Extracted tooth. Close-up of a lower incisor tooth which has been extracted. The tooth shows areas of plaque and tartar (brown). Dental plaque is a biofilm of bacteria that grows on teeth as a sticky deposit which hardens into yellow or brown tartar. It is associated with dental decay. Teeth may be extracted if they are too decayed or damaged to be repaired, or if they are causing crowding or other problems in the jaw.