Figure 4b. (a) Illustration of normal tooth anatomy. A = apical foramen, C = cementum, D = dentine, E = enamel, G = gingiva, L = lamina dura, N = neurovascular bundle, P = periodontal ligament, Pc = pulp chamber, R = root canal. (b) Illustration of dental caries (curved solid arrow), which allow bacteria to enter the pulp chamber and travel down the root canal to the apical foramen (arrowhead), where a periapical radiolucency develops (open arrows). Note how increased pressure from pulpitis compromises the blood supply to the tooth (straight solid arrow), rendering it nonvital. (Reprinted, with permission, from reference 8.)