Tooth decay - How / Why does it form?
1) Cavities are caused by tooth "demineralization."
Tooth demineralization refers to a process where an acidic environment leaches some of the mineral content (such as calcium) out of a tooth's calcified tissues (enamel and dentin).
2) Where do these acids come from?
The acids that cause the demineralization process are produced by specific types of bacteria (primarily lactobacilli and mutans streptococci) that live within dental plaque.
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 created are very acidic (they have a pH of 4 and lower). And it's these compounds (primarily lactic acid) that cause tooth demineralization.
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.
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."
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.
Take a look at our diagram to the left. 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.
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 immediately get diluted, buffered, and/or washed away by saliva or the foods and beverages we consume.
It's the acid underneath the plaque that forms 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 that the acid will remain relatively concentrated for an extended period. During this whole time, tooth demineralization will take place.
4) "Young" dental plaque is less harmful than "old" dental plaque.
The amount of tooth damage that bacteria can create after an exposure to sugar is, in part, related to the age of the dental plaque in which they live. (Age = How long a particular glob of plaque has been sitting on a particular location on a tooth.)
Factors such as plaque thickness, its chemical nature, and the types of bacteria living in it all correlate with its age. 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 with an identical exposure to sugar). That's why it's important to brush both thoroughly and frequently.