Many disease processes may go undiagnosed without radiography, which provides a useful diagnostic and monitoring tool. Radiography also allows us to plan our extractions or other treatments more carefully.
We have produced a comprehensive guide to dental positioning but here is a handy overview of what you should be aiming to achieve, especially if you’re using a handheld generator.
Required views for Veterinary X-rays
A full mouth series consists of rostral maxillary and mandibular views, right and left maxillary views, and right and left mandibular views.
The rostral maxillary and mandibular views should include the canine teeth.
Maxillary canine teeth are best imaged in separate oblique views to prevent superimposition of the first and second premolars upon the canine tooth roots.
In addition, of course, you may wish to take additional views for specific suspected or confirmed dental abnormalities.
A portable handheld X-ray generator is a great asset to aid you in getting the full set of views, as it gives full flexibility in positioning the tube head.
However, care must be taken to avoid inadvertent radiation exposure, and all local rules for radiography must of course be followed.
Positioning the dog or cat
When placing the sensor in the patient’s mouth, care needs to be taken so that it is not damaged, particularly with more flimsy films or sensors.
This may mean using positioning aids like small rubber-coated dental wedges, modeling clay placed in a plastic bag, or disposable gauze sponges/paper towel sheets.
A towel under the patient’s neck will also help to keep them straight during radiography. The tongue can lie between the sensor/film and the teeth in cats and small dogs, the soft tissue opacity will not interfere with image production.
When taking radiographs, you will need to bear in mind the position of the skull, the placement of the sensor/film, and the position of the tube head.
Broadly speaking, the two most common positioning techniques are the parallel technique and bisecting angles.
The parallel technique is used for the caudal mandibular premolars and molars. The bisecting angle technique is used for all the maxillary teeth and the rostral mandibular teeth.
Parallel technique
Place the patient in lateral recumbency with the relevant side facing upwards. The film/sensor will be placed intraorally on the lingual surface of the teeth. Use a film/sensor positioning aid as necessary to keep the film/sensor in place and as parallel as possible to the tooth of interest.
The film/sensor must cover the entire area of interest, from crown to root. The tube head or x-ray machine is set at a 90-degree angle (perpendicular to the film) to take the image.
Bisecting angle technique
The parallel technique has limited use, and so bisecting angles must be used to get the full set of views. The theory behind this is that the correct angle stops image distortion.
If the x-ray beam is too parallel to the sensor/film, it will make the image elongated (like a low setting sun casting long shadows).
If the image produced is abnormally short, then the beam has been made too perpendicular to the sensor/film (like a high sun at noon making short shadows).
The right angle between the two of these will create an image that is a true representation of the patient’s dental anatomy.
When obtaining views of the maxillary teeth the patient is placed in sternal recumbency and when the mandibular teeth are imaged the patient is usually in dorsal recumbency.
The sensor/film needs to be intraoral, placed in the area of interest with the patient biting on it.
You will then need to imagine a line running parallel to the sensor film and another that is parallel to the tooth (crown to root). Where these lines intersect, they will form an angle, which you will then need to divide in half. Aim the primary beam perpendicular to this imaginary line, keeping it centered over the tooth of interest.
This should produce a true image of the tooth at the correct height and width.
Tips for imaging specific teeth
Rostral mandibular incisors and canine teeth.
Place the patient in dorsal recumbency and make sure that the palate is parallel to the table. Put the sensor/film between the teeth and tongue using a positioning aid.
Position the tube head 90 degrees, perpendicular to the sensor. In small and medium dogs, it is possible to get the canines in the same image as the incisors. For large dogs, it might be necessary to move the sensor caudally to capture all the roots.
Rostral mandibular premolars
The patient is placed in dorsal recumbency with the skull parallel to the table. The sensor/film will be parallel to the table in the bite between the maxillary and mandibular premolars.
The tube head is aimed perpendicular to the bisecting angle line and centered over the premolars of interest.
Caudal right or left mandibular teeth
The cat or dog is in lateral recumbency with the side of interest facing upwards, ensuring the skull is parallel to the table.
The sensor/film should be intraoral on the lingual side of the tooth of interest. The sensor/film can be orientated in portrait or landscape. Aim the tube head perpendicular to the tooth of interest and sensor or film.
Rostral maxillary incisors and canine teeth
The patient needs to be in sternal recumbency with the skull parallel to the table. The film/sensor is placed between the maxillary and mandibular incisors with the help of a positioning aid to hold it in place.
The bisecting angle line is determined with the tube head perpendicular to it centering over the incisors. A 20–30-degree angle is often used which helps prevent superimposition of the maxillary first and second premolars.
Oblique views of the maxillary canine teeth
With the patient in sternal recumbency, position the skull with padding to ensure it is parallel to the floor. The film/sensor is placed intraorally and caudally towards the opposite arcade. This helps to get the root apex in the shot. You may need a positioning aid to keep it in place.
The tube head is aimed perpendicular to the bisecting angle from a rostrolateral approach (centered over the canine tooth). The tube head should be at a 45-degree angle to the sensor/film, ensuring the sensor/film is large enough to capture the crown and the root.
Right or left maxillary premolars
The patient should be in sternal recumbency with the sensor film placed beneath the maxillary teeth (so that the patient is biting the sensor/film). Positioning devices might be needed to make sure the sensor/film is kept parallel to the table.
The bisecting angle should be determined with the tube head aimed perpendicular to it. In dogs, the tube head is at a 30-45-degree angle, but cats require a steeper angle of 20-30 degrees due to their zygomatic arch.
Teeth with three roots may require a second view to assess their mesial roots, which can be achieved by moving the tube head rostrally while keeping the bisecting angle the same.
Summary
Hopefully, this guide gives you a few pointers when getting started with dental radiography.
One final parting tip that may be of help is if the image is distorted, check the beam angle. If the image is normal but not all areas of interest are visible, check the plate position.
