Feline odontoclastic resorptive lesions (FORL) are common and account for a large proportion of the clinical caseload in small animal veterinary practice.
Odontoclastic resorption refers to a disease process where the hard tissues of the tooth root surfaces are destroyed by the activity of multi-nucleated cells called odontoclasts. The destroyed root surface is replaced by cementum- or bone-like tissue. The process starts in cementum and progresses to involve the dentin where it spreads along the dentin tubules and eventually comes to involve the dentin of the crown as well as the root. The enamel is ultimately resorbed, or is so undermined that it fractures, and a cavity in the crown becomes clinically evident.
Prevalence rates ranging from 20 to 72% have been reported at different geographical sites (1-14). This large variation can be explained by the different population of cats studied (random versus dental versus mixed) and by the different methods used to diagnose FORL (clinical versus radiographical). The incidence was generally higher in the studies where the cats examined were presented for dental examination or treatment as compared to studies looking at a random or mixed (i.e., presented for dental or other problem) population of cats.
End stage lesions can usually be diagnosed clinically by visual and tactile examination. They commonly present as a cavity at or just below the cemento-enamel junction of the tooth. Studies, which included radiography, have demonstrated that the resorption can occur anywhere on the root surfaces, i.e., not only at or just below the cementoenamel junction (9,12,14). Clinical methods will only detect lesions that involve the crown, while radiography will detect lesions confined to the root. Thus, the prevalence of FORL in studies, which include radiography, is higher. Gengler et al. (9) showed in post-mortem specimens that when mandibles from 81 cats were examined radiographically, 2.4 times as many FORL were detected as compared to clinical examination. Verstraete et al. (12) demonstrated an increase in FORL prevalence rate from 53% to 61% when the cats were examined radiographically in addition to clinical examination.
Most of these studies have shown an increased incidence with increasing age. Differences in breed susceptibility have also been suggested in some studies, but differences in mean age among different breed groups make comparisons of significance suspect. The lesions have also been shown to occur in feral and wild cats (10,15, 16) and in other species (17,18)
In a recent study (14), which investigated the incidence of FORL in a clinically healthy population of 228 relatively young cats (mean age was 4.92 years), using a combination of clinical examination and radiography, it was found that the overall prevalence rate was 29% and that it increased with age. The mandibular (lower) 3rd premolars (307, 407) were the most commonly affected teeth and the pattern of FORL development was symmetrical in most cats. The risk of having FORL was found to increase with increasing age and cats with clinically missing teeth were more likely to have FORL. Neutering, sex, age at neutering or mean whole mouth gingivitis index did not affect the prevalence of FORL.
Whereas there is some information about the prevalence as well as of the pathological features, the aetiology or cause of odontoclastic resorption is not known. The hypothesis that FORL are part of periodontal disease is falling into disrepute as the evidence is mounting to show that these lesions can develop in the absence of gingival or periodontal inflammation (14).
FORL are the result of destruction of the root surface by odontoclasts. As already mentioned, the factor or factors that initiate the resorption are unknown. Once developed, resorptive lesions have been characterized into three stages, namely an acute, a chronic and a remodeling phase (19).
An initial surface resorption of root cementum is accompanied by reparative formation of bone- or cementum-like tissue. In the individuals that develop clinically and radiographically manifest FORL, the initial cementum resorption extends into the dentin, forming resorption channels that eventually extend into the dentin of the crown. The loss of crown dentin increases the fragility of the tooth and the unsupported enamel may flake off. Alternatively, the enamel is also resorbed. Either mechanism results in the classic clinical presentation, i.e., a cavity filled with connective tissue. In many cases the crown becomes so fragile that a minor trauma, e.g., during mastication, results in fracture and loss of the crown.
The lesions can be detected by means of a combination of:
1. Visual inspection
2. Tactile examination with a dental explorer
Visual inspection and tactile examination with a dental explorer will only identify end stage lesions, i.e., when the process is involving the crown and has resulted in an obvious cavity. Radiography will identify lesions that are localized to the root surfaces within the alveolar bone, which would not be detected by clinical methods. Consequently, radiography is required for diagnosis of FORL. In fact, full mouth radiographs is recommended for all cats presented for dental therapy.
The term 'full mouth radiographs' means a series of dental films where each tooth of the dentition is depicted, without significant artefacts (e.g., superimposition, lengthening, shortening), in at least one view. The use of dental X-ray film with intraoral film placement and a parallel (limited to the mandibular premolar/molar region) or bisecting angle (upper jaw and rostral mandible) technique is required. A veterinary or dental X-ray machine can be used. It is technically much easier to take the required views with a dental X-ray machine.
A full mouth series usually results requires 10 films. The views are as follows:
Maxillary incisors (1 film)
Maxillary canines (2 films; one for each side)
Maxillary premolars and molars (2 films; one for each side)
Mandibular incisors (1 film)
Mandibular canines (2 films; one for each side)
Mandibular premolars and molars (2 films; one for each side)
It is possible to depict the mandibular incisors and canines on one view and a survey may thus only require eight films. However, if abnormalities are detected additional views will be required. We routinely take 10 views and then complement as required.
Full mouth radiographs do not take a long time to take and their value in diagnosing the presence and extent of FORL is immense. In fact, adequate treatment planning is only possible with the aid of radiography. It is strongly recommended that all veterinarians performing dental procedures should be familiar with the techniques of dental radiography. In human patients, practicing dentistry without radiography would be considered negligent. In my opinion, the same applies in veterinary dentistry.
The aim of any treatment is to relieve pain, prevent progression of pathology and restore function. It remains a matter of debate as to whether FORL cause discomfort or pain to the affected individual. Based on the fact that pulpal inflammation occurs late in the disease process, it seems likely that lesions that are limited to the root surfaces and do not communicate with the oral environment are asymptomatic. However, once dentin destruction has progressed to such an extent that the process invades the pulp and/or a communication with the oral cavity has been established (when the enamel has been lost, thus revealing the dentin to the oral cavity), then discomfort and/or pain are likely.
To date, there is no known treatment, which prevents development and/or progression of FORL. It seems unlikely that such treatment can be developed without knowledge of the cause of the pathology. Currently, the suggested methods of managing odontoclastic resorptive lesions are:
1. Conservative management
2. Tooth extraction
3. Coronal amputation
Restoration of the tooth surface has been recommended for the treatment of accessible lesions, which extend into the dentin and do not involve pulp tissue. Several studies have shown that tooth resorption continues and the restorations are lost (20, 21). Consequently, the use of restoration of feline odontoclastic lesions as a major treatment technique can no longer be recommended.
Conservative management consists of monitoring the lesions clinically and radiographically. This approach is recommended for lesions that are not evident on clinical examination, i.e., only seen radiographically and there is no evidence of discomfort or pain. As most lesions are only diagnosed when pathology is extensive, conservative management is rarely indicated in the general practice situation.
In most cases, extraction or coronal amputation of an affected tooth is indicated. With extraction, the whole tooth is removed. This is the gold standard. However, when the root has been extensively resorbed it is often not possible to extract all tooth substance and coronal amputation is indicated. As already mentioned, preoperative radiographs are mandatory to allow selection of the appropriate treatment option.
Teeth with FORL are notoriously difficult, or impossible to, extract as the root is resorbing and being replaced by bone-like tissue. Moreover, there are areas of ankylosis, i.e., fusion of bone and tooth substance, along the root surface. In addition to pre-operative radiographs to detect the lesions and determine appropriate treatment, post-operative radiographs to ensure that the whole tooth has been removed are required.
There are two basic extraction techniques, namely closed and open. A closed extraction is defined as extraction using simple elevation, without the need to remove alveolar bone. The extraction socket is either left open to heal by granulation or it may be closed by suturing the gingiva over the defect. An open extraction is defined as a technique where a muco-periosteal flap must be raised, and alveolar bone removed, in order to remove the whole tooth root. The mucoperiosteal flap is replaced and sutured in place to close the extraction socket thus allowing primary healing.
Either technique can be used to extract teeth affected by FORL, but an open technique is usually easier to perform. In outline, the procedure for open extraction is to raise a mucoperiosteal flap on the buccal aspect of an affected tooth. Buccal bone can then be removed, using a small round bur, to facilitate the extraction and for multi-rooted teeth to expose the furcation in order to section the tooth into its constituent root/ crown units. In many cases, particularly in the maxilla, most of the buccal bone plate will need to be removed. A small luxator or elevator can be eased into the space created by the bur, to loosen and remove the roots. The mucoperiosteal flap is replaced and sutured to the lingual gingiva to close the extraction socket(s).
In the mandible, a modified technique, aimed at preserving alveolar bone, is recommended (22). The technique is to raise a small gingival flap both buccally and lingually, followed by the removal of just enough alveolar crestal bone to expose the furcation. A small round bur is used to make two cuts from the furcation, at 45 degrees, one distally, and one rostrally. These cuts will remove the bulk of the crown, leaving only a small point of crown on each individual root. The next stage is to remove the cancellous bone between the two roots, again using a small round bur. The depth should be the same as the root length, and should not enter the mandibular canal. If in doubt, measure the distance on your radiographs. Each root is then only supported by bone on three sides, and a small luxator or elevator can be eased into the space created by the bur, to loosen and remove the roots. The gingival flap is replaced and sutured in place.
As already mentioned, when the root has been extensively resorbed it is often not possible to extract all tooth substance, then coronal amputation is indicated. The indications for and outcome of coronal amputation has been well documented (23) and the procedure is recommended, but needs radiographic monitoring at regular intervals postoperatively to ensure that the root is resorbing and that healing is uneventful.
In brief, the technique involves raising a gingival flap both buccally and palatally/lingually to expose the alveolar crest. The crown of the affected tooth is amputated using a small round bur. A small amount of root tissue is also removed with the bur, just enough to ensure that the intentionally retained root(s) are apical to the alveolar crest. The gingival flap is replaced and sutured in place.
FORL are common.
The aetiology is not known, so prevention is not possible.
The lesions are progressive.
Diagnosis and treatment planning requires radiography.
The purpose of the treatment is the relief of discomfort or pain. In most instances, extraction of the tooth, or coronal amputation, remain the preferable treatment options.
Successful extraction and uncomplicated healing needs clinical and radiographic monitoring.
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