Biomedical Engineering Reference
In-Depth Information
To
fabricate
the
“NACP
NAg”
composite,
the Ag
TBAEMA was mixed with
1
BisGMA
TEGDMA, and then 30% NACP and 35% barium boroaluminosilicate glass were added
to the resin. Since the resin mass fraction was 35% in the composite, the 0.08% of Ag in the resin
yielded 0.028% of Ag mass fraction in the composite. To fabricate the “NACP
QADM
NAg”
1
1
composite, the Ag
QADM resin. NACP
and glass filler levels were selected to yield a cohesive paste that was readily mixed and not dry.
Each paste was placed into rectangular molds of 2
TBAEMA was mixed with the BisGMA
TEGDMA
25 mm for mechanical testing, and disk
molds of 9 mm in diameter and 2 mm in thickness for biofilm experiments. The specimens were
photo-polymerized (Triad 2000, Dentsply, York, PA) for 1 min on each side.
In addition, a commercial composite with glass nanoparticles of 40
2
3
3
200 nm and a low level of
fluoride (F) release was tested (Heliomolar, Ivoclar, ON, Canada) (referred to as CompositeF). The
fillers were silica and ytterbium-trifluoride with a filler level of 66.7%. Heliomolar is indicated for
Class I and Class II restorations in the posterior region, Class III and V restorations, and pit and fis-
sure sealing. Another commercial composite, Renamel (Cosmedent, Chicago, IL), served as a non-
releasing control (referred to as CompositeNoF). It consisted of nanofillers of 20
40 nm with 60%
(by mass) fillers in a multifunctional methacrylate ester resin. Renamel is indicated for Class III,
IV, and V restorations. The control specimens were also photocured in the same manner as
described above.
Figure 6.2
shows the composite mechanical properties: (A) flexural strength and (B) elastic
modulus (mean
6
sd; n
5
6). In (A), the resin with 30% NACP without glass had a slightly lower
flexural strength. Bars with dissimilar letters indicate values that are significantly different
(P
,
0.05). The NACP composite had a strength of 62
8 MPa, not significantly different from
6
the 57
12 MPa of CompositeF, and 56
9 MPa of CompositeNoF (P
.
0.1). Adding QADM,
6
6
NAg, or QADM
NAg yielded strengths of 53
7, 67
6, and 54
12 MPa, respectively
1
6
6
6
(P
0.1)
[21]
.
S. mutans bacteria were obtained commercially (ATCC 700610, UA159, American Type
Culture, Manassas, VA), and the use was approved by University of Maryland Baltimore IRB. The
growth medium consisted of brain heart infusion (BHI) broth (BD, Franklin Lakes, NJ) supplemen-
ted with 0.2% sucrose. Fifteen microliter of stock bacteria was added to 15 mL of growth medium
and incubated at 37
C with 5% CO
2
for 16 h, during which the S. mutans were suspended in the
growth medium. The inoculation medium was formed by diluting this S. mutans culture 10-fold in
growth medium
[21]
.
Colony-forming unit (CFU) counts were measured. Disks with biofilms were transferred into
tubes with 2 mL cysteine peptone water. The biofilms were harvested by sonicating (3510 R-MTH,
Branson, Danbury, CT) for 3 min and then vortexing at maximum speed for 20 s using a vortex
mixer (Fisher, Pittsburgh, PA). The bacterial suspensions were serially diluted, spread onto BHI
agar plates, and incubated for 3 days at 5% CO
2
and 37
C. At 1 day and 3 days, the numbers of
colonies were counted to calculate total CFU on each disk. The results are shown in
Figure 6.3
.
At 1 day, CFU counts were 27 million per disk for CompositeNoF and 21 million for NACP com-
posite. The CFU counts were greatly reduced to 12.5 million on NACP
.
1
QADM composite,
3.2 million on NACP
1
NAg composite, and 1.4 million on NACP
1
QADM
1
NAg composite
(P
NAg
composite having the least CFU counts, which were an order of magnitude less than that of
CompositeNoF.
0.05). The ranking of CFU at 1 day is maintained at 3 days, with the NACP
QADM
,
1
1
