Biomedical Engineering Reference
In-Depth Information
restored tooth surface. The use of nanotechnology offers the possibility to control the formation of
these and other oral biofilms through the use of nanoparticles with biocidal, antiadhesive, and
delivery capabilities.
10.2
Biofilms and oral infections
Biofilms of oral bacteria and yeasts can cause a number of localized diseases in the oral cavity,
including dental caries, gingivitis, periodontitis, candidiasis, endodontic infections, orthodontic
infections, and peri-implantitis
[6]
.
10.2.1
Formation and properties of oral biofilms
Within the oral cavity, the survival of microorganisms is dependent on their ability to adhere to sur-
faces and subsequently develop into a biofilm, a process influenced by the physical and chemical
properties of the underlying surface
[7]
. On the tooth surface, the initial colonizers adhere to the
acquired pellicle, a salivary/dietary-derived proteinaceous layer, which can then influence the sub-
sequent sequence of colonization by microorganisms
[8]
. The acquired pellicle also contains several
salivary components such as secretory immunoglobulin A (sIgA) and lysozyme, and these provide
both barrier and buffering functions
[9]
. Both de- and remineralization processes of the teeth are
also mediated by the pellicle. In terms of bacterial colonization, many of the proteins that make up
the pellicle act as receptors for the specific interaction with adhesins on the surface of pioneer
bacterial species
[9]
. The pellicle layer is therefore of particular relevance for the interactions of
both bacteria and nanoparticles with the tooth surface.
The strength of the forces involved in the initial attachment of bacteria is critical to their sur-
vival and the subsequent growth of the biofilm. The major growth of dental plaque mass then
occurs by bacterial cell division within the biofilm rather than by coaggregation at the surface of
the developing biofilm
[10]
. The initial communities of bacteria found within the supragingival
plaque biofilm are of a relatively low diversity in comparison to those present in the mature com-
munities of both supra- and subgingival plaque. Initial colonizers include Streptococcus oralis,
Streptococcus sanguinis, and Streptococcus mitis. The coaggregating partners with these bacteria
would then include predominantly gram-negative species, e.g., Veillonella atypica, Eikenella corro-
dens, and Prevotella loescheii. Coaggregation bridges between these early colonizers and
Fusobacterium nucleatum are common and the latter then coaggregates with numerous late coloni-
zers. Late colonizers include Aggregatibacter actinomycetemcomitans, Prevotella intermedia,
Treponema denticola, and Porphyromonas gingivalis
[10]
. The interactions between oral bacteria
are integral to biofilm development and maturation and include physical contact, metabolic
exchange, molecular communication, and genetic material exchange.
Biofilms will accumulate on both the hard and soft oral tissues, and this community of micro-
bial species is embedded in a matrix of bacterial components, salivary proteins/peptides, and food
debris
[8]
. Extracellular polymeric substances, produced by bacteria in a mature biofilm, contain
large amounts of polysaccharides, proteins, nucleic acids, and lipids. These maintain the structural
integrity of the biofilm and provide an ideal matrix for bacterial cell growth and survival
[11]
. The
biofilm mode of growth is clearly distinguished from planktonic growth by a number of features,
