Periodontitis is an advanced gum infection. It involves germs in the pocket between the gums and the tooth. The germs can start to destroy tissue and bone. If this is not treated, the germs may go deeper and cause periodontitis. You can lose bone and teeth if this problem becomes very serious. Not caring for your teeth properly is the main cause of periodontal disease. Other conditions like smoking or diabetes may increase your risk of periodontitis. Poorly-fitting dental crowns and fillings may also cause periodontitis. Good teeth and mouth care may help prevent this problem.