Gum (periodontal) disease is caused by bacteria. These bacteria, if left along the gum line, will irritate the gums and cause an inflammation reaction. The gums then begin to bleed and swell allowing the bacteria to go deeper under the gum line. If the inflammation is allowed to continue, the bone will begin to demineralize and dissolve. As the bone dissolves around the teeth, the teeth become unsupported and will fall out. Unfortunately, pain does not occur until the final stages of the disease and treatment at that time has very little chance of being successful. If your gums bleed regularly, seek treatment as soon as possible.