RADIOGRAPHIC AND HISTOLOGICAL METHODOLOGIES IN ESTIMATING THE CHRONOLOGY OF CROWN DEVELOPMENT IN MODERN HUMANS AND GREAT APES - A REVIEW, WITH SOME APPLICATIONS FOR STUDIES ON JUVENILE HOMINIDS

There has been a burgeoning of interest in the last decade on growth s tudies in hominids. These studies have relied heavily on dental develo pment, and have compared juvenile hominids to modern human and ape sta ndards, which are usually established using radiographic data. There h as been considerable discussion on the most appropriate methods of der iving population standards from radiographs, but very little on the ac curacy of the radiographic image itself Previous histological and diss ection studies have shown that age at onset of mineralization is overe stimated, and age at crown completion is underestimated using radiogra phs. This study considers the process of X-ray absorbence by mineraliz ed tissues and the formation of radiographic images of developing teet h. Following tooth initiation a critical mass of mineral is required f or the tooth to register superimposed on the absorbence of alveolar cr ypt bone, which accounts for the late identification of tooth initiati on. Determination of completion of crown growth depends upon the ident ification of the last formed enamel at the cervix. Recognition of this key stage is difficult as crown growth slows towards the cervix, and the last secreted enamel may take months to attain full mineralization levels due to the prolonged maturation process. Morphological and geo metric factors have a significant influence on the imaging of the comp leted crown. The last formed enamel is located on the buccal face, whe re enamel thins progressively to nothing. X-ray absorption by enamel a t the cervix becomes insignificant, and may be counterbalanced by incr eased dentine absorption. Approximal enamel in contrast is clearly vis ualized once maturation is complete. However, developmentally this ena mel face initiates later, and is completed much earlier than buccal en amel. All of the radiographic estimates of crown completion times are based upon interpretations of approximal enamel completion. These cons iderations suggest that the human population standards in current usag e may not represent true anatomical and chronological stages of crown development, and care should be taken in referring juvenile hominids t o these radiological standards. (C) 1998 Academic Press.