Biomedical Engineering Reference
In-Depth Information
investigated on human teeth ex vivo
[83]
. Atomic force microscopy demonstrated lower
nanometer-scale roughness obtained when silica nanoparticles were used to polish the surface of
teeth as compared with conventional polishing pastes. It was also shown that adherent S. mutans
could be more easily removed. However, concerns remain as to the longevity of the effect, and
whether the polished surface will inhibit mineralization and plaque formation in vivo. Spherical
silica nanoparticles (up to 21 nm) deposited onto polystyrene surfaces by polycationic binding have
been investigated with respect to the development of C. albicans biofilms and invasive filament
formation
[84]
. Modified surfaces were shown to reduce attachment and growth of C. albicans,
with the greatest effect observed with 7 and 14 nm particles. These effects could possibly be attrib-
uted to the surface topography or slow dissolution of the bound silica. Such treatment has the
advantages of being nontoxic, simple to apply and adaptable to three-dimensional surfaces.
Other novel systems based upon silica have been investigated with respect to the control of oral
biofilms. The use of nitric oxide (NO)-releasing silica nanoparticles to kill biofilm-based microbial
cells has been described
[85]
. The rapid diffusion of NO may well result in enhanced penetration
into the biofilm matrix and therefore improved efficacy against biofilm-embedded bacteria. In vitro
grown biofilms of P. aeruginosa, E. coli, S. aureus, Staphylococcus epidermidis, and C. albicans
were exposed to NO-releasing silica nanoparticles. Over 99% of cells from each type of biofilm
were killed via NO release. In comparison to small-molecule NO donors, the physicochemical
properties, for example, hydrophobicity, charge, and size of nanoparticles, can be altered to
increase antibiofilm efficacy
[25]
.
Bioactive glasses of the SiO
2
a
P
2
O
5
system have been shown to possess antimi-
crobial activity through the release of ionic alkaline species over time and are under consideration
as dentin disinfectants to offer an alternative to calcium hydroxide
[86]
. Those in the form of amor-
phous nanoparticles with a size of 20
Na
2
O
CaO
a
a
60 nm may show an advantage over micron-sized material
as the decrease in glass particle size should increase, by more than 10-fold, the active exchange sur-
face of glass and surrounding liquid. In turn, this would substantially increase ionic release into sus-
pension and enhance antimicrobial efficacy. Waltimo et al.
[86]
monitored ionic dissolution
profiles in simulated body fluid. Antimicrobial activity was assessed against E. faecalis as a patho-
gen often isolated from root canal infections. They found that a shift from a micron- to a nanosize
increased the release of silica by a factor of 10 and elicited a pH elevation of at least 3 units. The
killing efficacy was also significantly higher.
10.4.3
Hydroxyapatite and other calcium phosphate-based systems
The application of nanoscaled HA particles has been shown to impact on oral biofilm formation
and provides a remineralization capability
[87,88]
. Biomimetic approaches, based upon HA nano-
crystals which resemble the structure at the nanoscale of abraded dental enamel crystallites, should
allow adsorbed particles to interact with bacterial adhesins, reduce bacterial adherence, and hence
impact on biofilm formation
[89]
.
A number of oral health-care products, including dentifrices and mouth rinses, have been devel-
oped containing nanosized apatite particles with and without protein-based additives
[90,91]
.Itis
suggested that the efficacy of these compounds can be attributed to the size-specific effects of the
apatite nanoparticulates. Casein phosphopeptide (CPP)
amorphous calcium phosphate (ACP) nano-
complex (Recaldent
/MI Paste
) is a particular technology based upon ACP and stabilized by
t
t
