Longitudinal analysis of the microscopic dental enamel defects of children in the Imperial Roman community of Portus Romae (necropolis of Isola Sacra, 2nd to 4th century CE, Italy)

Infants in a skeletal population are important proxies of an ancient society's adaptation and well-being. This study uses microscopic dental enamel defects (Accentuated Retzius Lines, ALs) to provide a close-to-longitudinal and detailed estimate of the non-fatal stress prevalence in the first years of life in the community of Portus Romae (necropolis of Isola Sacra, 2nd to 4th century CE, Italy). Eighty-four teeth, 17 deciduous and 67 permanent, from 18 individuals were selected for histological thin sectioning. We scored and assessed the individual chronology of ALs across dental sets, by matching homologous intervals between ALs on several teeth in the same individual. After a steep increase following the 3rd month, AL prevalence distribution shows a maximum between the 9th and 11th month of life. Following the prevalence maximum, the distribution declines steadily until the 25th month, after which it remains almost stable. The ALs frequency by tooth type shows that the bulk of affected enamel is in the center of the tooth crown, with the apical and cervical portions less susceptible to recording stress. Our results illustrate how to derive a longitudinal profile of health status in the childhood segment of an ancient population through histomorphometry. Comparison of the ALs profile with the previously published δ15N and δ13C of Portus Romae and the application of a Bayesian statistical model allowed us to relate the prevalence maximum to the beginning of the weaning process. A multifactorial approach to the palaeobiology of a skeletal series is therefore rewarding and allows correlation with the biological life history of children in this ancient Roman Imperial community.