Britannica Sources used in this answer

Why do primary teeth fall out as permanent teeth grow in?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A labeled cross section illustration of an adult human molar shows the tooth's crown and root, with layers including enamel, dentin, and pulp, as well as gum, cementum, blood vessels, periodontal ligament, lateral canals, and nerve. — tooth Cross section of an adult human molar.

Primary teeth, also known as deciduous teeth, fall out because their roots are resorbed as permanent teeth grow and push toward the mouth cavity. This process is a natural part of human development, as humans possess two successive sets of teeth during their lifetime.1

While primary teeth are smaller and have more delicate roots, the permanent teeth eventually emerge to replace them, with the exception of the adult molars, which erupt behind the primary teeth. The shedding of the primary dentition typically begins around age 5 or 6 and is completed by age 13.1