The evolution of oral radiography in veterinary medicine

On a detailed oral examination you diagnose tooth resorption for a feline patient’s left mandibular third premolar, 307. How can you determine the best treatment option?

On another detailed oral examination for a canine patient you diagnose a complicated crown fracture with pulpal exposure and necrosis for the maxillary right 4th premolar, 108. How can you determine whether there are root fractures, root resorption, or periapical disease prior to planning a surgical extraction or root canal therapy?

The answer to both questions is oral radiography. It is indicated in small animal practice for the diagnosis and treatment of many presentations of oral and dental disease. Some of these include persistent deciduous teeth, periodontal disease, fractured roots during extractions, tooth resorption, endodontic disease with or without pulpal exposure, maxillary or mandibular fractures, and oral neoplasia (1–6). Although this has previously been referred to as “dental radiography,” we recommend using the term “oral radiography” as imaging is done for more than just dentition. Oral radiography includes both intraoral and extraoral techniques.

Oral radiography using dental films has been used in veterinary medicine for decades. As early as the 1960’s, veterinarians were using silver halide dental films borrowed from human dentistry. Originally, these were exposed with regular tabletop x-ray machines and processed with the developer and fixer used for standard x-ray films in the veterinary hospital’s darkroom. This can still be done today, and this means any veterinarian can take oral radiographs with the purchase of silver halide dental films. The most useful films for veterinary medicine are sizes 0, 1, 2, and 4, and the fastest “F” speed films are recommended as they permit the shortest exposure times.

The disadvantage to this type of system was that practitioners needed to move the patient back and forth from the x-ray room under general anesthesia. Also, with limited mobility of the standard x-ray machine head and its requirement for spacing from the patient for a standard 41-cm (16-in) focal-film distance, it was challenging to get the correct angle of the x-ray beam for the exposures. This resulted in many non-diagnostic images and re-shoots that wasted critical time under general anesthesia.

The next development was for veterinarians to get dental x-ray machines installed in a treatment area or a dental operatory. This eliminated having to move the patient while under general anesthesia. With the much greater mobility of the dental x-ray machine head in 3 planes and with the x-ray machine cone touching the patient’s head, it was much easier positioning for the correct angulation of the x-ray beam. During the same time, human dentistry chairside darkrooms, with rapid developer and fixer chemistries were introduced. These permitted much faster processing of dental films in approximately 45 s in room lighting, near the veterinary patient. The operator stayed in visual contact with the patient during processing. Together these resulted in a major time saving for procedures under general anesthesia.

In the past decade, digital systems for oral radiography have been developed in human dentistry and have been adapted for veterinary patients. These have been developed to replace silver halide dental films. The first systems developed were given the designation “digital radiography” (DR). These DR systems use a rigid CCD or CMOS sensor mounted in a rigid plastic wafer. After the sensor is exposed with x-rays, it sends a digitized image to a computer system through a cord or wirelessly using Bluetooth technology.

One of the advantages of the DR systems is that they have fast image acquisition, averaging 4 s. There are entry level DR systems with low resolution imaging that are less expensive.

A major limitation of these systems is that the sensors can be damaged if dropped and are very expensive to replace. Also, the rigid sensors are more difficult to position intraorally, and the cord must be worked around to avoid pulling the sensor out of the mouth. The most important limitation is that these sensors have been available only in size 2 and more recently in size 1. There have been no larger size 4 sensors or the smaller size 0 sensors manufactured to date.

Size 4 sensors are extremely useful for imaging many types of oral and dental pathology, even in small dogs. A good example is the imaging of a maxillary or mandibular arch. Size 0 sensors are very useful for very small dogs and cats, especially for lateral mandibular views. This is where the newer system of computed radiography (CR) has emerged as a more practical solution for veterinary dentistry. There is one CR system commercially available that has a full range of size 0, 1, 2, 3, and 4 phosphor plates (Scan-X Duo, ALLPRO Imaging, Air Techniques, 1295 Walt Whitman Road, Melville, New York, USA). These flexible plates are positioned and imaged just like silver halide dental film, then the phosphor plate is removed from the patient’s mouth and loaded into a laser scanner to acquire the digital image. It is important to note these plates do not become damaged if they are accidentally dropped on the floor.

The disadvantage of this CR system is that it is initially more expensive than a size 2 DR sensor system. However, the cost would be more for a DR system if both a size 2 and size 1 sensor were purchased. The time for image acquisition is longer with CR systems. For size 2 phosphor plates, a high resolution image acquisition is 17 s or less, depending upon the software.

There are several advantages of a digital CR system over silver halide dental film. There are no chemicals to handle and dispose of with CR systems. The phosphor plates typically permit 30% to 40% shorter exposure times. The images can be modified after acquisition to adjust contrast and density, so that fewer re-shoots are required. The images can be enhanced and magnified to aid in the diagnosis. They can also be sent to a specialist for interpretation and recommendations. They can be displayed on a computer screen to clients as an outstanding educational tool. Examples of computed radiography images are shown (Figures 1 to 5) to demonstrate some indications for oral radiography and the resolution of the CR images. Currently, only one of the commercially available DR systems acquires images of the same quality as the CR system.

Figure 1.

Computed radiography image for an 11-month-old male Doberman showing an asymmetrical periapical lesion for his left maxillary canine, 204 (arrows). This asymmetry indicates pathology and is due to pulpal exposure and necrosis. There are no vertical root fractures and no root resorption. The best treatment option is salvage with endodontic therapy, or else a surgical extraction is indicated.

Figure 5.

Detail of a size 4 computed radiography image of the rostral mandible of a 7-year-old spayed female German shepherd showing generalized dental abrasion with no pulpal exposure. There is evidence of pulpal necrosis for 304 (arrow) as noted by a wider canal than 404, mild apical root resorption and apical periodontitis. The best treatment option for 304 is root canal therapy, otherwise an extraction is indicated.

A recent cost-benefit analysis of oral radiography including digital systems concluded that “purchasing a dental x-ray unit will improve your bottom line” (7). As this is a real educational tool giving “face time” with clients, an investment in an oral radiography system was one of the suggested strategies for surviving an economic recession (8).

The other critical part of choosing to update to digital oral radiography is learning positioning technique and radiographic interpretation. This is where veterinary dentistry is also evolving. There are excellent publications on oral radiography, and we highly recommend the “Atlas of Dental Radiography in Dogs and Cats” by Dupont and DeBowes (6). Training is also provided at the Veterinary Dental Forums held annually in North America (see www.avdc.org).

Veterinary dental specialists in Canada are offering hands-on wet labs that teach oral radiography technique and interpretation. A compact disc is also available for continuing education on this subject. For information please contact the author at vetdentist@allstream.net

Figure 2.

Computed radiography image of the rostral mandible of a 17-year-old male neutered domestic shorthair cat showing marked tooth resorption involving primarily the roots for both mandibular canines, 304 and 404 (asterisks). Crown amputation is the best treatment option to prevent pain as the crowns will fracture off in the near future if left untreated. The patient’s left side is to the right in this labial mount.

Figure 3.

Computed radiography image of the right mandible of an 11-year-old spayed female Shih Tzu showing that the coronal mobility was due to a cervical fracture involving both the mesial and distal roots for the right mandibular fourth premolar, 408 (between arrows). A surgical extraction of 408 was indicated.

Figure 4.

Computed radiography image of the right mandible of a 10-year-old spayed female Shih Tzu showing advanced periodontal disease with > 50% attachment loss noted as bone loss for the remaining cheek teeth. There is also marked resorption for the distal root of 408 and mild resorption for the mesial root of 409. Surgical extractions are indicated for all of these teeth, and a bone graft is also indicated for the extraction site for 409 to help speed osseous healing.