The last of the hard tissues of the tooth is called the cementum. This mineralised material covers the root surfaces and joins the enamel at a juncture appropriately called the "Cemento-Enamel Junction." It is pictured on the image at right as a yellow line around the root.
The purpose of the cementum is two-fold. First of all it seals the dentinal tubule on the outside of the tooth, creating the closed system "piston-like" property of this important receptor. If pressure was not maintained within the tubule (i.e. it was open on the outer end) it could not function properly and tell the brain that you are pressing on your tooth.
The second purpose of the cementum is to provide a surface for the attachment fibers of the bone to anchor the tooth in the socket. Similarly, the cementum provides the surface for the fibers of the gingival attachment, which protects the bone. We will discuss these fibers in more detail in the section entitled "Soft Tissues of the Tooth."
Because it is usually buried under the gum line, the cementum is never disrupted...
...unless the gums recede!
Cementum and Gingival Recession
An important property of this material that covers the root surface is that, much like the enamel, cementum has no nerves and hence no feeling if it is exposed. And that is a good thing. Another property of the cementum is that it is a very thin layer of tissue.That is not such a good thing. In fact, if the gingiva ever recedes and the cementum is exposed to the hostile oral environment, it can be easily damaged.
If you look at the image to the left, the gingival attachment has obviously receded downward from the red dotted line and there is a very noticeable ditch along the root surface of the tooth. The cementum here is gone, either from acid erosion, toothbrush abrasion, or the result of occlusal trauma (the tooth bending laterally due to an imbalanced bite.)
Cementum, Gingival Recession, and Tooth Sensitivity
Many times, when there is recession like this, the tooth will become very sensitive to hot, cold, or sweets, I think you have learned enough to probably understand why.
If there is no cementum at the outside of the root surface, then the dentinal tubule is open. When the water within that tubule is stimulated, the nerve attached to the tubule will react.
What does cold due to water? It contracts. Hot makes it expand. Sweets change the pH of the water and metal will create a "galvanic shock" by transmitting electrical impulses through the water.
For much more on tooth sensitivity and how to interpret the signs and symptoms of your teeth, go to that section in the Learning Center of this website.
Can Cementum Regenerate?
Like the dentin, there are living cells in the
periodontal ligament in contact with the cementum. These cells, called cementoblasts can regenerate more cementum if necessary.
But that only happens in the sterile, sealed periodontal attachment. However, once the cementum is exposed and no longer in contact with these fibers, then it is impossible to regenerate it.
The regeneration of cementum is an important topic when it comes to regenerating bone and a healthy periodontal attachment in the aftermath of advanced periodontal disease. Unless you can regenerate new cementum for the fibers to attach to, you never truly regenerate a healthy periodontal attachment, even if bone was able to come back. Again, for more on the topic of tissue regeneration see this section in the Learning Center.
Cementum and Tartar Build Up (Calculus)
Unlike enamel, cementum is not smooth at all, but that is on purpose. This roughness is essential to allow both the gingival fibers and the attachment fibers of the periodontal ligament to be connected to the tooth.
However, when it is exposed, It is the rough nature of cementum that allows for bacterial plaque to stick to it so well. If the patient is not good with their oral hygiene and the plaque remains in place for long periods of time, it will harden on the root surface. This is what we commonly call "tartar buildup" but more properly called "calculus."
Look at the picture below and you will see how the plaque has accumulated at the cemento-enamel junction and hardened into place. Also note how inflamed the gingival tissue appears. When that tartar is removed you would expect for that gingival tissue to be very red indeed. But also notice that it will not, and indeed cannot buildup on the smooth enamel surface.
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