Merriam-Webster defines “caries” as a progressive destruction of bone or tooth.1 The singular and plural versions of the word are the same, describing one or more lesions on the teeth due to tooth decay. Dental caries are common in people but rare in our veterinary patients. Dental caries were first described in domesticated dogs in 1962.2 The National Institutes of Health (NIH) reports nearly 90 percent of adult humans between the ages of 20 and 64 have cavities in their permanent teeth.3 The prevalence of caries in dogs has historically been low, having been documented at five percent in a study of 435 dogs from 1998.4 However, is the prevalence of caries on the rise today? I am seeing more of them in dogs. Caries differ from the more common cause of tooth destruction—tooth resorption. Numerous factors play a role in the etiology of caries. Bacteria in the mouth (Streptococcus mutans) utilize carbohydrate substrates to form acids that eat away at the surface of a tooth. Often, a genetic predilection of a developmental abnormality of a tooth (pit and fissure defects of the enamel) allows the enamel to be penetrated by these acids. Caries in dogs and cats The most common location of pit and fissure caries is the occlusal surface of the maxillary first molars in dogs. These may present as a tiny recessed black dot on the occlusal surface and can be the “tip of the iceberg,” where the degree of dentin involvement beneath the enamel may be significant. Two other types of caries (smooth surface and root) can also occur, although these are less common. In dogs, the teeth most commonly affected by caries are the maxillary first molars (Figure 1), and the lesions are often bilateral when they occur. The distal occlusal surface of the mandibular first molars is another common site. The next common site for caries is the developmental groove of the maxillary and mandibular carnassial teeth (Figure 2). Figure 1. Caries lesions of teeth 209 and 210. These lesions are deep and have extended into the pulp chamber. Photos courtesy Dr. John R. Lewis Feline caries lesions are more difficult to characterize since they are so rare. There are no prevalence studies of caries in cats, but one study describes caries lesions in two 13th-century cats from archived mandibles at an archeological museum.5 The lesions described in the manuscript were so small that they were radiographically undetectable, and they were diagnosed with histologic stains and a test called the Knoop hardness test. In general, if a hard tissue defect is found on a cat tooth’s surface, it is likely due to resorption. Figure 2. Caries lesions of teeth 108 and 409 in the same patient seen in Figure 1. However, over the past 25 years, I have seen a few cases of possible feline caries. These lesions were found arising in the lingual developmental groove of the crown of the mandibular first molar tooth. They had a radiographic appearance of an almost perfectly circular lucency isolated to the crown, with no evidence of resorption at the gingival margin. Early caries lesions are not usually radiographically visible, but the radiographic appearance of advanced caries shows a circular loss of hard tissue radiating from a central point. Treatment Treating caries involves using a water-cooled high-speed handpiece to remove carious dentin and create a cavity preparation, which will be filled with a restorative material. The goals of restorative dentistry include providing optimum function, preventing further breakdown of tooth structure, protecting pulp tissue from further insult, and creating a proper or aesthetic tooth appearance.6 I use either a #10 round diamond bur or a cylindrical diamond bur to remove the carious dentin for the cavity preparation. “Extension for prevention” is a term credited to the father of restorative dentistry, G.V. Black, DDS (honorary). It serves as a reminder to remove all the visibly diseased dentin and a small amount of visibly normal tooth structure to minimize the chance of recurrence. This can be challenging if the caries lesion radiates apically and extends close to the pulp tissue. The cavity preparation is created in a way that allows for retention of the restoration, being ideally wider at the base of the preparation than at the coronal portion of the restoration. Once prepared, the site is etched with phosphoric acid, rinsed, and dried. Being careful not to contaminate the prepared site with moisture, a layer of unfilled resin is placed and light cured. Flowable or compactable composite is placed in layers of 2 mm and light-cured until the entire defect is filled. Care is taken to prevent the restoration from being overfilled since overfilling can cause much discomfort. The restoration is polished to ensure a smooth transition at the edges where the restoration meets the remaining tooth structure. A final layer of unfilled resin is placed over the restoration margins to minimize the chances of microleakage around the restoration. By the time a caries lesion is diagnosed (Figure 3), infection may have invaded the pulp chamber. Therefore, endodontic treatment may be necessary in addition to placing a restoration. Some caries lesions have resulted in much structural damage, leaving behind a shell of a tooth. In these cases, extraction is the only option. Figure 3. Radiograph of caries lesions of teeth 309 and 310 (arrows). Note the periapical lucency of tooth 309 secondary to infection of the root canal system. Look for caries lesions as part of your regular anesthetized oral exam and save those teeth before their lesions become untreatable. Let me know if you are seeing more caries lesions than what you have seen in the past: drop me an email at info@siloacademy.com. John R. Lewis, VMD, DAVDC, Fellow, AVDC OMFS, practices at Veterinary Dentistry Specialists and teaches at Silo Academy Education Center, both in Chadds Ford, Pa. References https://www.merriam-webster.com/dictionary/caries Gardner AF, Darke BH, Keary GT. Dental caries in domesticated dogs. J Am Vet Med Assoc. 1962;140:433-6. https://www.nidcr.nih.gov/research/data-statistics/dental-caries/adults Hale FA. Dental caries in the dog. J Vet Dent. 1998;15(2):79-83. Berger M, Stich H, Hüster H, Roux P, Schawalder P. Feline caries in two cats from a 13th century archeological excavation. J Vet Dent. 2006;23(1):13-7. Greenfield BA. Enamel defect restoration of the left mandibular first molar tooth. J Vet Dent. 2012;29:36-43.
