Bone changes
The classic finding, periradicular rarefaction, appears as a radiolucent area surrounding the apex of a root (Figure 11). On rare occasions, these areas may also be seen midroot, but they will virtually always be associated with periapical disease.
Other, more subtle changes include a widened periodontal space, a thickened or discontinuous lamina dura, or even periradicular
opacities.
Some superimposed radiolucencies are artifactual. These structures (i.e. mental foramina) can be imaged over an apex and falsely appear as osseous rarefaction. Two clues indicate that superimposed
radiolucencies are artifactual. First, superimposed artifacts are typically seen on only one root. In contrast, it is rare
to find a true periapical lesion on only one root of a multirooted tooth. In addition, artifacts tend to be regular in appearance,
whereas true periapical lesions typically have irregular margins (but can be regular as well).
If any area is in question, it is best to expose an additional film with a slightly different angle. If a periradicular lucency
is still centered over the apex, it is likely real and not an artifact.
Tooth changes
Figures 12, 13A & 13B
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As a tooth matures, secondary dentin production will cause a decrease in canal width.19 When a tooth becomes nonvital, this development stops secondary to the death of the dentin-producing odontoblasts. Consequently,
nonvital teeth have a wider root canal width than the surrounding vital teeth (Figure 12).19 Conversely, on rare occasions, pulpitis may result in increased dentin production and create an endodontically diseased
tooth with a narrower root canal width (Figures 13A & 13B). This situation is especially common in teeth that are also periodontally diseased19 and could lead to a misdiagnosis of the endodontically diseased tooth as healthy and vice versa with the contralateral tooth.
Hence, it is important to evaluate adjacent and contralateral teeth.
Width discrepancy can be compared with any tooth (taking the size of tooth into consideration), but it is most accurate to
compare the contralateral tooth. It is important to expose the comparison view at the same angle, as root canals (especially
those in the canines in dogs) are not perfect cylinders. A change in the beam angle may affect the canal width on the radiograph.16
Endodontic disease may also be manifested radiographically as internal resorption16 because of odontoclastic activity within the root canal system due to pulpitis. These changes create an irregularly enlarged
region within an area of the root canal system (Figure 14).
Finally, external root resorption can be seen with endodontic disease. It will appear as a defect of the root's external surface,
generally accompanied by bone loss in the area (Figure 15). External resorption most commonly occurs at the apex in companion animals and is common in cats with chronic endodontic
disease.
Differential diagnoses for endodontic disease include normal anatomy, superimposed structures, neoplasia, and cysts.
COMMON DISORDERS
Several disorders are commonly encountered on dental radiographs of dogs and cats.
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