Cementum

Cementum is the hard outside layer of a tooth root. It is not present in the crown (part above the gums) portion of a tooth. Cementum allows periodontal ligaments to attach onto it, allowing tooth to be connected to the maxilla or mandible.
Composition.
Cementum is made up of
Development.
The process of creating cementum is called cementogenesis. It is made by special type of cells known as cementoblasts. Cementoblasts are found on the surface of the cementum. When a cementoblast is no longer on the surface, or when it is found surrounded by cementum, it is then known as a cementocyte.
In contrast, cementoclasts are special cells that remove cementum instead of making cementum.
Cementoenamel junction.
The cementoenamel junction, or the cervical line, is the where enamel and cementum meet. The cementum and enamel may meet in different ways.
Types.
Cementum can be divided into two main types based on its location and whether it has cells or not.