It is important to leave at least 4 mm-5 mm of gutta percha at the apex of the root canal, even at the expense of a longer post, because it is within the apical 4 mm of the root canal that the apical delta anastomose with the exterior surface of the root. Should these lateral canals not be blocked with the gutta percha and the cement used to place the gutta percha, the chances of microleakage and percolation of microbes are greatly increased, thereby increasing the likelihood of an endodontic failure.