You have to know what’s normal in dental radiography before you look for the abnormal, said Dr. Barden Greenfield, DAVDC, at a recent CVC. If you have digital dental radiography you must be performing dental radiographs on every case, Dr. Greenfield stresses. Why? A recent UC Davis study found that three out of 10 dogs and four out of 10 cats had disease that can only be diagnosed with dental radiography. This study also found that of those dogs and cats that had pathology, 50% had more than one problem.1,2
What Dr. Greenfield is saying is that if you’ve got it, use it.
Be rad, not sad
Here are what Dr. Greenfield calls the 10 keys to better understanding of normal dental radiographs.
1. Know your terminology and anatomy.
> The periodontal ligament space is very important, says Dr. Greenfield. It widens with disease, so pay attention to this space when taking radiographs, and really get to know it. The periodontal ligament space is there for protection as a shock absorber—it responds to shock by signaling pain. It is attached to the tooth root cementum and to alveolar bone; without that space there will be ankylosis, and the patient won't feel anything.
> The coronal aspect is another name for the tip of the tooth. With immature teeth, the apex is open until 10 to 12 months of age. Once the apex closes, no more eruption of a tooth can happen. More important, apical closure is important in the continued maturation of a tooth, which continues to grow internally throughout the life of the pet.
> Tooth buds can be seen in radiographs at about 8 to 12 weeks of age. Dr. Greenfield says you can take images at 12 weeks of age to see if a full set of teeth will come in.
2. Know your breed differences.
A few examples from Dr. Greenfield: Portuguese water dogs may have delayed tooth eruption, boxers have a high incidence of embedded maxillary and/or mandibular first premolars, and bulldogs and boxers have a wide mandibular symphysis. Variances should be appreciated. Historically, the smaller the breed, the higher the potential for more problems like tooth crowding, rotation and embedded teeth.
3. When looking at radiographs, place them the way the mouth is oriented.
If you have all of your radiographs assembled in a way that mimics the natural way the teeth fall in the mouth, it helps with localizing any problems.
4. Symphyseal widening or separation may not mean symphyseal fracture.
If you notice a non-traumatic symphyseal separation or laxity, don’t wire it. This laxity can be a result of periodontal disease, so treat the affected teeth and forego any wiring techniques, says Dr. Greenfield. That method of fixation should only be used when traumatic separation occurs. Extract the infected teeth and let the area heal if the cause is periodontal disease.
5. Know your radiograph artifacts, but don't throw the baby out with the bath water.
Dr. Greenfield says foreshortening and elongation are two common errors that can give the interpreter difficulty in adequately interpreting images. This is especially true with addressing endodontic disease, as foreshortened images make visualization of the apices more difficult. So change your angle if this occurs.
Overexposing and underexposing images are also quite common problems for the novice dental radiographer. Dr. Greenfield warns that many times, increased contrast can be more appealing to the eyes, but at a cost. Marginal bone (the bone level just below the gum line) may not be visualized with high contrast, so lower contrast, which may be a bit less clear, is preferred in many instances.
6. Look at the whole picture, not just the radiographs.
Is the tooth discolored? Is it broken? A discolored tooth is a dead tooth 93% of the time, says Dr. Greenfield. However, you may not see evidence of endodontic disease in a discolored tooth. Only 43% of discolored teeth show radiographic signs of disease (wide pulp cavity, apical lucency).
7. If it looks abnormal, always shoot the other side.
For example, the mandibular first molar may have a wide periodontal ligament space compared to other teeth, so compare this space with the contralateral first molar to determine if one space is wider than the other (see Chevron effect below).
8. Recognize anomalies.
Anomalies are still within the realm of normal, so if they’re not causing spatial problems then they can be left alone. Dr. Greenfield’s list of common anomalies:
> Chevron effect—normal radiographic artifacts that extend apically from the apex and can be quite large. They are regular in shape, extending the contour of the alveolus in a gently pointed arc. Endodontic disease appears as an expanded circular space.3
> Three-rooted maxillary premolars (second and third premolars) and second molars—normal maxillary second and third premolars have two roots. On rare occasions, they can have three roots, so they should be investigated carefully radiographically.
> Gemination tooth—incompletely separate crowns but a single root, commonly seen in incisors and first premolars (which are normally single-rooted).
> Tooth fusion—a developmental anomaly that occurs because of a union of one or more adjacent teeth.
> Curved root tips—roots are usually straight. Knowing your anatomy will save your bacon when extracting these teeth.
> Microdontia—smaller than normal teeth
> Supernumerary teeth—extra teeth
> Twinning—two of the same tooth
> Missing teeth
9. Know the three-rooted teeth—everybody has their kryptonite.
Dr. Greenfield’s clarion call: Charge more for your three-rooted teeth extractions because they are more work! Also, make sure you section these teeth prior to extraction, giving yourself three, one-rooted extractions.
10. Stop using the word “dental.”
It's an adjective, not a verb. Dr. Greenfield calls it a complete periodontal exam and therapy. It is also known as Oral ATP (assessment, treatment, prevention) or COHAT (comprehensive oral health assessment and treatment).
1. Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in dogs. Am J Vet Res 1998;59:686-691.
2. Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in cats. Am J Vet Res 1998;59:692-695.
3. DuPont GA, Dubose LJ. Atlas of dental radiography in dogs and cats. St. Louis: Saunders, 2009;24.