Variation in the developing root cone angle of the permanent mandibular teeth of modern man and certain fossil hominids.

The radiographic appearance of the developing root apex of 461 mandibular teeth was studied using ellipsopantomographs of 77 individuals. The angle formed by the mesial and distal aspects of the developing root cone was measured for each quarter of root development in the permanent mandibular teeth of each subject. Large values for this angle in the more coronal part of the root gradually decreased towards the root apex where values were small in all teeth studied. This gradual decrease in the angle of the developing root cone is concordant with the faster increase in root length but slower rates of dentinogenesis reported for the apical region of human teeth in the literature, as the decrease is likely to reflect the increasing numbers of odontoblasts that become involved in root formation as it proceeds apically. The developing root cone angles of one of the five fossil hominid specimens studied (KMN-ER 820) fall outside the range for the developing root cone angle of the developing premolar and permanent second molar roots in modern Homo sapiens and is evidence of a faster rate of root elongation than is typical for modern man.