By Rebecca Ferrell Thomas
Doctor of Philosophy, The Pennsylvania State University, May (2003)
Abstract: Accentuated striae (AS) are developmental defects in tooth enamel that form during periods of physiological stress, and have been used in skeletal studies to measure stress and health levels in past populations. However, the assumption that the presence of AS necessarily indicates poor health has not been sufficiently tested. This project builds on past research by investigating the relationship between AS and age at death, since the presence of more AS in younger individuals (those with a higher risk of dying) would support the relationship between AS and poor health. Analytical improvements for testing this relationship include a focus on individuals as the unit of analysis and the use of survival analysis, which corrects for some skeletal sample biases and allows for both juveniles and adults to be included. “Weak” and “strong” AS in permanent teeth from 85 medieval Danish skeletons (ages at death: 0-30 years) are identified in digital images of tooth thin sections and developed into individual defect chronologies using daily and long-period increments in enamel. Chronologies span the period from birth until death or canine crown completion, whichever occurs first. Survival analysis is used to test the relationship of AS in different periods of childhood to the risk of dying at subsequent ages. Weak AS occurring before age seven predict a lower risk of dying after age seven while strong AS show the opposite pattern.
It could be that weak AS indicate “good” stress and should be distinguished from strong AS when trying to measure health for past populations. Strong AS occurring just between ages two and four are predictive of a lower risk of dying in that age interval, an example of the complex patterns of mortality selection during childhood. Research is needed to determine whether these patterns are population-specific; if populations vary in the ages of AS formation that are negatively and positively related to current or subsequent risk of dying, future comparisons of AS across populations will need to take this into account. The implications that these findings have for future enamel defect research and for interpreting health in medieval Denmark are discussed.