Effect of the birth process on the neonatal line in primary tooth enamel.

The neonatal line is a histologic landmark in primary tooth enamel corresponding to the event of birth. The average width of the neonatal line (NNL) in primary tooth enamel of 147 children was measured. In children with normal birth histories the width of the NNL was found to be 11.9 +/- 4.8 microns. It was wider (18.6 +/- 5.7 microns) in children born by difficult operative delivery and thinner (7.6 +/- 1.5 microns) in children born by Caesarean section. The data suggest that concomitant with the change from intrauterine to extrauterine environment, the birth process itself also contributes to the width of the NNL.