FORLs

What are FORLs?

Feline oral resorptive lesions (FORLs) are openings or holes in the tooth.  Other names for them include feline cavities, cervical neck lesions, external or internal root resorptions, and cervical line erosions. FORLs are usually found on the outside surface of the tooth where the gum meets the tooth surface.  

What is the cause?

Even with numerous studies to find a definitive cause, there are several theories but no conclusive answers.  We do know that they result from the activation of cells called odontoclasts. These cells are responsible for the normal remodeling of tooth structure. In this disease process, however, they will continue to resorb (eat away) tooth structure until in some instances the entire tooth is lost.  These lesions look and feel similar to a cavity in a person, but they are not caused by bacterial decay.  With people providing more preventative care for cats, FORLs have been identified and addressed more than in the past.  There is evidence, though, that this process is not new, nor is it limited to domestic felines.  Cat skeletons from past centuries have shown evidence of this disease. FORLs tend to occur in older cats, and purebred cats (especially Siamese and Persians) may be more susceptible.

Do they cause any problems?

They can be excruciatingly painful, especially when they are advanced. Sometimes touching the lesions (even when the cat is under general anesthetic) causes the jaw to twitch from pain.  Most cats, however, will not show evidence of oral pain, even when the tooth is fractured with an exposed root canal. 

Because cats are the master of disguise, people generally cannot tell when a cat is in pain from a hurting tooth.  In nature, an animal in pain or distress runs the risk of being chosen as prey.  Therefore, animals instinctually hide pain and continue eating and acting as if nothing is wrong even though they may be experiencing significant discomfort.  Sometimes people are surprised to see a difference in the behavior of their cat after the pain is eliminated.  We have had many clients offer feedback that their cat is more loveable, playful, or relaxed after having painful teeth removed.

How are they diagnosed?

Depending on how cooperative the cat is for an examination, FORLS may be seen during a routine physical exam.  Generally speaking, lesions are identified during a thorough oral exam with the patient under anesthesia.  A dental explorer is used on the teeth (like when a human dentist uses an instrument to press on the teeth).  If an abnormality (such as a rough indention) is found, it is further investigated.  Resorptive lesions are graded from stage 1 to 5 depending on the severity and what part of the tooth is affected.   Dental radiographs (x-rays) are essential in evaluating teeth for resorption because they allow the doctor to see the roots underneath the gum line.    

The tooth on the very left has gingival tissue growing into and over the tooth; that tooth has a FORL.  If the gingiva was pulled away from the tooth, there would be a "hole" in the tooth.  Incidentally, you can see tartar buildup on the two right teeth.  Also, the tooth in the middle has some redness to the gums that may signal the start of a FORL.  Compare the tooth on the left with the radiographs below.

Although these are not radiographs of the same cat, this cat had a resorptive lesion in the same tooth.  This is what radiographs of both cats would look like: "holes" in the crown (or upper part, visible above the gum line) and changes in the root below the gum line where the roots are being turned into bone.  Compare the roots of the tooth on the left with the other two teeth.

Here's another tooth with a FORL (the one on the right; actually the same tooth as the above cats but on the opposite side of the mouth).  Notice how the gums seem to be covering a large portion of the tooth?  The gums should be down at the same level as the other two teeth.  There would definitely be a large hole in that tooth if the gums were pulled back.  Just a piece of trivia: this particular tooth (called the mandibular 3rd premolar) is the most common tooth to get FORLs in cats.  It frequently happens on one or both sides of the mouth followed by the maxillar 3rd premolar (same tooth but on the upper jaws).

How are FORLs treated?

Treatment most often involves removing the affected tooth.  Restorations (fillings) can be performed in early stages of the disease, but they are usually temporary, as this disease process is progressive and continues underneath and around the fillings.  Since this process is not the same as a cavity in a human, the process is not halted by a filling.  Because affected teeth are not loose, removal requires oral surgery.  Depending on how advanced the process is, there are a few different methods of surgery.  Radiographs are required to guide the surgeon as to which method should be performed.

Can they be prevented?

An exact cause or set of circumstances that result in tooth resorption has not been established.  It is therefore not possible to effectively prevent tooth resorption.  Because some theories for the cause of FORLs include reaction against plaque, home tooth brushing and feeding diets and treats designed for oral care may be beneficial.  Early recognition during regular dental cleanings (including a thorough oral exam) is the best strategy.  Many cats that have regular cleanings starting at a young age have less incidence of FORLs than cats that have their first cleaning as seniors.  Please feel free to ask us for more information.  There are also many references online.