If these cats could talk: Cat Ailments A to Z - J ( nothing good for J so..)

http://www.petinsurance.com/healthzone/pet-tips/vet-pet-tips.aspx

Well isn't that just great. Poor kitties!

Cat cavities rarely form the same way Human cavities do.

Instead of affecting the top of the crown, feline cavities typically start eating away at the tooth around the gum line.

Cat cavities are not technically called cavities - I believe this is just for us 'normals' to understand Odontoclastic Resorptive Lesions - This is the doctor jargon.
So yeah.. Cavities.
That long doctory word means Tooth Dissolving Spots.
Cat cavities can be called several other things like simply Resorptive Lesions, Tooth Resorption, and Neck Lesions.
Again re-affirming that Cavity is the best word to use.
I hear tooth resorption and it sounds like the mouth is taking back the tooth. Back to where ever it came from...Hell probably.
Neck Lesions ? Well wouldn't that involve the neck.. and wouldn't it make more sense if it was on the outside?
Good thing I am neither a Vet or an English teacher.

These cat cavities usually start as a small hole, at the level of the gum line, on the cheek side of the tooth.
Pre molars are the most commonly affected
Second would be Molars
Third would be the Canines
Cavities can be associated with inflammation but can occur without inflammation, though this is less common.

I will try to use as many pictures as possible ... without using any that may be disturbing.. to me...

http://www.kingwestvets.com/category/dental/

A Cavity begins as a tiny hole that is difficult to detect ( I would agree - if you look at the stage 1 image you will see...nothing)

It will eventually progress to dissolving most of the tooth.

Any Cavity is at least a little painful but these become even worse once the nerves start to get exposed as the enamel of the tooth is dissolved away. ( I can attest to the pain a cavity can cause. I am not cat like so I do not hide it well)

In the end stages the crowns of the teeth can break off.

With advanced cat cavities we can also see the gum overgrow around the tooth and sometimes cover the tooth entirely.

An exposed nerve in your tooth can cause a Human to be in agony.
And we can try to dull it with drugs and Whiskey !
Neither of those things work, but at least we can attempt something.
Our Cats depend on us to make sure they are okay.

Resorptive lesions ( cavities )cannot be fixed.
Some veterinarians will fill in the defect but this does not prevent it from becoming worse.

I see no reason for a vet filling the defect if this does not prevent it from getting any worse.
A dentist can fill a human cavity - after they remove the bad part and this stops the tooth from decaying
( well at least that's the idea)
It does seem a bit weird to put a filling in a cats tooth.

There are no medications or secret remedies that prevent or fix cat cavities. ( And me with my magic potions just waiting to be used!)
The only way to ensure the tooth will not cause your kitty anymore pain, is to have it removed. (That seems like the only logical option to me. So maybe the vets can get together and lower the damn price!)
Often when one Cavity is noticed, there will be others that are discovered under anesthetic, when a more thorough dental examination can be performed.