What to do about tooth resorption in your veterinary patients


Intraoral radiography can help identify this pathology in your patients-and guide you toward the next step in your treatment plan.

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This is the third article of a five-part dvm360 series focusing on how to use an intraoral dental system as an adjunct to great patient care. We will explore images of internal and external tooth abnormalities.

What is that moth-eaten area you spot on a pet’s molar radiograph during an oral exam? It’s tooth resorption and it should not be ignored. But should you watch it, extract the tooth, perform a root canal or refer the patient? Before we consider treatment options, let’s take a look at what resorption is and how to identify it with the help of intraoral radiography.

The recognition of pathologic tooth resorption in cats and dogs is important for overall health and comfort. Resorption is the physiological or pathological loss of substance. Physiologic bone resorption allows tooth movement to take place during normal eruption. Usually the deciduous root apex resorbs, allowing the adult tooth to erupt in the proper position. Pathologic resorption occurs in and around the tooth and needs to be addressed (Photos 1 and 2).

Photo 1: Gingival fill secondary to external root tooth resorption in a dog’s left mandibular molar. (All photos courtesy of Dr. Jan Bellows.)

Photo 2: Gingival fill around the distal root of a cat’s left mandibular molar secondary to tooth resorption.

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Resorption around the tooth

Tooth support often decreases in periodontal disease as inflammation extends and bone is resorbed. Intraoral radiography is used to indirectly determine the degree of bone resorption in periodontal disease.

Distribution of bone loss is classified as either localized or generalized, depending on the number of areas affected. Localized bone loss occurs in isolated areas. Generalized bone loss involves the majority of the crestal alveolar bone. Specific areas of bone loss may be classified as horizontal (i.e., perpendicular to the tooth, Photo 3) and vertical (i.e., angular along the side of the root, Photo 4).

Photo 3: Horizontal bone resorption affecting the right mandibular third and fourth premolars.

Photo 4: Vertical bone resorption.

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There are four recognized stages of periodontal disease, based on the severity of radiographic and clinical signs present.

Stage 1 (PD 1; gingivitis) occurs when the gingiva appears inflamed. There is no periodontal support loss or radiographic change.

Stage 2 (PD 2; early periodontitis) occurs when attachment loss is less than 25 percent, as measured from the cementoenamel junction to the apex. Clinically, early periodontitis is typified by pocket formation or gingival recession. Radiographically, stage 2 disease appears as blunting (rounding) of the alveolar margin in addition to bone loss. There may also appear to be a loss of continuity of the lamina dura at the level of the alveolar margin (Photo 5).

Photo 5: Stage 2 periodontal disease (green arrow points to cementoenamel junction (CEJ); red arrows point decreased bone height).

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Stage 3 (PD 3; moderate periodontitis) is diagnosed when 25 to 50 percent of attachment loss occurs. The direction of bone loss may be horizontal or vertical (Photos 6A and 6B). Radiographically, horizontal bone loss appears as decreased alveolar bone along adjacent teeth. With horizontal bone loss, both the coronal buccal and lingual plates of bone, as well as interdental bone, have been resorbed. Vertical bone loss occurs when the walls of the pocket are within a bony housing. Radiographically, vertical bone defects are generally V-shaped and sharply outlined.

Photo 6A: Overlapping right mandibular fourth premolar.

Photo 6B: More than 25 percent bone resorption between the fourth premolar and first molar.

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Stage 4 (PD 4; advanced periodontal disease) is typified by deep pockets or marked gingival recession (or both), tooth mobility, gingival bleeding and purulent discharge. Attachment loss is greater than 50 percent of the root length as measured from the cementoenamel junction to the apex (Photo 7).

Furcation exposure results from bone loss at the root junction of multirooted teeth due to advanced periodontal disease. It’s sometimes difficult to determine radiographically whether the interradicular space is involved, unless there’s a radiolucent area in the region of the furcation.

Lack of radiographically detectable furcation involvement is not confirmation of the absence of periodontal destruction. Advanced furcation exposures, where both cortical plates are resorbed, are easily recognized on radiographs (Photo 8).

Photo 7: More than 50 percent bone resorption in stage 4 periodontal disease.

Photo 8: Advanced furcation exposure affecting a cat’s left maxillary fourth premolar.

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Resorption of the tooth proper

There are five stages of tooth resorption, based on the extent of resorption.

Stage 1 (TR 1) is typified by mild dental hard tissue loss (cementum alone or cementum and enamel).

Stage 2 (TR 2) is typified by moderate dental hard tissue loss (cementum alone or cementum and enamel with loss of dentin that does not extend to the pulp cavity, Photo 9).

Photo 9: Stage 2 root resorption affecting cementum and dentin.

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Stage 3 (TR 3) is typified by deep dental hard tissue loss (cementum alone or cementum and enamel with loss of dentin that extends to the pulp cavity). In this stage of disease, most of the tooth retains its integrity (Photos 10A and 10B).

Photo 10A: Intraoral radiograph of the left mandibular molar in photo 1. The external resorption radiolucency is apparent.

Photo 10B: Surgical exposure of the external resorption.

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Stage 4 (TR 4) is typified by extensive dental hard tissue loss (cementum alone or cementum and enamel with loss of dentin that extends to the pulp cavity). In this stage, most of the tooth has lost its integrity (Photos 11A, 11B and 11C).

Photo 11A: Stage TR 4A tooth resorption. The crown and root are equally affected.

Photo 11B: Stage TR 4B tooth resorption. The crown is more affected than the root.

Photo 11C: Stage TR 4C tooth resorption. The root is more affected than the crown.

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Stage 5 (TR 5) is typified by remnants of dental hard tissue that are visible only as irregular radiopacities. Gingival covering is complete (Photo 12).

Photo 12: Stage 5 tooth resorption affecting a cat’s mandibular third premolar.

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Classification by degree of bone replacement

It’s important to classify the type of tooth resorption in order to create the best treatment plan.

Type 1: Radiographically, in teeth with type 1 appearance, the focal or multifocal radiopacity of the lesion is present in a root with otherwise normal radiopacity and periodontal ligament space. In the cat, extraction is indicated; in the dog, if the lesion has not progressed to oral cavity exposure, clinical and radiographic follow-up is indicated. Once the tooth resorption is exposed to the oral cavity, extraction is the treatment of choice (Photo 13A).

Photo 13A: Intraoral radiograph of a cat’s molar. Note type 1 TR affecting the distal root.

Type 2: Radiographically, in teeth with type 2 appearance, the root radiopacity is decreased with considerable loss of the periodontal ligament space. The root is being replaced with bone. If there is exposure to the oral cavity, crown reduction followed by gingival closure is indicated (Photo 13B).

Photo 13B: Decreased opacity of the mandibular third premolar in a cat.

Type 3: Radiographically, teeth with type 3 appearance have changes seen in types 1 and 2 described above. Complete tooth extraction is indicated (Photo 13C).

Photo 13C: Type 3 TR in a cat’s right mandibular molar.

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Classification by anatomical location

It’s important to know if the resorption is internal or external and, if external, whether it has extended to the oral cavity.

Internal tooth resorption. Resorption of the internal surface of the tooth is initiated in the pulp. Internal resorption is an uncommon type of inflammatory resorption. It can occur anywhere in the pulp cavity (pulp chamber or root canal). External resorption that has extended through the internal tooth structure can also appear to be internal resorption (Photo 14).

Photo 14: Internal resorption of a cat’s left mandibular canine tooth.

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External tooth resorption. More than 50 percent of cats older than 3 years of age will be affected by external tooth resorption, which is radiographically characterized by radiolucency of the dentin. Lesions are usually located along the buccal margins of the root although they can occur anywhere in the dental hard tissues. The periodontal ligament space and lamina dura are not affected (Photo 15).

External tooth resorption is considered to be progressive. For minimal lesions that have not extended to the oral cavity, a wait-and-see approach can be taken. For those lesions that have affected a major part of the root or extended to the oral cavity, extraction is the treatment of choice.

Photo 15: External resorption of a cat’s left mandibular canine tooth. Note the stage 5 TR of the left third premolar.

Dr. Jan Bellows owns Hometown Animal Hospital and Dental Clinic in Weston, Fla. He is a diplomate of the American Veterinary Dental College and the American Board of Veterinary Practitioners. He can be reached at (954) 349-5800; e-mail: [email protected]

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