Diachronic Variation in Daily Secretion Rates of Human Dental Enamel

Human dental enamel is a valuable biological record for reconstructing ontogenetic trajectories and physiological stress prevalence in humans. This study investigates the variation in dental enamel daily secretion rates (DSRs, i.e. the daily rate of enamel secretion along the enamel prisms) of first permanent molars in the Roman Imperial period, comparing them with the values available in literature for the same period and for contemporary individuals. Few studies so far have reported a diachronic variation in DSRs: One study suggested a decrease in prenatal DSRs of deciduous incisors between Imperial Roman and contemporary individuals, while another highlighted a diachronic decreasing trend in first permanent molar DSRs in Britain. By examining variations in DSRs, this research aims to investigate possible developmental trends over time. Fifty-nine first permanent molars dated to Roman Imperial time from the necropolises of Isola Sacra, Centocelle, and Castel di Guido (Rome, Italy); Velia (southern Italy); Civitanova Marche, Urbino, Porto Recanati, and Villarey (central Italy) have been analysed. Histomorphometric assessments on thin sections of the dental crowns allowed quantification of enamel incremental markers to calculate the DSRs. Results reveal variability in DSRs among Roman Imperial samples. Comparisons with published Roman Imperial and contemporary datasets yield statistically significant differences in mean values, showing a decreasing trend in infants’ growth trajectories through time. The lateral inner enamel DSR shows a significant difference among the means of the necropolises, while for the cuspal inner enamel DSR means remain similar. This research underscores the importance of understanding the regional and temporal variation in enamel growth dynamics and the interplay of biological and environmental factors shaping dental ontogeny. Further studies involving larger datasets from different geographic and chronological horizons are needed to refine interpretations of diachronic changes in human enamel development and their implications for recent human evolution.