When root dentine has formed, Hertwig’s root sheath degenerates allowing adjacent cells from the dental follicle to come into contact with the root dentine. These cells differentiate into cementoblasts. Cementoblasts are cuboidal in shape and form a single layer on the surface of the root dentine. The cementoblasts secrete cementum matrix consisting of amorphous ground substance and collagen fibres. Ground substance is composed of glycosaminoglycans (acid mucopolysaccharides), proteoglycans (glycosaminoglycans and protein bound together) and glycoproteins (protein bound with sugars). Crystallites of hydroxyapatite are deposited in this matrix and mineralisation occurs. During formation, a thin layer of unmineralised cementum is always present on the surface; this is known as cementoid. Once cementogenesis has begun, collagen fibres within the dental follicle orientate themselves into bundles forming the principal fibres of the periodontal ligament. The ends of these fibres become embedded in the developing cementum and alveolar bone and are known as Sharpey’s fibres.