In anatomy the apical foramen is the opening at the apex of the root of a tooth, through which the nerve and blood vessels that supply the dental pulp pass. Thus it represents the junction of the pulp and the periodontal tissue. The average size of the orifice is 0.3 to 0.4 mm in diameter. There can be two or more foramina separated by a portion of dentin and cementum or by cementum only. If more than one foramen is present on each root, the largest one is designated as the apical foramen and the rest are considered accessory foramina. It is a point of interest in endodontics, as it is considered necessary to thoroughly chemomechanically debride the pulp space to remove all necrotic tissue and minimise bacterial load in the pulp space. Ideally this debridement would terminate exactly at the apical foramen. In reality determining the exact position of the apical foramen is problematic, requiring radiography and/or use of an electronic apex locator to produce a refined estimate. A tooth may have multiple small accessory canals in the root apex area forming an apical delta which can complicate the endodontic problem. An apical constriction is often present. In immature teeth the root is not fully formed leading to an open apex. This is also seen in some pathological teeth.