Biomedical Engineering Reference
In-Depth Information
(A)
(B)
FIGURE 5.2
Teeth were restored with Equia system (Fuji IX GP)
[53]
.
increased significantly. In this study, nanoparticles (50
100 nm) of both HA and fluoroapatite (FA)
were added to glass ionomer powder (5 wt%) and the mechanical test results showed that both of the
glass powders had higher strength compared to the Fuji II commercial GIC. Nano-FA/ionomers had
higher values for compressive strength (CS), diametral tensile strength (DTS) and biaxial flexural
strength (BFS) (179, 23, and 35 MPa, respectively) compared to HA/ionomer (178, 19, and 32 MPa,
respectively), which can be related to the stability of FA and lower dissolution rate of FA in distilled
water compared to the dissolution rate of nano-HA. Both nano-HA and FA take part in the acid/base
reaction of the GIC and react with inorganic component of GIC network via their phosphate and cal-
cium ions. The highest values for mechanical properties were obtained when both powder and liquid
were modified, although the difference was not remarkable when it compared to the glass ionomer
samples in which only their powder (by incorporation of nanoceramic particles) or liquid (by incorpo-
ration of NVP segments) were modified. By incorporation of both NVP and nanoparticles into the liq-
uid and powder of GIC, the highest increase in strength was observed. More than 14% increase in CS
was observed and the values for DTS doubled while the BFS tripled. This suggested that these additives
have an effect on the setting reaction, mechanism, and degree of polysalt bridge formation of the glass
ionomer, which cause higher mechanical properties of final set cement. There should be some physio-
chemical interactions between the carbonyl group of NVP in the polymer structure and phosphate and
hydroxyl and fluoride ions of apatite. This kind of physical bonding is weak, but since there are a large
number of these types of bonds, they might be partly responsible for increase in the mechanical proper-
ties of the resulting experimental glasses. Moreover, the possibility of formation of hydrogen bonds is
much more because of the presence of hydroxyl, phosphate, fluoride, and carbonyl groups in the
matrix. It is expected that stronger bonds between the organic and inorganic networks of the set cement
lead to higher mechanical strength of final set cement. Another role for incorporated apatite nanoparti-
cles is their ability to react with poly acrylic acid (PAA). Due to their small size, the incorporation of
nanoparticles into glass powder of glass ionomers leads to wider particle size distribution (the average
particle size of glass ionomer particles were around 10
m) which resulted in higher mechanical
values. Consequently, they can occupy the empty spaces between the glass ionomer particles and act as
a reinforcing material in the composition of the GIC.
20
μ
