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Equine Dental Radiography
R.M. Baratt
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Indications
The indications for dental radiography include, but are not limited to:
- Maxillofacial trauma
- Assessment and staging of periodontal disease
- Malocclusion assessment and orthodontic treatment planning
- Exodontia
- Abnormal tooth numbers
- Persistent deciduous teeth
- Supernumerary teeth
- Facial swelling, draining tracts, nasal discharge
- Tooth fracture
Equipment
The equipment used for equine extraoral dental radiology is generally the same that is used for radiographic examination of the horse for lameness: a portable x-ray generator is adequate. While standard film systems can be used, portable digital systems have distinct benefits for ambulatory practitioners:
- Multiple views and retakes can be anticipated in dental imaging; if processing in the field is not possible, the horse should be referred to a clinic where immediate processing can be performed.
- Similarly, intra- and postoperative images are often needed; without the ability to process the images in the field, the patient should be moved to a facility where this can be done at the time of the procedure.
Radiographic imaging systems presently available fall into 3 groups:
- Conventional film/rare earth cassettes and wet film processing.
- Computed radiography (CR) utilizing phosphor plates that are processed in a scanning device that generates a digital image.
- Direct radiography (DR) digital sensors that immediately generate a digital image.
The main disadvantage of traditional film is the inability to process the films in the field. For a clinic-based practice this is not a factor, and vinyl intraoral cassettes with rare earth screens can be purchased so that intraoral views of the maxillary cheek teeth can be obtained. The CR systems are portable, less than half the costs of the DR systems, but the image acquisition time is slower than the DR systems and they are more technique sensitive. In addition to the high cost, intraoral imaging of the cheek teeth is not possible with the DR sensors that are presently available.
Comparison of the 3 Systems
Radiographic Views/Positioning
Conventions and Labeling
The convention for presenting radiographic images of the dentition is somewhat different from that used by veterinary radiologists. As in human and small animal veterinary dentistry, the radiographs are presented as if a panoramic view of the dental arcades were being obtained. This standardized presentation eliminates the need for placing radiographic markers. However, since the digital imaging software may display the image incorrectly, requiring the clinician to rotate the image, an electronic label should be permanently imbedded in the DICOM image.
Incisors
The incisors are best viewed using intraoral placement of the cassette or digital sensor. Since the cassette/sensor is not parallel to the long axis of the incisor teeth, the bisecting angle technique is used to obtain an image of the teeth that minimizes foreshortening or lengthening of the image. Intraoral radiography in the horse requires sufficient sedation to eliminate chewing when the imaging cassette/sensor is placed in the mouth.
When the imaging plate cannot be placed parallel to the target tooth, the optimal image is obtained when the x-ray beam is directed 90° to the plane that bisects the angle between the target tooth and the plate (Fig. 1). In geriatric patients the inclination of the incisors diminishes, so that the bisecting angle decreases, and the x-ray beam approaches a perpendicular orientation to the plate.
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