypochlorite, the EndoActivator (Dentsply Sirona Endodontics) was used in each canal to improve the penetration and disinfecting action of the irrigant. The canals were dried and sealed with a System B Heat Source Downpack (Kerr Endodontics) and an Obtura Backfill Device (Obtura Spartan). A temporary restoration was placed, and then the patient was referred back to his general dentist for the definitive restoration (Figure 1b). A radiograph taken at a recall appointment 2 years later shows resolution of the PRRL (Figure 1c).

Endodontic therapy performed on necrotic teeth should show resolution of a PRRL over time. It typically can take 6 months to a year for a lesion to show resolution on a periapical radiograph.2 Repair of the eroded cortical plate needs time to occur in order for healing to be measured by a standard radiograph. If an asymptomatic tooth has endodontic therapy and a lesion is present radiographically, it is important to get an accurate history of when the initial treatment was performed. This will allow a clinician to assess whether a new patient has a tooth that is in the process of normal healing or if pathosis may be developing.

Anatomic Structures

Not all PRRLs are indicative of pathology requiring endodontic therapy. Pulp vitality tests are incredibly important to avoid unnecessary and misdirected treatment. There are some common anatomic structures that can be mistaken for apical lesions resulting from tooth necrosis. These include the mental foramen near lower premolars, the incisive canal, and the nasal floor.

A 51-year-old female presented for evaluation of tooth No. 20. The patient was asymptomatic, but the referring dentist was concerned about the possibility of an abscess associated with this tooth (Figure 2). Vitality testing with a cold stimulus produced a normal response in tooth No. 20. The tooth had a normal pulp, and the PRRL was determined to be the mental foramen. When in doubt, test the vitality of the teeth in the area. Not all PRRLs require endodontic therapy.

Oral Pathology

Continuing along with this concept that not all PRRLs require endodontic intervention, there are other non-odontogenic entities that can produce changes on a radiograph mimicking lesions of endodontic origin.

A 56-year-old female was referred for evaluation by her general dentist due to “multiple abscesses” and was placed on antibiotics by the referring dentist. The patient was told she may need multiple root canals. The patient was asymptomatic, and a periapical radiograph of the lower anterior teeth showed numerous areas of possible concern (Figure 3).

Are these teeth necrotic, and are there multiple abscesses present? The answers to these questions start with the proper tests. Thermal testing with a cold stimulant produced a normal, positive response. An electric pulp tester, the Digitest II Pulp Vitality Tester (Parkell), also showed a positive “alive” response. The patient was asymptomatic, and the gingival tissues appeared normal in color and texture. No, these teeth were not abscessed. The teeth were vital and normal. No endodontic therapy was necessary. The condition shown in Figure 3 is periapical cemento-osseous dysplasia. Other forms and variants exist, such as focal cemento-osseous dysplasia, florid cement-osseous dysplasia, and cementoma. The key point is that these teeth are vital. If we keep a clear line of pulp status in our heads, we will simplify our diagnostic process greatly and avoid unnecessary antibiotic use or, worse, unnecessary endodontic therapy.

There are numerous benign or malignant tumors that can present as PRRLs. Keratocystic odontogenic tumors, central giant cell lesions, ameloblastomas, and metastatic lesions are just a few of the possibilities.3 An oral pathology angle should always be explored when concerns are raised diagnostically.

Vertical Root Fractures

The presence of a vertical root fracture (VRF) in a tooth with previous endodontic therapy can lead to the presence of a PRRL. This type of lesion will typically display a J-shaped pattern on a periapical radiograph in conjunction with an isolated, deep periodontal probing depth.4

A 61-year-old female presented for evaluation of tooth No. 14 (Figure 4). The tooth had existing endodontic therapy that was performed several years earlier. The patient was experiencing pain when chewing. A periapical radiograph revealed a J-shaped lesion extending from the apex of the mesiobuccal root coronally. Periodontal probing depths were within normal ranges around the tooth except for on the buccal side of the mesiobuccal root. At this point, the probe sank to the apex. A diagnosis of VRF was made.

Cone beam computed tomography (CBCT) has recently become a tool used in endodontic diagnosis. One of the biggest misconceptions with regard to this technology relates to its reported ability to easily detect VRFs in teeth. In order for a VRF to be visualized, it must be large enough to be visualized within the resolution of the CBCT scanner. Often, this is not the case, and a VRF cannot be directly seen.5 Interpretation of surrounding radiographic changes in the bone pattern around a tooth in question is an indirect method to detect a VRF by CBCT and requires experience in reading scans.6 While limited in its ability to detect VRFs, the importance of CBCT use in endodontic evaluation of PRRLs should not be discounted. It has been shown that a CBCT scanner can detect a lesion that may otherwise not be visible on a standard periapical radiograph.7 Remember, for a lesion to be visible, erosion of a wall of the cortical plate is necessary. With CBCT, this is not necessary, and it can detect early lesions that are only in the medullary bone. Figure 5 illustrates a case in which a CBCT scan was, in fact, necessary to visualize a hidden PRRL.

Missed Canals

A 62-year-old male presented with spontaneous pain in the upper left quadrant. Tooth No. 15 was tender to chewing and percussion. Existing endodontic therapy was present on tooth No. 15 and had been performed several years ago. A conventional periapical radiograph did not reveal any obvious lesions (Figure 5a). A CBCT scan was taken with the CS 9000 (Carestream Dental), and a clear radiolucency was visible at the apex of the mesiobuccal root (Figure 5b). Retreatment of tooth No. 15 was done, and an untreated second canal was found in the mesiobuccal root. This example shows the value of CBCT in detecting lesions that are difficult to detect using standard radiographic techniques.

The next time a patient presents with a dark spot on the radiograph, consider the many possibilities of its etiology. Not all PRRLs are the result of pulp necrosis. Oral pathological conditions, anatomic structures, root fractures, and even radiographic artifacts can present themselves in ways that mimic an abscess. One of the keys to successful diagnosis in endodontics revolves around assessing pulp vitality. If a tooth is testing vital and asymptomatic, think twice about jumping into endodontic treatment. There is an old saying worth mentioning here: “If all you have is a hammer, everything looks like a nail.” Endodontic therapy is not the answer to all periradicular radiolucencies.


  1. Bender IB, Seltzer S. Roentgenographic and direct observation of experimental lesions in bone: I. 1961. J Endod. 2003;29:702-706.
  2. Orstavik D. Time-course and risk analyses of the development and healing of chronic apical periodontitis in man. Int Endod J. 1996;29:150-155.
  3. Sirotheau Corrêa Pontes F, Paiva Fonseca F, Souza de Jesus A, et al. Nonendodontic lesions misdiagnosed as apical periodontitis lesions: series of case reports and review of literature. J Endod. 2014;40:16-27.
  4. Tamse A, Fuss Z, Lustig J, et al. An evaluation of endodontically treated vertically fractured teeth. J Endod. 1999;25:506-508.
  5. Chang E, Lam E, Shah P, et al. Cone-beam computed tomography for detecting vertical root fractures in endodontically treated teeth: a systematic review. J Endod. 2016;42:177-185.
  6. Fayad MI, Ashkenaz PJ, Johnson BR. Different representations of vertical root fractures detected by cone-beam volumetric tomography: a case series report. J Endod. 2012;38:1435-1442.
  7. Estrela C, Bueno MR, Leles CR, et al. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod. 2008;34:273-279.

Dr. Beach graduated magna cum laude from the University of Florida College of Dentistry in 2003. He completed his endodontic residency there in 2005. Dr. Beach is currently a Diplomate of the American Board of Endodontics and maintains a private practice in Wesley Chapel, Fla. Dr. Beach frequently provides continuing education lectures at local, state, and national study clubs and conventions. He can be reached at drbeachdmdms@verizon.net.

Disclosures: Dr. Beach reports no disclosures.

Related Articles

Advances in Biomechanical Preparation

Assessing Postoperative Pain After Endodontic Therapy

Assessing Endodontic Case Difficulty