Feline tooth resorption stages, types, diagnosis and treatment

Definition, cause and risk factors

Merck describes tooth resorption, previously called cervical line lesion or feline odontoclastic resorptive lesion, as an inflammatory process that progressively destroys enamel, dentin and cementum and can eventually consume the whole tooth [1]. The resorbing cells, odontoclasts, are described by Merck as "virtually identical to osteoclasts" [1]. A 2012 peer-reviewed article in Today's Veterinary Practice (TVP) by Brook Niemiec lists other older names, including neck lesions and cat cavities [4].

No single cause has been identified. According to Merck, periodontitis-related inflammation likely explains resorption in areas of periodontal disease, but the cause of idiopathic resorption affecting many teeth is unknown [1]. The JFMS review by Cecilia Gorrel argues that at least two processes are being grouped together: an inflammatory type linked to periodontal disease, and a non-inflammatory replacement resorption that is "truly idiopathic" [2]. Excess dietary vitamin D has been proposed. Gorrel reports that one study linked raised 25-hydroxyvitamin D to resorption but later studies did not confirm it [2]. The TVP article also cites abfraction, flexing injury from chewing hard food, as an unproven theory for type 2 lesions [4].

Merck reports higher incidence in older and purebred cats [1]. Gorrel notes that suggested breed differences are hard to interpret because the breed groups studied differed in mean age [2]. She attributes the wide spread in prevalence figures to differences in the populations examined and in whether radiographs were used [2]. In one Australian mixed-population study she cites, 52% of cats were affected, averaging 3.2 lesions per affected cat [2].

Clinical presentation

Merck and the JFMS review agree that the mandibular third premolars are the teeth most often affected [1][2]. These are teeth 307 and 407 in the modified Triadan system [3]. The TVP article calls the lower third premolar a "sentinel tooth" [4].

According to Merck, visible lesions typically appear as loss of tooth structure near the gum line. They are often filled with inflamed granulation tissue and edged by a sharp lip of enamel [1]. Gorrel describes how resorption begins in root cementum, spreads through dentin, and undermines the crown until enamel is resorbed or breaks away. Weakened crowns may fracture during chewing and leave root remnants under intact gingiva [2]. Niemiec writes that any area of gingival enlargement in a cat is suspect for a resorptive lesion [4].

Pain is debated. Gorrel considers root-only lesions likely asymptomatic, with discomfort probable once the pulp is involved or the lesion opens to the mouth. She notes that some cats switch to soft food or eat less, "though many cats do not" show signs [2]. Niemiec states that exposed lesions cause pain but cats rarely show it [4].

Diagnosis

The sources describe two complementary methods, both requiring general anesthesia: tactile examination with a sharp explorer and intraoral radiography [2][4].

Merck notes that stage 1 lesions are found only on clinical examination because the loss is too shallow to appear on radiographs. Merck recommends careful examination of the cemento-enamel junction and notes that magnification helps [1]. Merck adds that marginal gingivitis on a single tooth without periodontitis may point to an early lesion below the gum line [1]. Niemiec describes resorptive lesions as feeling hard and rough under the explorer, unlike the smooth feel of periodontal furcation bone loss [4].

The main pitfall is relying on the clinical exam alone. Gorrel writes that visual and tactile methods detect only lesions that have reached the crown, while radiography also finds lesions confined to the root. She adds that only radiographs show the appearance and extent of the resorptive process needed to choose treatment [2]. She recommends full-mouth radiographs for all cats presented for dental therapy. Where cost prevents that, one view of each mandibular premolar-molar region can serve as a screen, since one study found disease in these views in 9 of 10 affected cats [2]. The review does not give that study's sample size. Niemiec recommends full-mouth radiographs in all cats 1 year of age or older [4].

Staging and radiographic types

The AVDC classification assumes resorption is progressive [3]. Stages describe depth of tissue loss in each tooth.

Stage	AVDC description
TR 1	"Mild dental hard tissue loss (cementum or cementum and enamel)" [3]
TR 2	Dentin loss that does not reach the pulp cavity [3]
TR 3	Dentin loss reaching the pulp cavity, with "most of the tooth" retaining its integrity [3]
TR 4	Pulp involved and most of the tooth has lost its integrity [3]
TR 5	"Remnants of dental hard tissue are visible only as irregular radiopacities, and gingival covering is complete" [3]

Stage 4 has three substages per the AVDC chart reproduced in TVP [4]:

• 4a: crown and root equally affected.
• 4b: crown worse than root.
• 4c: root worse than crown.

Types are assigned from radiographs. Per the AVDC [3]:

• Type 1 shows "a focal or multifocal radiolucency" with otherwise normal radiopacity and normal periodontal ligament space.
• Type 2 shows narrowing or loss of the periodontal ligament space and decreased radiopacity of part of the tooth.
• Type 3 shows features of both in one tooth.

Merck labels type 1 inflammatory resorption and type 2 replacement resorption with dentoalveolar ankylosis, producing "ghost" roots [1]. Niemiec writes that each type is currently believed to be a separate disease, so type 1 does not progress to type 2 [4]. He also notes the staging system may not change treatment recommendations, while the type does [4].

Treatment options

Gorrel states the treatment aims are to relieve pain, halt progression and restore function. She adds that no treatment is known to prevent the development or progression of the idiopathic form [2].

Extraction

Merck calls surgical extraction of teeth exposed to the oral environment the accepted treatment [1]. Gorrel describes whole-tooth extraction as "the gold standard" and says every effort should be made to fully remove type 1 roots. She also notes these teeth are "notoriously difficult to extract" [2]. Niemiec recommends a surgical approach with a gingival flap and buccal bone removal when weakening or ankylosis is significant [4]. Gorrel requires postoperative radiographs to confirm complete removal [2].

Crown amputation

Merck describes crown amputation with intentional root retention as an option for radiographically confirmed type 2 lesions without periodontitis, endodontic disease or stomatitis [1]. Gorrel excludes type 1 lesions, teeth with endodontic pathology, and FeLV- or FIV-positive cats, and calls for radiographic monitoring afterward [2]. Niemiec adds criteria of no identifiable periodontal ligament and no recognizable root canal. He writes that practitioners without dental radiology "should NOT perform crown amputation" [4]. He reports that general practitioners use the technique "far too often," which can leave painful or infected roots [4].

Conservative management and restoration

Gorrel describes monitoring alone as appropriate only for root-confined lesions seen on radiographs without signs of pain, and as rarely indicated in general practice [2]. Niemiec shares this view for lesions not clinically evident and calls for regular clinical and radiographic monitoring. He recommends prophylactic extraction if resorption is significant and near the gingival margin [4]. Gorrel reports that studies found resorption continues and restorations are lost, so restoration cannot be recommended as a major treatment technique [2]. Niemiec writes that, because the lesions are progressive, restoration carries a poor long-term prognosis and is rarely performed today [4].

For inflammatory lesions driven by periodontitis, Merck reports that oral hygiene can slow progression [1].

Monitoring, prognosis and client communication

Merck recommends annual anesthetized oral examinations with full-mouth radiographs after a diagnosis, to catch progression and remove affected teeth early [1]. Merck also states idiopathic lesions cannot be prevented [1]. The cited sources do not give survival or recurrence statistics, so a formal prognosis cannot be stated from them.

For client conversations, the points with source support are:

• The disease is common, progressive and of unknown cause in many cats [1][2].
• Cats often hide oral pain [2][4].
• Full diagnosis needs anesthesia and radiographs [2][4].
• Treatment generally means removing affected teeth [1].