|Year : 2016 | Volume
| Issue : 4 | Page : 139-143
Renaissance in orthodontics: Nanotechnology
Navaneetha Nambi1, NR Shrinivaasan1, L Xavier Dhayananth1, Vishal G Chajallani2, Ashwin Mathew George3
1 Department of Orthodontics, Sathyabama Dental College and Hospital, Ramapuram, India
2 Department of Orthodontics, SRM Dental College and Hospital, Ramapuram, India
3 Department of Orthodontics, Saveetha Dental College and Hospital, Chennai, Tamil Nadu, India
|Date of Web Publication||3-Jan-2017|
Ashwin Mathew George
Department of Orthodontics, Saveetha Dental College and Hospital, Chennai - 600 077, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Curiosity has its own reason for existing. For thousands of years, humanity has been harnessing its curiosity into inquiry and the process of scientific methodology. If we consider technology as an engine, then science is its fuel. Science of miniaturization (nanotechnology) is manipulating matter at nanometer level and the application of the same to medicine is called nanomedicine. Nanotechnology holds promise for advanced diagnostics, targeted drug delivery, and biosensors and is believed to create advances in the field of orthodontics to a great extent. When we gain access to hold the nanorobots, we will be able to treat very rapidly a number of diseases that are a continuous threat for humanity today. The present article aims to provide an early glimpse on the impact and future implication of nanotechnology in dentistry, especially in the field of orthodontics.
Keywords: Accelerated orthodontics; nanocoating; nanocomposites; nanorobotics.
|How to cite this article:|
Nambi N, Shrinivaasan N R, Dhayananth L X, Chajallani VG, George AM. Renaissance in orthodontics: Nanotechnology. Int J Orthod Rehabil 2016;7:139-43
| Introduction|| |
Over the past few years, a little word with big potential has been rapidly insinuating itself into the world's consciousness. That word is "nano." It has conjured up speculation about a seismic shift in almost every aspect of science and engineering with implications for ethics, economics, international relations, day-to-day life, and even humanity's conception of its place in the universe.
"Nanotechnology" - the terminology originates from the Greek word meaning "dwarf." The term nanotechnology was coined by Norio Taniguchi at the University of Tokyo, encompassing a multitude of rapidly emerging technologies based upon the scaling down of existing technologies to the next level of precision and miniaturization. In 1959, Richard P Feynman introduced the concept of nanotechnology, in his renowned talk titled - "there's plenty of Room at the Bottom" he explained the possibility of working with and controlling the atoms and molecules that make up matter, which is essentially the bottom up approach of nanotechnology. 
Quantum mechanics - it refers to the science of manipulating matter at the level of atoms measured in billionth of a meter or 1/80,000 of the diameter of human hair, or 10 times the diameter of a hydrogen atom. 
Convergence of nanotechnology with dentistry and medicine recently led to an interdisciplinary field, nanodentistry, and nanomedicine, which brings together engineers, physicists, biologists, chemists, mathematicians, and physicians striving to improve detection, imaging, and drug delivery devices.
Nanodentistry and nanomedicine is a sub-field of nanotechnology, and it is defined as the repair, construction, and control of human biological systems using devices built upon nanotechnology standards.  In short, nano dentistry and nanomedicine are the application of nanotechnology in a wide range of applications, such as the use of nanomaterials to nanoelectronic biosensors, and even possible future applications of molecular nanotechnology. Nanotechnology has begun its roadways in numerous engineering and medical fields and its future in orthodontic applications also seem to have potential, which has initiated a lot of research work. However, it is recognized that there is a need to understand the basic of this technology. The growing interest in the future of dental applications of nanotechnology is leading to the emergence of a new field called nanodentistry.
Nanorobots induce oral analgesia, desensitize tooth and manipulate the tissue to re-align and straighten irregular set of teeth and to improve the durability of teeth. ,
The current article dwells on this nano scenario and its implications, specifically in the world of orthodontics and some of the applications are listed below.
Different applications of nanotechnology in orthodontics are: 
- Nanorobotics in the acceleration of orthodontic tooth movement
- Nanocomposites for superior orthodontic bonding
- Nanotechnology in the prevention of white spot lesions (WSLs)
- Nanotechnology for coating of stainless steel brackets and stainless steel wires to increase the bioeffeciency of the bracket, and to reduce the friction in the arch wires used during routine orthodontic treatment.
| Nanotechnology in Accelerating Orthodontic Tooth Movement|| |
Orthodontics, being the oldest specialty of dentistry, continues to amaze the field of science with its brilliance and enormously increasing research and development, in the form of newer materials, methods of diagnostic aids and superior treatment mechanics. However, one aspect, which has not come under the control, is the rather delayed treatment duration. Currently, fixed orthodontic treatment requires a long duration of approximately 2-3 years, which eventually usually leads to a noncompliance patient. Apart from a noncompliant patient, there are other iatrogenic problems that can result from prolonged duration of treatment such as WSLs (commonly referred to as the scars of orthodontic treatment), gingival inflammation and root resorption. Currently, there is widespread interest for researches to focus on accelerating methods for tooth movement due to the huge demand for a shorter orthodontic treatment time. 
Recently, a lot of research has been focused on hastening orthodontic tooth movement, like corticotomy, distraction osteogenesis, prostoglandin injections, low-level laser therapy and mechanical vibration and now the interest in using nanorobots to hasten orthodontic tooth movement is slowly taking shape.
Orthodontic nanorobots could directly manipulate the periodontal tissues, allowing rapid and painless tooth straightening, rotating and vertical repositioning within minutes to hours. Optiflex impregnated with nanocomposite materials is revolutionary in orthodontics. 
| Nanocomposites for Superior Orthodontic Bonding|| |
The evolution of orthodontic materials used for bonding has triggered the interest to produce more efficient systems, which forms an integral part of the success of the orthodontic treatment. Ever since Buonocore introduced the acid etch technique in 1955, there has always been a zest for newer materials which have proved their success in the past, for example, self-etching primer, the incorporation of fluoride in bonding and the changes regarding the optimum viscosity and new powerful light curing sources for orthodontic bonding. Now with the introduction of nano-filled composites which have proved their success in restorative dentistry also promises a great deal of application in orthodontic bonding. The basic difference in nanocomposite bonding lies in the enamel composite resin interface. It is an established scientific concept that the resin tags formed after acid etching are filler free areas because due to the limitations of the large surface area of the conventional fillers. With the introduction of nanotechnology this limitation can be overcome and the advantage of the filler particle such as increasing the strength, decreasing thermal expansion and polymerization shrinkage, can now be incorporated in the resin tags which can overall improve the efficiency of bonding. Nanocomposites can have restorative clusters as small as 1 μm and that of nanomers 2-20 nm. 
The emergence of nanotechnology and its growing application in adhesive industry has influenced the manufacture of composite resin by introducing nano-filled composites. Although orthodontic adhesives have not yet incorporated these filler systems, adoption of nanofiller systems might have significant implication in orthodontic bonding.
Nanocomposites in restorative dentistry have gained great importance in past few years. The future of orthodontic bonding lies in the long-term study and usage of the nanocomposites, but at the same time requires certain changes to be made for it to suit the orthodontic specifications. 
Long-term developments in adhesive materials will probably involve biomimetic approaches, adopting mechanisms found in living organisms. In this promising field, research efforts have been already proven fruitful in developing bonding mechanisms for both dry and wet substrates.
Scientists discovered that the mechanism underlying this phenomenon relates to the formation of Van der Waals forces. They were then successful in formulating a network of carbon nanotubes, grown in silicon substrates and embedded in a polymer matrix.
Ken Welch et al.  in 2010 conducted an in vitro study which was aimed at the evaluation of a new interfacial bond-promoting material and method concept for on-demand long-term bacteria inhibition in dental restoration procedures. The parameters analyzed were:
- Mechanical bond strength
- Photocatalytic bactericidal properties.
All induced by low dose ultraviolet A (UV-A) irradiation of dental adhesives containing crystalline titanium nanoparticles.
They concluded that the combined features of bioactivity and on-demand bactericidal effect should open up the potential to create dental adhesives that reduce the incidence of secondary caries and promote closure of gaps forming at the interface toward the tooth through re-mineralization of adjacent tooth substance, as well as prevention of bacterial infections via on-demand UV-A irradiation.
| Nanotechnology in the Prevention of White Spot Lesions|| |
It is a well-established fact that the unaesthetic WSL caused due to demineralization is rightfully termed as the scars of orthodontic treatment. 
It is difficult to effectively educate, train, and encourage patients wearing orthodontic appliances with it numerous attachments, to reduce plaque solely by mechanical means since mechanical methods of plaque removal require time, motivation, and manual dexterity. Plaque in association with fixed appliances can result in clinical problems such as demineralization of the adjacent enamel and gingival inflammation.
Fluoride and chlorhexidine mouthwashes are considered the gold standard for preventing enamel demineralization and gingival inflammation. However, the drawback of the mouthwashes apart from the patient compliance, are epithelial desquamation causing altered taste sensation and brownish discoloration of teeth while using chlorhexidine mouthwash for prolonged periods which is warranted in patients wearing orthodontic appliances.
The use of certain nanoparticles (NPs) as antimicrobial agents has attracted much attention in medicine and dentistry. NPs are considered insoluble particles smaller than 100 nm. Compared with nonnanoscale particles, NPs particles present a greater surface-to-volume ratio (per unit mass), interacting more closely with microbial membranes and provide considerably larger surface area for antimicrobial activity. The growing numbers of bacterial strains are becoming antibiotic-resistant, and bacteria are less likely to develop resistance against metal NPs than conventional antibiotics. These facts have prompted a renewed interest in the use of alternative antibacterial agents such as metallic NPs.
Application of antimicrobial nanoparticles for controlling oral biofilm in orthodontics
In recent years, extensive efforts have been devoted to the use of potential pharmaceutical devices such as novel drug-delivery systems, since it proposes a suitable means of site-specific and/or time-controlled delivery of therapeutic agents. Among various kinds of polymeric systems, which have been used as drug containers or release rate controlling barriers, hydrogels have gained considerable interest. Hydrogels are cross-linked, three-dimensional hydrophilic networks that swell but not dissolve when brought into contact with water. Hydrogels can be formulated in a variety of physical forms, including slabs, microparticles, NPs, coatings, and films. As a result, they are commonly used in clinical practice and experimental medicine for a wide range of applications, including biosensors, tissue engineering and regenerative medicine, separation of biomolecules or cells and barrier materials to regulate biological adhesions. Among these applications, hydrogel-based drug delivery devices have become a major area of research interest. Hydrogels can protect drugs from hostile environments, for example, the presence of enzymes and low pH in the stomach. Their porosity permits loading of drugs into the hydrogel.
In the oral cavity, the antibacterial properties of NPs have been used through two broad mechanisms of combining dental materials with NPs or coating surfaces with NPs to prevent microbial adhesion, with the overall aim of reducing the biofilm formation. 
Due to biocidal or anti-adhesive capabilities of certain NPs, these have been incorporated into orthodontic adhesives to control the oral biofilm and reduce the demineralization around the brackets. When adding NPs to conventional orthodontic adhesives and appliances, the critical issue is that the physical and chemical properties should not be affected adversely, leading to less than ideal clinical performance. Further, the antimicrobial and anti-adhesive properties, as well as the safety of the new nanoadhesives, must be ensured over a clinically relevant time span. 
So far, combining orthodontic materials with NPs or coating the bracket surfaces with NPs have the potential for reducing WSL.
Nanorobotic dentifrice (dentifrobots) 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.
Chen et al. took advantage of these latest developments in the area of nanotechnology to simulate the natural biomineralization process to create the hardest tissue in the human body, dental enamel, using highly organized micro-architectural units of nano rod-like calcium hydroxyapatite crystals arranged roughly parallel to each other.
| Nanotechnology for Coating of Stainless Steel Brackets and Stainless Steel Wires to Increase the Bioeffeciency of the Bracket, and to Reduce the Friction in the Wires|| |
Nanocoating of stainless steel brackets
Cao et al. in 2013  used brackets coated with a thin film of nitrogen-doped titanium oxide (TiO 2 ) NPs and reported on the antimicrobial and bacterial adhesive properties against normal oral pathogenic bacteria through visible-light. The nitrogen doping and modification enable TiO 2 to exhibit catalytic activity within the visible-light region. The activation leads to the formation of OH, free radicals, superoxide ions (O 2 ), peroxyl radicals (HO 2 ), and hydrogen peroxide (H 2 O 2 ). These chemicals, through a series of oxidation reactions, react with biological molecules such as lipids, proteins, enzymes and nucleic acids, damage biological cell structures, but also exert antimicrobial activity. Good anti-adhesive properties against Streptococcus mutans were observed in this study. The rate of antimicrobial activity of the coated bracket against S. mutans, Lactobacillus acidophilus, Actinomyces viscous and Candida albicans were 95%, 91%, 69%, and 99%, respectively. These findings have implications in the prevention of enamel demineralization and gingivitis during orthodontic treatment.  Further research in the coating of orthodontic brackets with nanoparticles could prove very beneficial.
Nano coating of stainless steel wire
Gobi et al.  performed a study on calcium-precipitating oral bacterial adhesion on titanium nitride (TiN), TiO 2 single layer, and TiN/TiO 2 multilayer coatings were deposited on a 316L stainless steel substrate using reactive magnetron sputtering process with the aim of preventing bacterial adhesion. The crystal structures of as-prepared coatings were evaluated using X-ray diffraction analysis. The cubic structure of TiN, anatase, and rutile structure of TiO 2 was noticed. Atomic force microscopy images exhibited a relatively smooth surface for all coatings. The surface wettability studies confirmed that the coatings were hydrophilic in nature. The rate of bacterial adhesion was evaluated using scanning electron microscopy and epifluorescence microscopy. These results demonstrated that the coated substrates could help to effectively reduce the bacterial adhesion and biofilm formations. 
Another technique that has been studied is the antibacterial effects of silver-zirconia, nanocomposite coatings using pulsed laser deposition onto 316LS for bioimplants. In a study conducted by Pradhaba et al.,  it was found that combination Ag-ZrO 2 composite coatings showed superior activity against Escherichia coli and Staphylococcus aureus strains than plain ZrO 2 when coating stainless steel used in bioimplants. 
As a ceramic, ZrO 2 exhibits several advantages such as corrosion resistance, mechanical strength, and fracture toughness. The enhanced properties of ZrO 2 attributed to high crystallinity and nanocrystalline ZrO 2 .
Redlich  published a study in Cambridge journal regarding Friction reduction and wear resistance of electro-co-deposited inorganic fullerene (IF)-like WS 2 coating for improved stainless steel orthodontic wires. A new type of composite metal-NP coating that significantly reduces the friction force of various surfaces, particularly arch wires in orthodontic applications, is demonstrated. The coating is based on electrodeposited Ni film impregnated with IF like nanospheres of tungsten disulfide. The first encouraging tests have shown a reduction of up to 60% of the friction force between coated rectangular archwires and self-ligating brackets in comparison with uncoated arch wires. The coating not only significantly reduces friction of commercial arch wires but also maintains this low value of friction for the duration of the tests in comparison to arch wires coated with nickel film without the NPs. The coated surfaces of the wires were examined by scanning electron microscopy equipped with energy dispersive analyzer and by X-ray powder diffraction methods before and after the friction tests. Using these analyses, it was possible to qualitatively estimate the state of the Ni+IF-WS 2 coating before and after the friction test compared to Ni coated wires without IF.
| Conclusion|| |
Although nanotechnology in orthodontics is still in its infancy stage - "there is plenty of room at the bottom."  With advancement in science and technology, nanoscience could play a significant role also in the practice of orthodontics in the near future. Beneficial effects of nanotechnology with relation to faster orthodontic tooth movement, superior orthodontic bonding, prevention of WSL and the nano coating of arch wires to reduce friction could definitely prove a niche for the practicing orthodontist. The merging of nanotechnology with orthodontics would help the clinicians in improving the quality of patient care, and its applications should further be explored.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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