Biomedical Engineering Reference
In-Depth Information
crystallization. Another important result is that a maximum of around 70% crys-
talline phase (“butterfl y” morphology) can be obtained after heat treatment at
1000 °C for 24 hours, while a lower amount (~58%) of interlocked plate like mica
crystals is formed after heat treatment at 1040 °C for four hours. Also, the glass
ceramics with plate-like crystals exhibited the highest hardness of 5.5 GPa.
In a recent study
41
on slightly different compositions (48.94SiO
2
, 17.45MgO,
16.29Al
2
O
3
, 7.15K
2
O, 5.25B
2
O
3
, and 3.85F) of same glass ceramics with suitable
heat treatment schedule showed much improved hardness (
8 GPa).
The chemical durability of dental ceramics is an important property that
affects their clinical performances. This is due to the fact that they are constantly
exposed to various aqueous environments. The
in vitro
dissolution tests of similar
glass composition were carried out by immersing the selected glass ceramic
samples in artifi cial saliva (AS) for various time periods of up to six weeks. SEM
images and SEM-EDS analysis of the surface of the sample immersed in AS for
different time periods of two, three and six weeks were taken in order to assess
the extent of Ca-P layer formation on the surface. Figure 3.9 shows the spherical
particles of diameter 2 - 3
∼
m on the surface after six weeks of immersion in AS.
EDS analysis of spherical particles indicates the strong peaks of Ca, P and O,
thereby confi rming the formation of Ca-P compounds. Further, the analysis of
EDS data indicate that the composition of those spherical brighter contrasting
particles, which cover the majority of surface area, can be characterized by
Ca-P ratio of 1.57 (average). Ca-P is a highly bioactive material and therefore
the formation of these layers on the glass ceramics sample will increase its
bioactivity.
μ
Figure 3.9.
SEM observation of glass-ceramic surface (SiO
2
-MgO-Al
2
O
3
-K
2
O-B
2
O
3
-F, heat treat-
ed at 1040 °C for 12 hours), after immersing in AS solution for 6 weeks. EDS analysis of the
spherical particles is shown inset
41
.
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