Biomedical Engineering Reference
In-Depth Information
10.6 Biocompatibility of nanoparticles within the oral cavity................................................................ 219
10.7 Conclusions............................................................................................................................... 221
Acknowledgments ............................................................................................................................... 223
References ......................................................................................................................................... 223
10.1
Introduction
Nanoparticles can be classified as particles of a size no greater than 100 nm, and their unique attri-
butes to combat infections have received considerable attention within a range of diverse fields,
including medicine and dentistry. Nanomaterials are increasingly finding uses in products such as
antimicrobial surface coatings and semiconductors. These include spherical, cubic, and needle-like
nanoscaled particles (approximately 5
100 nm) and near-nanoscaled devices (up to micrometers)
[1]
. Properties of nanoparticles, for example, their active surface area, chemical reactivity, and bio-
logical activity, can be dramatically different from those of micrometer-sized particles
[2]
, and
indeed the biocidal effectiveness of metallic nanoparticles has been suggested to be due to both
their size and their high surface-to-volume ratio. These characteristics should allow them to closely
interact with microbial membranes, and thus elicit an antimicrobial effect that is not solely due to
the release of metal ions
[3]
. Metallic and other nanoparticles are now being combined with poly-
mers and other base materials and coated onto surfaces which may have a variety of potential anti-
microbial applications within the oral cavity
[4,5]
.
The oral cavity supports the growth of a wide diversity of microorganisms including bacteria,
yeasts, and viruses—members of all groups being associated with oral infections. Bacteria are the
predominant components of this resident microflora, and the diversity of species found in the oral
cavity reflects the wide range of endogenously derived nutrients, the varied types of habitat for col-
onization including surfaces on the teeth, mucosa, and tongue, and the opportunity to survive as a
biofilm. An oral biofilm can be classed as an aggregate of microorganisms in which cells adhere to
each other and to a surface
[6]
. However, the relationship between this microflora and the host can
be disrupted in a number of ways, resulting in the development of disease of the oral structures.
Potential habitats suitable for attachment within the oral cavity include the nonshedding hard
tooth surfaces or soft, constantly replaced epithelial surfaces, and conditions vary with respect to
oxygen levels and anaerobiosis, availability of nutrients, exposure to salivary secretions or gingival
crevicular fluid (GCF), masticatory forces, and other variables such as oral hygiene procedures.
The composition of the microbial flora of the mouth thus varies considerably from site to site and
at different time points. Up to 1000 different species of bacteria at 10
8
10
9
bacteria per milliliter
saliva or per milligram dental plaque are known to be associated with the oral cavity, and it has
been suggested that only 50% of the bacteria found at these sites can be cultured
[6]
.
Most bacterial infections within the oral cavity are polymicrobial in nature, and it is quite
unusual to find any that are clearly due to a single species. The relative contribution of different
bacterial components in such infections is thus difficult to determine. Oral infections may arise
either from an endogenous source, i.e., one yielding microorganisms normally found in the mouth,
such as plaque-related dental caries and periodontal disease, or an exogenous source yielding
microorganisms not normally found as part of the oral microflora. Dental caries and periodontal
disease involve the adherence of bacteria and development of biofilms on both the natural and the
