Oral disease is one of the most common conditions seen in general practice. Dental abnormalities have been noted in 85 percent of dogs, of which 60 percent were due to periodontal disease (Kyllar and Witter, 2005). The prevalence of dental disease is estimated to be present in 90 percent of cats (Lund et al., 1999).
A visual oral examination will disclose abnormalities only on the crown and at the gingival margin. The visible component only comprises approximately 30 percent of tooth length; the root structure embedded in the alveolar bone makes up the rest (70 percent). The majority of periodontal, endodontic disease and dental pathology is hidden beneath the gingival margin in dogs and cats.
Twenty-eight percent of dogs with visibly normal teeth were found to have clinically relevant dental issues identified radiographically (Verstraete et al., 1998a). Dental radiography of visually identified diseased teeth identified further pathology in 50 percent of dogs (Kim et al., 2013).
Dental radiography revealed clinically relevant information in 42 percent of cats with visually normal teeth. In cats with visually diseased teeth, further pathology was identified radiographically in 32 percent of cats. More importantly, in 98 percent of cats with clinical indications of tooth resorption (TR), radiography provided additional information paramount to diagnosis, planning and treatment (Verstraete et al., 1998b).
Most general practices are no stranger to digital radiography. This modality produces good quality 2D images of structures within the body. It is low cost and produces images instantaneously. The availability and accessibility of radiography is also deemed part of the core standard of care for the RCVS Practice Standard Scheme. The same should hold true for dental radiography. Without dental radiography, it would be impossible to diagnose and plan treatments adequately, making it difficult to provide a prognosis or allow appropriate review of the progression or improvement of most dental conditions.
Dental radiography offers patients a high standard of care, whilst also providing practices with higher diagnostic yields and an increase in procedures, generating an additional revenue stream. Radiographs also constitute an important part of the medico-legal record-keeping process and are a useful tool for client education.
For efficiency and accuracy of taking dental radiographs, these criteria need to be fulfilled:
- Target tooth/teeth centrally positioned and the main focus
- Root apex/apices clearly seen with a surrounding 2 to 3mm border of bone
- Good definition between the four main hard tissues (cortical bone, cancellous bone, tooth dentine and enamel)
- No superimpositions on the target tooth/teeth with other teeth or other objects
- No artefacts visible on the main focus of the radiograph, such as blood, film scratches or fingerprints
- Optimal exposure times
It is advisable to perform dental prophylaxis prior to radiography. Calculus is radio-opaque and can obscure or confuse the interpretation of the radiographs. Indications for taking dental radiographs are as follows:
- Missing/fractured/discoloured teeth
- Tooth resorption
- Pre- and post-extraction
- Periodontal pockets
- Worn/abraded teeth
- Gingival enlargement/masses/tumours
- Painful or sensitive teeth
- Draining tracts
- Nasal discharge/epistaxis
- History of oral pain, hypersalivation or pawing at the mouth
- Decreased interest in toys or food
- Evaluation of prior treatment
- Any form of dental trauma
- Evaluation of disease progression
While the above list provides the criteria on when to take dental radiographs, the American Animal Hospital Association (AAHA) and the World Small Animal Veterinary Association (WSAVA) suggest that full mouth dental radiographs should constitute an essential part of a complete dental/oral exam in all new dental patients. Dental radiography units need to be manoeuvrable and located close to the dental station for ease of use. When units are located far away from the dental area, or are cumbersome, they tend to be used infrequently. Radiographic exposures are dependent on three things: kilovolt peak (kV), milliamperage (mA) and exposure times. Most modern dental radiography units have pre-set values of 70kV and 8mA, so the only variation is the exposure time set by the operator. This is dependent on patient skull size/ soft tissue coverage and ranges from 0.15 seconds (cat) to 0.80 seconds (large dog), depending on your radiography unit’s specifications.
Patient positioning should be consistent and radiographs taken in a systematic way. This eliminates the variability of angles required and minimises the risk of missing areas of the dental arcade. Positioning needs to take into consideration the frequent turning of patients during procedures. In this article, we describe angles used in a patient positioned in lateral recumbency, with the hard palate perpendicular to the table (Figures 1 to 10). This position allows the operator to perform dental treatments with minimal turning of the patient. Note that the patient will need to be turned once to gain access to the opposite side of the mouth.
Several techniques can be used to obtain dental radiographs. The simplified technique (Woodward, 2009) is described here, as it uses predetermined angles. The angles are set at 20°, 45° and 90°. These angles are set based on the tube head being aligned with the nasal philtrum. This would read 0° on your radiography head and is your reference point at all times.
In dogs, size 4 plates are commonly used for dental surveys and size 2 plates in cats. Swabs or paper towels can help to keep the film positioned in place. The care and storage of films need to be considered to obtain optimal image quality. Film plates need to be cleaned frequently to avoid artefacts such as thumb prints and blood smears. Thorough examination of films prior to use avoids the use of damaged or scratched plates which will be visible on the images.
The consistent and practised use of these techniques will make intra-oral dental radiography easy and quick to perform, reducing patient anaesthetic time whilst giving good diagnostic yields and effective treatment planning.
Canine radiography angles and positioning
Feline radiography angles and positioning
The angles and techniques are the same as those for dog teeth, except for the maxillary premolars and first molar. The above projection causes superimposition of the zygomatic arch over the root apices in the cat. Three different techniques can be used (Figures 8 to 10).