Surface, external inflammatory, and noninflammatory replacement resorption are the most common tooth resorptions in dogs and cats.

Surface resorption may occur secondary to release of osteoclast-activating factors at the site of cementum injury triggered by inflammation. Resorption can occur at any location on the root surface and progress into dentin apically and/or coronally. Surface root resorption (Figure 1) is radiographically characterized by one or more shallow voids that affect the cementum, which can extend into dentin located along the margins of the root. The periodontal ligament space and lamina dura may be locally affected. 

When resorption stops, cells from the periodontal ligament proliferate and populate the resorbed area, depositing reparative tissue. Surface resorption is generally self-limiting unless it is exposed to the oral cavity; this is often quite painful because dentin tubules are exposed to heat, cold, and pressure.

External inflammatory resorption begins in the periodontal ligament apical to the cementoenamel junction and at furcations where dentin is exposed. The etiology is unknown. In early stages, odontoclasts resorb and undermine unsupported enamel or cementum, which subsequently breaks away. As the process continues, deeper and more significant amounts of dental tissue are involved. For resorption that begins near the cementoenamel junction and progresses toward the crown, loss of dentin and enamel near the gingival attachment exposes the defect to the oral environment. Inflammation of surrounding tissues occurs, leading to increased sensitivity. 

On radiographs, voids (ie, radiolucencies) often extend into the pulp cavity and root canal. With external inflammatory resorption, the tooth roots have similar opacity as surrounding teeth, and periodontal ligament space is visible.

Noninflammatory tooth replacement of unknown etiology occurs in dogs and cats, in which the root fuses to the bone (ie, dentoalveolar ankylosis), and the tooth is eventually resorbed, becoming part of the alveolar bone remodeling process. This process can take years to complete and is considered a form of healing, as the bone integrates dental hard tissue as part of itself, and the tooth becomes involved in normal skeletal turnover. Osteoblasts form bone in the resorbed area when the resorptive process is complete; thus, dental hard tissues are gradually replaced by bone. 

Replacement resorption does not preclude the presence of viable pulp; the pulp can be normal in affected teeth. Lesions sealed below the gingival sulcus may not be painful; however, bacteria can invade the pulp if it is exposed to the oral cavity, leading to painful inflammation. The resorptive process can penetrate the root canal or pulp chamber and, in advanced cases, gradually fill the pulp cavity with new bone. External replacement tooth resorption radiographically appears as a mottled or moth-eaten tooth.

Companion animal tooth resorption is often classified by stage and type based on anatomic location and radiographic appearance.¹ Stage refers to anatomic loss of dental hard tissue, and type refers to radiographic root opacity and the presence or absence of periodontal ligament space.

Resorption should also be identified as internal or external. Internal resorption takes place in the pulp chamber or root canal and progresses outward; external resorption starts on the outside of the tooth (ie, enamel, cementum) and progresses inward. External resorption should be examined for exposure to the oral cavity and to determine whether roots are significantly replaced with surrounding bone.

External tooth resorption stage is a classification system based on affected anatomy. Clinical examination with an explorer and intraoral imaging are used to determine stage (see Stages of Tooth Resorption).

Tooth resorption type is determined via intraoral radiography based on root opacity and periodontal ligament space (see Types of Tooth Resorption Based on Radiographic Appearance and Figure 2).

Treatment for tooth resorption is largely based on stage, type, and internal/external classification (Table). Extraction is the treatment of choice unless resorption appears to minimally affect the tooth and is confined subgingivally (ie, not exposed to the oral cavity). Intraoral radiography has therapeutic clinical significance for diagnosing patients and creating a treatment plan because only Type 2 resorption should be considered for crown amputation (ie, coronectomy) with gingival closure.

Bone and cementum‐like tissue eventually replace all or part of the periodontal ligament, dentin, and pulp in teeth with Type 2 resorption. Although complete extraction is the generally accepted treatment for resorption, intentional crown amputation with gingival closure can be effective for cases of Stage 2 to 5 with moderate to advanced Type 2 resorptions or Type 2 resorptions exposed to the oral cavity (ie, external noninflammatory replacement resorption).

Crown amputation with gingival closure is an advanced dental procedure involving creation of a mucogingival flap; use of a water-cooled, high-speed delivery system; and closure without tension that should only be performed after intraoral radiography confirms complete root extraction is not possible based on marked decrease in root opacity and absence of periodontal ligament space. The resorption is sealed off from the oral cavity, and the root continues being replaced by bone. 

In teeth affected by Type 3 resorption, roots affected by Type 2 resorption can be treated with crown amputation; the remaining roots should be extracted. Crown amputation typically results in subjectively less trauma and faster healing compared with complete extraction.² 

Contraindications for crown amputation with intentional partial root retention include periodontal disease evidenced by horizontal or vertical bone loss, endodontic disease, radiographic presence of a root canal, and chronic gingivostomatitis. Crown amputation should not be performed if intraoral dental radiography is not possible.

• #11 scalpel blade and blade handle
• Fine periosteal elevator
• High-speed delivery system
• Tapered crosscut fissure bur
• #2 round or football diamond bur
• Suture holder 
• 4-0 absorbable monofilament or catgut suture on a P-3 needle

Identify clinical (A) and radiographic (B) evidence of Type 2 tooth resorption.

Use a #11 scalpel blade to make a caudal incision in the gingiva for flap exposure of the coronal root.

Use a fine periosteal elevator (eg, molt elevator) to separate attached gingiva from the alveolar juga.

Use a #2 to #8 sterile round or end‐cutting crosscut fissure bur (A) on a high‐speed, water‐cooled handpiece to remove the tooth crown and 2 to 4 mm of the coronal root apical to the alveolar margin (B).

Remove sharp alveolar margin projections with a #2 round or football diamond bur.

Perform postamputation intraoral radiography to document the result and confirm all dental hard tissue coronal to the alveolar margin has been removed.

Draw the mucoperiosteal flap over the alveolus and place single sutures without tension using 4-0 catgut or absorbable monofilament suture.

Prescribe anti-inflammatory pain relief medication, and recommend feeding soft food for 2 weeks.