Imaging I: Radiography

Take Home Message—Standardized radiographic views of the equine dentition are essential for diagnosis of equine dental disease and differentiating primary from secondary sinusitis.

I. Introduction

The diagnosis of dental disease and diseases of the closely associated sinus and nasal structures of the horse’s head is largely dependent on the ability of the equine practitioner to obtain diagnostic radiographs in the field. Equine practitioners should not only be aware of the clinical signs that are indications for obtaining radiographs, they need to be able to obtain the standard radiographic projections of the equine skull and dentition. The objective of this paper is to present the technique for obtaining diagnostic radiographs with equipment readily available to the equine practitioner.

II. Materials and methods

The radiographic equipment that the equine practitioner uses for examination of the distal extremities of the horse is suitable for imaging the skull. In general, this will include a portable xray generator and either a digital imaging system or a high speed film and rare earth screen combination. While traditional xray film can be used, the inability to process the images in field makes it impractical in ambulatory practices. The portable digital systems presently available are the computed radiography (CR) and direct digital radiography (DR) systems. The CR systems have the advantage of small cassette sizes for intraoral imaging of the cheek teeth. However, both systems can provide exceptional dental imaging in the field.

A radiographic evaluation of the equine dentition and paranasal sinuses is only possible when the patient is adequately sedated. The choice of sedation is largely a matter of personal preference, but the level of sedation required is important, both for obtaining diagnostic images and for the protection of the operators and expensive equipment. With profound sedation, the technicians can position themselves further from the primary beam, and the number of retake exposures will be minimized. A typical sedation protocol would be xylazine alone (1 mg/kg, IV) or in combination with butorphanol (xylazine, 0.25 mg/kg, and butorphanol, 0.02 mg/kg, IV). Regardless of the alpha-2 agonist selected, the effect must be of the patient standing steadily with the head lowered and unresponsive to the operator’s movement around the head with the xray generator. To minimize motion artifact the plate or sensor is secured to the horse’s head, or both the head and the sensor are supported together.

Standard radiographic views include intraoral views of the incisors and canine teeth, and extraoral views of the cheek teeth.

• Intraoral views of the incisors and canine teeth
  • Positioning. The cassette or sensor is placed within the horse’s mouth for these views. If gradual placement of the cassette/sensor results in chewing or lifting of the head, then additional sedation is required. The bisecting angle technique is used to obtain an anatomically proportional image free of foreshortening or lengthening artifact (Fig. 1). The occlusal views can be augmented with tangential views (Fig. 2). Extraoral imaging of the maxillary canine teeth may be necessary with a DR system (Fig. 3).

• Extraoral views of the cheek teeth
  • Positioning. The DV and straight lateral views are obtained with the mouth closed, with the xray beam perpendicular to the long axis of the head and at the level of the rostral end of the facial crest (approximate center of the cheek teeth quadrant). Due to the superimposition of the cheek teeth, the lateral view is obtained largely for evaluation of the sinus structures, and care must be taken to use a technique that does not “burn out” the fine bony detail (Fig. 5). The DV view with an off-set mandible can be used to remove some of the superimposition of the maxillary and mandibular cheek teeth in the DV projection (Fig. 6).
     

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