What is plaque and why is it bad for your teeth?

Film of bacteria: Plaque is a film of bacteria stuck to the outside surface of your teeth. Bacteria produce acid, which demineralizes your teeth and causes decay. Acid also irritates the gums and the irritation can result in periodontal disease. Left on long enough, it hardens into calculus, which gives you bad breath. Hope this info helps.

Bacterial coating: Dental plaque is a biofilm, usually a pale yellow, that develops naturally on the teeth. It is formed by colonizing bacteria trying to attach themselves to the tooth's smooth surface. It can give rise to dental caries (decay)—the localized destruction of the tissues of the tooth by acid produced from the bacterial degradation of fermentable sugars and periodontal problems such as gingivitis.