Feline Tooth Resorption (FORL, cavities, resorptive lesions, cervical line lesion, neck lesion, carie)

FORLs (Feline Odontoclastic Resorptive Lesions) usually present clinically as very painful areas of granulation tissue extending into the crown surface of the tooth. Often they are not detected until the oral cavity is examined carefully under general anesthesia. Clinicians may be suspicious of FORLs when there is an area of gingivitis at the furca of multi-rooted teeth. The furca are the areas between the roots of multi-rooted teeth. Examination with a dental explorer at the gingival margin will reveal an "erosion" or "cavity" that feels rough. A normal furcation will be smooth since it is covered with cementum. If the resorption has progressed through the entire tooth, the crown may be missing or partially missing as the enamel of the crown is undermined by resorbed dentin. If the defect is exposed to the oral cavity, these lesions can be very painful for the patient and even under general anesthesia, the cat may "chatter" when the tooth is touched with any instrument. Coronal lesions may be covered by granulation tissue which may be interpreted only as inflamed gingiva. Resorptive lesions with no communication to the oral cavity do not seem to cause pain. It is only when the crown fractures or a lesion progresses coronal to the alveolar bone that it becomes evident clinically and is painful.

Dental Xrays are very important in both diagnosing and treating FORLs. An early shallow lesion (Statge 1 or 2), may be treated with a restoration. This may not be a "cure", but may allow the cat to have the function of the tooth for months or years.

We do not understand the pathogenesis of FORL at this time. Drs. Gregg DuPont and Linda DeBowes, described two types of FORL in the Journal of Veterinary Dentistry (JVD 19:2, pp 71-75) based upon the appearance of the periodontal ligament space on dental Xrays.

• Type I: radiodensity similar to adjacent tooth roots and normal appearance of the periodontal ligament (PDL) space; more often associated with periodontitis
• Type II: radiolucent compared to adjacent roots and absence of the PDL space; associated with root replacement resorption

The AVDC ( American Veterinary Dental College) Nomenclature Committee has classified the following stages of tooth resorption:

• Stage1 (TR1): Mild dental hard tissue loss (cementum or cementum and enamel).
• Stage2 (TR2): Moderage dental hard tissue loss (cementum or cementum and enamel with loss of dentin that does not extend to the pulp cavity).
• Stage3 (TR3): Deep dental hard tissue loss (cementum or cementum and enamel with loss of dentin that extends to the pulp cavity); most of the tooth retains its integrity.
• Stage4 (TR4): Extensive dental hard tissue loss (cementum or cementum and enamel with loss of dentin that extends to the pulp cavity); most of the tooth has lost its integrity.
• (TR4a) Crown and root are equally affected;
• (TR4b) Crown is more severely affected than the root;
• (TR4c) Root is more severely affected than the crown.
• Stage5 (TR5): Remnants of dental hard tissue are visible only as irregular radiopacities, and gingival covering is complete.

These stages and types are only detected with intraoral radiographs.

Type I lesions may be initiated by periodontitis, but there is still no concrete evidence for a cause and effect relationship. In unpublished reports, some investigators have detected an increase in crevicular fluid enzymes with Type I lesions.

At this time, our understanding is that Type II FORLs begin on cementum or dentin. Something triggers cells to differentiate into odontoclasts along the periodontal ligament causing resorption into the root cementum (root replacement resorption) and into the dentin causing internal resorption. When coronal dentin is involved, the enamel of the crown is undermined and the crown can be lost or fractured. When the root dentin is involved entire root replacement resorption occurs and may involve the pulp. With root replacement resorption bone-cementum tissue is laid down and the periodontal ligament is destroyed. The tooth does not flex with mastication, so the crown easily fractures. This is also why extraction of these teeth is challenging since the root is ankylosed (or fused) to the adjacent bone as the periodontal ligament is replaced with the bone-cementum tissue.

Often external resorption of Type II FORLs starts at the furca or in areas of crowded teeth. The upper 3rd and 4th premolars, lower 3rd premolars and 1st molars are the most commonly affected teeth; however any tooth can be affected.

Data presented at the Veterinary Dental Forum November, 2003 showed that if a cat has one clinical or radiographic resorptive lesion, the unaffected teeth show histologic changes of early resorption. Therefore, we can assume that all teeth are affected by resorption in those cats. We will want to monitor these cats carefully for progression of resorption and treat those lesions as they enter the oral cavity when they become painful.

The same data also presented early information that treatment with alendronate (Fosamax) may be effective in arresting and in some cases reversing the lesions. At the present time, I am not prescribing alendronate, but may do so in the future if the treatment proves to be effective.