Biomedical Engineering Reference
In-Depth Information
normal tissue due to an abnormal biochemistry with disturbances
in the calcium or phosphorus metabolism [821]. Common causes of
the metastatic calcification include hyperparathyroidism, chronic
renal disease, massive bone destruction in widespread bone
metastases and increased intestinal calcium absorption. One author
has mentioned on “apatite diseases” which are characterized by
the appearance of needle-like crystals comparable to those of bone
apatite in the fibrous connective tissue [822]. All these cases are
examples of a calcinosis [823-825], which might be described as a
formation of calcium orthophosphate deposits in any soft tissue. In
dentistry, a calculus or a tartar refers to a hardened plaque on the
teeth, formed by the presence of saliva, debris and minerals [826].
Its rough surface provides an ideal medium for bacterial growth,
threatening the health of the gums and absorbing unaesthetic stains
far more easily than natural teeth [27].
Calcifying nanodimensional particles are the first calcium
orthophosphate mineral containing particles isolated from human
blood and were detected in numerous pathologic calcification
related diseases [827]. Interestingly, but contrary to the mineral
phases of normal calcifications (bone, dentine, enamel, cementum,
antlers), which consist of only one type of calcium orthophosphate
(namely, biological apatite), the mineral phases of abnormal and/
or pathological calcifications are found to occur as single or
mixed phases of other types of calcium orthophosphates (ACP,
DCPD, OCP, β-(Ca,mg)
) and/or other phosphatic and non-
phosphatic compounds (e.g., magnesium orthophosphates, calcium
pyrophosphates, calcium oxalates, etc.) in addition to or in place of
biological apatite (Table 1.4) [27, 29, 84, 107, 147, 223, 229-232,
313, 828-832]. However, precipitation of biological apatite in wrong
places is also possible; this is so-called “HA deposition disease”
[833-836].
Occurrence of non-apatite phases in the pathological calcifications
may indicate that they were crystallized under the conditions
different from homeostasis or crystallization of the apatite structures
was inhibited and less stable phases crystallized instead, without
further change to the more stable one. Furthermore, in the places
of pathological calcifications the solution pH is often relatively low.
Given that nucleation and crystal growth is not a highly regulated
process in any pathological deposits, there is not likely just one
fundamental formation mechanism for all possible calcification types.
(PO
)
3
4
2
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