Cecilia Gorrel, BSc, MA, Vet MB, DDS, MRCVS, HonFAVD, DEVDC, European and RCVS-Recognised Specialist in Veterinary Dentistry
Radiography is a vital diagnostic tool in veterinary dentistry. Radiographs are required to:
1. Reach a diagnosis
2. Assess extent of pathology
3. Plan optimal treatment
4. Perform certain procedures
5. Assess outcome of treatment performed
General anaesthesia is required for radiography. Ideally, clinical examination and recording should precede the radiographic evaluation. It is also useful to clean the teeth before any radiographs are taken. Dental calculus, because it is radio-dense, can obscure pathological lesions on a radiograph.
For a dental radiograph to be diagnostic, it should be an accurate representation of the size and shape of the tooth without superimposition of adjacent structures. Intraoral (film placed inside mouth and X-ray beam directed from outside the mouth through tooth and adjacent structures onto the film) radiographic techniques are therefore required. The two basic techniques1 are:
1. Parallel technique for the mandibular premolars and molars
The patient is placed in lateral recumbency (with the side to be radiographed uppermost). Film is placed between the tongue and the teeth and pushed as far down into the sublingual fossa as possible The X-ray beam is then directed from lateral to medial at right angles to the long axis of the tooth.
2. Bisecting angle technique for all other teeth
The film is positioned at an angle behind the tooth. An imaginary plane is drawn half way between the plane of the film and a plane through the long axis of the tooth, i.e., at the bisecting angle, and the X-ray beam is directed perpendicular to this plane.
Full mouth radiographs describes a series of films where each tooth of the dentition is accurately depicted in at least one view. A full mouth radiographic series of all animals undergoing dental examination provides valuable information, but is not always practically or financially viable. However, it is strongly recommended that all adult cats have full mouth radiographs taken as part of the oral and dental examination. Odontoclastic resorptive lesions are common in cats and clinical examination without radiography will only detect end stage lesions. In cats, it is necessary to take a minimum of 8 views, but 10 views are recommended, to ensure that all teeth are properly visualised. In the case of dogs, full mouth radiographs are encouraged, especially at first examination. If this is not possible (time or financial restrictions) then radiographs are taken where indicated based on the findings during the clinical examination. In the event of full mouth radiographs, the size of film and the number of films used will depend upon the breed of dog and the shape of its face.
Equipment and materials for conventional intra-oral radiography:
Mounts or envelopes for film storage
A dental X-ray machine is preferable to a veterinary X-ray machine. However, most veterinary X-ray machines can be used for dental radiography, but the film-focus distance will need to be adjusted to between 30–50 cm.
To allow intra-oral film placement and achieve high definition, dental film should be used. Dental film is single emulsion, non-screen, and is available in three sizes (occlusal, adult periapical and child periapical) and different speeds. The dental film is packed in either a paper or a plastic envelope and the film is flanked by black paper and backed by a thin lead sheet (foil) that reduces scattered radiation.
Automated processors are available for dental film processing, but excellent results can be obtained with the use of a chair-side processor.
In the last five years the major development has been in the introduction of digital dental radiography. The techniques for taking radiographs have not changed. However, the processing using digital is much simpler, cheaper and faster than conventional methods. Given the relative low cost of entry for a digital system and the benefits in terms of speed and ability to manipulate the images via the software I would strongly recommend investing in such a system from the outset. There is a fast payback of the initial investment.
Extra-oral views are not ideal for dental examination mainly due to superimposition of the contra-lateral side, which obscures the image and causes distortion of the image. However, it may be possible to obtain diagnostic radiographs of the maxillary and mandibular premolars and molars using extra-oral film placement, especially in dogs with wide skulls. Some examiners routinely use extra-oral film placement to radiograph the maxillary premolars and molar in the cat. The technique1 is as follows:
The film is placed on the table and the animal is placed in dorsolateral recumbency with the side to be radiographed closest to the film; the mouth is held wide open using a radiolucent device, e.g., plastic needle cap and the head is tilted so that the maxillary (or mandibular) teeth are almost parallel to the film. The direction of the beam is adjusted according to the bisecting angle technique to reduce image distortion
Radiographs should be viewed on a viewing box with minimal peripheral light and preferably using magnification. It is recommended to radiograph the contra-lateral structures, to those being evaluated, for comparative purposes. A good knowledge of the radiographic appearance of normal structures of the upper jaw and mandible is imperative to avoid misdiagnosis.
During the presentation clinical cases will be used to highlight normal and abnormal radiographic features and to demonstrate the importance of including radiographs in dentistry. It is in fact impossible to practice dentistry without the use of imaging.
1. Gorrel C. Radiography. In: Gorrel C. Small Animal Dentistry. Saunders Elsevier. 2008:22–28.