How to Obtain a Diagnostic Radiographic Study of the Equine Cheek Teeth

1. Introduction

The use of standardized radiographic views of the equine skull greatly facilitates interpretation of dental pathology. Digital radiographic systems are rapidly replacing traditional radiographic film in clinical equine practice. The methods for obtaining diagnostic radiographs of the equine cheek teeth with digital radiographic systems are presented. Standardized labeling and presentation are important for interpretation of skull radiographs.

2. Materials and Methods

Images presented were obtained with a digital system.^a

The American Veterinary Dental College and the American College of Veterinary Radiologists (ACVR) have differing conventions for radiographic presentation of extraoral dental radiographs. For the purposes of this paper, the ACVR presentation and labeling conventions are used.¹ With regard to the head, lateral images are always presented with the horse’s nose facing the viewer’s left. The plane of the hard palate is used as the reference when considering angles of obliquity to the dorsal plane. Radiographic projections are described using the direction of travel of the primary beam, and for the purposes of this manuscript, the following terms and abbreviations have been utilized when naming radiographic views: left (L), right (R), ventral (V), dorsal (D), and oblique (O). A series of radiographs of the skull that enables evaluation of the entire dentition includes:

• Latero-lateral view: The right lateral view is obtained with the X-ray detector on the right side of the head (and the generator on the left side) and presented with the horse’s nose to the viewer’s left. A RIGHT label would be used.
• Dorsoventral (DV) views: The X-ray detector is positioned on the ventral aspect of the mandibles, and the central X-ray beam is directed perpendicular to the dorsal plane (the palate). The rostral aspect of the image is on the bottom, with the horse’s right side to the viewer’s left.
• Oblique views: 
  • Left dorsal-right ventral oblique (LD-RVO) and right dorsal-left ventral oblique (RD-LVO). A LD30RVO is obtained with the X-ray generator on the horse’s left side and the X-ray detector on the right. The X-ray beam is directed in a left dorsolateral to right ventrolateral fashion, 30° to the dorsal plane. For comparison, the opposite oblique image should be obtained. This view will project the apical aspect of the maxillary cheek teeth closest to the X-ray detector. For example, the RD30LVO will project the apices of the left maxillary cheek teeth. For this view a LEFT marker would be used (and placed dorsal to the image). With the horse’s mouth opened for the RD30LVO view, the crowns of the left mandibular cheek teeth will be projected.
  • Left ventral-right dorsal oblique (LV-RDO) and right ventral-left dorsal oblique (RV- LDO). A LV45RDO is obtained with the detector on the right side of the horse’s head and the generator on the left. In this image, the reserve crown-roots of the right mandibular cheek teeth would be highlighted. A RIGHT marker would be placed on the ventral aspect of the image. When the horse’s mouth is opened for the LV45RDO view, the apical portion of the right maxillary cheek teeth is projected.
• Intra-oral (occlusal) images of the maxillary and mandibular incisors are presented with the maxillary crowns down, mandibular crowns up, and the horse’s right to the viewer’s left.²

While the straight lateral and DV views are obtained with the mouth closed, the lateral oblique views are obtained with the mouth held wide open with a speculum or a bite block. The speculum^b used by the author does not significantly interfere with imaging of the cheek teeth. The open-mouth positioning of the oblique projections eliminates much of the superimpositioning of the cheek teeth. More importantly, these projections of the apical aspect of the maxillary cheek teeth and the coronal aspects of the mandibular cheek teeth in the space between the maxillary and mandibular arcades provide excellent dental detail, comparable to the images obtained with intraoral placement of the detector using a computed radiography (CR) system (Figs. 2 and 3). The increased apical detail of the maxillary cheek teeth with the open-mouth oblique views (LV45RDO and RV45LDO) compared with the other oblique views (RD30LVO and LD30RVO) is due to the fact that the X-ray beam is passing through only one maxilla in the former, as compared with both maxillae in the latter.

3. Results

The lateral image (Fig. 1) is used primarily to evaluate the paradental anatomy. The paired sinus structures are superimposed in the lateral image; therefore, laterality of the sinus pathologic change is not possible. However, fluid lines and soft tissue masses within the sinus spaces are readily appreciated (Fig. 2). In the oblique views (LD30RVO and RD30LVO), images of the right and left sinuses are separated which facilitates evaluation of these structures and localization of pathology (Fig. 3).
 

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