Tooth decay, or dental caries, is caused by prolonged exposure to acids produced by bacteria in the mouth. We cannot avoid bacteria in the air. When we breathe it enters the mouth and attaches itself to everything, including the teeth. In fact, there are more microcosms in one mouth than there are people on the earth.
Sugar is the main culprit in tooth decay, because that is what the bacteria eat. Bacteria then produce acids as a byproduct. Those acids eat at the enamel of our teeth, until hole or cavity in the tooth appears.
Our story begins in the 17th century, when sugar plantations developed in the "new world." Until then food was produced and prepared with much less added sugar. Then the 18th century saw sugar beets being harvested in England. Now, virtually everything we consume, from cereal in the morning to steak and eggs at night contains extra sugar. Bacteria on our teeth count themselves lucky to live in the 21st century, where there is an almost unlimited supply of free food for them to thrive on.
We are in cahoots with sugar and bacteria when we do not brush and clean our teeth. Leaving the bacteria to feed upon sugar and produce acids in our mouths allows the bacteria time to form a visibly organized colony between the gums and the tooth that we call plaque. Plaque actually acts as a cover for the acids that sit on the surface of our enamel. Without cleaning, acids will eat at out enamel almost at will, creating tooth decay and dental caries.
Decay is demineralization. In other words, the outer tissue of the tooth is so hard because it is 95% mineral. The inner tissue of the tooth, dentin, is a little softer because it is only 66% mineral. Normally, saliva is a natural remineralizer when acids have begun demineralizing, but when plaque is involved saliva is almost powerless to repair the damage. Acids will begin with a little hole in the enamel, and once it makes it through to the dentin, it eats the tooth tissue from the inside out. This means serious dental action: fillings, or even a root canal.
With plaque the acid concentration is also higher (Ph 4 or lower), packing a more potent punch through the outer enamel tissue of the tooth. Saliva could take two or more hours to even penetrate the plaque and begin the healing process.
There are a variety of preventative measures to take. I know people who have taken to a no-sweets diet to cut down on their sugar intake. There are many who bring toothpaste and a toothbrush to school or work with them in order to clean after each time they eat. Many more carry floss with them.
May I caution against two things? Please do not depend too heavily on fluoride. Little children who take in too much fluoride, even by swallowing toothpaste accidentally or unwittingly, develop dental flourosis, or yellow and white stains on their teeth in later childhood. Take it in healthy doses.
The second caution is to avoid too much brushing. People who brush excessively or applying too much pressure tear away the gums and expose the roots directly to the acids.
Now, may I suggest two things? Clean frequently and softly by brushing and by flossing. If you can hear the brushing sound as much as the other noise around the house, you are brushing too loudly. With brushing and floss, you don't need to try too hard to eliminate the plaque or the bacteria.
My next suggestion is to carry around gum that is not only sugarless but also supplemented by a natural element called xylitol. Be careful that you choose a gum where xylitol is the leading ingredient. Xylitol fights against the habit bacteria has of settling into tissue to live. Xylitol is a natural bouncer, making cleaning throughout the day easier and cleaning in the morning or at night more thorough.
One transcendent element is sugar. It is almost impossible to escape, and it is not healthy to escape altogether. Though we cannot and should not escape it completely, we can control it and prevent its decaying effects on our teeth.