Biomedical Engineering Reference
In-Depth Information
recently discovered by a combination of atomic and chemical force
microscopy [716]. Binding of organic molecules (e.g., amelogenin
[716]) at physiological solution pH appears to occur on the charged
surface domains of apatite. The modern visions on dental tissue
research have been reviewed recently [717].
As teeth consist of several materials, there are mutual junctions
among them. For example, a dentine-enamel junction (DEJ) is the
interface between dentine and enamel. It is a remnant of the onset
of enamel formation because enamel grows outwards from this
junction [677, 718, 719]. DEJ plays an important role in preventing
crack propagation from enamel into dentine [720]. The major steps
of enamel crystal growth at the junction have been described above
but the mechanism of the junction formation is still debatable.
Some authors claim that enamel crystals grow epitaxially on the
pre-existing dentine crystals because of a high continuity between
enamel and dentine crystals [721-723]. Others have shown that
enamel crystals are formed at a given distance from the dentine
surface [701-703, 724] and could either reach dentine crystals by a
subsequent growth [725] or remain distant [724, 726]. In addition,
there are a cementum-enamel junction (CEJ) [727], which is quite
similar to DEJ, and a cementum-dentine junction (CDJ) [681-683,
728].
Enamel formation, or amelogenesis, is a highly regulated
process involving precise genetic control as well as protein-protein
interactions, protein-mineral interactions and interactions involving
the cell membrane. Much is still unknown about the interactions
among proteins present in enamel matrix and the final crystalline
phase of biological apatite [533, 729]. At some point before a
tooth erupts into the mouth, the ameloblasts are broken down.
Consequently, enamel, unlike bones, has no way to regenerate itself
using the process of “active mineralization” (see bone formation)
because there is no biological process that repairs degraded or
damaged enamel [676, 677]. In addition, certain bacteria in the
mouth feed on the remains of foods, especially sugars. They produce
lactic acid, which dissolves the biological apatite of enamel in a
process known as enamel demineralization that takes place below
the critical pH of about 5.5. Similar process called enamel erosion
occurs when a person consumes acid-containing (citric, lactic,
phosphoric, etc.) soft drinks [689, 730-733]. Evidences exist that
there is a preferential loss of carbonates and Mg during acidic
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