Radiography

4 Radiography


Radiography is a vital diagnostic tool in veterinary dentistry. Radiographs are required to:


• Reach a diagnosis

• Plan optimal treatment

• Perform certain procedures

• Assess the 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 radiodense, can obscure pathological lesions on a radiograph.



DENTAL RADIOGRAPHY


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 (Fig. 4.1). Intra-oral (film placed inside mouth and X-ray beam directed from outside the mouth through the tooth and adjacent structures onto the film) radiographic techniques are therefore required. The two basic techniques are:


1. Parallel technique for the mandibular premolars and molars

2. Bisecting angle technique for all other teeth.

image

Figure 4.1 A diagnostic view. 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. Intra-oral placement of dental film and parallel technique gives an accurate representation of the mandibular third and fourth premolars and the first molar, as well as detail of the mandibular bone in a cat. In this view, the component structures of the tooth and its supporting tissues are well defined. The enamel is seen as an incompletely visualized radiodense band that covers the crown and tapers to a fine edge at the cervical margin of the tooth. The dentine is less radiodense than enamel and accounts for the bulk of the hard tissues of the tooth. The cementum is not visible. The pulp cavity is the continuous radiolucent space in the centre of the tooth which extends from the coronal portion to the apex of the roots. The wall of the alveolar tooth socket (the lamina dura) is the radiodense line which runs parallel to the root of the tooth. The periodontal ligament space is the fine radiolucent line between the lamina dura and the root of the tooth. The cortical bone on the crest of the alveolar ridge is continuous with the lamina dura. The mandibular canal is clearly visible.


Contralateral (same teeth, opposite side) views should routinely be taken for comparison.



FULL-MOUTH RADIOGRAPHS


Full-mouth radiographs describe 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 eight views, but 10 views are recommended, to ensure that all teeth are properly visualized. These are as follows:


Essential radiographic views


• Incisor view in the upper jaw

• Lateral view for each of the canines of the upper jaw

• Left and right maxillary premolar and molar views

• Mandibular incisor and canine view

• Left and right mandibular premolar and molar views.

Recommended radiographic views


• Lateral view for each of the canines of the mandible (in addition to the eight essential views).

The choice of film size for each view is subjective. The smallest film that will depict the area of interest should be used to facilitate film positioning. Adult periapical size film can be used for all cat views.


In the case of dogs, full-mouth radiographs are encouraged, especially at first examination. If this is not possible then radiographs should be 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



• X-ray machine

• X-ray film

• Processing facilities

• Mounts or envelopes for film storage.


The X-ray unit


A dental X-ray machine (Fig. 4.2) 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 and 50 cm.


image

Figure 4.2 A dental X-ray unit installed in the designated dental theatre is the ideal situation. These units are available as free standing or wall mounted. Wall mounting is usually preferable to save space.



X-ray film


To allow intra-oral film placement and achieve high definition, dental film (Fig. 4.3) 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.


image

Figure 4.3 Sizes of dental film. Dental film is available in three sizes, namely occlusal (5 cm × 7 cm), periapical (3 cm × 4 cm) and paediatric (2 cm × 3 cm). The smallest film that depicts the area of interest should be used to facilitate film positioning in the mouth.



Orientation


Ensure the correct side of the film envelope is facing the incident beam; the envelope is marked or labelled. If exposed through the back of the envelope, the lead sheet will absorb much of the X-ray beam, resulting in an underexposed radiograph with the pattern of the lead sheet imposed on it.


Each film has a raised dot in one corner. The dot helps with orientation when viewing and mounting dental radiographs if the following procedure is adhered to. Firstly, the dot should face the incident beam. Secondly, the film should be placed in the mouth so that the dot is always facing a specific direction. We position the dot so that it is always facing forward in the mouth. Another way of doing it is to ensure that the film is placed so that the dot is always in the same position, i.e. facing forward in the mouth on one side and backward in the mouth on the contralateral side.

Related posts:

  1. The tooth and its periodontium
  2. Multiple tooth and jaw fracture
  3. Chronic gingivostomatitis as a consequence of periodontitis and iatrogenic injuries
  4. Enamel dysplasia

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Radiography

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