Feline Dental Resorptive Lesions – What’s Old, What’s New, And What To Do
Gregg DuPont, DVM, Fellow AVD, Diplomate AVDC
Dental resorptive lesions (RL’s), one of the most common oral lesions of cats, occur in all domestic breeds of cats as well as in non-domestic cats, dogs, humans, rats, mice, marmosets, and pigs. Feline RL’s were described and characterized in detail in the literature as early as 1930. Described as “root caries” in 1955, they were finally recognized as non-caries-related odontoclastic resorptions in the 70’s. The syndrome has progressed from very rare prior to the 20th century to a prevalence of between 30 to 60% (studies vary) in domestic cats today. In the literature, feline RL’s have been referred to as feline odontoclastic resorptive lesions (FORLS), neck lesions, root resorptions, cervical line lesions, cervical line erosions, buccal cervical root resorptions, external resorptions, cat caries, invasive resorptions, and ….. initiocircocervical desmodentiopathy!
Although their clinical appearance, progression, and many aspects of their pathophysiology have been well described in the literature, their etiopathogenesis has not been proven. Some of the proposed theories for their etiology include:
- abnormal dental forces resulting when sectorial teeth, designed for slicing rather than masticating, bite down on hard cat foods. The resultant non-physiologic lateral forces can cause abfraction as stresses are transferred to the base of the crown at the gingival margin. Repeated micro-flexure of the tooth at this precise location (where its support by the periodontal structures prevents flexure of the root) causes crazing of the enamel and eventual loss of tooth structure
- inflammation from poor dental hygiene can result in an external resorption as bacterial action and mediators of inflammation damage the cementum and allow osteoclastic activity
- infectious agents
- immune system disorders
- the mineral content or balance of cats’ diets
- the acid pH of cat foods
It seems most plausible that RL’s are the clinical manifestation of a syndrome with multiple different etiologies. This would complicate studies designed to determine a single cause.
Following are some observations that we have made, and that have very recently been experimentally evaluated. We want to share with you our methods of evaluating and treating these lesions. We feel that there are two clinically distinct types of RL’s. The most common form, that we call Type II, is not generally associated with endodontic disease or periodontitis. They frequently have only a mild localized gingivitis or a local gingival granuloma filling the resorption lacuna. In these lesions, the gingivitis is probably a result, not a cause, of the RL’s. They commonly show generalized root resorption on radiographs, as indicated by loss of radio-opacity of the roots of the involved tooth. This radiolucency is often quite dramatic when the roots are compared with those of adjacent teeth. When this radiographic appearance is evident, the root is very likely being replaced by a cementum-like tissue that eventually converts to newly formed haversion bone.
The second form of RL’s that we call Type I seem to be those described in the second theory above; inflammatory resorptions caused by adjacent inflammation and periodontal disease. These are characterized by marginal periodontitis including gingival recession and often bone loss. These routinely manifest as cervical region resorptions with minimal or no general root resorption. Although the lesions may extend down onto the root, the remaining root does not seem to “disappear”, maintaining a normal radiodensity (unlike the Type II lesions). Type I lesions also commonly present with concurrent endodontic disease, again unlike Type II lesions.
RL’s have been reported to cause anorexia, ptyalism, lethargy, depression, dysphagia, halitosis, and discomfort. They begin as a superficial (usually cemental) resorption of tooth substance, most frequently at or close to the cementoenamel junction (CEJ) or cervical area. They also sometimes begin higher up on the crown or further apical on a deep root surface. The surface lesions are concave defects lined by odontoclasts. For many of these lesions, the surrounding dentin and adjacent pulp are generally normal with minimal inflammation. As mentioned above, the most common type is not associated with actual periodontitis. In both types, the resorption lacuna becomes filled with granulation tissue as the tooth is destroyed by the action of odontoclastic cells. When this occurs on the tooth crown, the gingiva will often appear to grow up onto the tooth surface. The facial (outside or “buccal”) surfaces of the lower third (clinically the first) premolar teeth are often the first surfaces affected. If a lesion begins under the gingival margin in the “furcation area” of a premolar or molar (where a multi-rooted tooth’s roots meet to form the crown), it may first present as an area of very localized gingivitis. Reflecting the gingival margin with an instrument or a gentle flow of air exposes the lesion. As a lesion progresses, it eventually extends through the enamel to the dentin. Finally, even more of the crown is destroyed until very little remains. When a lesion has progressed to its final stages with complete destruction of the crown, it may appear as a raised area of gingiva with no clinical crown remaining above the gums.
Grades of RL’s by severity:
RL’S are diagnosed by direct visual observation or by probing with a dental probe. Localized marginal gingivitis, particularly on the mid-buccal surface of premolars and canine teeth, should prompt further investigation. If an affected area is probed with a fingernail or dental explorer, cats often react with an immediate jaw movement and a pain response, but this can also occur in the absence of lesions and is not a reliable test. General anesthesia, removing any accumulation of calculus in the area, and examination with a dental explorer may be necessary to know whether a lesion is present and to determine its severity. Some lesions may be completely subgingival, and found only on deep subgingival probing or on radiographs. A sharp ledge of undercut enamel is commonly found around lesions on tooth crowns. A lesion that appears relatively small clinically may actually have extensive resorption of the tooth visible on a radiograph. One must take care in natural furcation areas to avoid over diagnosis;p root furcations can mimic a RL, but will not have the characteristic irregular enamel lip.
The current most popular recommendation for treatment of RL’s in cats includes treating very early lesions with a fluoride varnish or a dental sealant. Larger and deeper lesions can be filled with a restorative if a radiograph demonstrates healthy roots. Restorations are now infrequently placed, since their success rate is 20-60% (study results vary) by two years after placement, and most clients do not choose this treatment given the expected poor long-term clinical outcome. This failure rate is due to the fact that restoration does not address the etiology, and the lesions tend to continue, often progressing apically from the restoration. When a lesion has invaded the pulp cavity or destroyed a large amount of the tooth’s crown, extraction to remove the uncomfortable and poorly functional tooth is generally recommended. Some operators have reported success with pulpectomy and calcium hydroxide endodontic treatment for these teeth, but significant studies have yet to be done. Canine teeth are the exception, in that we will sometimes place restoratives in them to keep them functional and comfortable as long as possible. The clients are advised of the poor long-term prognosis for saving the teeth, and they are followed clinically. Our choice for restorative material, when they are restored, is a glass ionomer. This is used due to the facts that they release fluoride to the surrounding tooth structure, self bond to dentin, and have a modulus of elasticity similar to the tooth to allow flexion along with the tooth.
An alternative treatment to complete tooth extraction for lesions that are Grade II through IV involves amputating the remaining crown and leaving the roots to be resorbed. This has a number of advantages. The roots of affected teeth frequently show evidence of resorption and repair. Their abnormal root structure and ankylosis complicates extraction, making root fractures common. Extraction is often technically difficult, tedious, and prone to complications, given the frequency with which root fragments are encountered. It is common to find root fragments undergoing continued resorption and resolution in areas of the jaws showing no evidence of discomfort, gingival inflammation, or fistulation.
The procedure of crown amputation with intentional root retention is quick and simple; a very limited envelope flap is developed, consisting only of minimal elevation of the gingiva from the tooth and marginal alveolar bone using a Pritchard PR3 or smaller periosteal elevator. The gingiva is protected with the flat end of the elevator. A small (#1 or #2) round bur in a high speed handpiece is used to remove the crown of the tooth to, or slightly below, the level of the alveolar crest. Any sharp bony ridge projections are smoothed, and the gingiva is closed with a single 4-0 suture. Gentle digital pressure is placed on the gingiva for 30 seconds to stabilize the clot and to adapt the gingiva to the underlying structures. The entire procedure takes only a few minutes.
This procedure is more comfortable for the cat, faster for the operator, less damaging to periodontal tissues, and helps nature on the way to resolving the lesion rather than working against it. Crown amputation prevents iatrogenic alveolar bone trauma caused by attempts to retrieve root fragments either by gouging with extraction instruments or by “atomization” with high speed dental burs. When performed, the client must be aware of the procedure you are doing and the rationale behind it.
Important caveats must be followed when deciding whether to amputate tooth crowns versus fully extracting the teeth. It is vital that selected cases must have no buried pathology. Pre-procedural radiographs must be taken. There should be no periodontal disease, no clinical deep periodontal probing defects, no abnormal tooth mobility, and no radiographic evidence of endodontic disease or apical pathology. Ideally, the roots should be showing generalized increased radiolucency. One must never “bury pathology” because it will not remain buried! The roots that can be retained are those that are already turning into normal healthy bone. Another very important selection criterion is that there must be no clinical evidence of ulcero-proliferative faucitis (“plasmacytic-lymphocytic stomatitis”). These patients will often need full extraction of all the premolars and molars in an attempt to cure or improve their faucitis. For them, it is critical that all fragments of all roots are completely removed, and ideally also the associated periodontal ligament. A final selection criterion is that, if the retrovirus status of the patient is known, roots should not be left behind on a patient that is positive for FIV or FeLV.
Until we have identified the exact cause or causes of RL’s, prevention will be difficult. Regular dental cleaning and home care will minimize the periodontitis that is suspected to contribute to the progression of, and possibly be the cause of, the inflammatory-type RL’s (not the most common type). In individuals predisposed to the lesions (i.e. that have had one or more previously diagnosed), weekly home fluoride treatments may be helpful to slow their progression and desensitize any affected areas, although this has not been proven. If topical fluoride is prescribed, care should be taken to use only small amounts, and it should not be used in geriatric cats or those with renal insufficiency. Until we know the exact causes, however, we cannot make any specific recommendations for prevention other than oral hygiene measures. We recommend dental diets for cats, formulated to help self-cleaning of the teeth mechanically during mastication. Plaque control by this method could decrease inflammation that may predispose to some RL’s. Additionally, the diets are less hard than some other dry commercial diets, possibly minimizing abfractive forces on the teeth at the same time.