Dental plaque is a biofilm that forms on teeth. It progresses from an initial bacterial coating to a mature biofilm with complex microbial communities. Early plaque is predominantly gram-positive cocci while mature plaque contains more gram-negative rods and anaerobes. Plaque composition changes with periodontal disease, shifting from gram-positive to gram-negative and non-motile to motile organisms. Plaque initiates periodontal diseases through its noxious metabolic byproducts and through stimulating the host immune response, ultimately leading to tissue destruction if left unchecked.