Dr. Charlier brings to dentistry continuing education more than 35 years of small animal practice, specialty practice, and ownership experience. She has received the Peter Emily Outstanding Candidate Award and the Fellow of the Year award. In 2004, she created VDENT (Veterinary Dental Education, Networking & Training) to educate the entire veterinary healthcare team about the value of oral health and its effects on all of our patients. In 2017, she was named the NAVC Small Animal Speaker of the Year.Read Articles Written by Cindy Charlier
Full-mouth intraoral radiographs are an essential part of the evaluation of oral health. Combined with extraoral and intraoral examinations of an anesthetized patient, intraoral radiographs provide information needed to diagnose and treat oral disease. As with any skill in veterinary medicine, interpreting intraoral radiographs improves with time and experience. To appreciate abnormal, you first need to understand normal. This article explains why full-mouth radiographs should be taken for every dentistry patient and later reviews:
- normal radiographic dental anatomy
- criteria for diagnostic radiographs
- steps for reading an intraoral radiograph
- radiographic tooth development in pediatric patients
- normal anatomic structures that may be misinterpreted as pathology
By the end of this article, general practitioners should be able to appreciate the benefits of full-mouth radiographs and know how to recognize normal anatomic structures on intraoral radiographs of dogs and cats.
Why Take Full-Mouth Radiographs?
To determine the full extent of oral disease and develop a treatment plan for your patients, an oral examination and full-mouth radiography performed with the patient under general anesthesia are required. Not including full-mouth radiographs as the standard of care for every dentistry patient could result in sending patients out the door with undiagnosed, untreated, painful oral disease. Research confirms that the diagnostic yield of full-mouth radiographs is high and that routine use of full-mouth radiographs is justifiable (BOX 1).1,2
Use of intraoral radiographs is supported by the American Veterinary Medical Association (AVMA) and the American Animal Hospital Association (AAHA). After a 2015 review of cases of jaw fractures and retained tooth roots, the AVMA professional liability newsletter stated that it would be difficult to defend complications resulting from dentistry procedures if the veterinarian did not have access to dental radiographs.3 The AAHA Guidelines Task Force strongly recommends obtaining full-mouth intraoral dental radiographs for all dentistry patients.4
For proper evaluation of intraoral radiographs, knowledge of normal anatomy of the tooth, the mandible, and the maxilla is essential. Recognizing pathology requires familiarity with normal dental anatomy (FIGURE 1). The radiographic components of the tooth and its supporting structures are provided in TABLE 1.
Criteria For Diagnostic Radiographs
A diagnostic radiograph must include the following anatomic landmarks (FIGURES 2–4):
- The level of alveolar bone (alveolar margin)
- The periodontal ligament space
- The entire tooth root, including 2 to 3 mm around the apex of each root
- As much of the crown as possible
Both roots of the same tooth do not need to appear on the same radiograph, nor do the entire crown and root(s). Obtaining a diagnostic image of 1 tooth may require 2 radiographs (e.g., the mandibular first molar in a larger dog [FIGURE 5]). Similarly, 2 radiographic images of a canine tooth in a dog may be required: 1 image of the coronal portion of the root showing the level of alveolar bone to evaluate presence/absence of periodontal disease and 1 image of the most apical portion of the tooth root and the periapical area to evaluate presence/absence of endodontic disease (FIGURE 6).
Two radiographic views are also needed for complete evaluation of the maxillary canine teeth in dogs and cats (FIGURE 7). The occlusal view is useful for comparing the pulp cavity sizes of the maxillary canine teeth and examining the buccal aspects of the teeth for signs of periodontitis. Lateral views of the right and left maxillary canine teeth are required for accurately evaluating the periapical region without superimposition on the maxillary premolar teeth and for evaluating periodontal status at the mesial and distal aspects of the canine teeth.5 The palatal side of maxillary canine teeth cannot be fully evaluated with radiographs; evaluating the maxillary canine tooth for periodontal disease on the palatal side requires use of a periodontal probe.
Some veterinary software programs will label the image with the tooth number(s) as they are exposed and will orient them correctly on the computer screen. If images are not labeled and correctly oriented by the software, certain clues will help determine whether the image is of the maxillary or mandibular arcade (TABLE 2).
When viewing intraoral radiographs, orient the image the same way each time (just as you would do with thoracic or abdominal radiographs). If the tooth on the image is a maxillary tooth, then the radiograph should be rotated so the crowns of the teeth point downward (in their natural position) on the computer screen. If the tooth on the image is a mandibular tooth, then the radiograph should be rotated so the crowns of the teeth point upward. After determining if the tooth is in the maxilla or the mandible and orienting the radiograph accordingly, ask yourself whether the radiograph is of the right or left side of the mouth. If the rostral mandibular or maxillary premolars or molars are toward the right side of the radiograph, then you are looking at the right maxillary or mandibular premolars and molars. If the rostral teeth are located toward the left side of the radiograph, then you are looking at the left mandibular or maxillary premolars and molars (FIGURE 8). When viewing incisors, the right maxillary or mandibular incisors are on the left side of the image and the left maxillary or mandibular incisors are on the right side of the image (similar to a ventrodorsal abdominal or thoracic radiograph) (FIGURE 9).
The number of full-mouth radiographs needed to see all the teeth, including the level of alveolar bone and the periapical area around each tooth root, can vary with patient size (the larger the patient, the more images usually needed). Mount full-mouth radiographs so that the patient’s right maxilla and right mandible are on the viewer’s left side and the patient’s left maxilla and left mandible are on the right side (FIGURE 10).
Steps For Reading An Intraoral Radiograph
Every time you read an intraoral radiograph, follow the same steps in the same order, just as you do for thoracic or abdominal radiographs.
- Evaluate the level of alveolar bone around each tooth; alveolar bone should be 1 to 2 mm apical to the cementoenamel junction.
- Follow the periodontal ligament space around each root, pausing at the apex to evaluate the periapical area. The periodontal ligament space should be of uniform width around the entire tooth root.
- Evaluate the size of the pulp cavity of each tooth. The pulp cavity size should be consistent with the age of the patient and with the contralateral tooth.
- Look at all the bone and soft tissue visible on the radiograph; additional pathology may be present in these tissues.
If you are not sure of the significance of a radiographic finding, take another view or look at the radiograph of the contralateral tooth. Remember that normal anatomy can sometimes mimic pathology.
Radiographs Of Pediatric Patients
Interpreting intraoral radiographs of pediatric patients can be challenging because of the presence of deciduous teeth and permanent tooth buds. The permanent maxillary canine teeth erupt mesial to the deciduous maxillary canine teeth. All other permanent teeth erupt lingual or palatal to their deciduous tooth counterparts. There are no deciduous precursors for the permanent first premolar or molars. In dogs, the maxilla and mandible have 3 deciduous premolars: the second, third, and fourth premolars, named for the teeth that succeed them in the jaw rather than their function or anatomy. The deciduous maxillary third premolar is anatomically similar to the permanent maxillary fourth premolar. The deciduous maxillary fourth premolar is anatomically similar to the permanent maxillary first molar (3 roots and a large occlusal surface). The deciduous mandibular fourth premolar has the function and morphology of a molar but is replaced by the permanent fourth premolar (FIGURE 11).6
Permanent Tooth Development
At the time of permanent tooth eruption, the apex is incomplete, the pulp cavity is wide, and the primary dentin layer is thin. As the tooth develops, the apex closes and secondary dentin is produced by odontoblasts within the pulp cavity. Apical closure occurs by 7 to 9.5 months of age in dogs7 and 7 to 11 months in cats.8 As the dog or cat continues to mature, the pulp cavity continues to get smaller as the thickness of the secondary dentin layer increases (FIGURE 12).
Why is the tooth development process important? Radiographs of a tooth in a mature dog or cat should show a small pulp cavity and a thick layer of dentin. In a mature dog or cat, if the radiograph of a tooth shows a large pulp cavity and a narrow layer of dentin, development of that tooth has arrested and the tooth is nonvital. When the tooth dies, the pulp cavity of that tooth stays the same size for the rest of the animal’s life.
Normal Anatomy That May Mimic Pathology
Two “White Lines” in the Maxilla
For dogs, 2 radiopaque lines appear on radiographs of the maxillary canine and premolar teeth: the junction of the vertical body of the maxilla and its palatine process and the maxillary conchal crest. These normal anatomic structures can mimic the lamina dura and interfere with interpretation of apical structures.
- The junction of the vertical body of the maxilla and its palatine process is visualized as a radiopaque line that crosses the midroot of the maxillary canine tooth and continues caudally and is apical to the roots of the maxillary premolars.
- The maxillary conchal crest is seen as a radiopaque line that begins just mesial to the root of the canine tooth and continues caudally to reach the level of the third premolar. Because of its location close to the apex of the maxillary canine tooth, it is difficult to change its location by changing angulation of the x-ray beam (FIGURE 13A).9
For cats, the 2 lines are also formed by the junction of the vertical body of the maxilla and its palatine process and the conchal crest.
- The vertical body of the maxilla and its palatine process is visualized as a radiopaque line that crosses the middle third of the maxillary canine tooth root.
- The conchal crest appears as a radiopaque line that begins just mesial to the root apex and ends at the third premolar. Because of the anatomic location of these 2 structures close to the apex of the maxillary canine tooth, the linear opacities always appear close to the tooth root (FIGURE 13B).10
A chevron artifact is a very regular chevron-shaped radiolucency commonly associated with the maxillary incisors and canine teeth in dogs (FIGURE 14); radiographically, it looks similar to lesions of endodontic origin. This effect is created by trabecular bone and vascular channels around the apices, contrasted with the dense compact bone of the alveolar walls and incisive bone.11
In general, periapical lesions associated with endodontic disease will be more circular or irregularly shaped lucencies and the periodontal ligament space will not be visible around the root tip. The root tip of an endodontically diseased tooth may exhibit signs of apical root resorption.
Other lucencies and opacities are created by the summation effect of superimposed structures, projecting overlying anatomy in a way that makes the structure appear to be associated with a tooth root or its supporting bone.11 Summation of the mandibular first molar apices superimposed over the mandibular canal can be confused as an endodontic lesion (FIGURE 15). BOX 2 lists clues for differentiating summation of normal structures from pathology.
When in doubt, consult with a board-certified veterinary dentist or take follow-up radiographs in 3 to 6 months to evaluate changes in the appearance of the periapical lucency.
The caudal and middle mental foramina may be mistaken for periapical pathology associated with the rostral mandibular premolars.
In the dog, the middle mental foramen is ventral to the mesial root of the second premolar and the caudal mental foramen is ventral to the mandibular third premolar (FIGURE 16).
In the cat, the middle mental foramen is in the interdental space between the mandibular canine tooth and third premolar and the caudal mental foramen is ventral to the mandibular third premolar (FIGURE 17). To distinguish between a foramen and a periapical radiolucency, change the angle of the tube head when obtaining the radiograph. The foramen will move relative to the root as the angle of the tube head is changed. If the lucency remains associated with the apex of the tooth, then it is periapical pathology.
Radicular Groove of Mandibular First Molar
The periodontal ligament space on the distal aspect of the mesial root of the mandibular first molar in a dog may appear as a double line or shadow. This double line represents the radicular groove (FIGURE 18).6 Incorrectly interpreting this normal anatomic structure may lead you to believe that there are 2 mesial roots in the first molar.
To obtain essential information for determining appropriate treatment for each tooth in each patient, full-mouth radiographs are required.
As with most things in veterinary medicine, the first step in learning how to interpret intraoral radiographs is becoming familiar with normal dental anatomy. Radiographs are 2-dimensional, and superimposed structures may cause misinterpretation of normal anatomy as pathology. The second step in learning how to interpret intraoral radiographs is understanding radiographic findings associated with oral diseases. To read about pathology seen on intraoral radiographs, see “Intraoral Radiographs: Identifying Common Pathology” in the July/August 2022 issue of Today’s Veterinary Practice. The more intraoral radiographs you read, the more disease you will find and the more you will believe in the value of full-mouth intraoral radiographs for every dentistry patient.
Author’s note: Special thanks to the veterinary nurses who obtained these radiographs and are an integral part of the oral healthcare team.
1. Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in dogs. Am J Vet Res. 1998;59(6):686-691.
2. Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in cats. Am J Vet Res. 1998;59(6):692-695.
3. AVMA PLIT. Professional liability newsletter. 2015;34(3). Published Summer 2015. Accessed October 2021. im3vet.com/iM3US/media/Documents/professional_liability_Dental_X-ray.pdf
4. Bellows J, Berg ML, Dennis S, et al. 2019 AAHA dental care guidelines for dogs and cats. JAAHA. 2019;55(2):49-69.
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6. DuPont G, DeBowes L. Intraoral radiographic anatomy of the dog. In: Atlas of Dental Radiography in Dogs and Cats. Philadelphia, PA: WB Saunders; 2008:5-80.
7. Wilson GJ. Atlas of the radiographic closure of the apices of the teeth of the dog. Master’s thesis. School of Veterinary Science, University of Queensland; 1998.
8. Wilson GJ. Timing of apical closure of the maxillary canine and mandibular first molar teeth of cats. J Vet Dent. 1999;16(1);19-21.
9. Gracis M, Harvey CE. Radiographic study of the maxillary canine tooth in mesaticephalic dogs. J Vet Dent. 1998;15(2):73-78.
10. Gracis M. Radiographic study of the maxillary canine tooth of four mesaticephalic cats. J Vet Dent. 1999;16(3):115-128.
11. DuPont G, DeBowes L. Endodontic disease. In: Atlas of Dental Radiography in Dogs and Cats. Philadelphia, PA: WB Saunders; 2008: 142-171.