Figure 1511

Diagram showing the cellular relationships during enamel formation.

In the initial secretory stage, dentin is produced first by odontoblasts. Enamel matrix is then deposited directly on the surface of the previously formed dentin by secretory-stage ameloblasts. The secretory-stage ameloblasts continue to produce enamel matrix until the full thickness of the future enamel is achieved. (Adapted from Schour I. The neonatal line in the enamel and dentin of the human deciduous teeth and first permanent molar. J Am Dent Assoc 1936;23:1946. Fig 2. Copyright © 2002 American Dental Association. Adapted 2002 with permission of ADA Publishing, a Division of ADA Business Enterprises, Inc.)

highly heterogenous. It contains proteins encoded by a number of different genes. The principal proteins in the extracellular matrix of the developing enamel are

• Amelogenins, important proteins in establishing and maintaining the spacing between enamel rods in early stages of enamel development

• Ameloblastins, proteins produced by ameloblasts from the early secretory to late maturation stages. Their function is not well understood; however, their developmental pattern suggests that ameloblastins play a much broader role in amelogenesis than the other proteins, and they are believed to guide the enamel mineralization process by controlling elongation of the enamel crystals.

• Enamelins, proteins distributed throughout the enamel layer. These enamel proteinases (ameloproteases-I) are responsible for degradation of amelogenins in maturing enamel.

• Tuftelins, acidic enamel proteins located near the denti-noenamel junction that participate in the nucleation of enamel crystal. Tuftelins are present in enamel tufts and account for hypomineralization; i.e., enamel tufts have a higher percentage of organic material than the remainder of the mature enamel.

The maturation of the developing enamel results in its continued mineralization, so that it becomes the hardest odontoblasts

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