TOOTH.

1. Enamel. Chemically it is composed of: a) 95% inorganic substances –crystals of hydroxyapatities Ca10(PO)6(OH)2, b) 1,2% organic substances –proteins enamelins and amelogenins, c) 3,8% -water.

Microscopic structure. After eruption cells, nerves and vessels –are absent.
Enamel is composed of enamel prisms (or rods). Each prism has keyhole shape (on cross section) and S-shape (on longitudinal section). Prism within presented by enamelin fibrills, that infiltrated by crystals of hydroxyapatities.

2. Dentin. Chemically it is composed of: a) 70% – crystals of hydroxyapatities, b) 25% organic substances – collagen fibres, c) 5% -water. Microscopic structure. Cell bodies, nerves and vessels – are absent.

Dentin is composed of 2 components: a) noncalcified portion – dentinal tubules (or intratubular dentin) and b) calcified intertubular dentin. Dentinal tubule contains: a) process of odontoblast and b) tissue fluid. Intertubular dentin is composed of collagen fibres, that infiltrated by crystals of hydroxyapatities. It corresponds to calcified extracellular matrix.

3. Cementum. Chemically it is composed of: a) 50% –crystals of hydroxyapatities, b) 45% organic substances – collagen fibres, c) 5% - water. 2 types of cementum: a) cellular cementum, b) acellular cementum. Cellular cementum is composed of: a) cells, named cementocytes and cementoblasts, and b) calcified extracellular matrix. Cementocyte is star-shaped cell, located in cavity, named lacuna. Acellular cementum is composed of calcified extracellular matrix only. It means - collagen fibres, that infiltrated by crystals of hydroxyapatities. Cellular cementum covers root completely. Acellular cementum locates in apical one third of root only.

PULP. It is composed of loose irregular connective tissue (l.i.c.t.). Pulp has 4 layers (from centre to external): a) pulp core – l.i.c.t. proper with abundance of vessels, nerves, proteoglycans and glycosaminoglycans, b) cell-rich zone – l.i.c.t. proper with abundance of cells: fibroblasts, macrophages, lymphocytes, c) cell-free zone - contains subodontoblastic capillary plexus, d) odontoblastic zone - contains single layer of odontoblasts bodies.

1. CAP stage. It has 3 components: a) epithelial three-layered enamel organ – it has shape of cap. Enamel organ originates from ectoderm, b) dental papilla- it is mesenchyme, surrounding concave surface of enamel organ, c) dental sac- it is mesenchyme, surrounding convex surface of enamel organ. Enamel organ and surrounding mesenchyme collectively – is tooth germ.
2. BELL stage and HISTOGENESIS. It has four- layered enamel organ. Inner enamel epithelium becomes tall columnar and differentiates into ameloblasts. It are columnar cell, which composed of cell body and apical Thomes process. Ameloblasts are enamel-producing cells. It means: ameloblast secretes proteins enamelins and amelogenins. They form organic matrix of future enamel. Later, cells calcify that proteins. More later, ameloblasts calcify itself. Before tooth eruption ameloblasts are calcified completely and 4 calcified cells give rise 1 enamel prism .After eruption enamel presented by prisms ONLY. Enamel development – is enamelogenesis.

Dentin development – is dentinogenesis. It means: outer layer of mesenchyme of dental papilla differentiates into odontoblasts. They are dentin-producing cells. Odontoblasts are columnar cell, which composed of cell body and apical Thomes process. Cells secrete collagen and collagen fibres form organic matrix of future dentin. Later, cells calcify collagen fibres, resulting in formation of calcified intertubular dentin. Dentinal tubules are calcified never.
Cementum development – is cementogenesis. It means: inner layer of mesenchyme of dental sac differentiates into cementoblasts. They are cementum-producing cells. Cells secrete collagen and collagen fibres form organic matrix of future cementum.. Later, cells calcify collagen fibres, resulting in formation of calcified extracellular matrix.
Ectoderm: ameloblast –- enamel.  Inner layer of mesenchyme of dental sac – cementoblast – cementum. Outer layer of mesenchyme of dental papilla – odontoblast – dentin. Inner layer of mesenchyme of dental papilla – fibroblast – dental pulp.