Biomedical Engineering Reference
In-Depth Information
Fig. 4.3
Results of TR-SLS measurement of calcium phosphate formation. (a) Time-dependent
changes in calculated apparent molecular mass (M
w
, red), gyration radius (R
g
, green), and fractal
dimension (d
f
, blue) of calcium phosphate in presence of artificial protein (#64, 1
g/mL). Phase L
(latency) was followed by phase T (transformation), and phase P (precipitation). (b) Enlargement
corresponding to 75-95 min in (a). For comparison, the data obtained in the absence of #64
are shown in light colors. (c and d) Schematic representations of HAP mineralization via direct
transformation mediated by a protein (c) and in a simple system (d). Reprinted with permission
from [
66
]. (Copyright 2008, National Academy of Sciences of the United States of America)
from that of the mature inner enamel. This was attributed to the compositional
differences between the organic substances in the various areas resulting from
protein degradation during the enamel maturation process [
72
].
Observation of these areas using polarizing microscopy revealed birefringence
only in the inner area. In other words, immature outer enamel does not contain
crystals. Observation of sections from these areas by TEM revealed needle-shaped
mineral crystallites arranged in parallel arrays, the typical morphology of enamel.
The crystallites were several nm thick, 20 nm wide, and several hundred nm long,
and there was no significant variation in their shape or size. There was, however,
a significant difference in their patterns of electron diffraction. Those in the inner
area showed 002, 004, 112, and 311 diffraction patterns, which are characteristic
for HAP, whereas those in the outer area exhibited a broad ring, which is a typical
pattern for ACP. In other words, the degree of crystallization differed between
the inner and outer areas although the sizes and morphologies of the crystallites
were similar. This suggests that transformation from ACP to HAP is not caused
