July
August 2007
enamel varies in thickness over the surface of the tooth and is often thickest at the cusp, up to 2.5 mm, and thinnest at its border, which is seen clinically as the cementoenamel junction (CEJ).
enamel's primary mineral is hydroxyapatite, which is a crystalline calcium phosphate.
the large amount of minerals in enamel accounts not only for its strength but also for its brittleness.
dentin, which is less mineralized and less brittle, compensates for enamel and is necessary as a support.
unlike dentin and bone, enamel does not contain collagen.
instead, it has two unique classes of proteins called amelogenins and enamelins.
while the role of these proteins is not fully understood, it is believed that they aid in the development of enamel by serving as framework support among other functions.
dentin is the substance between enamel or cementum and the pulp chamber.
it is secreted by the odontoblasts of the dental pulp.
the formation of dentin is known as dentinogenesis.
the porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water by weight.
because it is softer than enamel, it decays more rapidly and is subject to severe cavities if not properly treated, but dentin still acts as a protective layer and supports the crown of the tooth.
dentin is a mineralized connective tissue with an organic matrix of collagenous proteins.
dentin has microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border.
although they may have tiny side-branches, the tubules do not intersect with each other.
their length is dictated by the radius of the tooth.
the three dimensional configuration of the dentinal tubules is genetically determined.
it is approximately 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly collagen) and 22% water.
cementum is excreted by cementoblasts within the root of the tooth and is thickest at the root apex.
its coloration is yellowish and it is softer than either dentin or enamel.
the principle role of cementum is to serve as a medium by which the periodontal ligaments can attach to the tooth for stability.
at the cementoenamel junction, the cementum is acellular due to its lack of cellular components, and this acellular type covers at least ⅔ of the root.
the more permeable form of cementum, cellular cementum, covers about ½ of the root apex.
this tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root.
along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin.
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