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Cats get an unusual dental disease. It's not
cavities. It's not periodontal disease. It
is a condition which happens very rarely to dogs or
people, but which is quite common in cats. We're
talking about Resorptive Lesions (but we'll call
them RL's for short from now on). They used to be
called FORL's, which is short for Feline Odontoclastic
Resorptive Lesion. The veterinary dental guru's
now just call them Resorptive Lesions, or RL's,
because as our understanding of them progressed, we
found that the odontoclasts weren't such a big part of
it after all. I guess the key point here is that
while we as veterinary dentists are very familiar with
what Resorptive Lesions look like, we really are just in
the investigative stages as far as understanding what
What is an RL? An RL is a hole in the tooth.
While there are some important differences between RL's
in cats and the cavities we have all had, there are many
similarities. A cavity is a hole in the tooth.
In the picture of a human tooth below, the cavity is the
brown spot visible at 9:00. Cavities are caused by
decay. Bacteria in the mouth feed off sugars, and
ferment them to make acids, which eat away the
Once the cavity gets through the hard enemel, it begins
to attack the softer, sensitive dentin underneath.
It is at this point that the tooth becomes painful.
As the cavity progresses, it erodes through the dentin
into the pulp of the tooth. The exposed pulp then
become infected, and abcesses
form at the tooth roots.The x-ray to the right is of a
cavity in a human tooth. The cavity istelf is the
dark "hole" seen in the right half of the tooth.
Cavities are caused by bacteria and happen from the
outside in. RL's are caused by some as-yet
undetermined process, likely involving either the cat's
own immune system or a defect in vitamin D metabolism,
or maybe both, and happen from the inside out. But
the net effect is the same. In the picture below,
we see the teeth in the bottom jaw of a cat.
Notice how red and inflammed the gums are. The
redness is worse around the tooth on the right. An
x-ray of these same teeth is posted beside the
Like the cavity, the RL is seen as a darker spot in the
tooth. In this case, the RL is located on the left
root of the righthand-most tooth. Notice the
similarity to the cavity in the human tooth shown above.
Like cavities, once there is a hole leading from the
sensitive dentin to the outside, the tooth becomes very
painful. How painful is it? The answer is
very painful. Most cats with RL's will exhibit
teeth-chattering when the RL's are touched even lightly
with even a Q-tip. Basically, the tooth is so
painful that merely touching it with a soft object will
send the cat into jaw spasms of pain. Your cat may
not show many other signs of pain, however. This
does not mean that the cat does not feel pain.
Click Here for a more detailed discussion about how
to tell if your cat is in pain.
The Treatment of Choice for RL's is Extraction. It
does no good to put a filling in an RL. The
erosive process that caused them in the first place will
dissolve the tooth out from around the filling, and the
filling will simply fall out. While it may seem a
bit extreme to extract a tooth with an RL, just consider
the alternative: Living daily with a very painful
There are things to know about extracting teeth with
RL's. Look again at the radiograph of
the cat tooth with an RL. This time observe the
roots closely. You wil note that the smallest
tooth has roots that seem
or indistinct when compared to the roots of the
neighboring teeth. This is because the roots are
starting to be resorbed too. The tooth as a whole
is undergoing a disease process, and not only is there a
hole eaten away from the crown, the roots are becoming
weak and brittle. If weak and brittle weren't
enough, the roots also become cemented into the jaw
This means that teeth with RL's can be very difficult to
extract. The roots tend to shatter and fragment,
making it difficult to get the whole root. It is
in general a bad idea to leave root fragments in place
because they are often infected, and retained root tips
can continue to
The radiograph at the left shows another cat with
two retained root tips. One is easily visible, and
the second is barely visible just to the left of
the obvious one. There is a fairly obvious dark
halo around the root tip we can easily see. This
halo is caused by infection in the retained root tip.
Infection trapped deep in this buried root tip is eating
away the bone at the tip of the retained root, causing
the dark halo.
It takes a lot delicate work using the proper techniques
and the right instruments to safely and completely
remove RL teeth. RL teeth must be removed
surgically. In a surgical extraction, the gums are cut,
moved out of the way, the tooth is cut carefully into
pieces, some of the overlying bone is removed, and the
tooth is gently removed. Then you MUST take
post-extraction x-rays to be sure you got all the root
tips. Then the gums are sewn back into place.
Because this can be a very lengthy, delicate procedure,
treating your cat's RL's can be fairly expensive.
Most cats develop RL's in more than one tooth. It
is quite common to have to extract many teeth at a time.
Sometimes all the teeth must be reomoved. However,
once the healing process is over, the cats are much
happier without all those painful teeth.
are a common and very painful dental condition in cats.
Many cats suffer years in silence with very painful
teeth. Treating RL's is not simple, but your cat
will definitely thank you for the relief!