Interpreting dental radiographs is quite similar to interpreting standard radiographs except dental pathologies and radiographic changes may be subtle and some pathologies are unique to the oral cavity. Also, several normal anatomical structures may mimic pathologic changes.
This article highlights the most common oral and dental pathologies, which are illustrated by classic examples. Note that in practice these lesions may often be less obvious. Continuing education meetings and consulting services can give you more confidence with difficult cases.
IDENTIFYING THE IMAGED TEETH
Determining which teeth have been imaged requires not only a firm knowledge of oral anatomy but also of dental film design. Digital systems with veterinary templates do not require the clinician to determine which teeth are imaged since they are placed into that position by the program, assuming the images were properly placed within the system. If your system does not support a veterinary template, there is a mark on the image in a consistent location. Review the system instructions regarding its use.
Determining which tooth or teeth have been imaged requires three steps. The key involves the embossed dot on one corner of the film.1-4 First, place the convex (raised) side of the dot toward you and do not flip the film over. (This step is automatically done for you when using digital dental film systems.) This is labial film mounting, which is the accepted standard of the American Veterinary Dental College for film viewing. This positioning orients the film as if you were looking at the patient from a few feet away, and your eyes are in the same position that the X-ray tube was in when the film was taken.
Next, determine whether the image is maxillary or mandibular. Then rotate the film so the roots of the maxillary teeth point up, as if you were outside the patient's mouth looking in. Rotate mandibular films so that the roots point down.
Finally, determine whether the film shows the right or left side. Identify which end of the radiograph is toward the front of the patient and which is toward the back. Then imagine that the patient is standing in front of you with its nose pointing toward the front end of the radiograph and facing that direction. If the patient's nose is pointed to the right, you are looking at the right side of the patient's mouth. If the patient's nose is pointed left, you are looking at the left side. When positioned as described above, views of the incisors have right and left swapped, similar to looking at ventrodorsal abdominal films. So the left side of the correctly positioned film is actually the right side of the patient.
NORMAL RADIOGRAPHIC ANATOMY
Numerous structures within the oral cavity mimic pathologic states depending on the placement of the tube head and film.1,5-8 Knowledge of normal radiographic anatomy will help avoid overinterpretation.
Normal alveolar bone (Figure 1) will appear gray and relatively uniform throughout the arcade unless it is near a tooth root or another anatomical landmark such as a mental foramen. It is slightly more radiolucent (darker) than tooth roots are. It also appears slightly but regularly mottled (uniform throughout the arcade as opposed to mottled in a single area such as with neoplasia). Alveolar bone should completely fill the area between the roots and extend coronally to the cementoenamel junction. The root canals should all be of the same diameter, allowing for root canal width differences in relation to the size of the tooth.
Other than normal anatomical variations, there should be no radiolucent areas in teeth or bone. Normal variations include
Figures 1, 2, 3, 4, 5, 6
- A regular, thin radiolucent line (periodontal space) is seen around the roots.
- On radiographs of the mandibular premolars and molars, a thick, horizontal radiolucent line courses parallel and just coronal to the ventral cortex of the mandible (Figure 2). This line is a two-dimensional representation of the tubular mandibular canal.
- Two circular radiolucent areas are seen in the area of the apices of the first three premolars, which are the middle and caudal mental foramina (Figure 3).
- On rostral mandibular views, a radiolucent line is often present between the first incisors (Figure 4). This line is the fibrocartilaginous mandibular symphysis.
- In the rostral maxillary area, paired radiolucent areas caudal to the first and second incisors are the palatine fissures (Figure 5).
- A widening of the periodontal space at the apex of the canines may be normal (Figure 6) and not a periapical lesion. It is differentiated from pathology because it is regular and v-shaped, as opposed to irregular and round.