Dental hard tissue is mineralised and enamel is made out of prisms or rods. The diameter of the rods is about 4 μm. The chemical composition of the rods is Calcium Hydroxyapatite – Ca10(PO4)6(OH)2. Enamel gradually gets thinner toward the root and terminates at the cervical line.
Cementum is the yellowish external surface of the anatomic root, covering the dentin. The composition of cementum is: 65% calcium hydroxyapatite (inorganic calcified substance), 12% water and 23% organic matter – collagen fibers. The thickness of the cementum layer is lowest near the CEJ, no more than 50-100 μm.
The periodontal fibers, connecting the root to the (jaw) alveolar bone are incorporated into the cementum. The CEJ is the transitional zone between the enamel of the crown and the cementum of the root.
Dentine is the basic, mostly inorganic, calcified substance of a tooth. It is a hard yellowish tissue underlying the enamel and cementum, making up the major bulk of the tooth.
The dentin is not visible – except on radiographic images or when the enamel is worn out, or on cross-sectional slices for microscopic examination.
The composition of Dentine is: 70% calcium hydroxyapatite (inorganic calcified substance), 12% water and 18% organic matter – collagen fibers. The dentin is composed of a great number of dentine tubules – 65 000/mm² near the pulp and 15 000- 20 000/mm² near the CEJ.
The Pulp is the soft non-calcified tissue in the pulp chamber – the cavity in the centre
of the crown and root.
The pulp is completely surrounded by dentin, except the root
apex. It is composed of loose connective tissue, fibroblasts, blood vessels for an
abundant, rich blood supply, and a great number of nerve endings, penetrating the pulp through the root apex.
The ground substance consists of water, carbohydrates and proteins. An important component of the pulp is the undifferentiated mesenchymal cells that serve to replace injured or destroyed odontoblasts – a repairing (regenerative) function of the pulp.
Functions Of The Pulp
– forming function – at the borderline to the dentine there are cells named odontoblasts. These cells produce new dentin throughout the whole lifetime. It is named secondary dentin.
The odontoblasts have cytoplasm processes penetrating into the dentin tubules. That’s why the dentin is extremely sensitive to mechanical, physical and chemical irritating factors – they are directly transferred by the odontoblast processes to the nerve endings into the pulp.
The sensory function – this means strong sensitivity to hot, cold, sweet, tooth decay, instrumental preparation for treatment, trauma, infection, etc.