Veterinary Dental Radiography in Practice

Dental radiographs are an essential part of the oral examination. Approximately two-thirds of the tooth lies below the gumline; therefore, dental radiography helps reveal pathology that is not immediately visible during an oral examination.^1-4 Radiographs also help confirm suspect pathology and demonstrate pathology to the client. Obtaining a complete series of dental radiographs in each patient can also increase the standard of care in a clinic (and the clinic’s revenue) by finding pathology that otherwise would have gone unnoticed, thus improving patients’ oral health.

As patient advocates, veterinary nurses have a duty to thoroughly examine normal oral pathology and further investigate abnormal oral pathology. Therefore, while dental radiography can be among the more frustrating skills for a veterinary nurse to master, it is also one of the most rewarding diagnostic tools in veterinary dentistry.

Radiography Techniques

Two intraoral radiography techniques are commonly used in veterinary dentistry: bisecting angle and parallel.

• The bisecting angle technique is used for the anterior mandibular teeth and all of the maxillary teeth, where the hard palate on the maxilla and the symphysis of the anterior mandible make it impossible to use the parallel technique. In this technique, the beam is aimed at the imaginary line bisecting the plane of the tooth and the plane of the film (FIGURE 1A).^1,2,5 If the beam is not perpendicular to the bisecting angle, the tooth will be distorted. If the angle is too low, the root will appear elongated (FIGURE 1B). If the angle is too high, the tooth will appear foreshortened (FIGURE 1C).^1,2,5
  Figure 1. The bisecting angle is used to prevent distortion of the teeth on the radiograph. (A) To use the bisecting angle technique, aim the beam perpendicular to the imaginary line that bisects the planes of the tooth and the sensor. Illustration: Kip Carter

  Figure 1B. The teeth in this radiograph appear elongated, meaning that the tube head is set too low. Illustration: Kip Carter

  Figure 1C. The teeth in this radiograph are foreshortened, meaning that the tube head is set too high. Illustration: Kip Carter
• The parallel technique is used for the posterior mandibular molars. The sensor is placed parallel to the lingual aspect of the jaw with the cone at a perpendicular angle to the sensor.

A series of diagnostic dental radiographs aims to get all the teeth in as few views as possible. The size of the animal determines the number of views needed. See TIPS FOR TAKING DENTAL RADIOGRAPHS sidebar for more recommendations.

Patient Positioning

Proper patient and sensor placement are essential to obtain diagnostic images and make performing dental radiographs easier. The patient should be placed in sternal recumbency with the muzzle parallel to the table for the maxillary views (FIGURE 2).¹ It can be helpful to place a square plastic box under the jaw to help hold the animal in the proper position. This device helps keep the maxilla parallel to the table and prevents the mouth from tilting to the side. The size of the box should be appropriate to the size of the patient (i.e., large for large dogs; smaller for small dogs and cats).

Figure 2A. Patient in sternal recumbency with muzzle parallel to the table.

Figure 2B. Note that the muzzle is square, not tilted.

For mandibular views, the patient should be placed in dorsal recumbency with a towel under the neck to hyperextend the neck and allow the jaw to be parallel to the table (FIGURE 3).¹ The use of a V-trough helps with this position. If the animal has spinal or cervical concerns, the mandibular views can be done in lateral recumbency. If the radiographs are taken in lateral recumbency, the angles used must be adjusted by 90°.

Figure 3. Patient in dorsal recumbency with muzzle parallel to the table.

Sensor Placement

For maxillary views, the teeth should be placed on the outer edge of the sensor, with most of the sensor inside or on the palatal aspect of the tooth (FIGURE 4A). If the tooth is placed in the middle of the sensor, the roots of the tooth will not appear in the image (FIGURE 4B AND 4C). In large-breed dogs, the tooth’s crown may be on the outside of the sensor, allowing more of the sensor to be in the mouth to ensure the roots are on the image. Adjusting the sensor placement a few millimeters can make a big difference in the radiograph.

Figure 4A. Correct sensor placement, with the tooth on the outer edge.

Figure 4B. Incorrect sensor placement, with the tooth in the center.

Figure 4C. Resulting image when the tooth is placed incorrectly in the center of the sensor.

Incorrect sensor placement is the most common cause of a nondiagnostic image. The sensor should always be placed in the mouth flat (or parallel to the table) with the cord coming out the front of the mouth (FIGURE 5) for all views except the posterior mandibular teeth in dogs (308 to 311 and 408 to 411), for which the sensor should be placed parallel to the mandible.

Figure 5. A folded piece of gauze can be placed between the palate and the sensor to keep the sensor flat.

Canine Dental Radiographs

Maxillary Views

109 to 110 and 209 to 210

For the caudal maxillary teeth, the sensor should be parallel to the table, moved caudal to the commissure of the jaw, and then rotated slightly to follow the curvature of the molar teeth. Proper sensor placement can be confirmed by using a finger to ensure the edge of the sensor is flush with the crowns of the teeth. The cone is adjusted to approximately a 50° angle, placed just caudal to the lateral canthus of the eye, and rotated slightly to follow the curvature of the molars (FIGURE 6).¹

Figure 6A. Proper cone position for 209 to 210 in a dog.

Figure 6B. Resulting radiograph.

108 and 208

For the maxillary fourth premolar in larger dogs, place the sensor parallel to the table and with the tooth on the very outer edge, with most of the sensor inside the mouth. In large breeds, the tip of the crown may need to be placed off the outer edge of the sensor to allow more of the sensor to stay inside the mouth. The tooth should also be placed toward the distal half of the sensor (lengthwise) to ensure the roots are visible. The cone is positioned at a 50° angle and moved to align with the tooth. Use the bottom line on the cone to point to the crown (FIGURE 7).¹

Figure 7A. Proper cone position for 208 in a dog, ensuring that the bottom of the tube head is lined up with the crown of the tooth.

Figure 7B. Resulting radiograph.

The straight-on view obtained with this technique will cause superimposition of the mesiobuccal and palatal roots (FIGURE 8A). This view is acceptable; however, if there is evidence of pathology, these roots may need to be separated. To do this, shift the cone slightly rostral or caudal to see all 3 roots. The position of the palatal root follows the direction in which the tube head is moved. Therefore, if the tube head is moved caudally, the palatal root will be the middle root on the radiograph (FIGURE 8B), and if the tube head is moved rostrally, the palatal root will be the most rostral root on the radiograph (FIGURE 8C). It is best to move the cone caudally to avoid superimposition of the distal root of the fourth premolar over the first molar.¹

Figure 8A. Representation of the straight-on view of 108 and 208 in a dog. The mesiobuccal root (index finger) is superimposed on the palatal root (middle finger). Illustration: Remie Geoffroi

Figure 8B. Representation of the view of 108 and 208 with the tube head shifted caudally. The palatal root (middle finger) is now the middle root in the image. Illustration: Remie Geoffroi

Figure 8C. Representation of the view of 108 and 208 with the tube head shifted rostrally. The palatal root (middle finger) is now the root on the left of the image. Illustration: Remie Geoffroi

105 to 107 and 205 to 207

Place the sensor parallel with the table with the crowns of the teeth on the edge of the sensor. Position the cone at 45° over the muzzle (FIGURE 9).¹

Figure 9A. Proper cone placement for the maxillary premolars (205, 206, and 207) in a dog.

Figure 9B. Resulting radiograph.

104 and 204

Canines can be a challenge, but it is not necessary to have the crown on the radiograph. The apex of the canine root is directly above the maxillary second premolar. For small dogs, place the tip of the canine tooth on the sensor’s front outer corner with the rest of the sensor inside the mouth. For large dogs, the sensor can be placed directly on the palate, ensuring the plate is past the second premolar. Adjust the angle of the cone to 65°, bringing the cone high over the muzzle at an oblique angle to the canine. Direct the bottom line on the cone at the crown of the canine tooth (FIGURE 10). A variation of this view is to move the cone lateral to the tooth.¹

Figure 10A. Proper cone placement for 204 in a dog.

Figure 10B. Resulting radiograph.

103 to 203

Depending on the dog’s size and the skull type, all maxillary incisors may be included in a single view. The crowns of the incisors should be on the edge of the sensor. Positioning the end of the cone parallel to the animal’s alar fold on the side of the nose, with the bottom line on the tube head pointing at the midline, will help in obtaining diagnostic images of the incisors in all skull types (FIGURE 11A AND 11B).^1,4

Figure 11A. Use the alar fold to help position for 103 to 203 in a dog.

Figure 11B. Resulting radiograph.

If the animal is large and all incisors cannot fit on the sensor, 2 views will be needed. Place the sensor as described. The cone can be aligned with the alar fold and then moved slightly left or right to obtain views of 3 incisors (FIGURE 11C).¹

Figure 11C. In large dogs, the cone can be moved to either side to create an oblique image showing 3 of the 6 incisors.

Mandibular Views

Place the animal in dorsal recumbency with the mandible parallel to the table for mandibular views. The parallel technique is used for the posterior mandibular molars. Due to the sensor’s rigidity and the dog’s anatomy, the remainder of the mandibular views require the use of the bisecting angle technique.¹

310 to 311 and 410 to 411

In most dogs, the caudal 3 molars can be obtained in a single view, but in larger breeds, 2 views are necessary: a view with 2 caudal molars and another with the first molar. The second and third mandibular molars have short roots.

Place the sensor parallel to the jaw between the tongue and jaw, with some of the sensor visible “above” the crowns (FIGURE 12). Gauze can be placed on the rostral side of the sensor to help keep it in this location (FIGURE 5). The cone is then positioned perpendicular to the sensor.¹

Figure 12A. Proper sensor placement for caudal molars in a dog. The cone would be at a 90° angle to the sensor.

Figure 12B. Resulting radiograph showing 411, 410, and the distal root of 409.

309 to 308 and 409 to 408

The roots on the first molar are longer and require the sensor to be placed deeper into the lingual region between the tongue and parallel to the jaw (FIGURE 13). The sensor may need to be angled to accommodate the lingual structures. Gauze can keep the sensor in the desired position. The cone is then positioned perpendicular to the sensor.¹

Figure 13A. Proper sensor placement for the mandibular molar (409) in a dog. The cone would be at a 90° angle to the sensor.

Figure 13B. Resulting radiograph.

305 to 307 and 405 to 407

Place the sensor parallel to the table. The tongue can be moved to the side or kept in its usual location to aid in positioning. The teeth should be positioned on the edge of the sensor, with the remainder of the sensor in the mouth. The cone is then adjusted to an approximately 50° angle and placed to follow the contour of the jaw to avoid distortion of the premolars (FIGURE 14).¹

Figure 14A. Proper positioning of the sensor and cone for 305 to 307 in a dog.

Figure 14B. Resulting radiograph.

304 and 404

In smaller dogs, the mandibular canines can be taken with the incisors. In larger breeds, they are radiographed separately. The apex of the canine tooth is located near the second premolar.

Place the sensor parallel to the table in the mouth, past the second premolar. Adjust the cone to 65° and place it over the jaw, with the lines on the cone’s side directed at the second premolar’s crown, providing a view of both canines (FIGURE 15A AND 15B). If only a singular canine is to be radiographed, the sensor and cone angle are the same, but the cone is moved to an oblique angle, and the bottom cone line is aimed at the crown of the desired canine tooth (FIGURE 15C AND 15D).¹

Figure 15A. Proper sensor and cone position for 304 and 404 in a dog.

Figure 15B. Resulting radiograph.

Figure 15C. Proper positioning for a single mandibular canine (304).

Figure 15D. Resulting radiograph.

303 to 403

The mandibular incisors can always be radiographed in a single view. Place the sensor flat in the mouth with its edge flush with the crowns of the incisors. Adjust the cone to 50° and place it high over the rostral jaw (FIGURE 16).¹

Figure 16A. Proper sensor and cone positioning for 303 to 403 in a dog.

Figure 16B. Resulting radiograph.

Feline Dental Radiographs

In the past, it was essential to avoid the zygomatic arch to see the maxillary premolar roots. With digital technology, the roots of the premolars are now visible through the zygomatic arch, making it easier to get diagnostic dental radiographs.¹

Maxillary Views

The cat should be placed in sternal recumbency with the maxilla as parallel to the table as possible. A small square box can be placed under the jaw to assist in the proper positioning. All the maxillary views can be taken with only a slight adjustment to the sensor placement.

106 to 109 and 206 to 209

The sensor is placed in the mouth flat and slightly rotated, with the premolars on the edge of the sensor. The cone is adjusted to approximately 35° and placed along the maxillary arcade. Remember to aim at the roots of the teeth, not the crowns (FIGURE 17).¹

Figure 17A. Proper placement of the sensor and cone for 106 to 109 in a cat.

Figure 17B. Resulting radiograph.

104 and 204

Adjust the cone to 50° without moving the sensor and bring it to an oblique angle to the canine. Line up the bottom line of the cone with the crown of the canine tooth (FIGURE 18).¹

Figure 18A. Proper sensor and cone placement for 204 in a cat. Note that the line on the cone is lined up with the crown of the canine tooth.

Figure 18B. Resulting radiograph.

103 to 203

The incisor view must always be taken separately from the canine view; otherwise, superimposition of the canines over the premolars will make a diagnostic reading impossible. For the maxillary incisors, the sensor can be kept in the same position or straightened. The cone is set at 50° and aimed at the animal’s nose (FIGURE 19).¹ If desired, one can use the alar fold technique, especially for brachycephalic breeds.

Figure 19A. Proper sensor and cone placement for 103 to 203 in a cat.

Figure 19B. Resulting radiograph. This image also demonstrates that the maxillary canines cannot be imaged with the incisors due to superimposition over the premolars.

Mandibular Views

With film, using the parallel view for the mandibular molars and premolars was simple, but with digital technology, this view may miss the apex of the mesial root of 307 and 407.

Place the cat in dorsal recumbency with the mandible as parallel to the table as possible. A towel under the neck will help with positioning. Dorsal positioning decreases the need to move the sensor and change the angle of the cone. If the distal root of the molar is not visible, move the cone caudally or complete the other mandibular views and then take a parallel view to obtain the distal root of the molar.¹

307 to 309 and 407 to 409

Place the sensor flat in the mouth with the tongue between the teeth and the sensor. The sensor will not need to be adjusted for all 3 mandibular views. The cone should be set to approximately 50° and placed to follow the jawline (FIGURE 20).¹

Figure 20A. Proper sensor and cone positioning for 407 to 409 in a cat.

Figure 20B. Resulting radiograph.

304 to 404

The mandibular canines and incisors can be taken in a single view. The sensor does not need to be moved from the position of premolar and molar views. The cone should remain at 50° and be moved to the rostral aspect of the jaw (FIGURE 21). If the jaw is not parallel to the table, the tube head may need to be at a steeper angle.¹

Figure 21A. Proper sensor and cone positioning for 304 to 404 in a cat.

Figure 21B. Resulting radiograph.

Summary

Dental radiographs are an essential tool in providing the best possible dental care. With practice, a full set of diagnostic radiographs can be obtained quickly and efficiently in every patient. A downloadable reference chart of the positions and angles described in this article is available from btcveted.com/shop.