HISTOLOGICAL STUDY ON THE CHRONOLOGY OF THE DEVELOPING DENTITION IN GORILLA AND ORANGUTAN

The single previous study on tooth development in great apes (Dean and Wood: Folia Primatol. (Basel) 36:111-127, 1981) is of limited value because it is based on cross-sectional radiographic data. This study considers problems in defining stages of tooth development in radiographs of developing ape dentitions and provides data on tooth chronology in Pongo pygmaeus and Gorilla gorilla by using histological methods of analysis. Crown formation times were estimated in individual teeth, and an overall chronology of dental development was found by registering teeth forming at the same time by using incremental growth lines. The earlier radiographic study correctly identified the molar and second premolar chronology and sequence in great apes, but significantly underestimated crown formation times in incisors, first premolars, and canine teeth in particular. Ape anterior tooth crowns take longer to form than the equivalent human teeth, but the overall dental developmental period in great apes is substantially shorter than in humans. Gorilla root extension rates appear to be fast, up to approximately 13-mu-m/day. This rapid root growth, associated with early tooth eruption, appears to be the developmental basis for the observed differences in timing between developing dentitions in great apes and humans.