The two main categories of periodontal disease are gingivitis and periodontitis. In most cases gingivitis proceeds periodontitis. These type of diseases affect the periodontal tissues which are the tissues that support the teeth. Inflammation and infection break down destroying the gums which can cause teeth to fall out.
Brushing your teeth regularly will help keep you from getting periodontal disease, however, almost everyone has some stage of gingivitis. Your gum tissue is subject to bacteria constantly. Some of this bacteria is collected into plaque which adheres to your teeth and can aggravate your gum tissue. Plaque is hard to get off with a tooth brush. That is why you need to have a dentist scrape of the plaque with special dental tools.
Severe periodontal disease can lead to other serious health problems such as heart disease, stroke and respiratory disease.