Nanotechnology is the emerging science of technology that deals with the study and application
of nano sized materials (10-9 mm) that can be
used in various engineering and medical fields.
Nanodentistry is the field of science and technology that deals with the diagnosing, treating and
preventing oral and dental diseases, relieving
pain, maintaining and improving dental health
using nano particles. In future, nanodentistry will
succeed in maintaining near-perfect oral health
through the aid of nanorobotics and nanomaterials. The new era of dental treatment emphasis on
nanomedicine, nanorobotics, nanodiagnostics,
nanodental materials, nanosurgery and nanodrugs. Nanodentistry may seem more science
fiction than fact, but with current advancements
in science, technology, and medicine, it may very
well be a reality in the distant future. It is important
to assess the biocompatibility of nanostructures
prior to their use in dentistry to avoid possible
pathological conditions. Social challenges like
ethical problems and public acceptance are of
major concern. The article aims to bring forth and
highlight the most recent and innovative research
outcomes leading to the application of nanotechnology in the field of dentistry.
A literature search was done by using the key
words “nanodentistry” “nanotechnology” “nanoparticles in dentistry” “application of nanotechnology in prosthodontics”. The reference articles
were taken from pubmed indexed journals. The full
text articles were obtained. The article focused on
nanotechnology in prosthodontics. Only articles
that were published in English were included.
The importance of acrylic resins in dentistry is evident. They are widely used in making temporary
prosthetic base materials, provisional prosthesis,
dentures and orthodontic removable appliances
such as retainers and functional appliances. These
resins commonly consist of methacrylates, especially poly methyl methacrylate (PMMA), and
additional copolymers.1
However one of the major
problems that patients and dentists commonly
faced using these removable acrylic appliances
is their potential for plaque accumulation due to surface porosities and food retentive configuration, which in turn increase bacterial activity of
cariogenic oral flora.2
The consequences will be
higher rate of decalcification and dental caries
along with marginal gingivitis. In efforts to add
antimicrobial activities to dental materials, some
nanoparticles have been applied.
TITANIUM DIOXIDE NANOPARTICLES have been
used as additives to biomaterials in order to induce
antimicrobial properties.3,4 Antimicrobial activities
of titanium dioxide against candida albicans,
staphylococcus aureus, pseudomonas aeruginosa,
escherichia coli, lactobacillus acidophilus, etc.
have been proved by recent studies.5-8 Along with
prominent catalytic effect, other characteristics
such as white color, low toxicity, high stability
and efficiency as well as availability have made
titanium dioxide an appropriate antimicrobial additive for use in acrylic resin.9,10 Among compounds
as inorganic carriers such as apatite, zeolite and
phosphate, Silica dioxide is more promising due
to its porous structure and adsorption properties.
NANOPARTICLES OF SILICA DIOXIDE possess
extremely high surface activity and adsorb various
ions and molecules.11
SILVER NANOPARTICLES due to their small size
possess greater dispersion in PMMA matrix and
produce larger area for oxidation.12
The release of silver ions plays the major role in
the antibacterial mechanism of silver nanoparticles by rupturing the cell wall causing protein
denaturation, blocking cell respiration, and finally
causing microbial death.13
However, disadvantages of silver nanoparticles
incorporated in acrylic resin are also evident. The
acrylic resin incorporated with silver nanoparticles
experienced a color change (an important functional property of dental materials) resulting from
the plasmon effect of the silver nanoparticles.14
Studies reported that silver nanoparticles are cytotoxic to different cell lines.15
Results showed that silver nanoparticles were
cytotoxicity in the case of exposure at high concentrations.16
Kvitek et al., reported that the silver nanoparticles
having the diameter of 25 nm caused death of the
human fibroblasts at the concentrations higher
than 60 mg/L.17
The authors concluded that silver nanoparticles do
not generate any danger in applications, but only
if the concentration is retained (it should be sufficient for the inhibition of microorganism growth).
These results suggest that tested composites with
concentrations to 40 ppm of silver nanoparticles
should be safe in an oral cavity environment.
Douglas Roberto Monteiro et al reported decrease
in the mechanical properties of the acrylic denture
base resin with increase in the concentrations of
the silver colloidal nanoparticles.18
Nanofillers are integrated in vinylpolysiloxanes,
producing a unique addition of siloxane impression materials.19 The material has better flow, improved hydrophilic properties hence fewer voids at
margin and better model pouring, and enhanced
detail precision. Advantages includes Increased
fluidity, High tear resistance, Hydrophilic properties, Resistance to distortion and heat resistance,
Snap set that consequently reduces errors caused
by micro movements. Trade name is Nanotech
Elite H-D
Tissue conditioners have been commonly used to
enhance the recovery of denture bearing tissues
from trauma, damage or residual ridge resorption
usually caused by ill-fitting dentures. However,
these materials are degenerated with time and
are susceptible to colonization by microorganisms.20 Tissue conditioners could be kept cleaby mechanical and chemical methods but this
can cause considerable damage to tissue conditioners.21,22 Silver has been well known for its
antimicrobial characteristic.23 So to overcome this
problem silver nanoparticles are added in tissue
conditioners because of their smaller size they
provide large surface area.
According to study conducted by Ki-Young Nam the
modified tissue conditioner combined with silver
nanoparticles displayed antimicrobial properties against S. aureus, S. mutans at 0.1% and C.
albicans at 0.5% after a 24 hrs and 72 hrs incubation period. The study could not jump to conclude
whether the antimicrobial effect was resulted from
release of silver cation from the modified sample
to incubation medium or direct contact between
Ag-tissue conditioner and microbial cells.24
Dental adhesives are the material used to promote adhesion or cohesion between two different
substances or between a material and natural
tooth structure. Polymerizable silane is added to
dental adhesives in order to increase the cohesive
strength. Since the adhesive liquid are not very
viscous the filler particles tend to settle out during storage which leads to inconsistency in their
performance. To overcome this disadvantage
discrete silane treated nanoparticles of silica or
zirconia in the size range of 5-7 nm are added
to dental adhesives25. According to a study by
N. Silikas et al., no decrease in bond strength of
dental adhesives after the incorporation of silica
or zirconia nanoparticles was obtained.26
1. Nanofill Composites - Nanofills are the dental
composites in which all the fillers are of 1-100 nm
range. Two types of nanoparticles are used for
preparing nanofill dental composite.27 The first
of these is the most common and are nanomeric
particles which are essentially monodispersed non-aggregated and non-agglomerated particles
of silica.
Advantages are good optical properties., dispersion rate is improved, increased polish retention
and increased surface gloss
Disadvantages are poor rheological properties
and handling properties
The second type of nanoparticle used to prepare
nanofill composites is NANOCLUSTERS. This is
done in order to overcome the disadvantages of
the previously used nanomeric nanoparticle. Nanoclusters are made by lightly sintering nanomeric
oxides to form clusters of a controlled particle size
distribution. Nanoclusters from silica sols only28 as
well as from mixed oxides of silica and zirconia
have been synthesized.29
Advantages are good optical properties, Dispersion rate is improved, Increased polish retention,
Increased surface gloss and Rheological properties better than the previous one.
Disadvantage is Poor handling properties
2. Nanohybrid Composites -
Prepolymerized organic fillers are incorporated so as to improve the
undesirable rheological properties of composites
where nanomers were included.30
Advantages are improved esthetic properties and
Improved rheological properties
Disadvantages are decreased Dispersion rate
and Decreased polish retention and surface gloss
3. Titanium Di-Oxide Reinforced Resin Based
Composites -
According to study conducted by
Yang Xia et al., titanium dioxide nanoparticles
treated with organosilaneallyltriethoxysilane
(ATES) are used in order to improve the microhardness and flexural strength of the resin-based
composites.31 G. Polizos conducted a study in which
titanium dioxide nanoparticles were synthesized
in an aqueous solution. They were dispersed into an epoxy polymer matrix. The obtained material
showed better mechanical properties.32
4. Nanocomposite with Alumina Nanoparticles
-
According to study conducted by M. AlHaik et
al., inclusion of alumina nanoparticles increases
the hardness of the nanocomposite as compared
to other nanocomposites. The production of alumina nanoparticles is done by using a low power
plasma torch.33 Zhanhu Guo et al., conducted a
study in which alumina nanoparticles have been
successfully functionalized with a bi-functional
silane surfactant by a facile method. The result
was significant increase in both modulus and
strength. The addition of the functionalized nanoparticles has no deleterious effect on the thermal
stability of the composite and the vinyl ester resin
after curing has effectively protected the alumina
nanoparticle from dissolution in both acidic and
basic solutions.34
5. Calcium phosphate and calcium fluoride nanoparticles-based composites -
Materials that
release calcium fluoride or phosphate ions have
been shown to provide remineralization to tooth
structure.35 Accordingly, the use of nanoparticles
based on calcium phosphate and calcium fluoride
in nanocomposites have been investigated. Xu et
al have reported the synthesis of anhydrous dicalcium phosphate nanoparticles incorporated
in composites.36 In an interesting approach, nanohydroxyapatites (HAP) having a particle size
of 20 nm were synthesized to mimic the natural
building blocks of human enamel and were found
to provide anticaries repair effect.37
In dentistry there is wide range of cements with
different applications where the antimicrobial
activity is relevant. Antibacterial activity of dental
luting cement is a very important property when
applying dental crowns, bridges, inlay, onlay, veneers because bacteria may be still present on the
walls of preparation or gain access to the cavity if there is microleakage present after cementation.
[38]In order to overcome this, addition of silver
nanoparticles in dental cements took place. Silver
has been used for its bactericidal properties for
many years.
It has been used in water purification, wound
care, bone prosthesis, cardiac devices and surgical appliances.39,40 Silver nanoparticles are used
because of their advantage that they show strong
antibacterial activity due to their higher surface
area to volume ratio.41 Yoshida et al., showed that
a resin composite cement incorporated with silver containing materials had a long-term inhibitory
effect against S. mutans and favorable mechanical properties.42
Dental porcelains currently used for ceramic restorations are brittle, and it is sometimes necessary to
replace fractured or chipped restorations. Porcelain
is fragile and exhibits elastic deformation rather
than plastic deformation, leading to fracture or
chipping of restorations.
Mitsunori Uno et al., conducted a study to investigate toughening of porcelain through the addition of silver nanoparticles to dental porcelain.
The addition of silver nanoparticles significantly
increased the fracture toughness and vickers hardness of the porcelain.31
Tokushifujieda et al., conducted a study in which
they incorporated nanoparticles of precious metals of silver and platinum in dental porcelain and
came to a conclusion that the addition of silver and
platinum nanoparticles enhanced the mechanical
properties of porcelain.
The addition of silver and platinum nanoparticles increased both the Young’s modulus and
the fracture toughness of dental porcelain. Silver
nanoparticles increased the fracture toughness
more than platinum.43
New coating technologies have also been developed for applying hydroxyapatite and related
calcium phosphates (CaP), the mineral of bone
onto the surface of implants.
Many studies have demonstrated that these CaP
coatings provided titanium implants with an osteoconductive surface.44,45 Following implantation,
the dissolution of CaP coatings in the periimplant
region increased ionic strength and saturation of
blood leading to the precipitation of biological
apatite nanocrystals onto the surface of implants.
This biological apatite layer incorporates proteins
and promotes the adhesion of osteoprogenitor
cells that would produce the extracellular matrix
of bone tissue
It has been also shown that osteoclasts, the bone
resorbing cells, are able to degrade the CaP coatings through enzymatic ways and created resorption pits on the coated surface.45
Finally, the presence of CaP coatings on metals
promotes an early Osseo integration of implants
with a direct bone bonding as compared to noncoated surfaces.
The challenge is to produce CaP coatings that
would dissolve at a similar rate than bone apposition in order to get a direct bone contact on
implant surfaces
Pesqueira et al evaluated the effect of disinfection
and accelerated ageing on the dimensional stability and detail reproduction of a facial silicone
with different types of nanoparticle. A total of 60
specimens were fabricated with Silastic MDX
4-4210 silicone and they were divided into three
groups: colorless and pigmented with nanoparticles (make-up powder and ceramic powder). Half
of the specimens of each group were disinfected
with Efferdent tablets and half with neutral soap for 60 days. Afterwards, all specimens were subjected to accelerated ageing. Both dimensional
stability and detail reproduction tests were performed, after specimen fabrication (initial period),
after chemical disinfection and after accelerated
aging periods (252, 504 and 1008 hours). The
dimensional stability test was conducted using
AutoCAD software, while detail reproduction was
analyzed using a stereoscope magnifying glass.
Dimensional stability values were statistically
evaluated by analysis of variance (ANOVA) followed by Tukey’s test (p< 0.01). Detail reproduction
results were compared using a score. Chemical
disinfection and also accelerated ageing affected
the dimensional stability of the facial silicone with
statistically significant results. The silicone’s detail
reproduction was not affected by these two factors
regardless of nanoparticle type, disinfection and
accelerated ageing.46
The uses of various nanoparticles in acrylic resin, tissue conditioner, dental adhesives, composites, dental cements, dental porcelain, implants and maxillofacial prosthesis are discussed. However, further studies are required to clarify the cytotoxicity of various nanoparticles, optimal concentration and mechanical stability for proper and safe clinical experience. Following are the list of most suitable nanoparticle used in combination with different dental materials used in field of prosthodontics
Presently, although the vast customization of nanoparticles in prosthodontics is increasing progressively, there is a lack of studies addressing
the safety and optimal concentrations of different
nanoparticles in dental materials. Further efforts
are needed to extend the arms of research where
release of particles from present and future dental materials could be scrutinized. Toxicological
studies where the uptake and possible effects are
determined will be perilous for the risk assessment. As we could acknowledge from the above
review, the identified knowledge breach calls for
extended research in this area.
Nanomaterials and nanorobots are of great interest when considering advances in nanotechnology. Although all the research activities for this
promising field are at the initial stage, the results
of the clinical studies have a strong potential to
revolutionize the diagnosis and treatment planning as well as tissue regenerative materials for
improving esthetics in dental field.
However more investigations and clinical trials are
required for the application of nanotechnology in
oral health and dental care.