Intraoral radiology (Proceedings)

Veterinary dentistry is emerging as one of the fastest growing "new" disciplines of veterinary patient care. The days of bypassing the oral cavity as the physical examination is being performed are over. Understanding that the condition of the oral mucosa and the dentition can play a significant role in the overall health of the pet is vitally important. Some conditions that begin in the mouth can affect the pet's overall health, i.e. periodontal disease, feline odontoclastic resorptive lesions or lymphocytic-plasmacytic stomatitis. While other systemic conditions may be manifested in the oral cavity, i.e. renal disease, FIV, FELV or autoimmune diseases.

In order to fully appreciate and diagnose conditions of the oral cavity, intraoral radiology is an absolute must. Adequate and proper treatment can only be accomplished when accurate diagnoses are made. Disease isolation, treatment planning and monitoring, evaluating presence or absence of missing teeth, evaluating vitality of teeth, evaluating tumor margins pre-surgically, evaluating fractured or diseased teeth pre-extraction along with accurate record keeping can be accomplished with the assistance of oral radiographs. Equally important are post-treatment radiographs to prove complete extraction and monitoring of endodontic and periodontic therapy.

Intraoral radiographs can be taken with a standard x-ray machine using either standard cassettes or intraoral dental films inserted into the mouth. However, because of logistics of moving the patient from the dental operatory to the radiology table and back, you won't realistically do this more than once.

From 26 years of owning a veterinary practice, I can tell you that the best return-on-investment in equipment is a dental radiographic unit. It should easily pay for itself in 6 months. However, in order for this to be true, you have to use it. Buying one and then not using it because you don't know how or won't spend the time learning how will not prove to be profitable.

The same diagnostic benefits can be derived from either film or digital radiology. The pros and cons of both need to be weighed when making that purchasing decision. The same x-ray unit is utilized for both methods. In reality I would recommend both systems, digital and film. With film, there are 5 different sizes that can be used depending on the patient size and what is being radiographed. The most common size film for cats is size 0 and size 2 for radiographing the dentition. For evaluation of the nasal cavity a size 4 would work best. When working with film, additional supplies needed would be a chairside darkroom, film holders, developer and fixer solutions, drying clips, film mounts, film clips, small view box with magnification, filing envelopes and a storage cabinet. With digital you need only to add the software and sensor, computer and monitor. The learning curve is much faster with digital because it only takes 15 seconds to see your results as opposed to 2 minutes with film. Also, you can take as many exposures as you need without adding to the cost unlike film that has a cost with every exposure. Granted, the initial cost of digital radiology is greater. But over the course of about 1 year you will spend about the same amount of money on chemicals, chairside darkroom, film holders, clips, mounts, and film that you would invest in the digital sensor and software. Those costs continue after the first year if you are using film.

There are times, however, when film is needed. This is why I say you should be familiar with both. Sensors can go bad just like computers can go bad. Sensors are limited to size 1 and size 2. There are times when a size 4 is really needed. So a small supply of film and chemicals will come in handy.

The diagnostic value of a radiograph depends on its quality, and the degree of quality is determined by technique. Patient positioning and film exposure and processing collectively affect the value of a radiograph. With the use of digital radiography, the processing errors are reduced; however, positioning of the film or sensor in the pet's mouth and then the corresponding placement of the x-ray source to expose the film or sensor is extremely important.

There are two basic projection techniques used in radiography. The parallel technique offers the most accurate radiographic representation of the desired tooth or teeth, but it is limited to the lower premolars and molar of our feline patients. All other teeth must be radiographed utilizing the bisecting angel technique.

With the parallel technique the film/sensor is positioned directly behind and parallel to the long axis of the tooth being radiographed and the x-ray beam is directed perpendicular to that tooth and the film.

When the film/sensor and tooth being radiographed are not positioned parallel to each other, the resultant image will probably be elongated, foreshortened, unclear or magnified. A bisecting angle is an imaginary plane that equally divides the distance between the planes of the long axis of the tooth/teeth being radiographed and the film. The tubehead on the x-ray machine is positioned to allow the primary beam to be perpendicular to this imaginary bisecting plane.

I know this is confusing to think about, but it is really not as hard as we try to make it. Think of a tree standing in a field. If you were to try to find shade at high noon, you would have to sit right up next to the trunk. By mid afternoon the shade of the tree on the ground is much larger than at noon and in fact may be equal to the height of the tree. Late in the afternoon there is plenty of shade for all as it is much larger than the actual tree. This concept you understand. Well, what we are doing when we radiograph a tooth is actually casting a shadow of that tooth onto the film or sensor and we want that shadow to be as close to the size of the original object as possible so that we don't get elongation, foreshortening or magnification.

We will be taking radiographs in the lab so that you will become at ease with the techniques and be able to utilize this most important diagnostic tool when you return to your practice.

I would encourage you to purchase and read the radiographic text referenced in this paper. This book is especially helpful and showing you normal developmental anatomy as well as developmental problems and dental anomalies.

References

Mulligan, TW, Aller, MS, Williams, CA. Atlas of Canine & Feline Dental Radiography. Pg 15-22. VLS, 1998.