hello Cavities are also called dental caries, and if you have a cavity, it's important to get it repaired. But why would your tooth develop a hole? Blame plaque. That's a sticky, slimy substance made up mostly of the germs that cause tooth decay. Bacteria – tiny colonies of living organisms are constantly on the move on your teeth, gums, lips and tongue. Having bacteria in your mouth is a normal thing. While some of the bacteria can be harmful, most are not and some are even helpful. on the tooth.This film is called plaque, and it's what causes cavities. 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. Please consult a dentist nearby in person..