ALSPAC is a population-based birth cohort study consisting of 14 541 women and their children recruited in the county of Avon, UK, in the early 1990s (52). Both mothers and children have been extensively followed from the eighth gestational week onwards using a combination of self-reported questionnaires, medical records and physical examinations. Biological samples including DNA have been collected from the participants. Ethical approval was obtained from the ALSPAC Law and Ethics Committee and relevant local ethics committees, and written informed consent provided by all parents. Tooth eruption phenotypes of the children were derived from questionnaires completed by the mothers and included items regarding the ‘age at first tooth’ (assessed at 15months) and the ‘number of teeth’ in the child's mouth (at 15 months).
