The neonatal line (NNL) of tooth is darker and larger than the rest of the striae of Retzius and presents in all deciduous teeth and in 10% of permanent teeth, which undergo mineralization in the prenatal time. This is the first hypomineralized layer of enamel down after birth. NNL expands from enamel–dentine junction of the cervical region of the tooth, separating time before birth and after birth. In forensic odontology, the NNL can be used to determine whether a child died before or after birth and to estimate how long a child lived after birth.