Tooth Decay (Dental Caries)

Cavities don't have to be a problem for anyone. All it takes is learning a little bit about the basics of why they form. Then, once you understand that (and implement your knowledge), you can put the issue of having cavities to rest.

Cavity Prevention 

On our pages, you'll learn about the conditions that cause cavity formation and how, if given an opportunity, the process of remineralization can actually help to reverse this damage.

We also describe syndromes that can place people at increased risk for having tooth decay. And explain how preventive measures (such as fluoride, tooth sealants, xylitol products) can be used to help to decrease this risk.

And, if you're interested, we'll show you the kinds of things a dentist looks for when checking for cavities on dental x-rays.


What is tooth decay?

Tooth decay is a disease process where acids created by specific types of oral bacteria cause damage to the calcified tissues of a tooth (primarily enamel and dentin).

On this page.

If left unchecked, a point can be reached where enough tooth structure has been damaged or lost, that a defect forms (surface damage or a hole) that's identifiable during a dentist's examination or through the use of x-rays.

Terminology - Dental caries.

The terms dental caries, tooth decay and cavity all refer to the same thing and can be used interchangeably.

It's pretty easy to see why the term "cavity," which means a hole, has come into usage. The same can be said for the term "decay," which makes reference to the destructive (decaying) aspect of this disease. Why the word "caries" is used may not be so obvious.

"Caries" is derived from the Latin word for "rot," which seems to be a reasonably accurate description of the decay process. "Dental caries" is the term you will find most frequently used in scientific literature.


Tooth anatomy as it relates to tooth decay.

Cavity formation is a process that starts on a tooth's outer surface, and then advances inward.

Calcified tooth tissues.

At any particular location on a tooth, its outer surface is composed of either enamel, dentin or cementum. These are a tooth's calcified tissues (tissues that have a high mineral content) and it's on and in them that decay forms.

a) Tooth Enamel

The calcified tissues of a tooth: Enamel and Dentin.

Most of a tooth's visible surface (and possibly even 100% of what you see) is covered by enamel. Every part of a tooth that has a white appearance is enamel.

You've probably heard that tooth enamel is the hardest tissue found in the human body. That's true. Its composition is more than 95% mineral. Most of this mineral content is a calcium-rich compound called hydroxyapatite.

b) Dentin

You might be surprised to learn that teeth are not solid enamel. Only the surface layer of a tooth's "crown" (that portion of a tooth that lies at and above the gum line) is enamel.

The bulk of a tooth, both its root and interior aspects, is composed of a tissue called dentin. It too contains a high concentration of minerals, including hydroxyapatite, but not as much as enamel. Only about two thirds of its composition is mineral so, relatively speaking, dentin is the "softer" type of tissue.

c) Cementum

Cementum is an ultra-thin mineralized layer that covers the surface of a tooth's root.

It's affected by the decay process, just like the other calcified tissues. But it's so thin and destroyed so readily that we've confined our discussion to just dentin and enamel.

Tooth decay takes place in calcified tissues.

It's the tissues listed above that are involved with decay formation via a process termed "demineralization." (How cavities form.) Yes, a tooth's nerve (a non-calcified tissue) can be damaged by the presence of decay but that's a separate issue (a side effect).


Reading dental x-rays.

When searching for cavities on dental x-rays, a dentist looks for signs that indicate that there's been a change in density in a tooth's enamel and/or dentin.

A dental x-ray that shows signs of tooth decay.

How x-rays work.

When a radiograph ("x-ray") is taken, the mineral content contained in a tooth's tissues will block some of the radiation that's aimed through it.

That means that the parts of the film that lie protected behind tissues such as enamel and dentin will be less exposed (have fewer x-rays hit them), and thus will look lighter in color.

In our graphic to the right, the enamel layer of the teeth has the lightest color. That's because it has a higher mineral content than the other tissues of the tooth. In comparison, the dentin layer (a less calcified tissue) appears slightly darker.

Why cavities show up on x-rays.

Since tooth decay is an area of tooth demineralization (and possibly even involving an outright hole), those locations where it has formed will appear as a darkened area on an x-ray.

That's because the decayed portion of the tooth is less "hard" (less dense or intact) and therefore the x-rays can penetrate that portion of the tooth more easily and ultimately expose the film to a greater extent.

Stages of tooth decay.

Our mockup of a dental x-ray shown below illustrates some of the stages that the decay process goes through.

  • Frame A: This frame illustrates the earliest stage of tooth decay formation that shows up on a dental x-ray. Notice how there is just ever so slightly a darkened area in the enamel portion of the tooth right exactly where it touches its neighboring tooth. That's the decay. (This person has not been flossing enough.)
          Most dentists won't recommend placing a filling until the x-ray shows that the decay has completely penetrated the enamel layer of the tooth (as shown in Frame B). The lesion shown in Frame A may not progress further if this person starts to floss effectively.

    A dental x-ray showing the development of tooth decay.
  • Frame B: Once a dental x-ray shows that the tooth decay has penetrated through the tooth's enamel and into its dentin layer, a dentist will recommend placing a filling.

  • Frame C: As discussed previously, the dentin portion of a tooth is less mineralized (less "hard") than a tooth's enamel layer. This means that dentin will decay at a faster rate.
          Notice how in Frame C the lesion in the enamel layer has only slightly increased in size while the decay in the dentin has advanced significantly.

  • Frame D: Frame D illustrates a worst-case scenario situation. If a developing cavity is left untreated, it can advance all the way to the tooth's nerve. If it does, not only must the decay be removed and the damaged tooth structure repaired but additionally the tooth's nerve will require root canal treatment.
          Clearly the early control of tooth decay (preferably at the point shown in Frame B) is a case where a stitch in time saves nine.

The history of tooth decay.

While throughout history tooth decay has always been around, it's only been fairly recently that it's become pandemic (an epidemic spread over a large geographic region).

  • It first became a widespread problem with the establishment of sugar plantations in the 1700's in the "New World."
  • It affected yet greater numbers of people when the cultivation of the sugar beet spread in Europe in the 1800's.
Dental Caries
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