Biomedical Engineering Reference
In-Depth Information
radicals) by the action of light energy and/or H
2
O in the air or water only at polar surfaces
[19]
.
These active oxygen radicals caused the structural damage in bacteria and lead to the damage or
even the death of the microorganisms, the so-called “oligodynamic action of silver”
[19,35]
.
14.3.3
Cytotoxic test on human gingival cell line
Human gingival fibroblasts (HGF; ATCC 2014) were used to evaluate the cytotoxicity of Ag
-tissue
conditioner by MTT (tetrazolium-based 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium
bromide) assay. The cells were grown and subcultured for 24 h at 37
C in an atmosphere of 5%
CO
2
in air and 100% relative humidity. HGF cell suspension was prepared at a concentration of
4
3
10
4
cells/mL and dispensed (180
µ
L/well) onto 96-well cell-culture plates. The multiwell plates
were incubated at 37
C and 5% CO
2
in air for 24 h. The culture medium was removed from the
wells and 20
L of the extracts from experimental Ag
-tissue conditioner (0%, 0.1%, 0.5%, 1.0%,
and 2.0%) were added into each well and incubated for 2, 8, 24, 48, and 72 h at 37
C and 5% CO
2
in
air. Then, 10% MTT (100
µ
L) was added to each well and kept in a dark environment for 4 h at
37
C and after MTT was aspirated, 100
µ
L of dimethyl sulfoxide was added to each well. OD for
each group was measured using ELISA reader under the absorbance at 570 nm. Cell viability (CV
(%)) was calculated using the following equation:
µ
Sample optical density
Control optical density
3
C
v
ð
%
Þ
5
100
and cytotoxicity was evaluated by the cell viability as highly cytotoxic when less than 25% and
less than 50
25% were qualified as moderately cytotoxic
[36]
.
It is generally accepted that Ag
express their toxicity through the generation of reactive oxygen
species (ROS)
[37]
. Increased cellular ROS levels are associated with the induction of genetically pro-
grammed cell death (apoptosis), as well as necrotic cell death in several cell lines
[38]
. Kim et al.
[39]
reported the subchronic oral toxicity and tissue accumulation of Ag
in rats for 90 days and highlighted
that Ag
have significant toxic effects on cells that primarily occur in a dose-dependent manner.
The results indicated that 2.0% Ag
group was expressed as highly cytotoxic effect to HGF at 24
and 72 h incubation periods while control (0%) and 0.1% and 0.5% groups were graded as noncyto-
toxic at all incubation periods even though the 0.5% group showed significant decrease in cell viability
at 24 and 72 h over the control group (
Figure 14.5
). Phthalates and other esters of aromatic carboxylic
acids are used as plasticizers in Soft-Liner
s
and they have been reported to elute from the conditioners
during masticatory force and to possibly be toxic
[40,41]
. However, control group, an acrylic tissue
conditioner “Soft-Liner
s
” without Ag
revealed no cytotoxic effect to HGF at all incubation periods.
This result could be related to in vitro, static experimental condition for tested samples unlike normal
functioning of tissue conditioner in oral cavity
[41]
.
14.4
Characterization of Ag
-tissue conditioner composites
14.4.1
Determination of eluted Ag
1
from the specimens
For Ag
1
determination, atomic absorption spectrophotometer and shaking incubator were utilized.
Ag
-tissue conditioner (0.5%, 1.0%, and 2.0%) specimens were put into 100 mL of sterile distilled
water. After storage at 37
C under agitation, the concentration of released Ag
1
determined at every
