The neonatal line (NNL) is an accentuated line visible in the enamel and dentine of primary teeth and in some of the cusps of the first permanent molars. It corresponds to the physiological stress associated with the event of birth. This study aimed to investigate the characteristics of the NNL, its relationship with prenatal and postnatal enamel, its correlation with health and life data of both contemporary and ancient individuals, and its potential to differentiate the prenatal from postnatal origin of enamel defects to better understand the life conditions of mother and child.

Following PRISMA guidelines and using the PICO framework, a systematic review was conducted across MEDLINE, Scopus, DOSS, and Google Scholar covering literature from 1937 to 2023.

A total of 1420 references were identified, from which 32 studies met the inclusion criteria. The selected studies examined the impact of maternal factors, perinatal conditions and gestation on the NNL. The width of the NNL varied according to maternal health and birth conditions. The NNL was also a marker of birth viability, with its presence indicating a live birth. Lastly, dietary shifts around birth were observed through variations in the perinatal enamel strontium/calcium ratio.

This study highlights the value of the NNL in reconstructing early life history by linking maternal health, prenatal and postnatal stress, and enamel development. Further research on the relationship between hypomineralized lesions in pathological enamel and the NNL could help identifying early (i.e., in utero or perinatal) risk factors.