The easiest way to prevent a cavity is to make sure your enamel is the strongest it can possibly be. There are a few ways to do this. The most well known enamel hardener is fluoride. It's in toothpaste and some mouth rinses that consumers can buy over-the-counter and there are professional fluoride treatments that can be provided at your dentist office.
Fluoride is a naturally occuring mineral that is found in most water supplies in the U.S. However, there is usually not enough fluoride in the water to be beneficial to the teeth and in rare instances there can be too much of the mineral in the water making it non-drinkable. In order to provide a therapeutic level in deficient counties or remove harmful high levels of fluoride, there is a fluoridation movement to provide safe drinking water that will help prevent tooth decay. For oodles of information about fluoride you can visit the Centers for Disease Control website. http://www.cdc.gov/fluoridation/index.htm
The greatest new developments in dentistry lately are the new generation enamel remineralizers. In simple words it helps to repair enamel that has been challenged by plaque and acid.
The names of these wonder enamel repair products are Recaldent™, Nova Min™, and Amorphous Calcium Phosphate (ACP)™. They can be found in toothpaste, chewing gum, professional polishing pastes, and products that are applied to the teeth by your dentist or hygienist. A simple Google search of these products can tell you where to find them.
If you would like a lot more information on what these products do, simply follow the link below for an article on tooth remineralization.