Biomedical Engineering Reference
In-Depth Information
Although nanotubes are some of the most thoroughly studied nanomaterials with important appli-
cations in several fields, their use in dentistry is still limited. Considering their extraordinary mechani-
cal properties and ultra-high-tensile strength, carbon nanotubes have been proposed as composites in
different formulations (e.g., dental resins). Zhang et al.
[39]
included single-walled carbon nanotubes
coated with a thin shell of nano-SiO
2
in dental resin-based composites. It was concluded that the com-
posite with modified carbon nanotubes exhibited an improved flexural strength. A similar use has
been reported for TiO
2
nanotubes when introduced into alloys for dental materials. Recently, Ma et al.
[47]
proposed a sophisticated system with Ag nanoparticles/fibroblast growth factor 2 (FGF-2) depos-
ited on a TiO
2
nanotubular surface, which has a large potential for use in dental implant abutment.
Nanoclays (natural silica) and their modified varieties (organoclays) are commonly used in den-
tal products (e.g., toothpaste abrasives). Essentially they are nontoxic and nonirritant when used
orally. In the last decade, silica nanoparticles (e.g., available under the trade names Aerosil
(Degussa), HDK (Wacker), Cab-O-Sil (Cabot Corp.)) have been proposed as nanoscale fillers to
enhance dental resins
[40]
. They can improve the rheological behavior, scratch/abrasion resistance,
and surface hardness of the final products
[41]
. Gaikwad et al.
[48]
studied the roughness of the
polished surfaces using atomic force microscopy after the use of different polishing materials,
including silica nanoparticles. Significantly lower nanometer-scale roughness was obtained when
silica nanoparticles were used to polish tooth surfaces, compared with conventional polishing
pastes. Furthermore, silica nanoparticles are efficient at removing bacteria (e.g., Streptococcus
mutans) from the polished areas. Silica nanoparticles demonstrate improved fixation of dental pros-
theses by increasing the strength, the adhesive ability and the resistance to oral fluid impact, and by
reducing film thickness and heat emission in formulations based on zinc
phosphate cement
[49]
.
Recently, an invention proposed by M¨ ller and Wiens
[43]
combined hydroxyapatite and nano- or
microspheres (e.g., silica) bound by an oligopeptide which can be used for sealing dental pits, fis-
sures, and dentinal tubules to prevent tooth decay formation and to reduce dentin hypersensivity.
23.2
Definitions
The term nanoparticles will be used as the collective name to describe both nanospheres and nano-
capsules
[50]
which differ in their morphology and architecture. Nanospheres are formed by a dense
polymeric matrix, whereas nanocapsules are composed of an oil core surrounded by a polymeric
membrane (see
Figure 23.3
). Nanoparticles show several advantages in relation to other materials
including colloids used in the dental field, such as (i) better stability in biological fluids and during
storage, (ii) easy preparation and diversity in preparation techniques, (iii) easy large-scale
manufacturing, (iv) batch-to-batch reproducibility, and (v) controlled release. Nanoparticles also sat-
isfy the purpose of encapsulating and delivering active substances to a target site (e.g., the dentogin-
gival sac) known as carriers or vectors. Solid lipid nanoparticles and nanostructured lipid carriers are
attractive modalities of nanoparticles. Both systems are solid at both room and body temperatures
and are highly suitable for carrying lipophilic substances. Solid lipid nanoparticles are constituted
only of solid lipids and nanostructured lipid carriers contain solid lipids and oils which increase their
capacity to load active substances. The reasons for using lipids are their low toxicity, high biodegrad-
ability, and the possibility of modifying the bioavailability of some active substances
[51]
.
