Biomedical Engineering Reference
In-Depth Information
chemical and physical properties change (e.g., transparency, color, and conductivity). In dentistry,
these properties are beginning to be used to prepare more efficient materials and devices.
Furthermore, the development of dental products tends toward more microscopic aspects; therefore,
nanotechnology is positioning itself as a tool for important dental applications [6,7] .
Several authors use the expression “top-down” to describe the preparation of nanosystems by
the rupture (e.g. milling) of a material block. The expression “bottom-up” however relates to the
fabrication of nanosystems by the assembly of basic components such as atoms or molecules [8,9] .
The idea of encapsulating substances into nanosystems has different purposes; it can serve as a pro-
tection capable of preserving the functionality and bioavailability of encapsulated substances.
Furthermore, encapsulation can be used for controlled release. Encapsulation can also modify the
physical characteristics of the original material thus extending the therapeutic effect next to, or
directly in contact with, the target site [10
12] . Representative nanomaterials used in dentistry are
shown in Figure 23.2 .
Nanocrystals are formed by the “top-down” approach using energy-intensive processes, where
the active ingredient is directly fragmented (e.g., ball milling, high-shear homogenization, and
ultrasonication) into submicron size from the bulk material [44] . Nanocrystals of potassium nitrate,
poorly water-soluble calcium salts, calcium fluoride, and carbonate-substituted hydroxyapatite have
been proposed as active substances for the treatment of dentine sensitivity, remineralization of tooth
surfaces, and caries inhibition. These nanocrystals can be formulated as compounds for oral or den-
tal hygiene such as solutions, suspensions, oils, resins, or other solid products. The enhanced effect
of nanocrystals compared with their powders can be explained by their tiny size, which enables the
nanocrystals to infiltrate and permeate the micronsized dentinal tubules or porous surfaces of
the teeth forming a therapeutic depot [13,14,16,17] .
Metal nanoparticles are submicron scale entities made of pure metals (e.g., gold, platinum,
silver, titanium, zinc, cerium, iron, and thallium) or their compounds (e.g., oxides, hydroxides,
sulfides, phosphates, fluorides, and chlorides) [44,45] . One of the most documented nanosystems in
dentistry is silver nanoparticles. Due to their small size, they have a large area available for oxida-
tion [38] . Silver nanoparticles, either as dispersion or incorporated into different materials, have
shown different properties and applications in dental practice as antimicrobials, caries inhibitors,
dental restorative materials, endodontic retrofilling cement, dental implants, and intraoral devices to
prevent microbial accumulation (e.g., mouth guards) [33,38] . Metal oxide nanoparticles also have
important dental applications. For example, Sevin¸ et al. [34] showed the antibacterial activity of
zinc oxide nanoparticles by reducing the biofilm growth or plaque accumulation when they were
included at 10% w/w in a resin-based formulation. Elsaka et al. [35] evaluated the addition of tita-
nium oxide nanoparticles to a conventional glass ionomer and confirmed their potent antibacterial
effect. Gold nanoparticles have also showed high bactericidal activity by a synergistic action with
gallic acid. This promising antibacterial effect has attracted considerable interest from researchers
and pharmaceutical companies due to their high microbial resistance to antibiotics and the develop-
ment of resistant strains [31] . An interesting property of metal oxides is their photocatalytic capac-
ity, which can be improved by increasing the surface area [10] . A recent patent [37] described the
use of zinc oxide and titanium dioxide nanoparticles as bleaching agents. The dispersion is applied
on the teeth and activated by a light source inducing a photocatalytic reaction promoting the
bleaching. Similar results have been reported for selenium nanoparticles, which also removed
smoking-induced dental stains and calculus [46] . An interesting approach with metal nanoparticles
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