What causes tooth decay? / How does it form? -
Here's a straight, by the numbers, outline of how and why cavities form.
1) Cavities are caused by "demineralization."
Tooth decay is the result of tooth demineralization, a process where an acidic environment leaches some of the mineral content out of a tooth's calcified tissues (enamel and dentin).
2) Where do these acids come from?
The acids that cause the demineralization are produced by specific types of bacteria (primarily lactobacilli and mutans streptococci) that live within dental plaque.
a) These acids are actually bacterial waste products.
The bacteria that cause cavities are living organisms. And that means they consume food and create waste products, just like we do.
As it happens, the waste products they create are very acidic (they have a pH of 4 and lower). And it's these compounds (primarily lactic acid) that cause tooth demineralization.
b) What kinds of foods are involved?
The primary food source for these bacteria is dietary sugars. This includes sucrose (table sugar), glucose, fructose, lactose and cooked starches.
As the bacteria digest these sugars, they are broken down into and ultimately excreted as acids.
c) Remember, you and your oral bacteria share the same menu.
Keep in mind that the things you eat are the same food items that are available to the bacteria that live in your mouth. So, when you consume foods that contain sugars, they get a meal too. And within minutes they start producing the acids that cause tooth decay.
3) The bacteria that cause cavities live in dental plaque.
Everyone's mouth is inhabited by bacteria. In fact, a single human mouth can contain more microorganisms than there are people on planet Earth.
And although you can't sterilize your mouth, there are things you can do to minimize your potential for experiencing tooth decay. You do this by preventing oral bacteria from forming organized colonies. These bacterial colonies are referred to as "dental plaque," and keeping it from building up is what brushing and flossing is all about.
a) It's the formation of plaque that's the problem.
Dental plaque not only provides a home for bacteria but it also acts as a medium that holds the acid they produce directly against a tooth's surface.
It's the acids that leach out underneath dental plaque that cause cavities.
Take a look at our diagram. When acid production is active (like after we consume something sugary), the acid that's formed can seep out of the plaque in one of two directions.
- It can either accumulate underneath the plaque (directly against the tooth's surface).
- Or else seep out into the mouth.
b) Some of the acid gets neutralized.
Any acidic waste products that seep out into the mouth won't be able to cause tooth decay. That's because they'll immediately get diluted, buffered, and/or washed away by saliva or the foods and beverages we consume.
c) It's the acid underneath the plaque that causes cavities.
The acid that's most instrumental in causing cavities (demineralization) is that which seeps through the plaque and on down to the tooth's surface.
The dental plaque above tends to act as a protective covering that helps to shield the acid from dilution, buffering, or being washed away. Over time, saliva will finally penetrate through the dental plaque and begin to create its neutralizing effect. But this can take as long as two hours or more.
That means the acid that finds its way to the tooth's surface will remain relatively concentrated for an extended period. During this whole time, demineralization will take place.
4) "Young" dental plaque is less harmful than "old."
The amount of tooth damage that occurs after an exposure to sugar is, in part, related to the age of the dental plaque. (Age = How long a particular glob of plaque has been sitting on a particular location on a tooth.)
Factors such as thickness, chemical nature, and the types of bacteria living in it all correlate with the age of plaque. Plaque that's just formed over the last few hours doesn't have the potential to create as much demineralization as that which is several days old (when each is given the same exposure to sugar). That's why it's important to brush both thoroughly and frequently.
Tooth anatomy as it relates to cavity formation.
If you're not totally squared away on the different parts of a tooth and how each is effected by decay, the following information should help.
The 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 primary calcified tissues of a tooth.
Most of a tooth's visible surface (everything you see that's white, and possibly even 100% of what you see at all) is covered by enamel.
You've probably heard that it's 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.
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 composed of it.
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 calcified tooth tissue.
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 the process of demineralization. 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) and certainly doesn't always occur.
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.
Full menu for this topic - ▼
- Cavity formation -
- Types of decay -
- How fluoride prevents cavities. / Side effects (fluorosis).