Counting them from a known reference point allows researchers to calculate how long a particular period of tooth formation took.

This technique, called dental histology, can tell researchers not only how long a tooth took to form but also whether there were periods of stress during development — marked by disruptions in the growth pattern called hypoplastic defects.

These defects, visible as horizontal lines or grooves on the tooth surface, can indicate periods of illness, nutritional stress, or other physiological disruption during childhood.

For Neanderthals, dental histology has provided some of the most precise life-history data available from the fossil record.