Biomedical Engineering Reference
In-Depth Information
manufactured only at low powder/liquid ratios, and higher powder/liquid ratio is unattainable
because of the low packing density of the nanosized powders. Therefore, low strength values were
obtained for the nanosized YSZ
GIC composites because of the low powder/liquid ratio.
A study in which preparation of niobium FAS glass powder by the sol
gel process for use as
cement formers was conducted. The resulting powder was in a nanoscale range with surface area of
19 m
2
/g, which affected its manipulative properties. The microhardness (Knoop Hardness: KHN)
values were higher (19) compared to conventional GIC (16.4)
[57]
.
A commercial glass ionomer powder (Riva SC) was blended in various proportions (1, 2, 5, 10,
15, and 25% (w/w)) with YbF
3
/BaSO
4
nanoparticles. It was found that with incorporation of these
nanoparticles, there was significant decrease in working and setting time of cements, which indicates
a significant interaction of the nanoparticles with the glass ionomer matrix. The longer working times
at 10% and 15% incorporation of nanoparticles are most likely a result of the inhibition by YbF
3
of
the initial, divalent-mediated, gelation stage of the glass ionomer reaction. The decrease in working
and initial setting time caused by the addition of BaSO
4
(significant at 2% BaSO
4
) was due to its
contribution to the initial gelation reaction of the GIC. Because of the nanostructure of the BaSO
4
particles, the barium ions are more easily available than the calcium or strontium ions, which are in
the glass. Up to 5% BaSO4 nanoparticles addition the working time decreased and a minimum work-
ing time was achieved at 15% nanoparticles. The low solubility and reactivity of the BaSO
4
resulted
in dilution or rate-reducing effect on the glass ionomer reaction. The CS was also decreased with
these nanoparticles. The decrease in CS of the GIC was only significant at concentrations of 5% or
higher, indicating that 1
2% YbF
3
addition had no significant deleterious effect. However, the
investigators expected the addition of YbF
3
to improve the CS of the GIC significantly for at least
three reasons. First, YbF
3
can be expected to act similarly to AlF
3
in glass ionomer systems because
of its similar chemical and physical structure. Second, the release of a trivalent ion into the glass
ionomer matrix may speed the cross-linking, improve its insolubility, and further its reaction extent
and strength. Third, the reactivity of the YbF
3
with the glass ionomer matrix indicated that the ytter-
bium ions were being incorporated into the matrix and accelerating the setting reaction
[58]
.
5.8
Conclusions
More research is needed to investigate other mechanical properties of the nanoionomer, its biochemical
stability in the oral environment, fluoride release, and so on. Ultimately, well-designed randomized
clinical trials will reveal the longevity and anticariogenic effect of this material in clinical conditions.
However, nanofilled glass ionomers have acquired a prominent place among the restorative materials
employed in direct techniques. Their considerable chemical linkage, smooth surface, and esthetic possi-
bilities give rise to a variety of clinical applications, which continue to grow as a result of the great
versatility of the presentations offered; also, these materials conserve the tooth structure better because
they are retained by adhesive methods rather than depending on cavity design. However, they are tech-
nique sensitive, and hence there is a need to control certain aspects such as correct indication,
good isolation, and choice of the right material for each situation. Further research in the area related
to the biochemical stability of glass ionomer materials, supported by both industry and clinicians, is
required.
