The root formation begins as an extension of the inner and outer dental epithelium in the cervical loop region which fence a bilayer structure called Hosting's epithelial root sheath.

It takes place as the crown is completely shaped & the tooth begins to erupt.

The cervical loop begins to grow down into the dental sac and forms HERS.

It grows down to encompass all but the basal portion of the pulp.

The sheath shapes the root and induces dentin formation, in the root area by the odontoblasts of dental papilla.

Hence dentin and cementum are formed and as the root lengthens the crown moves occlusally.