Plaque is a sticky substance that adheres to tooth structure and is teeming with bacteria. Over time, plaque becomes calcified (hardens) and at this stage, it becomes what is called calculus. Plaque and calculus are actually irritants to the tissues of your mouth. The reaction of your body to the irritants and the subsequent gum inflammation, gum recession, bleeding and eventual bone loss around the teeth constitute periodontal (gum) disease. The earliest stage of periodontal disease is called gingivitis (which is reversible) and is characterized by bleeding gums, especially when one brushes and flosses. If the disease is not addressed, it will progress to periodontitis, which is far more destructive, and is characterized by further gum deterioration, bone loss, and ultimately tooth loss.