Smoking is the main reason why people have gum disease today. The study shows that our oral health has become worse over the past 2,000 years. Gum disease could start going down if more people stop smoking. A researcher said: "As smoking declines…we should see a decline in the [numbers of people with] the disease." Gum disease is because bacteria build up in your mouth. The bacteria attack your gums and can make your teeth fall out. People can lower the risk of gum disease by regular brushing, using mouthwash and not smoking.