On the mechanistic role of the dentin-enamel junction in preventing the fracture of human teeth Page: 3 of 18
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The dentin-enamel junction (DEJ) in teeth represents the zone between two distinct
calcified tissues with very different biomechanical properties: enamel and dentin'.
Enamel is the hard and brittle outer portion of the tooth that envelops the softer dentin;
it is comprised of defective carbonate-rich apatite (AP) crystals arranged in enamel rods
(4-5 m in diameter) or prisms that lie nearly perpendicular to the DEJ22,3. Its fracture
toughness is typically K.~0.7-1.3 MPa\m in respective directions parallel and
perpendicular to the enamel rods45. Dentin, conversely, is a biological composite which
is tougher than enamel and similar at the nanostructural level to bone. It has a unique
architecture consisting of dentinal tubules, -1 m in diameter, surrounded by
peritubular dentin, consisting of ~0.5-1 m thick cylinders of randomly-oriented apatite
crystallites. These tubular units are embedded in a collagen matrix-apatite reinforced
composite. Since the tubules are the formative tracks of the odontoblastic cells that
move inward and reside on the pulp chamber surface, there are substantial variations in
morphology and structure of the dentin from the DEJ to the pulp chamber6. Dentin has
a K, toughness that varies between 1.0 and 2.0 MPa1m in directions perpendicular and
parallel to the tubules7'8. The toughness of dentin adjacent to the DEJ, so-called mantle
dentin, is supposedly higher due to its lower mineral content and reduced modulus9; the
tubules in this region are comparatively rare or absent.
The DEJ itself has a hierarchical microstructure with a three-dimensional scalloped
appearance along the interface'. It is an anatomically thin region with a broader
functional width; the enamel and dentin close to the interface have slightly different
microstructures and properties than the more distant bulk phases. Specifically, the
morphology of the collagen is such that type-I fibrils emanate from the dentin and
project fibrils (-100 nm in diameter) perpendicular to the DEJPO; such Von Korfs fibrils
cross the DEJ and appear to be inserted directly into the enamel. In contrast, collagen
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Imbeni, V.; Kruzic, J.J.; Marshall, G.W.; Marshall, S.J. & Ritchie, R.O. On the mechanistic role of the dentin-enamel junction in preventing the fracture of human teeth, article, September 1, 2004; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc785232/m1/3/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.