CHAPTER 2 Intraoral Radiographic Anatomy of the Dog
THE NORMAL TOOTH
FIGURE 2-1 Anatomy of the teeth and supporting structures. A and B, Radiograph of a left mandibular fourth premolar tooth. The third premolar tooth on the left and the first molar tooth on the right are partially imaged. C (facing page bottom), Prepared mandible sectioned to expose the internal anatomy. Intraoral radiographs clearly depict the anatomy of the teeth and the surrounding structures. Significant variability exists between individuals. A structure may be absent, be difficult to identify, or appear unusual in any particular individual radiograph. Note that the lamina dura, the white line around the root made by the compact bone of the alveolus (the tooth socket), is visible in some areas but absent in others. The bony plate of the alveolus is more apparent in areas where it is either parallel to the x-ray beam or is superimposed over other radiodense structures and much less apparent where it is perpendicular or tangential to the x-ray beam or is superimposed over radiolucent structures. There is significant variability in lamina dura density and presence between individuals. It is separated from the root by a radiolucent line that represents the periodontal ligament space. Enamel, the densest material in the tooth, covers the tooth crown and is also the most radiopaque material. It can appear as a narrow white line bordering the crown of a tooth, an effect that is enhanced on surfaces that are oriented more parallel to the axis of the x-ray beam. The enamel is often difficult or impossible to visualize on a radiograph because it is generally less than 0.6 mm thick. In many cases, the enamel only diffusely adds to the radiopacity of the crown. Dentin forms the majority of the mature tooth. It is less radiodense than enamel, but the roots appear to have a similar radiodensity to the enamel-covered crowns due to the superimposition of alveolar bone over the roots. The cervical area of the tooth, between the enamel of the crown and the alveolar bony margin, has neither enamel nor bone superimposed and is therefore less radiodense. This is referred to as “cervical burn-out” and should not be mistaken for caries or dental resorption. The bone of the alveolar margin should be relatively horizontal and positioned 1 to 2 mm apical to the cementoenamel junction. The interradicular marginal bone often has a slightly convex contour, filling the furcation area and closely approximating the contour of the furcation. In contrast, the interalveolar marginal bone (margin of septal bone) can have a horizontal, a slightly concave, or a slightly convex contour depending on the proximity of the adjacent roots and the particular region in the arch. The pulp cavity includes the root canal, found in the center of each root, and the pulp chamber in the crown. It appears radiographically as a comparatively radiolucent area within the tooth.
MAXILLARY INCISOR TEETH
FIGURE 2-2 Normal incisor teeth. A, Radiograph of the incisor teeth and rostral maxillary region of a young adult dog. B, Dorsal view of prepared skull. C, Palatal (mirror) view of skull. D, Same radiograph as A. The crowns of the incisor teeth are foreshortened due to a projection angle that makes an image of the roots without elongation artifact (see Chapter 12).
FIGURE 2-5 Radiographs of maxillary incisor teeth often have periapical chevron-shaped lucencies that appear radiographically similar to lesions of endodontic origin (LEO) The trabecular bone and vascular channels around the apices, contrasted with the dense compact bone of the alveolar walls and incisive bone create this effect. The above photos and radiograph were made from the skull of a dog without incisor pathology. A, The labial bone and some root structure have been removed. There are large trabecular spaces in the bone around the apices of all three incisor teeth. B, At a slightly more lateral angle and with rear illumination, one can view along a natural infrabony channel. C, With more intense rear illumination, the relatively thin bone density along the axis that an x-ray beam would travel becomes apparent. D, A radiograph of this skull preparation prior to removing any bone has typical chevron lucencies.
FIGURE 2-6 In CT images, the periapical bone is characterized by large areas of hypoattenuation These correspond to the region of decreased bone density around incisor root tips that result in radiolucent areas. A, Sagittal plane image at the level of the maxillary third incisor tooth. B, Transverse plane image at the level of the maxillary third incisor tooth apices. C, Dorsal plane image at the level of the first and second incisor tooth root apices. D, Transverse plane image at the level of the second incisor tooth root apices.
FIGURE 2-3 In large dogs, the maxillary third incisor tooth can be better imaged using a more lateral projection angle. A and B, Radiograph of the left maxillary incisors. C, Labial view of a prepared skull. D, Palatal (mirror image) view of the skull. The left wing of the vomer is parallel to the x-ray beam and therefore more radiopaque than the right wing.
FIGURE 2-4 Effect of aging on the size of the pulp chambers and root canals of incisor teeth As teeth mature, secondary dentin is produced on the periphery of the pulp resulting in a progressively smaller pulp cavity with age. When the pulp experiences inflammation, dentin production can be accelerated resulting in a smaller pulp space compared to a healthy tooth. This can occur focally at the site of localized pulpitis. When it affects the entire pulp, the pulp appears more mature than normal. When a tooth pulp dies, maturation stops, making it appear less mature than normal (see Chapter 6). A, Three-month-old puppy. B, Five-month-old puppy. C, Eight-month-old puppy. D, Fifteen-month-old dog. E, Eighteen-month-old dog. F, Seven-year-old dog.
FIGURE 2-7 Normal anatomy Summation effect can also mimic a lesion of endododontic origin when local radiodense structures are positioned in certain ways. A and B, The relative radiolucency around the apex of the left upper third incisor tooth is consistent with a LEO. However, the periodontal ligament space is intact around the apex. The appearance of an ovoid lucency is created by the normal compact bone of surrounding structures. C and D, The x-ray tube has been shifted from lateral to medial, providing a different view that more clearly displays the anatomy.
FIGURE 2-8 Another example of summation effect mimicking a periapical lucency A and B, Apparent radiolucency around the apex of the third incisor tooth. C, Skull showing how the nasal process of the incisive bone (arrow) makes a curved opacity that can appear to be the border of an endodontic lesion. D and E, The x-ray tube has been shifted to a more lateral position. The image of the incisive bone has shifted relative to the root apex, demonstrating that it is in a different plane from the root apex. The line of the incisive bone moved medially as the tube was shifted laterally indicating that the structure responsible for the linear opacity is labial to the tooth root (see Chapter 12). F, Skull showing how shifting the tube laterally moves the nasal process medially.
FIGURE 2-9 True lesions of endodontic origin A, Periapical lucency of the bone around the apex of the left upper first incisor tooth (arrow). Note also the relative immature (wider) root canal and pulp chamber compared to the other incisor teeth (open arrow), consistent with pulp necrosis and arrested dentin production. B, Periapical lucency of the bone around the apex of the left upper second incisor tooth (arrow). C, Periapical lucency of the bone around the apex of the left upper third incisor tooth (arrow). Note the more circular shape compared to the chevron lucencies on the first and second incisor teeth. The radiopaque border is consistent with a chronic endodontic lesion (see Chapter 6).
FIGURE 2-10 Superimposed hard and soft tissues can mimic oblique or vertical root fractures A, Radiolucent lines where the nasal cartilage crosses the incisor roots. B, Same radiograph as A with cartilage outlined. C, Different soft tissue relationship. D, Same radiograph as C.
FIGURE 2-11 Superimposed structures mimic oblique root fracture A, The left maxillary second incisor tooth has an oblique radiolucent line that appears to be a fractured root (arrow). However, the root canal space and the periodontal ligament spaces on both the mesial and distal sides remain perfectly linear with no disruption. B, A second view at a slightly different angle shows that the root is intact. Dental radiography is similar to general radiography in that two views provide more information than a single view.
FIGURE 2-12 Miscellaneous findings on radiographs of geriatric dogs A and B, Cemental hyperplasia can occur unrelated to pathology or in the presence of pulpitis. It may often be a nonpathologic anomaly. It most commonly affects the apical third of the root creating a club-like appearance but can also affect the entire root. In A, there is also external root resorption (arrow). C, Horizontal bone loss of the alveolar margin in a geriatric dog with chronic periodontitis.
FIGURE 2-13 A, Persistent deciduous teeth. The first and second incisor teeth are permanent teeth. The third incisor teeth (arrows) are deciduous teeth with no succedaneous permanent teeth. The third incisor teeth should be larger than the first or second incisor teeth. B, In this dog, it is easier to see the difference; the right maxillary third incisor tooth (arrow) is a deciduous tooth, but the left maxillary third incisor tooth (open arrow) is a permanent tooth. C, This dog’s permanent third incisor teeth (arrows) have the appearance of deciduous teeth due to rotation. The lateral view of the crowns makes them appear small. However, the roots are a normal size for permanent third incisor teeth.
FIGURE 2-15 Normal dog canine tooth A, Radiograph of the skull of a young dog showing the canine tooth and surrounding structures. B, Dorsal view of prepared skull. C, Ventral (mirror) view of skull. D, Same radiograph as A.
FIGURE 2-16 Radiographs of canine teeth of different aged dogs shows the effect of age on size of the pulp chamber and root canal A, Five-month-old Standard Poodle. B, Eight-month-old Bouvier. C, Eleven-month-old Labrador. D, Same dog as in C at 2 years of age. E, Nine-year-old Akita. F, Thirteen-year-old Terrier mix. The radiopaque spots are remnants of pumice polish.
FIGURE 2-17 Individual variation in tooth maturation and apical closure A, Radiograph from an 8-month-old Yorkshire Terrier. The apex is wide open with no apical constriction (arrow). Radiographs of small patients can include the entire canine tooth as well as surrounding anatomy, even on a size 2 film or digital sensor. This dog is missing the first premolar tooth and has a persistent deciduous canine tooth and a deciduous second premolar cap ready to exfoliate. B, Radiograph from a 9-month-old Bearded Collie. This tooth is significantly more mature than the tooth in A even though the dog is only 1 month older. The apex is already closed. The mesial root of the second premolar tooth is dilacerated at the apex (open arrow).
FIGURE 2-18 Normal canine tooth with a periapical chevron shaped lucency similar to those seen on incisor teeth These lucencies extend apically from the apex and are sometimes quite large. They can be mistaken for lesions of endodontic origin. However, they are very regular in shape, extending the contour of the alveolus in a gently pointed arc rather than appearing as an expanded circular or irregular shape that is typical of endodontic lesions. With careful scrutiny, a periodontal ligament space and a faint lamina dura can often be seen closely approximating the root itself. This dog also has an anomalous first premolar tooth. A very prominent white line is made by the nasal surface of the alveolar process. This bony plate forms the ventrolateral wall of the nasal cavity, diagonally connecting the nasal surfaces of the palatal process (horizontal plate) and the body (vertical plate) of the maxilla. Its marked radiopacity is a result of its orientation parallel to the x-ray beam during bisecting angle technique radiographs of canine and premolar teeth. Further caudal this dorsal plate of the alveolar process forms the floor of the infraorbital canal. In the molar area it forms the floor of the pterygopalatine fossa.
FIGURE 2-19 CT scan images A, Sagittal plane. B, Transverse plane. C, Dorsal plane. The hypoattenuated areas around the apices of the canine teeth are caused by relatively less bone in an irregular cone shape. The borders are composed of the compact bone of the facial surface of the maxilla laterally and dorsally, and of the nasal surface of the maxilla medially and ventrally.
FIGURE 2-20 The summation of multiple superimposed radiopaque and radiolucent structures can also mimic a lesion of endodontic origin (asterisks). A and B demonstrate the anatomic variability in appearance of the conchal crest (arrow) and nasal surface of the alveolar process (open arrow) in a long-nosed (A) and a short-nosed (B) dog.
FIGURE 2-21 This patient has a periapical lesion caused by endodontic disease (arrows). The lesion is not contiguous with normal anatomical structures.
FIGURE 2-22 Radiopaque structures on nasal surface of maxillary bones A, Frontal view into the nasal aperture of a dog skull. The attachments of the middle and dorsal conchae to the nasal surface of the maxilla are visible. B, View of the nasal surface of the bones lining the nasal cavity. The conchae have been removed to reveal the contour of the conchal crest.
MAXILLARY PREMOLAR TEETH
FIGURE 2-23 Normal maxillary premolar teeth The facial and palatal region of the dog consists of 36 bones designed to provide a large surface area for the sense of smell and to hold the teeth. The premolar teeth are all within the alveolar process of the maxilla. However, radiographs of the premolar teeth may project through the nasal, frontal, palatine, and zygomatic bones. A, Radiograph of the left maxillary premolar region of a young dog. B, Buccal (vestibular) view of prepared skull. C, Nasal surface of maxilla. D, Same radiograph as A. Correct use of the bisecting angle technique makes an image with accurate root length. The apical anatomy, however, will be slightly enlarged due to an increased object-to-film distance at the apex.