Cementum

Cementum is a bone-like connective tissue that covers the root of the tooth. It is cream in colour.  The cementum is a very thin layer covering the dentine.  The dentine forms the bulk of the tissue within the tooth root. If the gum recedes from the tooth, then cementum is exposed, this cementum is easily worn away thus exposing the underlying dentine*.    
^{*Patients feel a sharp sensation when brushing the teeth or eating cold or sweet food. This may be referred to as having ‘sensitive teeth’ and is usually an adult condition.}

Cementum is also responsible for anchoring the periodontal ligament to the tooth which in turn anchors the tooth to the alveolar bone (jaw).