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Dental Disease
Dental disease is THE most common ailment we find in dogs and cats. Dental disease is both treatable and preventable when caught early.
Dogs and cats have teeth. Dogs and cats don't brush their teeth. It should therefore not be surprising that they frequently develop dental problems. In order to better understand dental disease, lets start with a brief review of the pertinent anatomy. I will use drawings from human dental texts because they are easier to find. The tooth shapes are different but all the parts are the same.
Teeth are composed of a really hard outer layer called enamel. Underneath the enamel is a layer of a somewhat softer hard material called dentin. Inside the center of the tooth is the pulp, which is composed of blood vessels and nerves. A tooth is alive, and it is the pulp that keeps it alive by providing blood, oxygen, and nutrition to the living tissues of the tooth.
The tooth sits in a socket in the bone of the jaw. It is held in place by its roots. The dentin of the roots is covered with a layer called cementum, which helps cement the tooth in place. The periodontal membrane, or periodontal ligament as it is more properly called, is a ligament just like any other ligament in the body. The periodontal ligament is made out of tough connective tissue, and runs between the bone of the jaw and the cementum of the roots, and holds the two together in a strong, flexible, elastic bond. The gums, or gingiva, cover the bone of the jaw and attatch to the cementum of the roots leaving a small pocket, or gingival sulcus, normally less than 2mm deep in dogs, between the enamel of the crown and the gingiva.
The mouth is an excellent place for bacteria to grow. It is warm, moist, and there is periodic access to food for bacteria to grow on. As a result, there are lots of bacteria present in the mouth. Mostly they behave and mind their own business. However, there is the constant temptation for them to get out of control. This doesn't happen if all the mouth's defensive mechanisms work right.
Bacteria on the surface of a tooth normally form what is called plaque. Plaque i s a biofilm, a thin, translucent film made up of bacteria, proteins they secrete, and food particles. Normally, plaque is removed soon after it forms by the simple act of chewing. Dog and cat teeth are arranged differently than human teeth in that most of them do not touch together. That means that chewing is more likely to be an effective way to remove plaque than in people. Not surprisingly, we see the most problems in places where the teeth do touch together: the incisors in front and between the big molars in back, and in toy dogs where all the teeth are jammed tightly in to a small mouth.
If plaque is not removed, the bacteria that form it continue to multiply. The plaque gets thicker, and the nature of the bacteria that make it changes to a more sinister character. The thick persistant plaque will mineralize, forming tartar. Tartar, although it looks like it might be mineral deposits, but it is actually about 80% bacteria. And unlike plaque, tartar is firmly adherent to the tooth, and neither brushing nor chewing is effective in removing it.
Problems start to happen when tartar builds up, especially when it bui lds up under the gums. In dogs and cats, cavities are not a real problem. This type of decay seldom happens in pets' mouths. However, the bacteria in tartar make toxins and harmful waste products that can damage the gums and other soft tissues. The inflammation that results from tartar's interaction with the soft tissues releases other damaging compounds.
In the images to the right, we see brown tartar building up both above and below the gum line, and the tissues are becoming red and swollen because of the inflammation. As the infection progresses, the gums and soft tissues are eaten away by the bacteria. The gingival sulcus becomes abnormally deep, and is now called a periodontal pocket. The difference between a gingival sulcus and a periodontal pocket is that in a gingival sulcus (normal), the root is not exposed. In a periodontal pocket (abnormal), the root is exposed. As the periodontal pocket deepens, soon even the bone itself begins to be resorbed. Then the infection invades the periodontal ligament and destroys it,and the tooth becomes loose.
The progression of periodontal disease is often divided into stages. Although the stages are somewhat artificial, it is nonetheless very useful to classify it this way.
Stage One: Mild Gingivitis. Plaque is present, but tartar is minimal.  The gums are mildly inflammed, as evidenced by a slight reddening of the margin, and they are swollen. There is no soft tissue loss, no abnormally-deep pockets, and no bone loss. The damage done at stage one is reversible, meaning we can make it return to the original, undiseased state with treatment.
Stage Two: Mild Periodontal Disease. Here there is more advanced tartar build-up with the accompanying  inflammation, but there is beginning to be soft tissue loss, gum recession, abnormally-deep periodontal pocket formation. There will be early bone loss too, but less than 25%. The teeth are not loose at this point. To the right is an image of a dog's molar with stage two periodontal disease, and an x-ray of the same tooth. Notice the bone loss lurking under the gums! The damage that happens in stage stage 2 periodontal disease in not reversible! Although we can often achieve soft tissue regeneration, bone loss is especially hard to deal with, and we may not ever be able to get the bone to regenerate. The deep periodontal pockets that form pose a particular problem in that they are "tartar traps." Plaque will form in the pockets, and it can be difficult to remove it by chewing or brushing, and this makes it difficult to stop the progression of the disease.
Stage Three: Periodontal Disease.
Here there is severe tartar build-up, advanced soft tissue loss, dee p peri odontal pockets, and considerable bone loss somewhere between 25% and 50%. The teeth, especially the single-rooted teeth, begin to be noticably loose. Under these ravaged gums significant bone loss has occurred. Note particularly the "hole" that has appeared between the roots of this tooth. Once this occurs, it is often best to remove the tooth because plaque and tartar will build up in that hole almost immediately after it is cleaned.
Stage Four: End-Stage Periodontal Disease.
  This is as bad as periodontal disease gets. The tooth has lost over 50% of it's bony support, and is very loose. The infection has eaten the jaw away from the tooth. Nothing can save this tooth, and the patient will be much better off without it. It is loose, wobbly, and stinky. Needless to say, this damage is not reversible.
It is important to remember that any one individual can have some teeth that are perfectly normal, some teeth that are Grade One, some teeth that are Grade Two, some teeth that are Grade Three, and some teeth that are Grade Four, all in the same mouth. It is also important to remember that we can not grade a given tooth accurately unless we both probe and x-ray it. This means that when we examine a patient awake, we are only guessing at what dental problems may be there.
I hope you have enjoyed this discussion of dental disease. Click here for a discussion on when to have your pet's teeth cleaned, and click here to go to an article on how to brush your pet's teeth.
http://www.sunnysidevetclinic.com/site/view/78866_DentalDisease.pml
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