Tooth decay bacteria. Artwork of tooth decay bact- eria on a tooth. The image on the left shows the bacterial coating (plaque, black globules) on the dentine (pink) of a tooth's neck. The neck is embedded in the gum (gingiva, red, far left). The tooth's root is attached to the jawbone (porous, beige) by cementum (blue strands). At top is the hard covering (enamel, dark yellow) of the tooth's crown. The image on the right shows the plaque close-up. It consists of bacteria (blobs) within a layer (buff-coloured) of salivary mucus & food particles. Acids produced by the bacteria whilst digesting food cause tooth decay (dental caries) & gum inflammation (gum disease or gingivitis).