SYNONYMS
Synonyms for feline odontoclastic resorptive lesions (FORL) include neck lesions, cervical line lesions, subgingival resorptive lesions, dental resorptive lesions of the cat, external osteoclastic resorptive lesions, idiopathic buccocervical erosions, odontoclastic resorptive lesions, etc.
AETIOPATHOGENESIS
The aetiology of FORL is unclear. The various hypotheses include:
- A local immune-type response and release of substances, such as cytokines, suggested to be responsible for attracting the odontoclasts.
- Local and systemic imbalances in the metabolism of calcium caused, for example, by diet not containing a sufficient amount of this element. No other factors related to the diet have been identified so far.
From among the studies carried out on FORL, two have shown that the acid covering of dry foods for cats does not predispose to the development of this pathology.
FORL is not a carious process (cats do not suffer from dental cavities). A cavity is characterized in the initial stage by an inorganic demineralisation of the enamel, whereas in FORL there is active, progressive destruction of dental tissues by odontoclasts and cementoclasts.
From a histopathological point of view, two phases of FORL can be identified: an acute phase during which there are numerous odontoclasts on the surface of the lacunae and destruction of the dental tissues, which alternates with repair phases in which there is apposition of newly formed bone and cementum-like tissue. The continuous alternation of these two phases leads to continual loss of root tissue and ankylosis between the bone socket and the root of the tooth.
CLINICAL FEATURES
The symptoms vary from case to case: some cats do not have any clinical signs, while others manifest a series of non-specific signs:
- tenderness when grasping food, often together with loss of appetite;
- refusal of hard foods;
- food left to fall from the mouth after having been masticated briefly;
- a tendency to teeth chattering or grinding;
- depression;
- lethargy;
- dysphagia;
- excessive salivation when the resorptive lesions are associated with severe gingivitis.
The physical examination of an unsedated cat with FORL often triggers a violent reaction in the animal, making it impossible to inspect the oral cavity. Sedating the animal enables the examination to be conducted, often revealing inflammation and/or hyperplasia of the gums, which tend to bleed easily. X-ray studies are essential in order to determine the real condition of the dental tissues.
The prevalence rate of FORL in domestic cats in the last 15 years has been reported to be between 28.5 and 67% and this pathology has also been found in wild and feral cats.
CLASSIFICATION
The classification of FORL, like that of many other disorders, is a decisive factor when making therapeutic choices. Most authors distinguish four stages, based on the degree of involvement of the dental tissues.
Stage 1 – This stage often passes unnoticed and only a careful examination may reveal a slight depression involving the enamel and/or cementum, without reaching the dentin. The lack of involvement of the dentin means that the lesions are often asymptomatic. A thorough inspection of the area of the neck of the tooth is necessary to observe the pathology at this stage, while a sensation of irregularity of the surface can be felt when using a probe for hard tissues to explore the area.
Stage 2 -The erosion reaches the dentin and exposes the nerve endings within the dentin tubules. This condition generates a pain response that is so marked that it is often detectable even in anaesthetised cats. At this stage, as in the subsequent ones, the lesions may be covered by hyperplastic tissue or by tartar which must be removed in order to be able to see any lesions (Figs. 1 [3], 2 [4]and 3 [5]); X-rays confirm this stage of the disease, by excluding involvement of the pulp or lesions of the root.
Stage 3 – In this stage the process proceeds until reaching the pulp causing a variable degree of loss of dental structure. During instrumental examination a probe for hard tissues causes a pain response and bleeding of the pulp; X-rays are need to evaluate the extent of the erosion since there may be minimal involvement of the crown but extensive resorption of the root (Fig. 4).
Stage 4 – As it progresses, the pathology causes severe loss of structure of the tooth, resorption phenomena, sometimes accompanied by ankylosis of the root, coronal fractures and gingival inflammation which may be severe. Teeth thatreach this stage are often so fragile that they lose the crown; when this happens, the gingival tissue reacts and, by trying to repair the lesion, can cover the underlying root fragments that can then only be identified by radiography.
DIAGNOSIS
A suspected diagnosis of FORL can be made from the history and preliminary physical examination, but diagnostic certainty can only be reached after having examined the patient under general anaesthesia. 
During inspection of the oral cavity all the teeth must be individually examined and the findings reported on the animal’s dental chart.When the lesions are above the gingiva, bleeding or covered with hyperplastic gingival tissue they are easy to identify, but when they are below the gingiva, they have to be identified with the aid of a very fine retraction wire introduced into the gingival sulcus with appropriate spatulas. Once the suspected sites have been identified, a tactile examination is performed with a probe for hard tissues to detect the rough areas typical of stage 1 and 2 lesions, pain (often detectable even in anaesthetised animals with stage 2, 3, and 4 lesions) and any endodontic involvement; in fact, the loss of dental tissues enables the probe to penetrate to the pulp without encountering any obstacles. Accurate staging of FORL, on which the therapeutic choices depend, can only be achieved with the aid of X-ray studies (Fig. 4). All the teeth must be examined, including the ones suspected to be affected and the apparently healthy ones, to check the integrity of the hard tissues below the gingiva.
TREATMENT
The treatment of FORL depends on the stage of the disease. In some cases the expectations of the owner, who often opposes a proposed extraction of affected teeth, can give rise to misunderstandings: it is important to be clear that odontoclastic resorptive lesions are progressive and, despite appropriate therapy, can continue to evolve, obliging further interventions until the point of having to extract the affected teeth anyway. The management must be aimed at the patient’s wellbeing, the health of its oral cavity and the relief of pain. Over the years various therapeutic options have been proposed.
Polishing the dental surfaces and applying a cavity varnish
In the case of stage 1 FORL, after careful scaling and polishing of all the teeth, the affected teeth can be gently buffed and a dental sealant applied. Such sealants remain in situ for about 30 to 60 days. This treatment appears to be useful for slowing the progression of the disease, but certainly not for stopping it and, for this reason, it is important that the evolution of the lesion is monitored. It has been hypothesised that the application of sealants or fluoride-containing gels provides benefits, but this supposition has been extrapolated from results in human medicine and there are no reliable data on the use of these products for the treatment of FORL.
Filling
Filling with glass ionomers has been proposed as a therapeutic option for teeth affected by stage 2 FORL. Unfortunately, besides being difficult to perform, particularly for subgingival lesions, fillings have an estimated success rate of about 33% making frequent clinical and radiological follow-up of the treated teeth essential. It should be emphasised that teeth not responding positively to this treatment will continue to cause pain.
Root canal therapy (devitalisation)
Endodontic treatment has not been demonstrated to be useful in halting the evolution of the disease given that after 1 year less than 20% of subjects treated in this way have slowed progression of the lesions.
Extraction
Dental extraction is currently the treatment of choice for all lesions that have involved the endodontic system (stage 3 or higher) and should also be considered for stage 2 FORL. The healing of the extraction site should be monitored both clinically and radiologically.
Coronal amputation
This is a therapeutic option for animals that do not have pathologies incompatible with the presence of root fragments (e.g. chronic feline gingivitis-stomatitis) and when it has been determined that any ankylosis present would make it difficult, if not impossible, to remove the tooth completely. Coronal amputation is justified, and useful, only in these cases and must be followed by radiographic monitoring until it has been seen that the root, deliberately left in situ, has been resorbed completely. The technique is simple: a turbine-mounted, elongated, diamond-tipped bur is used to amputate the crown at the level of the neck of the tooth. An ‘envelope’ flap is then created to cover the ankylosed portion of tooth left in situ.
Whatever treatment is chosen good oral hygiene must be maintained at home in order to limit the development of periodontal disease which would further compromise the health of the oral cavity.
Suggested readings
1. DeBowes L.J., (1994) Lesioni da riassorbimento odontoclastico nel gatto - Waltham Focus vol. 4 n. 1 1994.
2. DeForge D.H., Colmery B.H. (2000) An atlas of veterinary dental radiology –Iowa State University Press, First edition, 2000.
3. DuPontGA, DeBowes LJ: Atlas of Dental Radiography in Dogs and Cats. St. Louis, Mo;
Saunders Elsevier, 2009.
4. DuPont G., (1995) Crown amputation with intentional root retention for advanced feline resorptive lesions – A clinical study – Journal of Veterinary Dentistry – Vol. 12, N. 1, March 1995 – pp. 15-17.
5. Emily P.P., Penman S., (1992) Manuale di odontoiatria dei piccoli animali - Edizioni SCIVAC, pp. 14-15, pp. 63-65.
6. Gauthier O., Boudigues S., Pilet P., Aguado E., Heymann D., Daculsi G., (2001) Scanning electron microscopic description of cellular activity and mineral changes in feline odontoclastic resorptive lesions – Journal of Veterinary Dentistry – Vol. 18, N. 4, December 2001 – pp. 171-176.
7. Gorrel, Cecilia (2003). "Feline Odontoclastic Resorptive Lesions". Proceedings of the 28th World Congress of the World Small Animal Veterinary Association. http://www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2003&PID=6524&O=Generic. Retrieved 2006-10-22.
8. HarveyC.E, Emily P.P., (1993) Small Animal Dentistry. Ediz.Mosby, St. Louis.
9. Hopewell-Smith A., (1930) The process of osteolysis and odontolysis, or so called ‘absorption’of calcified tissues: a new and original investigation. The evidence in the cat – Dental Cosmos 1930 pp. 1036-1048.
10.Ingham K.E., Gorrel C. (2002) Il trattamento delle affezioni orali nel cane e nel gatto - Waltham Focus vol. 12 n. 1 2002 pp. 21-27.
11.Logan E.I., (1997) Oral disease in the domestic cat – Canine and feline oral health – Hill’s Pet Nutrition Inc. 1997 pp. 31-33.
12.Lyon, Kenneth F. (2005). "Odontoclastic Resorptive Lesions". in August, John R. (ed.). Consultations in Feline Internal Medicine Vol. 5. Elsevier Saunders.
13.Mulligan TW, Aller MS, Williams CA. Atlas of Canine & Feline Dental Radiography,
Trenton: Veterinary Learning Systems, 1998.
14.Verstrate F., (1998) An update on feline dentystry – 4th European FECAVA – SCIVAC Congress – Bologna, Italy, 18 - 21 June.
15.Wiggs R.B., Lobprise H.B.(1997) Veterinary dentistry Principles & Practice. Ediz. Lippincott – Raven 1997pp. 87-103, pp. 487-496.