Biomedical Engineering Reference
In-Depth Information
using a poly(methyl methacrylate) (PMMA) biofilm model, demonstrated that Candida albicans
biofilms are potentially highly resistant to the currently used antifungal agents, with resistance
developing with time and showing a correlation with biofilm maturation.
10.2.3
Control of oral biofilms
Agents classified as antiplaque generally function by removing or disrupting biofilms or by
preventing the formation of a new biofilm. However, they do not necessarily kill the microorgan-
isms within the biofilm. Whereas, agents classified as antimicrobial act by inhibiting the growth
(bacteriostatic) or killing (bactericidal) microorganisms, as defined by minimum inhibitory concen-
tration (MIC) and minimum bactericidal concentration (MBC), respectively. The uptake and pene-
tration of antimicrobial agents into biofilms are key considerations in the administration of
therapeutics
[21]
. This is of particular importance within the oral cavity when these agents have to
reach less accessible stagnation sites or through plaque to the enamel. The development of plaque
control measures that require a minimum of patient compliance and professional health-care inter-
vention are therefore of particular interest
[22]
. Within this context, antimicrobial nanoparticles
may be of particular value if retained at approximal teeth surfaces and below the gum margin. The
anticaries potential of fluoride and other conventional antimicrobial/antiplaque agents, which are
mostly deployed in mouthwashes and toothpastes, have been well characterized
[16]
. The potential
of nanoparticles as constituents of topical agents to control oral biofilms through either their bio-
cidal or antiadhesive capabilities has now emerged as an area that should be given serious consider-
ation. The studies by Robinson et al. using the “Leeds in situ model,” a device that allows dental
plaque to develop in situ on a removable human enamel surface, have helped in the assessment of
novel antimicrobial agents and take into account the extremely complex microbial composition and
architecture of plaque biofilms
[23]
. The use of such intact biofilms on natural tooth surfaces would
be of particular value to a study of the penetration of nanoparticles and released ions. This model
has indicated that plaque contains voids and channels, sometimes extending completely through the
biomass to the underlying enamel
[24]
and may have considerable influence on the transfer of
nanoparticles through biofilms. The main considerations are the physical and chemical characteris-
tics of the particular nanoparticles used, including the surface charge and degree of hydrophobicity,
the surface area-to-mass ratio of the plaque biofilm and the ability of the particles to adsorb to/be
taken up at the biofilm surface. Within this context, nanoparticles are potentially useful because it
is possible to alter their surface charge, hydrophobicity, and other physical and chemical character-
istics
[25]
.
10.3
Antimicrobial nanoparticles and oral biofilm control
10.3.1
Nanoparticulate metals as antimicrobial agents
Metals have been used for centuries as antimicrobial agents. Silver, copper, gold, titanium, and
zinc have attracted particular attention, each having different properties and spectra of activity.
Many oral products, including toothpastes, now incorporate powdered (micron-sized) zinc citrate or
acetate to control the formation of dental plaque
[26]
. Powdered titanium dioxide is also commonly
used as a whitener in toothpastes.
