NANOTECHNOLOGY: THE FUTURE OF DENTISTRY (A REVIEW)

Nanotechnology era is fast approaching which was unheard three decades ago. All

disciplines of human life will be impacted by advances in nanotechnology in the near

future. The growing interest in this field is giving emergence to new field called

Nanomedicine, a science & technology of diagnosing, treating & preventing

diseases, and preserving & improving human health, using nanoscale structured

materials. Once one considers other potential applications of nanotechnology to

medicine, it is not difficult to imagine what nanodentistry would look like.

Nanotechnology is a field of applied science and technology covering a broad range

of topics. The main unifying theme is the control of matter on a scale smaller than 1

micrometre, normally between 1-100 nanometers, as well as the fabrication of

devices on this same length scale. It is a highly multidisciplinary field, drawing from

fields such as colloidal science, device physics and supramolecular chemistry. Much

speculation exists as to what new science and technology might result from these

lines of research. Some view nanotechnology as a marketing term that describes

pre-existing lines of research applied to the sub-micron size scale.1

“Nanotechnology” was coined by Prof. Kerie Drexler. Nano is derived from the greek

word “υαυος” which means dwarf.2 A nanometer is 10–9 meter, or one-billionth of a

meter. It is engineering at the molecular scale. Nanotechnology helps us to exploit

the atomic or molecular properties of materials. Nobel prize(1959) laureate Prof

Richard Fenyman had a vision that smaller and smaller machines could be created

to work at the molecular level. With advancement in nanotechnology this vision now

seems not too distant.

In 1959, the late Nobel Prize winning physicist Richard P. Feynman presented a talk

entitled “There’s Plenty of Room at the Bottom” at the annual meeting of the

American Physical Society. Feynman proposed using machine tools to make smaller

machine tools, which, in turn, would be used to make still smaller machine tools, and

so on all the way down to the molecular level. He suggested that such

nanomachines, nanorobots and nanodevices ultimately could be used to develop a

wide range of atomically precise microscopic instrumentation and manufacturing

tools. 3

The basic concept is to create such small machines / robots and products

which will work at the atomic level.

1. Building up particles by combining atomic elements.

2. Using equipment to create mechanical nanoscale objects.

Individual atoms + Molecules = Complex structures (extraordinary

properties)4

Two main approaches are used in nanotechnology: one is a "bottom-up"

approach where materials and devices are built from molecular components which

assemble themselves chemically using principles of molecular recognition; the other

being a "top-down" approach where nano-objects are constructed from larger

entities without atomic-level control.2

PERSPECTIVES OF NANOTECHNOLOGY

1. Larger to smaller: a materials perspective

2. Simple to complex: a molecular perspective

1. Larger to smaller: a materials perspective2

A unique aspect of nanotechnology is the vastly increased ratio of surface area to

volume present in many nanoscale materials which opens new possibilities in

surface-based science, such as catalysis. A number of physical phenomena become

noticeably pronounced as the size of the system decreases. This effect does not

come into play by going from macro to micro dimensions.

2. Simple to complex: a molecular perspective2

Modern synthetic chemistry has reached the point where it is possible to

prepare small molecules to almost any structure. These methods are used today to

produce a wide variety of useful chemicals such as pharmaceuticals or commercial

polymers. This ability raises the question of extending this kind of control to the next-

larger level, seeking methods to assemble these single molecules into

supramolecular assemblies consisting of many molecules arranged in a well defined

manner.

These approaches utilize the concepts of molecular self-assembly and/or

supramolecular chemistry to automatically arrange themselves into some useful

conformation through a bottom-up approach. The concept of molecular recognition

is especially important: molecules can be designed so that a specific conformation or

arrangement is made.

NANOMEDICINE

Nanomedicine, an offshoot of nanotechnology, refers to highly specific

medical intervention at the molecular scale for curing disease or repairing damaged

tissues, such as bone, muscle, or nerve. Nanomedicine is the medical application of

nanotechnology that will hopefully lead to useful research tools, advanced drug

delivery systems, and new ways to treat disease or repair damaged tissues and

cells. Drug delivery is currently the most advanced application of nanotechnology in

medicine. Nanoscale particles are being developed to improve drug bioavailability, a

major limitation in the design of new drugs. Poor bioavailability is especially

problematic with newer and still experimental RNA interference therapy. Lipid or

polymer-based nanoparticles are taken up by cells due to their small size, rather

than being cleared from the body. These nanoparticles can be used to shuttle drugs

into cells which may not have been accepted the drug on their own. The nanoparticle

chaperone may also be able to specifically target certain cell types, possibly

reducing toxicity and improving efficacy. 3

Nanocomputers would assume the important task of activating, controlling

and deactivating such nanomechanical devices. Nanocomputers would store and

execute mission plans, receive and process external signals and stimuli,

communicate with other nanocomputers or external control and monitoring devices,

and possess contextual knowledge to ensure safe functioning of the nanomechanical

devices.

A list of some of the applications of nanomaterials to biology or medicine

Drug and gene delivery

Bio detection of pathogens

Detection of proteins

Probing of DNA structure

Tissue engine

Tumor destruction

NANODENTISTRY

Nanodentistry is an offshoot of nanomedicine. Application of

nanomedicine to dentistry has lead to the emergence of a branch of science

called Nanodentistry. Development of “Nanodentistry” will make possible the

maintenance of near-perfect oral health through the use of nanomaterials,

biotechnology including tissue engineering and nanorobotics. The nanorobotic

functions may be controlled by an onboard nanocomputer that executes

preprogrammed instructions in response to local sensor stimuli.4

CURRENT APPLICATIONS OF NANODENTISTRY 5

1. Nanocomposites

2. Nano-Composite Denture Teeth

3. Plasma Laser application for periodontia

4. Nano Impression Materials

5. Bonding Agents

6. Prosthetic Implants

7. Nano Light-Curing Glass Ionomer Restorative

1) NANOCOMPOSITE:

Nano-composite dental filling material is a material that can be used in all

areas of the mouth with superior polish (typical of microfills), as well as excellent

mechanical properties suitable for high stress - bearing restorations (typical of hybrid

composite).10

3M ESPE has two products which come under the category of nanocomposites: 3M

ESPE Filtek™ Z350 Universal Restorative and 3M™ ESPE™ Filtek™ Supreme Plus

Flowable Restorative. 3M ESPE's has synthesized two new types of nanofiller

particles: Nanomeric, or NM, particles and nanoclusters, or NCs. The NM particles

are monodisperse nonaggregated and nonagglomerated silica nanoparticles

Compressive and diametral tensile strengths of the nanocomposite (FSS and

FST) are equivalent to or higher that those of the other commercial composites. The

flexural strength of FSS and FST is higher than that of other composites. Fracture

resistance of FSS and FST is higher than that of the composites.

2) NANO-COMPOSITE DENTURE TEETH 6

Porcelain denture teeth have been considered the most wear resistant;

however, porcelain possesses a number of major disadvantages, including

brittleness, lack of bonding to the denture base, and difficulty in polishing." Acrylic

denture teeth commonly undergo substantial attrition in relatively short periods of

time. In an effort to retain the acceptable clinical characteristics of acrylic resin teeth

while gaining acceptable wear resistance, several new types of resin denture teeth

have been introduced. These include those made of cross - linked acrylic and micro -

filled composite resins. Nano filled denture teeth and conventional acrylic teeth. New

type of denture tooth, fabricated of nanocomposite resin, has recently, been,

developed as a highly polishable, stain and impact resistant material. It consists of a

comonomer of urethane dimethacrylate (UDMA) and methylmethacrylate (MMA).

Polymethylmethacrylate (PMMA), and uniformly dispersed nano - sized filler

particles. Based upon the limited aspect of in vitro study results, and for the range of

representative materials tested, it appears that the nano - composite denture tooth

sued in this study possesses superior surface hardness and wear resistance

compared to the conventional acrylic denture tooth.7 The new Veracia anterior and

posterior teeth have been manufactured according to the standards set by nature

and offer exceptional aesthetics and a lively impression. It is indiacted for Full

denture prosthetics, Implant restorations, Telescopic restorations, Attachment work

and CrCo dentures. It has the advantage of having lively surface structure, matching

the morphology of natural teeth.

3) IMPRESSION MATERIALS 8

Impression materials Nanotech Elite H-D13 from the company Zhermack is

available with nanotechnology application. Here nanofillers are integrated in the

vinylpolysiloxanes, producing a unique addition siloxane impression material

Zhermack Elite H-D impressions formulation incorporates a combination of organic

polymers, inorganic particles and nano fillers. The result is an a Silicone with

increased fluidity, high tear resistance, hydrophilic properties, resistance to distortion

and heat resistance.  Elite H-D + has also been design to produce a snap set that

consequently reduces errors caused by micro movements.

4) LASER PLASMA APPLICATION FOR PERIODONTIA

When TiO2 particle sizes are reduced to nanoscale (20-50 nm diameter

particles), and present on human skin in the form of a gel-like emulsion, it has some

interesting properties such that when irradiated with laser pulses from a HPPL, these

particles can be optically broken down with accompanying effects.

a. Shock wave

b. Micro-abrasion hard tissue

c. Stimulation of collagen production

Laser plasma is based on HPPL combined with TiO2 nanotechnology and has

been proven effective in a number of dental treatments including:

1) Periodontal treatments. Most dental lasers in the market can do

periodontal treatment of gum diseases. Equilase-10, with rep. rate up to lOO Hz,

pulse width of 100 microsecond and energy per pulse up to 350 mJ, is by far more

powerful than the most powerful dental laser in the market (Figure 11). With a

dimension of 210 mm Wx463mm D x 380 mm H, it is very compact compared with

other in the market. Equilase-10 can treat gum disease alone, but with TiO2

nanotechnology it can be done cleaner and quicker.

2) Melanin removal. On the gums, it gives a lighter color and prettier gum

appearance.

3) Incision of soft tissue without anesthesia

4) Caries preparation. Equilase-10 combined with TiO2 nanotechnology can be

used to prepare caries with no anesthesia required.

5) Cutting of enamel. HPPL combined with TiO2 nanotechnology results in

cutting speed of the enamel hard tissue comparable to using drills, but the result is

much cleaner, smoother, and no anesthesia required.

6) Dentine cutting. Just like hard tissue enamel HPPL combined with TiO2

nanotechnology results in rapid cutting of dentine.

5) BONDING AGENT

In the past, bonding materials required three steps : etching, priming and

bonding, but the all-in-one system integrates these three steps into one; hence, it is

also called the "one-step" system. The G-Bond one-bottle system, which was

launched recently by GC Corporation, eliminates mixing procedures and is easy to

handle in daily dental clinical practice. It has been shown that the adhesive strength

of current all-in-one systems is lower than that of two-step systems. G-Bond exhibits

an adhesive strength of more than 40 MPa, which is comparable to the adhesion of

two-step systems to dentin. This indicates that G-bone has a satisfactory initial

adhesive strength. The interface formed by G-bond is totally different from that of the

interface formed by earlier bonding materials. The surface of the dentin is decalcified

only slightly, and there is almost no exposure of collagen fibers. This suggests that

an extremely thin (300 nanometers or less) interface is formed and that in this area,

functional monomers contained in the bonding material react with hydroxyapatite at

the "nano" level, to form insoluble calcium.G-Bond is expected to exhibit good

performance in daily dental clinical practice.

6) PROSTHETIC IMPLANT

The biomedical engineers have proven that cells attach better to metals with

nanometer-scale surface features, offering hope for improved prosthetic implants.

Conventional titanium alloys used in replacements are relatively smooth and the

body often reacts to areas, as it would to any foreign invader, by covering the parts

with a fibrous tissue intended to remove the unwanted material. The fibrous tissue

prevents prostheses from making good contact with the body by getting between

prosthetic devices and damaged body parts. This in turn impedes their

performance.9

By covering the implant materials with nanometer-scale bumps, they have

shown that not only can it keep the body form rejecting artificial parts but that the tiny

bumps stimulate the body to regroup bone and other types of tissue. Compared with

titanium alloy covered in micron-sized bumps, about 60% more new cells are grown

on the same alloy containing nanometer-scale features. Besides this the new

released alumina-zirconia nanocomposite, have a high resistance to crack

propagation, and as a consequence improving lifetime and reliability of ceramic joint

prostheses. With these nanocomposites it will be possible to extend the lifetime of

implants up to a minimum of 30 years, so contributing to improve the quality of life of

a large number of patients. Further surgical operations and consequently the

suffering of people as well as the high cost of such operations will be avoided.

7) NANO LIGHT-CURING GLASS IONOMER RESTORATIVE

The world's first nano-glass-ionomer is Ketac™ Nano Light-Curing Glass

Ionomer Restorative (Figure 14). In a clinical evaluation, over 60% of the dentists

who used Ketac™ Nano Light-Curing Glass Ionomer Restorative in their practice

rated the final overall esthetics the same or better than their current composite

restorative material.

It gives an esthetically-pleasing Class V restoration. Ketac Nano is an ideal

alternative esthetic glass ionomer solution for everyday dentistry. Advantages of this

material are:

Superb polish: In-vitro testing results show Ketac Nano restorative has

higher initial polish than other glass ionomer restorative materials.

Excellent esthetics: Shades of Ketac Nano restorative were developed to

match the shade targets of Filtek™ Supreme Plus Universal Restorative.

Ketac™ Nano Light-Curing Glass Ionomer Restorative paste/paste formula

can be used in a dispenser to make it faster and easier to dispense.

This product meets a Wide Range of Clinical Indications:

Primary teeth restorations

Transitional restorations

Small Class I restorations

Sandwich restorations

Class III and V restorations

Core build-ups

FUTURE AND SCOPE OF NANODENTISTRY

When the first micron-size dental nanorobots can be constructed, perhaps 10-

20 years from today, how might they be applied to dentistry? Freitas has

described how medical nanorobots might utilize specific motility mechanisms

to crawl or swim through human body tissues with navigational precision,

acquire energy, sense and manipulate their surroundings, achieve safe

cytopenetration (e.g., pass through plasma membranes such as the

odontoblastic process without disrupting the cell), and employ any of a

multitude of techniques to monitor, interrupt, or alter nerve impulse traffic in

individual nerve cells, in real time. These nanorobot functions may be

controlled by an onboard nanocomputer executing preprogrammed

instructions in response to local sensor stimuli. Alternatively, the dentist may

issue strategic instructions by transmitting his orders directly to in vivo

nanorobots via acoustic signals (e.g., ultrasound) or by other means – like an

admiral commanding a fleet.

New treatment opportunities in Nanodentistry may include:

1. Major Tooth Repair

2. Tooth Renaturalization

3. Hypersensitivity Cure

4. Orthodontic nanorobots

5. Dental Durability and Cosmetics

6. Nanorobotic Dentifrice (dentifrobots)

7. Tooth repositionin

8. Inducing anesthesia

(1) Tooth Repair.

Nanodental techniques for major tooth repair may evolve through several

stages of technological development, first using genetic engineering, tissue

engineering and tissue regeneration, and later growing whole new teeth in vitro and

installing them. Ultimately, the nanorobotic manufacture and installation of a

biologically autologous whole replacement tooth including both mineral and cellular

components – e.g., complete dentition replacement therapy – should become

feasible to undertake within the time and economic constraints of an ordinary office

visit, using an affordable desktop manufacturing facility in the dentist's office.

(2) Tooth Renaturalization.

Dentition renaturalization procedures may become a popular addition to the

typical dental practice, providing perfect methods for esthetic dentistry. This trend

may begin with patients who desire to have their old dental amalgams excavated

and their teeth remanufactured with native biological materials. But demand will grow

for full coronal renaturalizations in which all fillings, crowns, and other necessary

20th century modifications to the visible dentition are removed, with the affected

teeth remanufactured so as to be indistinguishable from the natural originals.

(3) Hypersensitivity Cure.

Dentin hypersensitivity is another pathologic phenomenon that may be

amenable to a nanodental cure. Dentin hypersensitivity may be caused by changes

in pressure transmitted hydrodynamically to the pulp. This etiology is suggested by

the finding that hypersensitive teeth have 8 times higher surface density of dentinal

tubules – and tubules with diameters twice as large – than nonsensitive teeth. There

are many therapeutic agents for this common painful condition that provide

temporary relief, but reconstructive dental nanorobots could selectively and precisely

occlude selected tubules in minutes, using native biological materials, offering

patients a quick and permanent cure.

(4) Orthodontic nanorobots.

Orthodontic nanorobots could directly manipulate the periodontal tissues

including gingiva, periodontal ligament, cementum and alveolar bone, allowing rapid

painless tooth straightening, rotating, and vertical repositioning in minutes to hours,

in contrast to current molar uprighting techniques which require weeks or months to

proceed to completion.

(5) Dental Durability and Cosmetics.

Tooth durability and appearance may be improved by replacing upper enamel

layers with covalently-bonded artificial materials such as sapphire or diamond which

have 20-100 times the hardness and failure strength of natural enamel or

contemporary ceramic veneers, and good biocompatibility.

Pure sapphire and diamond are brittle and prone to fracture if sufficient shear

forces are imposed but can be made more fracture resistant as nanostructured

composites, possibly including embedded carbon nanotubes.

(6) Nanorobotic Dentifrice (dentifrobots).

Effective prevention has reduced caries in children and a caries vaccine may

soon be available, but a subocclusal-dwelling nanorobotic dentifrice delivered by

mouthwash or toothpaste could patrol all supragingival and subgingival surfaces at

least once a day, metabolizing trapped organic matter into harmless and odorless

vapors and performing continuous calculus debridement. These invisibly small (1-10

micron) dentifrobots, perhaps numbering 103-105 nanodevices per oral cavity and

crawling at 1-10 microns/sec, might have the mobility of tooth amoebas but would be

inexpensive purely mechanical devices that would safely deactivate themselves if

swallowed and would be programmed with strict occlusal avoidance protocols.

(7) Tooth repositioning.

Orthodontic nanorobots could directly manipulate the periodontal tissues,

including gingivae, periodontal ligament, cementum and alveolar bone, allowing rapid

and painless tooth straightening, rotating and vertical repositioning within minutes to

hours. This is in contrast to current molar-uprighting techniques, which require weeks

or months to complete.

(8) Inducing anesthesia.

One of the most common procedures in dentistry is the injection of local

anesthetic, which can involve long waits and varying degrees of efficacy, patient

discomfort and complications. Well-known alternatives, such as transcutaneous

electronic nerve stimulation, cell demodulated electronic targeted anesthesia and

other transmucosal, intraosseous or topical echniques, are of limited clinical

effectiveness.

To induce oral anesthesia in the era of nanodentistry, dental professionals will

instill a colloidal suspension containing millions of active analgesic micrometer-sized

dental nanorobot "particles" on the patient’s gingivae. After contacting the surface of

the crown or mucosa, the ambulating nanorobots reach the dentin by migrating into

the gingival sulcus and passing painlessly through the lamina propria or the 1- to 3-

µm–thick layer of loose tissue at the cemento-dentinal junction. On reaching the

dentin, the nanorobots enter dentinal tubule holes that are 1 to 4 µm in diameter, and

proceed toward the pulp, guided by a combination of chemical gradients, temperature

differentials and even positional navigation, all under the control of the onboard

nanocomputer, as directed by the dentist.

HAZARDS OF NANOTECHNOLOGY

Billions and billions of dollars have already been given to the study of

nanotechnology. Items which are unbelievable to some have already been selling.

Yet, tests have shown that nanotechnology can function as venom to the

communities we live in and nanoparticles are known to biomagnify in animal organs.

Scientists are also concerned about soil and plant life. The first of two studies to look

for these dilemmas was a study sponsored by NASA, the space agency which looks

to take advantage of nanomaterials. In this study a scientist and his partners

transferred three types of nanotubes into mice. The nanotubes traveled to the lungs

of the rodents. All of the nanotubes had resulted in lung infections that get in the way

with oxygen receiving and may end up to lung disease ¡X what is known as

granulomas. Each mouse got one contact with the nanotubes, but the wound got

awful leading to tissue death. Quartz fragments, considered by toxicologists as a

poisonous substance, had less dangerous reactions than the nanoparticles.10

CONCLUSION

"Nanoscale science and engineering promise to be as important as the steam

engine, the transistor, and the Internet, and have the potential to revolutionize all

other technologies," according to Neal Lane, former science advisor to U.S.

President Bill Clinton. "But that outcome is not guaranteed."11

Oral health and disease trends may also change the focus on specific

diagnostic and treatment modalities. Increasingly preventive approaches will reduce

the need for curative or restorative interventions, as has already happened with

dental caries. Deeper understanding of the etiology and pathogenesis of other

disease processes, such as periodontal disease, developmental craniofacial defects,

and malignant neoplasms should make prevention for most of them a viable

approach.

The visions described above may sound unlikely, implausible, or even heretic.

Yet, the theoretical and applied research to turn them into reality is progressing

rapidly. Nanotechnological developments are expected to accelerate significantly

through new governmental and private-sector initiatives. It is unimportant which ones

of these scenarios will actually come to pass. The important point is that advances in

nanotechnological research and development have made such applications

theoretically possible. Time, specific advances, resources, and needs will determine

which ones will become reality.