back teeth can be plaque

As everyone who brushes and flosses their teeth knows, your back teeth are harder to reach and to keep clean than your front teeth. The back teeth are designed with grooves and ridges that help you to chew food, but the down side is that these grooves and ridges can also collect tiny food particles, which can increase the risk of cavities and bacteria in plaque, which in turn can lead to gum disease.
To remove bacteria and plaque, it's important to floss around the back teeth. If it is hard for you to reach this area, consider using a flosser or an electric flosser. 
Tooth decay doesn't happen overnight. But if you allow plaque to build up on teeth by not flossing properly over many years, the bacteria and acids that they produce will break down the tooth enamel. If plaque goes unremoved, tooth decay can progress inward and affect the nerves in the pulp of the tooth. This progressive decay can cause symptoms including pain and swelling, and may result in tooth loss in extreme cases.
Bacteria can convert fermenting carbohydrates (which are sugars and are found in cooked starchy foods) into plaque within 20 minutes. Be sure to clean around the back teeth with your toothbrush and dental floss every day.

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