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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.
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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
intratubula
r 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.
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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.
Tooth development.
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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.
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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.
Составитель – доцент В.В. Бондаренко.