Dental plaque and tartar (dark brown) on teeth. Tartar (calculus) is a calcified deposit that is formed on tooth surfaces. It hinders the cleaning of teeth. Plaque is the main cause of tooth decay. It is a sticky coating that consists of saliva, bacteria and particles of food. The bacteria feed on the sugars in food, producing acid as a waste product. This acid can corrode the enamel coating of the teeth, resulting in tooth decay (dental caries). Regular toothbrushing removes plaque and prevents caries.