Feline Odontoclastic Resorptive Lesions

Also known as: FORL — Neck lesions — Feline tooth resorption — cervical line lesions — neck lesions — dental resorptive lesions — feline caries — RL

Introduction

Feline tooth resorption or feline odontoclastic resorptive lesions (RL) (also been referred to as cervical line lesions, neck lesions, dental resorptive lesions and feline caries) affect more than one third of adult domestic cats and are the second most common oral problem seen in cats (after periodontitis), with prevalence increasing with age. (picTR1)

On examination, there is a loss of dental tissue on the crown or at the neck of the teeth. The crown may be completely resorbed with the remaining root covered with gingiva.

Aetiology and Pathogenesis

The aetiology and pathogenesis of FORLs has not yet been demonstrated but is almost certainly multifactorial. Possible hypotheses that have been suggested include, the texture of the diet, abnormal calcium regulation, hypervitaminosis A, mechanical stress, anatomical abnormalities of the teeth, viral infections and plaque bacteria and periodontal disease.

Hard tissues are protected from resorption by their surface layers of blast cells. It appears that as long as these layers are intact, resorption cannot occur. Although bone, dentine and cementum are mesenchymal, mineralized tissues composed mainly of collagen and hydroxyapatite, they differ markedly in their susceptibility to resorption.

Two mechanisms are involved in resorption of hard tissue:

1. The trigger
2. A reason for the resorption to continue.

The trigger mechanism in root resorption is a root surface detached from its protective blast cell layer. For the resorption to continue, a stimulus is required, e.g. infection or a continuous mechanical force.

Root resorption always starts at a surface, and is termed internal if emanating from the root canal wall and as external if emanating from the root surface. Internal resorption is rare in permanent teeth. Histological examination reveals resorption of the internal aspect of the root by multinucleated giant cells adjacent to granulation tissue in the pulp. There are different theories regarding the origin of the pulpal granulation tissue involved in internal resorption. The most logical explanation is that it is pulp tissue that is inflamed because of an infected coronal pulp space. In addition to the requirement of the presence of granulation tissue, root resorption takes place only if the odontoblast layer and predentine are lost or altered. Traditionally, a pink tooth has been thought pathognomonic of internal root resorption; the pink colour is caused by granulation tissue in the coronal dentine undermining the crown enamel. However, a pink tooth can also be a feature of a specific type of external root resorption, namely peripheral inflammatory external root resorption (detailed later in this chapter), which must be ruled out before a diagnosis of internal root resorption is made. A pink tooth can also be due to pulpal haemorrhage. There are different forms of external root resorption described in man. The underlying mechanism is understood for some of these, whereas other forms are still unexplained and therefore termed idiopathic. A classification system for external root resorption that have a known mechanism has been proposed in man and is as follows:

1. Surface resorption
2. Replacement resorption associated with ankylosis
3. Inflammatory resorption.

This classification system works for external root resorption in cats and dogs as well.

SURFACE RESORPTION - is initiated subsequent to injury of the cementoblast layer. It is thought that minor traumas caused by unintentional biting on hard objects, bruxism, etc. can cause localized damage to the periodontal ligament and trigger this type of resorption. The process is self-limiting and reversible.

REPLACEMENT RESORPTION - results in replacement of the dental hard tissue by bone. When a surface resorption stops, cells from the periodontal ligament will proliferate and populate the resorbed area. Cells from the nearby bone may then arrive first and establish themselves on the resorbed surface. Bone will thus be formed directly upon the dental hard tissue. This results in fusion between bone and tooth, i.e. ankylosis. When the resorptive process is over, the osteoblasts will form bone in the resorbed area. In this way the dental tissues will gradually be replaced by bone.

INFLAMMATORY RESORPTION - In addition to apical root resorption caused by apical periodontitis as a consequence of pulpal necrosis, there are two main forms of external resorption associated with inflammation in the periodontal tissues, namely:

1. Peripheral inflammatory root resorption (PIRR)
2. External inflammatory root resorption (EIRR).

Both forms are triggered by destruction of the cementoblasts. In PIRR, the osteoclast-activating factors, which perpetuate the resorptive process, are provided by an inflammatory lesion in the adjacent periodontal tissues. EIRR, on the other hand, receives its stimulus for continued resorption from an infected necrotic pulp. In other words, the common factor for these two types of resorption is inflammation in the adjacent tissues.

Typical Signalment

There are no sex or breed predispositions, however, it does become more prevalent with increasing age.

Diagnosis

Clinical Signs

Anorexia, drooling, lethargy and pain on contact with the lesions.

Oral Examination

Visual Examination will identify the lesions or inflammed gingiva that overlies the remaining root.

Lesions that are subgingival may be identified using a dental probe.

Diagnostic Imaging

Radiographic signs of FORLs include erosion of alveolar bone at the cementoenamel junction, root resorption, root ankylosis and subsequent periodontal space loss and resorption of the dental crown.

Classifying the Lesions

Classifying the lesions allows a logical treatment regime to be implemented. It can be based on the severity of the resorptive lesions.

Disease type	Area affected
Stage 1	Enamel only
Stage 2	Enamel and dentine
Stage 3	Pulp exposure
Stage 4	Extensive structural damage
Stage 5a	Crown is resorbed but the roots are retained.
Stage 5b	Crown is intact but the root is resorbed

Pathology

Odontoclasts attack external and internal to the tooth. Initially they start at the neck/cervical region and extend into tooth root they also enter the root via the apical foramen (stage 3 lesions). Odontoclasts are normally only active in young animals to resorb the deciduous teeth to make way for the permanent teeth so this is abnormal activation in adults.

FORLs are different from dental caries which is demineralization by bacteria fermenting carbohydrate on the enamel.

Additionally there may also be inflammatory infiltrates into the resportive lesions.

Treatment

There are various treatment options available for the different stages of disease.

Stage 1-2 These require a scale and polish, fluoride treatment and the use of pit and fissure sealant.

Stage 2 Firstly a Scale and polish followed by restoration of the tooth using glass ionomer, compomer or composite (high failure rate.)

Stage 2-4 Extractions are necessary and also crown amputation whilst retaining the root.

Stage 5a Extractions again whilst retaining the root.

Stage 5b Lesions require crown amputation.

Feline Odontoclastic Resorptive Lesions Learning Resources
Literature Search Search for recent publications via CAB Abstract (CABI log in required)	Feline odontoclastic resorptive lesions publications

References

Tutt, C., Deeprose, J. and Crossley, D. (2007) BSAVA Manual of Canine and Feline Dentistry (3rd Edition) BSAVA

Merck & Co (2008) The Merck Veterinary Manual Merial

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