Interpreting Dental Radiographs

FIGURE 1A Patient positioned in lateral recumbency; the bisecting angle technique is used to obtain radiographs of the right maxillary fourth premolar (A). The plate or film should be parallel to the hard palate (white line). The direction of the tooth root to be imaged is represented by a black line. An imaginary line can be drawn halfway between the angle of the plate or film and tooth roots (ie, bisecting angle [gray line]), usually a 45-degree angle for the maxilla. The beam (ie, x-ray tube head) should be oriented perpendicular to the bisecting angle (gray line) so the actual size of the tooth is shown (B); a crown fracture with suspected pulp exposure is visible (arrow), and radiolucency can be seen around the apex of the distal root (arrowheads).

FIGURE 1B Patient positioned in lateral recumbency; the bisecting angle technique is used to obtain radiographs of the right maxillary fourth premolar (A). The plate or film should be parallel to the hard palate (white line). The direction of the tooth root to be imaged is represented by a black line. An imaginary line can be drawn halfway between the angle of the plate or film and tooth roots (ie, bisecting angle [gray line]), usually a 45-degree angle for the maxilla. The beam (ie, x-ray tube head) should be oriented perpendicular to the bisecting angle (gray line) so the actual size of the tooth is shown (B); a crown fracture with suspected pulp exposure is visible (arrow), and radiolucency can be seen around the apex of the distal root (arrowheads).

FIGURE 2A Patient’s head positioned in lateral recumbency; the parallel technique is used to obtain radiographs of the left mandibular first molar (A). The beam is perpendicular to the surface of the plate or film. The plate is parallel to the tooth in the mandible, caudal to the symphysis, so the actual size of the tooth is shown. A healthy tooth with no alveolar bone loss can be seen (B). The roots are completely covered with bone near the level of the cementoenamel junction and in the space between the roots (furcation). The periodontal ligament anchors the tooth to the alveolar bone, can be evaluated on the radiograph, and appears as a uniformly narrow, radiolucent space between the root and surrounding alveolar bone (arrowheads). Radiolucent areas at the apexes of certain teeth (eg, canines, mandibular first molars) are normal.^4,8 Comparison with the contralateral tooth likely shows a similarly small, uniform area of radiolucency and can be used to differentiate between artifact and pathology.

FIGURE 2B Patient’s head positioned in lateral recumbency; the parallel technique is used to obtain radiographs of the left mandibular first molar (A). The beam is perpendicular to the surface of the plate or film. The plate is parallel to the tooth in the mandible, caudal to the symphysis, so the actual size of the tooth is shown. A healthy tooth with no alveolar bone loss can be seen (B). The roots are completely covered with bone near the level of the cementoenamel junction and in the space between the roots (furcation). The periodontal ligament anchors the tooth to the alveolar bone, can be evaluated on the radiograph, and appears as a uniformly narrow, radiolucent space between the root and surrounding alveolar bone (arrowheads). Radiolucent areas at the apexes of certain teeth (eg, canines, mandibular first molars) are normal.^4,8 Comparison with the contralateral tooth likely shows a similarly small, uniform area of radiolucency and can be used to differentiate between artifact and pathology.

FIGURE 3 Radiograph of a normal mandibular canine. The periodontal ligament space is visible as a radiolucent line and is uniform in all areas surrounding the root (arrows).

FIGURE 4 Widening of the periodontal ligament space can indicate pathology, which is suspected in this right mandibular canine tooth. Radiographs of the tooth can be compared with its contralateral counterpart when there is concern about pathology (eg, tooth vitality, root resorption, periapical radiolucency). Widening of the periodontal ligament space is evident at the apex (arrows) when compared with the contralateral canine radiograph in Figure 3.

FIGURE 5 Radiograph of a left mandibular first molar with a uniform periodontal ligament space surrounding the roots

FIGURE 6 Radiograph of a contralateral right mandibular first molar showing widening of the periodontal ligament, seen as a large radiolucent area surrounding the mesial and distal root apexes (arrowheads)

FIGURE 7 Radiograph showing both horizontal (line) and vertical (arrows) alveolar bone loss. Bone loss from periodontal disease is often described radiographically as horizontal or vertical, and both types can occur simultaneously. Horizontal bone loss appears as a radiolucent area along the alveolar border; vertical bone loss appears as a radiolucent area along the long axis of the tooth root.⁴

FIGURE 8 Radiograph showing horizontal alveolar bone loss (solid line) along a right maxillary arcade. The normal level of the alveolar crest is also visible (dashed line).

FIGURE 9 Radiograph showing severe horizontal alveolar bone loss (solid line) around mandibular incisor teeth. The normal level of the alveolar crest is also visible (dashed line).

FIGURE 10 Radiograph showing tooth resorption in a dog that appears as loss of detail between the root and bone as well as loss of the periodontal ligament space. The periodontal ligament space is no longer visible in many areas around the right mandibular third premolar. Roots are difficult to distinguish from surrounding bone.

FIGURE 11 Radiograph showing tooth resorption in a cat. A large radiolucent area is visible in the crown of the mandibular first molar (white star), and there is loss of detail between the root and bone of both teeth. The third mandibular premolar has undergone complete stage 5 tooth resorption and has no visible tooth structure (black star).

FIGURE 12 Radiograph of mandibular canine teeth. The right mandibular canine pulp chamber is larger and likely nonvital (star). Visual inspection can help identify intrinsic staining if discoloration raises suspicion that a tooth is nonvital. Radiographs are still needed for complete examination. Assessment of pulp canal size can be particularly useful for diagnosing nonvital teeth. A common misconception is that the canal becomes uniformly wider after a tooth dies. In actuality it appears wider as compared with other canals because dentin production ceases once the tooth becomes nonvital. Vital teeth with intact pulp typically have odontoblasts that produce secondary dentin, causing the pulp chamber to continue to narrow.⁹ Radiolucent periapical areas and root resorption on radiographs also indicate a nonvital tooth. Lack of radiographic signs does not mean a tooth is vital. In this image, the pulp chamber of the right mandibular canine is significantly larger than the left, indicating the pulp is no longer producing secondary dentin and is nonvital. Enlargement of the pulp chamber is a definitive sign of nonvitality, but absence of enlargement does not confirm vitality.¹⁰ The nonvital tooth root is also shorter than its normal counterpart, indicating root resorption occurred secondary to endodontic disease.

FIGURE 13 Radiograph showing periapical radiolucency on the apexes of a left mandibular first molar. The tooth also has a congenital abnormality (ie, molar malformation). The pulp chamber is occluded by abnormal formation of dentin, visible as a radiopaque area (arrows). Malformation of the pulp chamber leads to the tooth becoming nonvital at some point after eruption.¹¹

FIGURE 14 Molar malformation is often bilateral, and the patient can be presented with draining tracts visible on the skin ventral to the mandible.

FIGURE 15 Radiograph of the right mandible in a cat, showing large, proliferative bone lesion with areas of radiolucency suggestive of bone lysis. Dental radiographs can help identify areas of abnormal bone and support suspicion of neoplasia. Histopathology can help confirm neoplasia and determine prognosis.

FIGURE 16 Age cannot be accurately determined with dental radiographs, but the open apexes in this image indicate a younger patient (likely <10 months of age). There is a radiolucent area at the apex and no end to the root (circle). Dentin walls are thin and more radiopaque than the wide pulp chamber (double-headed arrow) in younger patients.