Endodontics in 3D

Dr. Richard Kahan discusses case studies using cone beam computed tomography (CBCT) 

For a patient and the treating endodontist, a vertical root fracture (VRF) is a fairly catastrophic event. Bacteria from the canal spaces or from the gingival crevice will contaminate the crack surface with effective decontamination being impossible. Prognosis for the affected tooth will be hopeless. 

A VRF can be “crown up” (in the maxilla), which will be the extension of a vertical crown fracture through the root, or possibly less commonly, “apex down,” as a result of high forces of root canal obturation or rarely trauma. 

Early diagnosis of a VRF is critical to avoid the consequences of further fracture propagation, extensive related periradicular bone loss, and expensive and unsuccessful endodontic treatment. Recognition of the fracture though can often be impossible, particularly in the case of the “apex up” fracture. 

If the position of a fracture is favorable for direct vision, a “crown down” VRF can sometimes be seen on the outside of the root if the gingivae are not covering it. It will also be visible within a pulp chamber and at canal orifice level with magnification and maybe staining, but the extent of a fracture line running up along the canal wall can rarely be objectively assessed. This visual clarification can often only be done following extensive deconstruction of the tooth and effective debridement of the pulp chamber and canal orifices, which can take time. Another option can be surgical investigation taking back a gingival flap, which is invasive and also costly. 

A further clinical sign of a “crown up” VRF is the presence of an isolated narrow periodontal pocket. Bacteria from the gingival crevice will grow along the root fracture and cause adjacent bone loss, creating a fine vertical pocket to the level of fracture termination. This sign will be pathognomonic for a root fracture, but the narrowness of early pocket formation can make it difficult to find and effectively track. This is particularly so if the fracture is positioned interdentally, which it frequently is. 

This classical sign of pocketing can be radiographically recognized as increased widening of the periradicular periodontal ligament space on one or both sides of the root wall (Figure 1). These signs will be present as long as the fracture is relatively perpendicular to the X-ray beam. In more advanced cases where the fracture reaches the apex, it can be seen as a rather classic, J-shaped lesion as it loops around the root apex. 

Whereas picking up a root fracture from a standard periapical radiographic image can therefore be a  matter of luck, CBCT could be the diagnostic answer. The ability for CBCT to visualize tooth and root fractures is a controversial area, and the subject of a number of frankly ridiculous in-vitro investigations. Clinically, the contrast level of even the highest resolution CBCT scan is only likely to be able to visualize open crown and root fractures. The vast majority of the VRFs are closed, and the fracture line itself will not be visible. Furthermore, as root fractures are often associated with root filling materials, pins and posts, metallic and beam hardening artifacts will superimpose upon the root structure, rendering any image of the fracture unreadable. 

However, the main change that provides the diagnostic sign of VRF is within the periradicular bone, and CBCT offers an accurate circumferential view of the bone surrounding the root which can often be separated out from artifacts generated from internal materials. 

This ability to diagnose VRFs using CBCT before invasive and expensive investigations, or even endodontic treatment, offers significant advantages to both operator and patients. If a fracture can be quickly and accurately confirmed, the tooth can be removed before money is wasted on unsuccessful treatment, and the tooth replaced without the problems associated with severe alveolar bone loss. 

The case below describes how the consequences of misdiagnosis can be avoided with the use of a limited-volume CBCT scan. 

Clinical details 

A 32-year-old female was referred by her general dental practitioner for re-root canal treatment of her upper left second premolar (UL5). She had been complaining of a sore lump on the side of the gum adjacent to the UL5 that had appeared a few months before consultation. The lump would be variable in size, but the related teeth were comfortable in function with no significant discomfort. An onlay had been placed on the tooth a year earlier, and it had been root treated 13 years previously. 

Clinical examination revealed a good quality ceramic onlay present on the UL5. The tooth was slightly tender to percussion, and a small hard buccal swelling was present over the root apex which was tender to palpation. The gingival tissues were pink and healthy with no signs of bleeding on probing or deep pocketing. 

The general dental practitioner supplied a periapical radiograph (Figure 2), which showed a small coronal radiolucency (void) with a substantial centrally placed root filling terminating 1-2 mm from the radiographic apex. The root filling followed the slight distal curve in the apical third of the root with filaments of radiopacity extending from the termination of the fill suggesting some sealer spread into the apical deltas. Tracing the periodontal ligament spaces around the root showed some thickening of the ligament space along the distal root surface, and a second ligament space at mid-root level indicated either a second root or a groove along the primary root, which could be indicative of two root canals. The main periapical lesion was present at the mesial root apex with a smaller Iesion present at the distal apex. 

A provisional diagnosis of chronic periapical periodontitis was due to either apical recontamination or the presence of an untreated second canal. To further assess the cause of the problem, a limited volume (4 cm x 4 cm) CBCT scan was taken. Without access to this technology, a second angled periapical would have been taken. 

Scan analysis showed a single root with a cross-sectional figure-eight shape. A single canal was present and intra- and extraradicular symmetrical radiolucencies surrounding the root filling were present and due to beam hardening artifacts. There were no suggestions of voids within the canal system where untreated contaminants could have been present. Of particular significance was the presence of buccal and lingual vertical bone defects extending the full length of the root which culminated in a large lingually placed periapical lesion (Figures 3 and 4, vertical bone defects arrowed). A smaller buccal lesion had perforated the buccal cortical plate, resulting in the clinical symptoms of a lump (Figure 5). 

The appearance of vertical defects along the root surfaces were pathonomonic of VRF and present due to bacteria sitting along the fracture line causing adjacent bone loss. Despite the coronal extension of the vertical defects, no pocketing could be found using a fine gutta-percha cone; this was due to the fracture being “apex-up.” The lack of any disturbance to the mesial and distal PDL spaces was due to the fracture being bucco-lingual and in line with the beam of the periapical X-ray. 

The patient was advised that any treatment would be futile, and that the tooth should be extracted. She returned to her dentist for the extraction, and the diagnosis was confirmed on inspection (Figure 6).  

Discussion 

It would be useful to consider how the diagnosis and treatment plan would have turned out using purely conventional radiography as I would have done 6 years ago. A second angled radiograph would have been taken by a competent specialist endodontist, and this has been created virtually using a thick slice technique and angled from the mesial aspect, whereas the original periapical was angled a little from the distal aspect (Figure 7). Using this technique does show the reduced resolution of a CBCT thick slice, but no significant difference can be detected from this secondary angle. The diagnosis would therefore firmly be chronic periapical periodontitis with the likely causes possibly listed as coronal leakage, apical leakage, or missed/untreated canal anatomy. 

Treatment recommendation for the patient keen to save her tooth would have been conventional endodontic retreatment, likely to have a fair to good prognosis if treatment aims of full canal decontamination and sealing could be achieved. Access through the porcelain onlay and entrance into the canal system would have been uneventful with no signs of fracture along the buccal and lingual canal walls observed within the coronal third. 

The buccal apical swelling would have been unlikely to have receded following the first clean and dressing visit, and further disinfection may have been necessary a second time. Occasionally, the presence of heavy disinfection can reduce the bacterial load enough to reduce acute symptoms; however, in this case, this effect would not be long lasting; and at some point, either after completion or before, it would become obvious that treatment had not been successful or was not being successful. 

At this juncture, etiological theories may change to contamination of apical delta canals, extraradicular infection, or possibly cystic transformation; and apical surgery would be suggested; and it would only be at the stage of flap retraction and removal of some buccal bone that a vertical root fracture would be recognized and prognosis understood to be hopeless. 

By this time, the patient would have invested significant amounts of time, money, and aggravation in a futile attempt to save her tooth, further resulting in more bone loss and possibly a reduced prognosis for successful implant placement. Although the practitioners involved would be blameless, the whole episode would not reflect particularly well on them from the patient’s point of view. If it were me, I would be frustrated by my inability to effectively diagnose a hopeless situation. 

In reality though, early recognition through a simple 9-second scan identified the problem, and early extraction saved time, money, aggravation, and the unnecessary loss of bone vital for successful implant therapy. 

As a postscript, it is interesting to note that this case would not fulfill the current guidelines for CBCT scan justification. It would seem to be a fairly routine periapical lesion as a result of primary endodontic treatment failure, which is the daily bread and butter for the specialist endodontist. This prompts the question of when one should scan and when one should not. A tricky question for future discussion. 

My thanks to Dr. Piotr Strojek, BDS, MSc, for the referral and the use of his radiograph and clinical picture.