ABSTRACT: Dental radiography is a useful – and in some cases essential – diagnostic tool, still under-utilised in small animal dentistry. When one considers that most of the structure of the tooth lies below the gingival margin, within the bone, many structures are not visible and much pathology can remain undetected unless radiography is performed. Intra-oral film placement, utilising different techniques and specific dental film, allow individual teeth and the surrounding bone to be evaluated to check for subtle changes, without superimposition of the opposing jaw or dental arcade. Indications for taking intra-oral radiographs are numerous.

In general practice, dental radiography is becoming more widely used as a diagnostic tool but it is still under utilised in small animal dentistry. When one considers that most of the structure of the tooth lies below the gingival margin, within the bone, many structures are not visible and much pathology can remain undetected unless radiography is performed.

A full examination of the mouth is not possible without the aid of radiographs. Dental radiography allows individual teeth and the surrounding bone to be evaluated to check for subtle changes, without superimposition of the opposing jaw or dental arcade (Figure 1).

Figure 1: Lateral skull radiographs showing superimposition of dental arcades, eliminating the fine detail required to examine the teeth

Radiographic equipment required

Radiographic unit

Although dental X-ray machines are easier and more convenient to use, a medical X-ray unit can be used to obtain good dental radiographs. They are most useful if the tube head can be raised or lowered, and angled or rotated. If the tube head is not manoeuvrable, it is then necessary to position the patients head differently for each view taken (Figure 2).

Figure 2: The patient's head is positioned to allow for the correct image rather than a mobile dental tube head

One other disadvantage of using a standard medical X-ray unit is that it is often located in a separate room from where the dental procedure may be taking place and the patient will then need to be moved in order to take the radiographs. This can be a problem when performing procedures that require radiographs during the procedure – for example, if a root fractures during extraction.

Dental X-ray units are smaller and more mobile and manoeuvrable than medical X-ray units. A stand-alone machine or wall-mounted dental X-ray unit can be fitted in the dental procedure room, enabling easy access whilst performing procedures. Secondhand machines are easy to come by and good value for money (Figure 3).

Figure 3: A dental radiography unit being positioned

Dental X-ray units have a fixed kV and mA and the only adjustment required is the time setting. The collimation is limited to the diameter of the cone, and the focal distance is the length of the cone.

Intraoral film

Whether using a medical or dental X-ray machine, it is always advisable to use intraoral dental film. The film is small, flexible, and inexpensive. Dental film is non-screen film, so provides good detailed images and it is this high definition that allows interpretation of sometimes very subtle dental pathology.

These films are designed to be placed inside the mouth and the outer wrapping protects them from moisture and light. A lead foil backing is found on the side facing away from the beam and its purpose is to absorb any radiation passing through the film. We mostly use three sizes of film:

•   occlusal (5cm x 7cm) – useful for canine teeth in dogs and rabbit skull radiographs

•   adult periapical (3cm x 4cm) – useful for most other teeth in dogs and cats

•   child periapical (2cm x 3.5cm) – useful for small cats (Figures 4a & 4b).

Figures 4a & b: Sizes of dental film available and (4b) the contents of the film pouch

Exposure factors will vary depending on the machine being used. Dental film requires higher exposure settings as it is non-screen film. If using a medical X-ray unit with a film focus distance of 30-50cm, exposures range from 60kV -80 kV with mAs of 20-30.
Processing the film

Exposed film must be protected from light until it is developed. It can be developed in a darkroom or in a chair- side developer, which has a translucent safety filter top (Figure 5). Automatic processors can be used, but most of the veterinary medical processors do not have an adequate system for such small film to be carried through the rollers.

Figure 5: Chair-side developer

The film needs to be developed, rinsed, fixed and then washed. Rapid developer and fixer solutions are available for dental film, which reduce developing and fixing times to as little as 30 seconds. This allows a film to be viewed within minutes of its being taken.

A self-contained film with two pouches – one holding a dental film and the other, processing chemicals – is available. However, the film is available in one size only and the chemicals do have a limited shelf life.

Use of this system involves activation of the pouch containing the chemicals by compressing them in to the area containing the previously exposed film. The film is agitated for one minute and then the pouch is opened and rinsed under running water. Relatively, the films are more expensive than individually purchased films and chemicals, but it can be quite convenient for some practices. This system also has a higher rate of development faults and the films need to be fixed for longer as they do discolour with time (Figure 6).

Figure 6: Self-contained pouches of film and chemicals

Labelling and storage

It is not possible to label dental film in the same way as cassette film. Small intraoral radiographs can best be identified by la
belling the cardboard mounts or envelopes/plastic sleeves used for storage.

Avoid using a marker pen directly onto the film as this may inadvertently obscure the image or pathology present. The films all have a raised dot in one corner used for positioning the film and also helping with left/right orientation when viewing the film as no other left or right marker can be placed.

All radiographs must be thoroughly fixed and completely dry before they are stored. Inadequately fixed radiographs discolour after a few months. If the film is not completely dry, stains develop and the film may adhere to the package. The radiographs should be placed in labelled protective envelopes and stored in a system suitable for dental radiographs or, alternatively, they may be kept with the patient s file.

Digital radiography

Digital radiography refers to the system of producing computer-generated images of radiographs. Indirect methods of obtaining digital images make the exposure on a phosphor plate, followed by transferring the latent image to a computer for processing.

Direct-to-digital equipment uses either a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) sensor as a data input device that sends the X-ray image directly to a computer. This is the easiest and most time-efficient method.

Advantages of direct digital systems include the production of an image within seconds, no need for wet processing thus reducing developmental errors, ease of storage and availability for future viewing. Furthermore digital radiography requires much less exposure time. Disadvantages include cost, and the fact that a limited number of sizes of sensors and plates are available (Figures 7a – 7c).

Figure 7a, b, c: Digital systems in use – both direct and indirect

 

Techniques for intraoral radiography

The main advantage of intraoral – rather than extraoral – radiography is that an image is produced with no superimposition of the contra-lateral side.

Parallel technique

This technique is used for mandibular teeth, caudal to the first premolar. The film is placed intra-orally, parallel to the tooth to be radiographed, and the beam is then positioned perpendicular to the film and tooth (Figure 8).

Figure 8: A demonstration of the placement of the intra-oral film using the parallel technique

Bisecting angle technique

This technique is used for all other teeth in the mouth as it is not anatomically possible to place the film parallel to these teeth.

The film should be placed as close to parallel as possible. The bisecting line is an imaginary line that equally divides the long axis of the tooth being radiographed, and the film. The beam is placed perpendicular to the bisecting angle. This will then project an image of the tooth being radiographed onto the film, avoiding elongation or shortening of the image (Figure 9).

Figure 9: Placement and positioning of the dental unit, demonstrating the bisecting angle technique

If the beam is directed perpendicular to the film, the image will be foreshortened (Figure 10). Conversely, if the beam is directed perpendicular to the tooth, the image will be elongated (Figure 11).

Figure 10: Image results – foreshortened image

Figure 11: Image results – elongated image

Figure 12: Image results- correct size image

Extra-oral dental radiography

An extra-oral technique is used when performing lateral skull radiographs of rabbits and chinchillas. Extra-oral film placement is also used to take radiographs of the temperomandibular joints. An extra oral oblique technique is also described for taking radiographs of the upper 4th premolar in cats without superimposition of the zygomatic arch. Further details about the techniques involved can be found in the references cited below.

Some indications for taking dental radiographs

There are many instances where intra oral radiography is required on a daily basis in small animal practice:

•   fractured teeth

•   moderate to severe periodontitis

•   resorptive lesions

•   discoloured teeth

•   missing teeth

•   swellings in the mouth

•   persistent deciduous teeth (to check whether there is root resorption)

•   pre- and post extractions

•   complications

•   jaw fractures.

Dentistry is an area of small animal surgery where nurses are very involved. The Royal College of Veterinary Surgeons advises that veterinary nurses are not allowed to perform extractions, but they should be able to perform a thorough oral examination, record the findings on a dental chart, take intra-oral dental radiographs, perform periodontal therapy (excluding periodontal surgery) and, perhaps the most important role, offer instruction in home care and ongoing oral hygiene.

Dental radiographs help establish a diagnosis and aid in treatment, but also help the owner to understand the disease process involved, why treatment was carried out and, most importantly, the need for ongoing care. 

Author

Lisa Milella BVSc DipEVDC

Lisa graduated from the University of Pretoria (Onderstepoort), South Africa, in 1997 and has since been working in the UK. She soon developed an enthusiasm for dentistry and decided to pursue this interest to specialist level.

She is a Diplomat of the European Veterinary Dental College and principal of a dedicated dental and oral surgery referral practice in Byfleet, Surrey.

To cite this article use either

DOI: 10.1111/j.2045-0648.2011.00088.x or Veterinary Nursing Journal Vol 26 pp 395-398

Further reading

•   Du PONT and De BOWES (2008) Atlas of Dental Radiography in Dogs and Cats. Elsevier.

•   MULLIGAN. ALLER and WILLIAMS 119981 Allas of Canine and Feline Dental Radiography. VLS.

•   CROSSLEY and PENMAN Eds 119951 BSAVA Manual of Small Animal Dentistry. BSAVA. Gloucester.

 

 

• VOL 26 • November 2011 • Veterinary Nursing Journal