Biomedical Engineering Reference
In-Depth Information
are known to possess several disadvantages including development of biofilms on both teeth
and the restorative material
[4]
. The traditional methods for preparing antibacterial composite
materials have been to impregnate them with low-molecular-weight agents, such as Ag
1
ions or
iodine that are then released slowly. Apart from the possible adverse effects on the mechanical
properties of the composite, difficulties in controlling the release of such agents may be a potential
drawback.
QA-PEI nanoparticles at a concentration of 1% w/w enabled complete in vitro growth inhibition
of S. mutans to be achieved for at least 3 months
[78]
. The proposed mechanism of action of
QA-PEI is suggested to be as a result of transfusion across, and damage to, the bacterial cell wall.
The hydrophobic nature and positive charge of these particles are also thought to further enhance
the antimicrobial activity. Surface chemical analysis of the restorative composite embedded with
QA-PEI demonstrated a surface modification of higher hydrophobicity and the presence of quater-
nary amines when compared to the unmodified material. Further studies to optimize the release
characteristics of QA-PEI and other potentially useful nanoparticulates from dental materials will
be required.
10.4
Antiadhesive nanoparticles and oral biofilm control
10.4.1
Chitosan nano- and microparticles
Chitosan is a biopolymer derived by the deacetylation of chitin, a natural polymer occurring in the
exoskeleton of crustaceans. Chitosan is positively charged and soluble in acidic to neutral solution,
enabling it to bind to mucosal surfaces. Both chitosan nano- and microparticles have been investi-
gated as a potential platform for local delivery of drugs
[79]
. Although the antimicrobial irrigants
(without chitosan) are used to disinfect root canals in the treatment of endodontic infections are
capable of killing Enterococcus faecalis, the bacterium frequently associated with this condition,
endodontic restorations often fail
[80]
. The in vitro study of Kishen et al.
[81]
demonstrated that
root canal surfaces treated with cationic antibacterial nanoparticulates such as zinc oxide alone
and a combination of zinc oxide and chitosan nanoparticulates are able to significantly reduce
E. faecalis adherence to dentin. In theory, such surface treatment could prevent bacterial recoloni-
zation and biofilm formation in vivo.
10.4.2
Silica and silicon nanoparticles
Particles of a nano and micro size based upon the element silicon, designed to rapidly deliver anti-
microbial and antiadhesive capabilities to the desired site within the oral cavity, have received
attention
[82]
. Companies have used silica (silicon dioxide “SiO
2
” and often classed as “microfine,”
but with a particle size within the definition of nanoparticles) in toothpastes for many years, and some
have actively sought new directions in this area through the use of porous silicon and nanocrystalline
silicon technology to carry and deliver antimicrobials, e.g., triclosan. These may well offer advantages
to some of the slower and more prolonged delivery systems under investigation.
The use of silica nanoparticles to polish the tooth surface may help protect against damage by
cariogenic bacteria, presumably because the bacteria can more easily be removed. This has been
