It's An Infection.
Millions of bacteria swim around in our mouths. Many of them are harmless, and some are even beneficial. But a few love nothing more than to eat away at the hard and soft tissues of the mouth. Like all living creatures, they need an energy source. Sugars are their snack of choice, and they use simple carbohydrates from our diet to manufacture energy.
Like all living creatures making energy, they also produce waste. These acidic wastes deposited on the teeth erode the hard surfaces, weaken the enamel, and form holes known as cavities.
Some bacteria produce a toxic waste that causes bleeding gums, and the destruction of bone around the teeth, which is called periodontal disease. Periodontal disease is the leading reason people lose their teeth and end up with dentures.