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InFocus

Intra-oral dental radiography for the general practitioner

Dental radiography offers patients a high standard of care, whilst also providing practices with higher diagnostic yields and an increase in procedures

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

FIGURE (1A) Maxillary and mandibular incisors: The film is placed flat against the incisors and parallel to the hard palate. With your starting point at 0° (midline of the head), direct the beam in a rostro-caudal direction to a tilt of 20°, aiming at the maxillary/mandibular canines. The use of a paperclip at a corner of the film can help orientate the right from the left incisive arcade.
FIGURE (1B) Radiography of the maxillary incisors.
FIGURE (2A) Maxillary canines: The film is placed flat against the canines, parallel to the hard palate. With your starting point at 0°, angle the beam 20° to 45° over the canine. The variation of 20° to 45° depends on the width of the maxilla. Use the smaller angle for a narrower maxilla. The aim is to obtain a lateral view of the canines without superimposition of the conchal crest, neighbouring incisor and premolar and bony palate over the root apex.
FIGURE (2B) Radiography of the maxillary canines.
FIGURE (3A) Mandibular canines: Film and angles placed as for maxillary canines. Once in place, tilt the beam in a rostro-caudal direction. This will prevent superimposition of the canine over the mandibular symphysis and opposite mandible.
FIGURE (3B) Radiography of the mandibular canines.
FIGURE (4A) Maxillary and mandibular premolars: Film placed over the premolars, parallel to the hard palate. With your starting point at 0°, angle the beam 45° over the premolars.
FIGURE (4B) Radiography of the maxillary premolars.
FIGURE (5A) Maxillary fourth premolar and molars: Film placed as far caudal in the mouth as possible, and parallel to the hard palate. With your starting point at 0°, angle the beam 45° over the fourth premolar and molars. This projection will allow you to view the distal root, but will cause superimposition of the mesiobuccal and mesiopalatal roots of the fourth premolar.
FIGURE (5B) Radiography of the maxillary fourth premolar and molars.
FIGURE (6A) Maxillary fourth premolar and molars: A minimum of two views will be required to separate the roots of the fourth premolar. The second view should utilise the same 45° angle, but with a caudo-rostral or rostro-caudal tilt, which will separate the mesial roots for assessment.
FIGURE (6B) Radiography of the maxillary fourth premolar and molars – second view.
FIGURE (7A) Mandibular molars: Film is placed parallel to the mandibular body, between the mandible and the tongue. The beam is angled at 90° to the film. This projection is used for teeth caudal to the second mandibular premolars.
FIGURE (7B) Radiography of the mandibular premolars and molars.

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).

FIGURE (8) The modified conventional approach: Film placed as far caudally in the mouth as possible, parallel to the hard palate. With your starting point at 0°, angle the beam 60° in a rostro-caudal direction.
FIGURE (9A) The intra-oral near parallel approach: Film is placed diagonally with the edge of film resting palatal to the lowermost maxillary cheek teeth and lingual to the uppermost mandibular cheek teeth, allowing the uppermost maxillary cheek teeth to be imaged. With your starting point at 0°, angle the beam at 70° aiming towards the target cheek teeth. The film is nearly parallel to the tooth roots.
FIGURE (9B) Intra-oral cat radiography.
FIGURE (10A) The extra-oral approach: The patient is in lateral recumbency (the hard palate is perpendicular to the table) with the target teeth nearest the table. The film is placed under the target teeth on the table. A radiolucent mouth gag is used to hold the mouth open. The beam is aimed through the mouth onto the target teeth.There are no specific angles used and is positioned by line of sight.
FIGURE (10B) Extra-oral cat radiography.

References

Kim, C., Lee, S., Kim, J., Park, H.

2013

Assessment of Dental Abnormalities by Full-Mouth Radiography in Small Breed Dogs. Journal of the American Animal Hospital Association, 49, 23-30

Kyllar, M. and Witter, K.

2012

Prevalence of dental disorders in pet dogs. Veterinární Medicína, 50, 496-505

Lund, E., Armstrong, J., Kirk, C., Kolar, L.M. and Klausner, J.S.

1999

Health status and population characteristics of dogs and cats examined at private veterinary practices in the United States. Journal of the American Veterinary Medical Association, 214, 1336-41

Verstraete, F., Kass, P. and Terpak, C.

1998a

Diagnostic value of full-mouth radiography in dogs. American journal of veterinary research, 59, 686-91

Verstraete, F., Kass, P. and Terpak, C.

1998b

Diagnostic value of full-mouth radiography in cats. American journal of veterinary research, 59, 692-5

Woodward, T.

2009

Dental Radiology, Topics in Companion Animal Medicine, 24, 20-36

Paik Koh

Paik Koh, BVM&S, PgCert(SAS), MRCVS, is a veterinary surgeon at Dental Vets. Having spent 16 years in general practice, she transitioned from mixed practice to 100 percent companion animals and surgery.


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