Cavities are what you get from tooth decay — damage to the tooth. Tooth decay can affect both the outer coating of a tooth (called enamel) and the inner layer (called dentin).
What causes decay? When foods with carbohydrates like bread, cereal, milk, soda, fruit, cake, or candy stay on your teeth. The bacteria in your mouth turn them into acids. The bacteria, acid, food debris, and your saliva combine to form plaque, which clings to the teeth. The acids in plaque dissolve the enamel, creating holes called cavities.
Who Gets Cavities?
Many people think only children get cavities, but changes in your mouth as you age make them an adult problem, too. As you get older, your gums pull away from your teeth. They can also pull away because of gum disease. This exposes the roots of your teeth to plaque. And if you eat a lot of sugary or high-carb foods, you’re more likely to get cavities.
Older adults sometimes get decay around the edges of fillings. Seniors often have a lot of dental work because they didn’t get fluoride or good oral care when they were kids. Over the years, these fillings can weaken teeth and break. Bacteria gather in the gaps and cause decay.
How Do I Know If I Have One?
Your dentist finds cavities during a regular dental checkup. He’ll probe your teeth, looking for soft spots, or use X-rays to check between your teeth.
If you’ve had a cavity for a while, you might get a toothache, especially after you eat or drink something sweet, hot, or cold. Sometimes you can see pits or holes in your teeth.
How Are They Treated?
Treatment depends on how bad the cavity is. Most often, the dentist removes the decayed portion of your tooth with a drill. He fills in the hole with a filling made of either silver alloy, gold, porcelain, or a composite resin. These materials are safe.
Some people have raised concerns about mercury-based fillings called amalgams, but the American Dental Association, the FDA, and other public health agencies say they are safe. Allergies to fillings are rare.
Crowns are used when a tooth is so badly decayed that not much of it remains. Your dentist removes and repairs the damaged part. He fits a crown made from gold, porcelain, or porcelain fused to metal over the rest of the tooth.
You might need a root canal if the root or pulp of your tooth is dead. The dentist removes the nerve, blood vessels, and tissue along with the decayed portions of the tooth. He fills in the roots with a sealing material. You may need a crown over the filled tooth.
Source of article from here: http://www.webmd.com/oral-health/guide/dental-health-cavities