Tooth decay and gum disease are caused by plaque, a sticky combination of bacteria and food. Plaque begins to build up on teeth within a few minutes after eating. If teeth are not cleaned well each day, plaque will lead to tooth decay or gum disease. If you do not remove plaque, it turns into a hard deposit called tartar that becomes trapped at the base of the tooth. Plaque and tartar irritate and inflame the gums.