Focus Meeting on Dentistry Charlotte, NC, USA Aug. 4-6, 2013

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Dentistry Charlotte, NC, USA Aug. 4-6, 2013 Next Meeting: Annual Convention Dec.

1 Proceedings of the American Association of Equine Practitioners Focus Meeting on Dentistry Charlotte, NC, USA Aug. 4-6, 2013 Next Meeting: Annual Convention Dec. 7-11, Nashville, TN, USA Resort Symposium Feb. 6-8, Rio Grande, Puerto Rico, USA Reprinted in the IVIS website with the permission of the AAEP

2 Imaging I: Radiography Robert M. Baratt, DVM, MS, FAVD (equine/small animal) Take Home Message Standardized radiographic views of the equine dentition are essential for diagnosis of equine dental disease and differentiating primary from secondary sinusitis. Author s address Salem Valley Veterinary Clinic, 12 Center Street, Salem, CT Rbaratt1dvm@gmail.com. T I. INTRODUCTION he 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 o 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). o Extraoral views of the cheek teeth o 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). 38

The xray beam (red) is perpendicular to the plane (yellow line) that bisects the angle

3 1A 2B 1B Fig. 1. A) Demonstration of the bisecting angle technique used to image the maxillary incisors (occlusal view). The xray beam (red) is perpendicular to the plane (yellow line) that bisects the angle formed by the long axis of the tooth (black line) and the imaging plate/sensor. Note that the curvature of the tooth is significant. B) If the bisecting angle is determined using the crown of the tooth, especially in the young horse, then the xray beam will be directed at too obtuse an angle and the image will be too long. 2C 2A 2D 39

2E Fig. 4. Intraoral radiograph of the maxillary incisors of a 5-yearold Quarter Horse gelding. The enamel lined infundibulum (white arrow) lies lingual to the flattened pulp chamber (blue arrow).

Maturation of the roots is evident as a lengthening of the root and narrowing of the apex in the older 1 st incisors compared with the more recently erupted 3 rd incisors with an open apex (yellow

The occlusal view of the mandibular incisors and canine teeth (D); note the persistent deciduous right mandibular 3 rd incisor (arrow).

For the extraoral lateral oblique projection of canine teeth, the cassette/sensor is placed on the side of the head and the xray beam is directed slightly dorsoventral, which separates the canine

4 2E Fig. 4. Intraoral radiograph of the maxillary incisors of a 5-yearold Quarter Horse gelding. The enamel lined infundibulum (white arrow) lies lingual to the flattened pulp chamber (blue arrow). Peripheral enamel (red arrow) extends apically the length of the reserve crown. Maturation of the roots is evident as a lengthening of the root and narrowing of the apex in the older 1 st incisors compared with the more recently erupted 3 rd incisors with an open apex (yellow arrow). 2F Fig. 2. Intraoral radiographs of the incisors of a 5-year-old Quarter Horse gelding. The occlusal view of the maxillary incisors (A) and the right and left oblique views (B, C). The occlusal view of the mandibular incisors and canine teeth (D); note the persistent deciduous right mandibular 3 rd incisor (arrow). Right and left oblique views of the mandibular incisors and canine teeth (E, F). Fig. 3. For the extraoral lateral oblique projection of canine teeth, the cassette/sensor is placed on the side of the head and the xray beam is directed slightly dorsoventral, which separates the canine teeth. In this case the sensor was on the left side of the horse s head, so the right canine teeth are slightly magnified. Courtesy of Leah Limone, DVM. Fig. 5. This straight lateral radiograph was obtained with the CR plate placed on the left side of the head. As the cheek teeth are superimposed, the technique is chosen to enhance the delicate bony structure of the paranasal sinuses. The paired infraorbital canals (*), rostral maxillary sinuses (RMS), caudal maxillary sinuses (CMS), frontal sinuses (FS) and dorsal conchal sinuses are also superimposed. Courtesy of Jennifer Rawlinson, DVM, DAVCD. 40

6A face, and the xray beam directed at a 30º DV angle from the straight lateral, remaining perpendicular to the long axis of the head (Fig. 7A).

This projection of the maxillary cheek teeth is quite similar to that obtained with an intraoral technique (Figs. 8A, B).

5 6A face, and the xray beam directed at a 30º DV angle from the straight lateral, remaining perpendicular to the long axis of the head (Fig. 7A). The VD lateral oblique view of the left mandibular cheek teeth is obtained by placing the plate or sensor on the left side of the horses head, and lowering the generator about 50º from the straight lateral (Fig. 7B).Note that the open mouth lateral VD projection will many times isolate the apical region of the ipsilateral maxillary cheek teeth in the space between the maxillary and mandibular quadrants. This projection of the maxillary cheek teeth is quite similar to that obtained with an intraoral technique (Figs. 8A, B). The mandibular cheek teeth can also be imaged with the plate placed ventrally, as for the DV view, with a bisecting angle technique (Fig. 7C). 7A 6B Fig. 6. The offset mandible DV view is readily obtained by placing ropes or baling twine around the maxilla and mandibles at the level of the diastema between the incisors and cheek teeth, and having assistants pull gently in opposite directions. When the mandible is pulled to the horse s right (A) the left mandibular and maxillary cheek teeth are imaged without superimposition. Note the crown fracture of the left mandibular 1 st molar (arrow). Compare with the mandible drawn to the horse s left (B). Courtesy of Ryland Edwards, DVM, DACVS. The lateral oblique views of the cheek teeth are obtained with the mouth open. With adequate sedation, the CR plate or DR sensor can be placed between the head and the strap holding the speculum, so that there is minimal interference by the speculum. Alternately, a bite block can be placed between the incisors. The DV lateral oblique view of the left maxillary quadrant is obtained with the plate on the left side of the 41 7B

8A 7C Fig. 7. Positioning for the DV lateral oblique (A) and the VD lateral oblique (B).

Failure to do this will result in significant rostro-caudal obliquity.

An assistant is holding the DR sensor (A, B), and the beam is collimated so that the gloved hands are not in the direct beam.

6 8A 7C Fig. 7. Positioning for the DV lateral oblique (A) and the VD lateral oblique (B). Care should be taken to keep the xray beam perpendicular to the long axis of the head as the generator is moved dorsally or ventrally from the straight lateral. Failure to do this will result in significant rostro-caudal obliquity. If the long axis of the head is nearly perpendicular to the ground, then the xray beam should be approximately parallel to the ground. An assistant is holding the DR sensor (A, B), and the beam is collimated so that the gloved hands are not in the direct beam. With CR plates, the speculum and/or elastic cords can be used to secure the plate to the horse s head (C). This eliminates the need for an assistant holding the plate. This photo (C) illustrates an alternative method for imaging the mandibular cheek teeth. The xray beam is directed at the plane that bisects the angle between the plate and the long axis of the cheek teeth (about a 45 degree angle to the plate). The image is quite similar to that obtained with the VD lateral oblique (Fig. 13). 8B o Presentation of the lateral projections of the right maxillary and mandibular cheek teeth, as shown in Figs. 8-12, is with the horse s nose to the viewer s right, and conversely, when the plate or sensor is on the left side of the horse s head, the image is presented with the horse s nose to the viewer s left. This is not necessarily the way the image is presented with many imaging software programs used with CR and DR systems, and may require a horizontal flip of the image for correct presentation. The radiographic anatomy of the cheek teeth is obscured by the infolding enamel, so that the pulp horns and infundibulae are generally not well-defined. However, the lateral and DV projections do allow evaluation of cheek tooth roots, apical alveolar bone and periapical sinus structures (Fig.13). 8C Fig. 8. Using the positioning illustrated in Figure 7B, one can image the left maxillary cheek teeth in the space between the right maxillary and mandibular quadrants (A). This approximates the level of detail obtained with the intraoral technique (B), which is not possible to obtain with the DR systems. This is an excellent complementary view to the standard DV lateral oblique (C). 42

9A 9C Fig. 9. The CR system uses a phosphor plate for image capture.

The plate is protected from light with a vinyl cassette and from moisture with a clear plastic bag.

With a full mouth speculum in place, the cassette is positioned against the palate (B).

The xray beam must also be 90º to the long axis of the head and centered on the rostral end of the facial crest (C). Fig. 10.

7 9A 9C Fig. 9. The CR system uses a phosphor plate for image capture. The plates are available in any size; the size generally chosen for the intraoral imaging of the maxillary cheek teeth is 4x8 inches. The plate is protected from light with a vinyl cassette and from moisture with a clear plastic bag. A ½ inch diameter section of PVC plumbing pipe has be slotted at one end to fabricate a cassette holder (A). With a full mouth speculum in place, the cassette is positioned against the palate (B). The xray beam is directed at the plane that bisects the angle formed by the tooth and the cassette, or approximately 45º to the cassette. The xray beam must also be 90º to the long axis of the head and centered on the rostral end of the facial crest (C). Fig. 10. Intraoral radiograph of the left maxillary cheek teeth in a 5-year-old Quarter Horse. The periodontal ligament space is evident on some of the cheek teeth (white arrows). The three roots can only be differentiated on the 2 nd premolar (MB, DB and P mesiobuccal, distobuccal and palatal). The 3 rd molar is often not imaged in this view. 9B 43

11A 11B Fig. 11. Intraoral radiograph of the right mandibular premolars. In the young horse, only the clinical crown and a portion of the reserve crowns can be imaged (A).

$In this case the sensor was on the horse s right side, and the right mandibular cheek teeth crowns are imaged (note the crown fracture of the right mandibular 4 th premolar). Fig. 13.$ The apical reserve crown and roots of the mandibular cheek teeth are best imaged with the VD lateral oblique view.

The apical reserve crown and roots of the mandibular cheek teeth are best imaged with the VD lateral oblique view.

Note the periapical alveolar bone lysis (halo) and the ventral cortical bone sclerosis and soft tissue swelling (arrow). Intraoral views of the cheek teeth o Positioning.

8 11A 11B Fig. 11. Intraoral radiograph of the right mandibular premolars. In the young horse, only the clinical crown and a portion of the reserve crowns can be imaged (A). In the geriatric horse nearly all of the mandibular premolars can be imaged (B, intraoral radiograph of the left mandibular cheek teeth). Fig. 12. The DV lateral oblique positioning can be used to project the crowns of the mandibular cheek teeth in the space between the maxillary and mandibular quadrants. In this case the sensor was on the horse s right side, and the right mandibular cheek teeth crowns are imaged (note the crown fracture of the right mandibular 4 th premolar). Fig. 13. The apical reserve crown and roots of the mandibular cheek teeth are best imaged with the VD lateral oblique view. This radiograph complements the DV lateral oblique view, which images the coronal portion of the mandibular cheek teeth. This VD lateral oblique view is the same horse as in Figure 11. Note the periapical alveolar bone lysis (halo) and the ventral cortical bone sclerosis and soft tissue swelling (arrow). Intraoral views of the cheek teeth o Positioning. These views require vinyl intraoral cassettes and phosphor imaging plates with a CR digital processing system. For the left maxillary cheek teeth the 4x8 inch cassette is placed flat against the palate and the xray beam is directed from the left side, perpendicular to the long axis of the head and the plane that bisects the angle formed by the long axis of the tooth and the cassette (Fig. 9). Since the long axis of the tooth is almost 90º to the cassette, the xray beam is at about 45º to the cassette. In the young horse (less than 10 years) the length of the cheek teeth may require intentional foreshortening so that the apical region is projected on the plate. Due to their caudal location in the mouth, it may not be possible to image the 2 nd and 3 rd maxillary molars in the young horse (Fig. 10). The intraoral view of the mandibular cheek teeth is obtained by placing a 2.5 x 8 inch cassette between the tongue and mandible.. The xray beam is perpendicular to the long axis of the mandibular cheek tooth. The apical region of the mandibular cheek teeth is generally not imaged with this technique (Fig. 11). This view requires profound sedation so that the cassette placement does not stimulate chewing motion artifact. An alternate view of the coronal aspect of the mandibular cheek teeth can be obtained with the DV lateral oblique 44

9 of the maxillary cheek teeth, described above, which projects the crowns of the mandibular cheek teeth in the space between the maxillary and mandibular quadrants (Fig. 12). III. RESULTS With some practice the veterinarian and technicians can obtain dental radiographs of diagnostic quality. Attention to proper positioning is most important, as unintentional obliquity makes interpretation much more difficult. Every effort should be made to properly label the radiographs and present them in a standard fashion. IV. DISCUSSION While practitioners are understandably intimidated by the process of obtaining and interpreting dental radiographs of the horse, this is an important skill to develop in primary equine practice. In many instances, the pathology is unilateral and comparison to the unaffected side facilitates radiographic interpretation. Therefore, it is important to routinely obtain both right and left views. When standard views are obtained, consultation with veterinary dentists is more productive. Additionally, comparison with other horses and with follow up studies of the same horse is facilitated. consultation with a radiologist or equine dentist is more likely to be productive and lead to earlier appropriate treatment. REFERENCES 1. Taylor L, Dixon PM. Equine idiopathic cheek teeth fractures: Part 2: A practice-based survey of 147 affected horses in Britain and Ireland. Equine vet J 2007, 39(4); Dixon PM, Barakzai SZ, Collins NM, Yates J. Equine idiopathic cheek teeth fractures: Part 3: A hospital-based survey of 68 referred horses ( Equine vet. J 2007, 39(4): van den Enden MSD, Dixon PM. Prevalence of occlusal pulpar exposure in 110 equine cheek teeth with apical infection and idiopathic fractures. Vet J 2008, 178; Townsend NB, Hawkes CS, et.al. Investigation of the sensitivity and specificity of radiological signs for diagnosis of periapical infection of equine cheek teeth. Equine vet. J. 2011; 43 (2): While crown fractures are routinely observed in both incisors and cheek teeth, radiographic signs of apical abscessation secondary to pulp exposure from crown fractures is relatively rare in incisors and probably occurs in less than 50% of fractures of cheek teeth (excluding sagittal fractures). 1,2,3 Apical abscessation is most reliably recognized radiographically as apical alveolar bone lysis (so-called halo ), blunting of the root(s) from external root resorption and periapical alveolar bone sclerosis (condensing osteitis). 4 Apical infection, with similar clinical signs may also be due to extension of periodontal disease or infundibular decay, and may occur by anachoresis in horses 5-10 years old. 3 Unilateral nasal discharge is a relatively common presenting clinical sign in horses, and is an indication for radiographic examination of the skull. Even with good quality radiographs, it is not always possible to differentiate between a primary sinusitis and that secondary to dental disease. Computed tomography (CT) has been demonstrated to be significantly more sensitive than standard radiography in the detection of apical disease of cheek teeth. 4 Due to the complex 3- dimentional sinus anatomy, CT is generally a more reliable imaging modality for the diagnosis sinus disease. V. CONCLUSION The equine practitioner in general practice should be comfortable with obtaining diagnostic radiographs of the horse s head. If the radiographs are properly positioned, then 45

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