The root of a tooth develops after the crown is completed. The inner and outer enamel epithelium proliferate to form Hertwig's root sheath, which consists of two epithelial layers that bend to form a disc-like structure called the epithelial diaphragm. As the root sheath lengthens at the angle of the diaphragm, it induces the dental papilla cells beneath it to differentiate into odontoblasts, which then go on to form the root dentin. In multi-rooted teeth, the epithelial diaphragm develops extensions that divide the root into two or three parts. After dentin formation, the epithelial root sheath breaks down and its remnants become epithelial rests of Malassez