Biomedical Engineering Reference
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dissolution of mineral in dental caries. Luckily, saliva gradually
neutralizes the acids that cause pH on teeth surface to rise above
the critical pH. This might cause partial enamel remineralization,
i.e. a return of the dissolved calcium orthophosphates to the enamel
surface. Until recently, it was generally agreed, that if there was
sufficient time between the intake of foods (generally, two to three
hours) and damage was very limited, teeth could repair themselves
by the “passive mineralization” process [734]. Data on increased
remineralization of tooth enamel by milk containing added casein
phosphopeptide — ACP nanodimensional complexes [735] are in
support of this hypothesis.
However, studies performed by using atomic force microscopy
nano-indentation technique revealed that previously demineralized
samples of dental enamel further exposed to remineralizing
solutions did show a crystalline layer of calcium orthophosphates
formed on their surface. Unfortunately, the re-precipitated deposits of
calcium orthophosphates always consisted of loosely packed crystals
and did not protect the underlying enamel from a subsequent acid
attack. Furthermore, these surface deposits were completely removed
by either a toothbrush or a short exposure to an erosive acidic solution
[689, 736-738]. In this context, it should be emphasized that the
term “remineralization”, which is often misused in the literature,
should imply the process of mineral growth that goes hand in hand
with a strengthening effect of the weakened enamel surface. Since no
strengthening of an exposure to remineralizing solutions was observed,
it might be considered that no “passive mineralization” was found (in
spite of the real evidence of the re-precipitated surface deposits of
calcium orthophosphates) [689, 737, 738].
An interesting hypothesis that nano-sized apatite crystallites
occur in the oral cavity during extensive physiological wear of the
hierarchical structured enamel surface due to dental abrasion and
attrition has been published recently [739]. These nano-scaled
apatite enamel crystallites might promote remineralization at the
tooth surface. However, this idea should be verified experimentally.
Thus, according to the current knowledge, the enamel self-repairing
ability by a passive remineralization appears to be doubtful, while an
active remineralization is impossible. Nevertheless, investigations
in this field keep going [213-215, 740-751]. For example, ACP-
containing orthodontic biocomposite resins might reduce the enamel
decalcification found in patients with poor oral hygiene [751].
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