What are tooth plaque and tooth decay? Plaque is a creamy, sticky coating of germs (bacteria) that collects on everybody's teeth every day. The germs won't harm you, but they can harm your teeth. Tooth decay is caused by acid from the bacteria (plaque acids), which can cause a hole (cavity) in the enamel of your tooth. Tooth decay may make your tooth ache. If this happens you need to see a dentist, who may have to clean the hole and put a filling in the tooth to repair it.