How to incorporate dental radiology into your practice

All small animal practitioners routinely take radiographs of patients where indicated. Radiographs simply put, help the veterinarian evaluate the patient.

In a study conducted at the University of California, Davis ( Am J Vet Res 1998, 59, pgs. 686-691 and 692-695), where all dogs and cats presented for dental cleanings were radiographed, significant lesions requiring therapy were uncovered in a majority of the cases. Currently, less than 10 percent of practices use dental radiology to help their patients. This low percentage is due to many factors including set up expense, inexperience with radiographic technique and processing as well as inexperience with film interpretation.

Figure 1: Dental radiographic units allow for use on the operatory table.

What are the advantages, equipment needed and techniques used to expose and process dental films?

Advantages of taking dental radiographs are many:

• Viewing pathology below the gingiva and inside the tooth documenting the presence of lesions to support treatment decisions.

• Evaluating an area where the teeth are not clinically apparent for root fragments.

• Determining the cause of chronic nasal discharge.

• Evaluating tooth vitality

• Evaluating the number of permanent teeth present in a puppy or kitten as part of a detailed soundness examination before the secondary teeth erupt. Some breeds must have a minimum number of teeth to be accepted in the show ring.

• Anatomical orientation and documentation of root structure before extraction.

• Evaluation after extraction to confirm all root fragments were removed.

• Pre-operative evaluation of gross tumor margins to help plan surgery.

• Treatment planning evaluation when periodontal disease is present (gingival bleeding on probing, tooth mobility, gingival recession, furcation exposure, increased probing depths).

• Evaluating feline odontoclastic resorptive lesions (FORLs).

• Evaluating jaw fractures.

• Evaluating oral and facial swellings.

• Evaluating pre-operative, intra-operative and post-operative endodontic treatment.

The radiographic unit

A conventional radiograph unit can expose quality films using 100 ma 10 mas technique at 40(cat)-60 (large dog) Kv, with a film focal distance of 16-in. While the veterinarian does not need to own a dedicated dental unit, it makes the process more efficient.

Figure 2: There are three film speeds: D, E, F.

There are great advantages in owning a dental radiograph unit: most dental units cost between $3,000-$5,000; shorter film focal length and automatic collimation result in less scattered radiation and exposure to the patient; extension arms of various lengths allow vertical, horizontal, and rotational movement resulting in less patient repositioning; and radiographs can be obtained on the dental operatory table rather than moving the patient to a radiography area (Figure 1).

The film

The efficiency which a film (Figure 2) responds to X-ray exposure is known as film sensitivity or speed. The three film speeds are:

Figure 3: Dental film sizes

• D speed (Ultraspeed, Kodak) provides high contrast and fine detail. Ultraspeed is the most popular film used in veterinary dentistry.

• E speed (Ektaspeed, Kodak) requires 25 percent less exposure time, compared to D speed film, with minimal loss of contrast.

• F speed (InSight, Kodak) requires 60 percent less exposure time than D speed film, and 20 percent less than E speed film.

Exposure example for a typical 20-pound dog using a dental radiograph unit is 55kVp, 10 mA: Ultraspeed 0.40 sec, Ektaspeed 0.30 sec, InSight 0.16 sec.

Figure 4: EVA digital dental sensor and holster (AFP Imaging).

Four sizes of dental film are used (Figure 3, p. 12S):

• Child periapical (size 0) measures 7¼8 x 15¼8 inches. Size 0 is used mostly in cats, exotics and small dogs.

• Adult bitewing (size 2) measures 11¼4 x 15¼8 inches and is the most commonly used size in veterinary dentistry. Size 2 fits into 35 mm slide mounts for use in presentations.

• Bitewing (size 3) film measures 11¼16 by 21¼8 inches. Size 3 films adapt well to the mandibular cheek teeth.

• Occlusal (size 4) film measures 21¼4 by 3 inches. Occlusal film is used to radiograph large breeds.

Digital dental radiology uses a sensor rather than film. The image captured on the sensor is displayed on a computer screen. (Figure 4, p. 12S).

Figure 5: Positioning for incisor images.

A radiographic dental survey consists of a minimum of eight views:

• Rostral maxilla

• Lateral left canine

• Lateral right canine

• Rostral mandible

• Right maxillary cheek (premolars and molars) teeth.

• Left maxillary cheek teeth

• Right mandibular cheek teeth

• Left mandibular cheek teeth

Tube/film/patient positioning

For the maxillary views, the patient is positioned in sternal recumbency with support placed under the chin at a height where the muzzle is parallel to the tabletop:

Figure 6: Bisecting angle technique.

• Incisors: Place the film packet toward the tube head against the incisors and palate. Position the PID perpendicular to an angle bisecting the film and teeth planes (Figure 5).

• Canine: Place the film packet facing the tube, between the tongue and maxilla beneath the canine tooth root. Center the PID over the mesial root of the second maxillary premolar, dorsally or laterally depending on the view needed.

Determine the angle between the plane of the canine root and the plane of the film. Position the cone perpendicular to the bisected angle (Figure 6).

Figure 7: Maxillary premolar tube position.

• Premolars: Place the film packet as close as possible to the inner surface of the cheek teeth. Aim the PID at the roots of the premolars at approximately 45-degrees.

The maxillary fourth premolar has three roots (mesial buccal, mesial palatal and distal). To avoid overlap of the mesial buccal and palatal roots, position the PID 20-degrees in the horizontal plane (rostral oblique) in the medium- to long-muzzled dog, and caudal oblique in brachycephalic breeds. In cats, the zygomatic arch is superimposed over the maxillary fourth premolar root. To avoid the arch, use a rostral oblique bisecting angle projection, aimed at the premolar roots with the PID positioned just ventral to the arch. Alternatively, extraoral near-parallel technique may be used to visualize the maxillary cheek teeth (Figure 7).

Figure 8: Maxillary molar tube and film position.

• Molars: Place the film packet against the maxilla beneath the molar teeth. Aim the PID at the eye and film in a caudoventral direction (Figure 8).

When radiographing the mandible, place the patient in ventral or lateral recumbency with support under the neck to place the muzzle parallel to the tabletop.

Figure 9: Mandibular incisor position.

• Incisors: Position the film packet toward the tube head against the incisors and the lingual frenulum. Position the PID perpendicular to the bisecting angle (Figure 9).

• Canine: Place the patient in ventral recumbency. Position the film between the tongue and mandible, pushing the lingual frenulum distally. To obtain a lateral view, position the PID approximately 45° toward the canine (Figure 10).

• Anterior premolars: Place the patient in lateral recumbency, with the film against the anterior premolars to include the periapical area. Aim the PID at the apex of the first premolar 20 degrees to the ventral border of the mandible (Figure 11).

• Posterior premolars and molars: Place the patient in lateral recumbency. Position the film at the floor of the mouth lingual to the premolars. Place gauze or a hemostat to help depress the film into the floor of the mouth. Aim the PID perpendicular to the tooth roots and film (parallel technique) larger teeth, survey studies, and maxillary occlusal views in dogs and cats (Figure 12).

Film may be developed in the following ways:

Figure 10: Mandibular canine tube and film position.

Manually, using developer, water and fixer solutions in the practice darkroom.

With the chairside darkroom, a portable light-safe box containing rapid developer, distilled water and fixer in small containers is placed in the dental operatory. The chair- side darkroom is covered with a plexiglas safety filter, which enables operators to see their hands while handling the film(s). The filter is either amber (when D speed film is exposed), or red (for E or F speed films). Processing time from opening the film packet to initial examination of a rinsed film takes approximately two minutes (Figure 13).

Figure 11: Position of film and tube head to expose mandibular premolars.

Using an automatic dental processor (preferred by author) delivers dry films in six minutes.

Manual processing

Manual processing includes the following steps:

1. After exposure, carry the film into the practice darkroom or chairside darkroom for processing. Slide the film packet tab down to present film, cardboard and lead blocker. The film will feel firm to the touch, compared to the other film pack contents.

Figure 12: Position of film and tube head for exposure of mandibular molars.

2. A film hanger is attached to the film edge. Touch only the sides of the film with fingers. Apply a gentle tug to make certain the film is firmly attached to the clip.

3. Place the film in prestirred developer solution for the specified time recommended by the manufacturer (Kodak Rapid Access Chemistry: 15 seconds at 68-degrees). Note: an alternative method starts manual film processing with water immersion to soften the emulsion before placement in the developer.

4. After placement in the developer, rinse the film in fresh distilled water (wash) for 10-15 seconds. Rinsing removes the alkaline developer from the film surface, preventing mixture with the acid fixer.

Figure 13: Manual chairside darkroom.

5. Place the film in the prestirred fixing solution for at least two minutes. Fixer removes the unexposed or underdeveloped silver halide crystals and rehardens the emulsion.

6. Rinse the film for 30 seconds in distilled water.

7. After viewing, place the film back in the fixer for five minutes, followed by distilled water rinse for 10 minutes.

8. When rinsing is complete, attach the radiograph to a clip on the drying rack. Dental radiology is as important to patient dental care as radiology in any other organ system. The information gained is crucial to perform quality dentistry. The next article will concern evaluating dental films to help formulate a dental treatment plan.

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