Biomedical Engineering Reference
In-Depth Information
a computer-controlled Universal Testing Machine (MTS, Eden Prairie, MN) and held parallel to
the composite
dentin interface. Load was applied at a rate of 0.5 mm/min until the bond failed.
Dentin shear bond strength, S D , was calculated as: S D 5
d 2 ), where P is the load at failure and
d is the diameter of the composite. Ten teeth were tested for each group (n
4P/(
π
10). The results are
plotted in Figure 6.8C . The six groups had shear bond strengths that were not significantly different
(P
5
0.1), indicating that adding QADM and NAg to adhesive and primer did not compromise the
dentin shear bond strength [55] .
For biofilm experiments, layered disk specimens for biofilm experiments were fabricated fol-
lowing previous studies [25,46] . Six groups were tested in biofilm experiments ( Figure 6.9 ).
Groups 1
.
5 had specimens with adhesives covering the top surface of the composite disk, without
primer, in order to test the antibacterial properties of the adhesives, as shown in Figure 6.9A .
Group 6 had the QADM
NAg primer covering the adhesive on the composite disk in order to test
the antibacterial properties of the primer/adhesive combination ( Figure 6.9B ).
Figure 6.9C plots the MTT metabolic activity of microcosm biofilms. Microcosm bio-
films on the commercial adhesive had a high metabolic activity. Incorporation of QADM and
NAg each markedly reduced the metabolic activity (P
0.05). Adding QADM and NAg
together in the adhesive resulted in a much lower metabolic activity than using QADM or NAg
alone (P
,
0.05). Adding QADM and NAg both in the primer and in the adhesive yielded
the lowest biofilm metabolic activity (P
,
0.05). The metabolic activity of biofilms on
A&P 1 10QADM 1 0.05NAg was nearly an order of magnitude less than that on the commercial
adhesive control [55] .
,
6.6 Antibacterial and remineralizing adhesive containing NACP
NACPs were incorporated into the adhesive. The purpose was for the NACP to flow with the adhe-
sive into the hybrid layer as well as the dentinal tubules to form resin tags, with Ca and P ions to
remineralize remnants of lesions in the prepared tooth cavity. The NACP mass fraction in the adhe-
sive varied from 10% to 40% [57] . Typical SEM images of the dentin
adhesive interfaces are
shown in Figure 6.10 : (A) SBMP adhesive control, (B) SBMP primer P
NAg, SBMP adhesive
A 1 NAg 1 20NACP (with 20% NACP), and (C) P 1 NAg, A 1 NAg 1 40NACP (with 40%
NACP). Numerous resin tags “T” from well-filled dentinal tubules were visible in all the samples.
“HL” refers to the hybrid layer between the adhesive and the underlying mineralized dentin. At a
higher magnification, the NACP nanoparticles were visible in (D) with 20% NACP as an example.
Arrows in (D) indicate examples of NACP nanoparticles which successfully infiltrated into the den-
tinal tubules. This feature became more visible at higher magnifications in (E) and (F), where
arrows indicate NACP, which successfully infiltrated into not only the straight and smooth tubules
(E) but also the bent and irregularly-shaped tubules (F) [57] .
These results show the high promise of novel bonding agents and composites containing anti-
bacterial agents and remineralizing nanoparticles to combat biofilms and secondary caries. Further
studies are needed to investigate caries inhibition in extracted human teeth at the nanostructured
restoration
1
tooth margins cultured under biofilms.
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