Biomedical Engineering Reference
In-Depth Information
precipitation and capturing of S. mutans cells under in vitro conditions [67] . It has been shown that
multiwalled carbon nanotubes with a diameter of approximately 30 nm had the highest precipitation
efficiency which is attributable to both their dispersibility and adequate aggregation activity.
Bundles of flexible single-walled and multiwalled carbon nanotubes (with average diameters of
30 nm) can wind around the curved surface of S. mutans. However, from a toxicological point of
view, such artificial nanotubes could mean a considerable harm for the human organism in contrast
to biomimetic apatites or other biomimetic preparations based on components of foodstuffs.
Various attempts to inhibit biofilm formation have been performed in recent years with newly
developed coating materials characterized by (supposed) self-cleaning properties. Surface coatings
providing self-cleaning properties could be applied to the natural tooth as well as to any artificial
solid surface and restorative material used in dentistry (i.e., fissure sealants, restorations, crown and
bridge work, dentures or implants) in order to topically control biofilm formation. Experimental coat-
ing materials containing fluoroalkylated acrylic acid oligomers (FAAO) have been applied to dental
resin composite substrates [68] . Contact angle measurements have shown that an increase in the con-
centration of FAAO in the coating material enhanced surface hydrophobicity and oil repellence.
However, biofilm assays clearly demonstrated that the amount of in vitro biofilm formation on these
surface coatings decreased only gradually when the concentration of FAAO increased [68] . Thus, the
data indicate that this type of coating material containing incorporated FAAO does not possess suf-
ficient self-cleansing properties and will not inhibit biofilm [68] . In addition, experimental resin
composites with incorporated poly-tetrafluoro-ethylene (PTFE) microparticles have been developed,
which theoretically could improve the surface properties of the materials and thus inhibit bacterial
adherence [69] . Although the hydrophobicity of the resin composites is significantly increased by
incorporation of the PTFE microfillers, the surface resistance against biofilm formation is not
improved. Resin composites with and without microsized PTFE particles harbors the same amount
of bacteria under in vitro conditions [69] . In contrast, a recently developed nanocomposite surface
coating composed of nanoscaled inorganic particles integrated into a fluoropolymer matrix indeed pro-
vides easy-to-clean properties due to a low surface free energy of 20
25 mJ/m 2 . Coating of enamel or
titanium surfaces by this nanocomposite material leads to the detachment of the outer pellicle layers
and adherent biofilms, as confirmed by an in situ study [70] . Such nanocomposite coatings are conceiv-
able for the coating of implant necks or fissure sealants, just to give some examples. It has been postu-
lated that the bacteria are faced with different physicochemical surface characteristics alternating at the
nanoscale. This could result in a low tenacity of the adherent bacteria or bacterial biofilm [70] .Incon-
trast to the above mentioned coatings, this nanomaterial yields the physicochemical properties required
for adoption in the oral cavity.
Further approaches to gain durable easy-to-clean surfaces are in advance in materials science;
thereby, novel manufacturing techniques such as spraying are established. Though some of these pre-
parations might be of interest for dentistry, their efficacy must be proved under the specific conditions
of the oral cavity after ascertainment of toxicological innocuousness [71,72] . It is noteworthy that these
new approaches are also based on the hierarchical arrangement of particles to achieve certain surface
properties [72] .
The lotus effect in its classical sense based on an ultrahydrophobic surface is not suitable for
the application in the oral cavity due to the very low mechanical stability [73,74] . Even if this sub-
tle surface texture would be of high tenacity, it will be masked by the ubiquitous pellicle layer
under the conditions prevailing in the oral cavity. Thereby, it has to be pointed out that the surface
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