Biomedical Engineering Reference
In-Depth Information
Figure 8-1. Schematic illustration of enamel hierarchical structure (modified from Nanci 22 ),
and SEM images of different faces. (R: rod; IR: interrod).
2.2. Formation and structure of dentin
As with enamel, the formation of dentin starts with the activation of
cells, namely odontoblasts. As the dental mesenchyme cells begin to
differentiate into odontoblasts, they begin to secrete several molecules
that promote mineralization of the extracellular matrix. These proteins
include tenascin, bono-1, dental sialophosphoprotein, and alkaline
phosphatase. 23 Finally, as the odontoblast phenotype emerges,
osteonectin and type I collagen are secreted as components of the
extracellular matrix and form an approximately 10-30 μm wide
unmineralized zone between the mineralized dentin and odontoblasts,
namely predentin. Thus, totally different to that of enamel, the
mineralization pattern of dentin is developed layer by layer immediately
after the secretion of the protein matrix. Similarly, as described above,
the matrix proteins in predentin (newly secreted protein-rich
unmineralized dentin) regulate the growth and deposition of the HAP
crystals. Moreover, odontoblasts synthesize and secrete type I collagen to
the predentin layer. In predentin, collagen molecule fibers aggregate with
their long axes in parallel into fibrils, which further arrange to bundles,
possibly with the help of proteoglycans, 24 to form the collagen
component of mature dentin.
 
 
 
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