Nanotechnology in dentistry

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Nanotechnology in dentistry

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Anton Ficai1, Denisa Ficai2, Ecaterina Andronescu1, Mehmet Yetmez3, Nurhat Ozkalayci4, Omer Birkan Agrali5, Yesim Muge Sahin6, Oguzhan Gunduz7,8 and Faik Nuzhet Oktar8,9 1

Department of Science and Engineering of Oxide Materials and Nanomaterials, Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, Bucharest, Romania 2Department of Inorganic Chemistry, Physical Chemistry & Electrochemistry, Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, Bucharest, Romania 3Department of Mechanical Engineering, Faculty of Engineering, Bulent Ecevit University, Zonguldak, Turkey 4Department of Orthodontics, Faculty of Dentistry, Bulent Ecevit University, Zonguldak, Turkey 5Department of Periodontology, Faculty of Dentistry, Marmara University, Istanbul, Turkey 6Department of Biomedical Engineering, Faculty of Engineering and Architecture, Istanbul Arel University, Istanbul, Turkey 7Department of Metallurgy and Materials Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey 8Advanced Nanomaterials Research Laboratory, Faculty of Technology, Marmara University, Istanbul, Turkey 9Department of Bioengineering, Faculty of Engineering, Marmara University, Istanbul, Turkey

8.1 INTRODUCTION As defined by the National Nanotechnology Initiative, nanotechnology is a huge scientific field including physics, optics, material science, chemistry, biochemistry, engineering, and medicine concerned with direct management of structures measured in the billionths of meters or nanometers in at least one dimension and deals with producing materials or devices on the atomic scale (Huang et al., 2004). From the dimensional point of view this means if a meter was to represent the whole world, the nanometer represents a small marble. With respect to traditional materials, nanomaterials have enhanced toughness, stiffness, transparency, abrasion, solvent resistance, heat resistance (Patil et al., 2008), and decreased gas permeability, together with the property of self-assembly, which means self-directed association of components into patterns or compositions without human involvement (Hemalatha et al., 2014; Kong et al., 2006). This dimensional and characteristic revolution in the material science brings new prospects to dentistry and led to the birth of a new field called nanodentistry.

Nanobiomaterials in Dentistry. DOI: http://dx.doi.org/10.1016/B978-0-323-42867-5.00008-4 © 2016 Elsevier Inc. All rights reserved.

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8.2 A SHORT HISTORY ABOUT CARIES TREATMENT BEFORE DENTAL COMPOSITES Dental caries is one of the most widespread diseases (Kumar, 2009) with the highest prevalence (Hannig et al., 2013). When the teeth on the skulls of prehistoric primates are investigated, it is not very surprising to see little or no caries because of the poor carbohydrate nutrition regimen (Hannig et al., 2013). Also, when human enamel is more closely investigated, it is detected that 97% of the enamel consists of inorganic apatite (Kumar, 2009). Those apatitic formations can sometimes loosen their strength because of the junk food regime. It is not very surprising to see caries formation as explained above. Nowadays there are many foods and soft drinks containing high levels of sugar and acid (e.g., Coca Cola®). These are one of the main causes of caries formation. For centuries, humans have tried to restore their tooth with replacements, using different materials both for aesthetics and to restore function (Mirsasaani et al., 2011). In ancient times, they used ivory tooth carvings, which were attached with gold strips to existing tooth/teeth. For instance, some Mayan Indians had used carved nacre tooth attached to the jaw bones (4000 years ago) (Sarkar, 2010). It is also known that the teeth of dead soldiers (i.e., Waterloo War, American Civil War) were collected by some people who sneaked into the battle field and subsequently good-looking white teeth were sold to dentists and surgeons who used them to replace false teeth on prostheses (The Chirurgeon’s Apprentice, 2014). Actually, modern restorative dentistry begins with the invention of many restorative materials. Amalgam is the most successfully implemented filling materials for caries treatment. It is also very economical material, but it is not an aesthetic material (Mirsasaani et al., 2011) for use in the anterior area. When comparing amalgam with composite fillings, it lasts much longer than the others. This is why it is still a popular material after 150 years (Chan et al., 2010). It was stated by Fortin and Vargas (Radz, 2013) that restorative composites will take the place of amalgam. For a long time, amalgam fillings have been accused of releasing quicksilver (mercury, Hg) after setting. However, it is has been proved that the use of amalgam is very safe, especially in the United States. It is also reported that there is much more concentrated Hg in seafood (Oktar et al., 1999).

8.3 HISTORICAL DEVELOPMENT OF DENTAL COMPOSITES Basically, it is recollected that the term composite defines a mixture manufactured from at least from two different classes of materials. A traditional dental composite consists of synthetic polymer phase, reinforcement materials (i.e., fillers), monomer (for polymerization), and a silanization agent (coupling agent) (Patodiya and Hegde, 2012).

8.4 Vision in Dentistry From Micro- to Nanoscale

Historically, the development of resin-based composites began with glass-filled poly(methyl methacrylate) (PMMA) (Ferracane, 2011), which was the most important development for dentistry in 1950s (Mitra, 2012). In the 1960s, Bis-GMA (Bisphenol-A bismethacrylate) replaced PMMA (Ferracane, 2011). PMMA and Bis-GMA as self-cured materials were followed by UV (ultraviolet)cured composites. It is generally known that UV-cured resins possess some problems for users because direct UV light is very harmful to the eye. The user and the patient must wear protective goggles against UV light. In the late 1970s macrofill and microfill composites were developed. On one hand, although macrofill composites were strong resins made from small particles filled with either quartz or glass, they were very difficult to polish (Wikipedia, 2015; The Free Dictionary, 2015). On the other hand, microfill composites were resins with very fine grounded silica. They were used for anterior aesthetic restorations and could be polished very well (The Free Dictionary, 2015). In the early 1980s, hybrid composites were developed from macrofill resins. They were made of a mixture of macrofill and microfill particles (Ferracane, 2011; The Free Dictionary, 2015). In the mid-1980s, both direct and indirect composites were introduced into dental practice. Direct composites were filling materials set by the dentist in the mouth, while indirect composites were cured outside of the mouth (Ferracane, 2011; Wikipedia, 2015). In the late 1980s, hybrid composites were introduced. They contained blends of micron and submicron size fillers with small particles. In the mid-1990s, flowable and packable composites were discovered. Flowable resin materials had been suggested as liners beneath packable composites to improve marginal integrity (Ferracane, 2011; Neme et al., 2002). At that time, small-particle microhybrid composites were also improved (Ferracane, 2011). Microhybrid composites were the next step in production of hybrid composites (Doctor Spiller, 2015). In 2000, nanofill and nanohybrid composites appeared. Those composites had nanoparticles as fillers. In the mid-2000s, composites with low-shrink formulations were developed. Nowadays, flowable restorative dental composites are very much requested (Ferracane, 2011).

8.4 VISION IN DENTISTRY FROM MICRO- TO NANOSCALE In the field of dentistry, resin-based composites are among the most popular dental restorative materials, replacing the conventional dental amalgams, especially due to the toxicity of mercury (Xia et al., 2008). In the last 15 20 years, the use of amalgam and metals/alloys has dropped dramatically primarily due to improvements in the composite and ceramic materials for dental restoration (Hickel, 2009). There are an increasing number of composite materials on the market, the desired properties being tailored by the nature or polymeric matrix and filler by the composition (the ratio between these phases), the size and shape of the filler, the used compatibilization agent, etc. The polymerization shrinkage (PS) is

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strongly dependent on the nature of the polymer matrix as well as on the content, size, and shape of filler. For instance, TPH Spectrumt, which contain 57.1% by volume filler (42.9% matrix), exhibits the higher PS. The highest flexural strength (FS) of Grandiot could be explained based on the highest filler content, the higher content of filler usually favoring the higher macro- and micromechanical properties, also tends to reduce PS. The modulus of elasticity is strongly dependent on the polymeric matrix as well as the content of filler, while size and shape had only a limited influence. The high filler content of the composite gave high modulus of elasticity, and, in this case, the composite with Grandiot resin showed the highest modulus of elasticity. It can be seen that the three properties are dependent on the above-mentioned characteristics. The compatibility between polymer and filler was extensively studied for both medical and industrial applications, as well. Most often the functionalization of the filler is recommended to improve the compatibility between the phases. These composite materials are derived from the heating of silica particles with organic agents which can lead to organo-functionalized silica’s improved compatibility with the polymers (Bowen, 1963). In this case, the surface plays an important role and the nanofillers exhibit by far the highest specific surface area and consequently the highest ability for binding highly equivalent functionalization agents and this leads to high compatibility between the phases. Resin-based composite materials are considered materials of choice particularly for restoration of anterior teeth, because in these cases the aesthetic appearance (color matching and polishability) is very important. Therefore, the composite materials designed for the anterior restoration are obtained starting with nanometric fillers because these reduce fracture strength and Young’s modulus. From an evolutionary point of view, since the 1980s, the microfilled materials were able to assure the required aesthetic properties but were not able to assure the mechanical properties to be used in posterior restorations. For almost 20 years, composite nanomaterials were used and served as universal composites for anterior and posterior applications, the required properties being superior compared with the properties of analogue microcomposites (Xia et al., 2008; Zantner et al., 2004; Li et al., 1985; Leinfelder, 1993). The strong differences between the properties of micro- and nanocomposites are explained based on the increasing interfacial interactions as well as due to a stronger compacting possibility. The interfacial interaction is proportional to the specific surface area. The surface/volume ratio (mathematically, A/V 5 3/R) is substantially increased with the decreasing of the particles’ size. Zantner et al. (2004) studied the correlation between the wear of some composite materials and the particle size of the reinforcing agent. They found that the loss of height is slightly dependent on the particle size of the composites with small filler particles and high filler fraction volumes present lower wear resistance; data also supported by other papers were suggested to wear less in earlier studies (Zantner et al., 2004; Li et al., 1985; Condon and Ferracane, 1997). The interparticle spacing could also influence the wear behavior of dental

8.4 Vision in Dentistry From Micro- to Nanoscale

composites, because smaller particles are more embedded in the matrix and as a consequence they will not be torn out of the matrix by the oscillating antagonist when compared to larger fillers (Zantner et al., 2004; Mair et al., 1996). Using small interparticle spacing, the soft matrix is protected from wear (Zantner et al., 2004; Bayne et al., 1992). Furthermore, the number of microcontacts between the filler particle and the antagonist influences the wear behavior. The smaller the particles, the smaller is the load on the individual particle and this mean a more homogeneous distribution of the load between the particles, which means that the load is distributed over a larger area (Zantner et al., 2004; Axen and Jacobson, 1994). The failure rate of the composite materials increased annually and reached comparative longevity with the amalgams (Bowen, 1963). The longevity of these composite materials is influenced by clinically related factors, operator and patient, socioeconomical behaviors, and certainly material characteristics including FS and comprehensive strength, elastic modulus, fracture strength and toughness, hardness, or wear resistance. These characteristics are generally accepted to be a direct result of composition and nature of components, filler volumetric ratio, filler size, and morphology (Demarco et al., 2012; De Caluwe et al., 2014). A very important issue related to dental materials is the biofilm formation/suppression ability. Recent works show that biofilm formation is dependent on the composition of the materials but also on the microstructure of the surface. From a compositional point of view, biofilm formation increases from glass ionomer cement to resin composite and amalgam (Wang et al., 2014a c). Polymer matrix composites which are based on UDMA (urethane dimethacrylate), Bis-GMA (bisglycidyl methacrylate), and HEMA (hydroxyethyl methacrylate) have more biofilm formation, like resin composite and amalgam (Reichl et al., 2006). The microstructures which are produced with the aid of nanotechnology usually affect the formation of biofilm. The microstructure also exhibits a smoother surface and this type of surface has an important inhibiting effect on the level of bacterial adhesion. Restorative dental composites which are incorporated with different nanoparticles or with different type of biocides have more antimicrobial activity than conventional ones (Zhang et al., 2013, 2014; Wang et al., 2014a c; Bressan et al., 2014). In the case of composite materials, the polishing of the surface leads to a smoother surface and less Streptococcus mutans biofilm formation was observed during 4 days incubation. This is, most probably, due to the changing of the proportions of resin matrix and filler particles onto the surface (Wang et al., 2014a c; Ono et al., 2007). de Freitas et al. (2011) correlated the surface roughness with the bacterial cell adherence. They proved that for a similar material, the increasing roughness leads to better bacterial adhesion, the adhesion being the first stage of biofilm formation (de Freitas et al., 2011; Teughels et al., 2006). Hydrophilicity of the surface is also very important for the bacterial adhesion because the bacterial cells are electrically charged (Palmer et al., 2007). The advantages and disadvantages of the resin-based composite materials compared with the amalgams are summarized in Table 8.1.

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Table 8.1 General Comparison Between Composites and Amalgams Resin-Based Composite Materials

Amalgam

Advantages (dos Santos et al., 2010; Correa et al., 2012 and Whitters et al., 1999) • good esthetic properties, can be used also for anterior teeth; • the longevity of the nanocomposites can reach the longevity of the amalgams; • in the case of nanocomposite, universal materials can be designed for both interior and posterior restoration; • good adherence to the dental structure; • smaller filler lead to better aesthetic and mechanical properties; • the overall properties are strongly dependent on the nature of polymer(s) and filler, size and shape of filler, composition, etc.

• Good mechanical properties; • Good/very good durability/ longevity; • Ease of application; low cost.

Disadvantages (Reichl et al., 2006; Hickel, 2009; Cenci et al., 2008; Correa et al., 2012) • Nanocomposites have medial mechanical properties like average wear resistance, hardness, and shrinkage; Microcomposites possess average durability. However, nanocomposites have substantially increased durability; • Monomer or solvent release/leakage.

• High toxicity due to the presence of Hg; • Bad aesthetic properties: can be used only for posterior teeth; • The absence of adhesion to dental tissues; • High thermal and electrical conductivity.

8.5 NANOTECHNOLOGY IN RESTORATIVE DENTISTRY 8.5.1 NANO-CONCEPT IN RESTORATIVE DENTISTRY If any application of nanomaterials in clinical restorative materials is taken into consideration, there are two main groups, nanocomposites and nanoadhesives. On one hand, nanoadhesives consist of nanosolutions and have dispersible nanoparticles which suppress agglomerations (Nagpal et al., 2011). On the other hand, there are two major challenges to the development of nanocomposites: (1) to prevent secondary caries formation, (2) to prevent the fracture of restoration, especially at large posterior restorations (Xu et al., 2010). At that point, two types of nanocomposites are to be concerned: 1. Nanofills; 2. Nanohybrids.

8.5.1.1 Nanofills Those composites include 1 100-nm-sized particles dispersed in the resin matrix. They do not have larger primary particles added. Two types of

8.5 Nanotechnology in Restorative Dentistry

nanoparticles are prepared for restorative nanofill composites. The first nanoparticles are silica particles prepared as monodispersed nonaggregated and as nonagglomerated. The surface is silanizated with coupling agents. Silanization forms a chemical bonding with silica particles to polymeric matrix, otherwise the mechanical interlocking of particles to resin matrix is much weaker when compared with mechanical interlocking and chemical interlocking. Silanized composites have lower shrinkage rates when compared with nonsilanized composites (Tekerek et al., 2013). They are used in one of the studies of silanized hydroxyapatite (HA) in polymer matrix. The biggest problem in the dental composites is shrinkage. Shrinkage occurs with polymerization. Shrinkage can lead to leakage around the cavity (Tekerek et al., 2015). All composites tend to shrink. In the earlier systems, the shrinkage is very extreme. However, nowadays, the shrinkage caused by polymerization is about , 2.5% and in some products the shrinkage rate is approaching about 1% (Radz, 2013). If nanomers are highly filled into composites, the rheological properties will be poorer. The second nanoparticle type is nanoclusters (Mitra, 2012). Nanoclusters are agglomerates that have a size between 0.6 1.4 μm and 5 20 nm sized primary Zr/silica nanoparticles (Radz, 2013). These control particle size and are produced from light-sintering of nanomeric oxides. Nanoclusters can be prepared from silica sols and can be prepared also from mixed zirconia and silica oxides. Composites with nanoclusters have better rheological properties (Mitra, 2012). Before nanofills, microfill composites were used for a long time. However, they can be used only at anterior restorations (because of superpolishing) and cannot be used at posterior restorations because they are weak in stress-bearing areas of the tooth. It is thought that nanofills are much better than those microfills (Mitra, 2012). Nanofilled composite resins have higher resistance against wear when compared with hybrid composite resins (Hamouda and Elkader, 2012). It is also claimed by companies that resin composites with nanofills have shown low PS and high mechanical strength (Endo et al., 2010).

8.5.1.2 Nanohybrids These composites include, as well as nanosized particles, some larger particles of about 0.4 5 μm (Mitra, 2012). Nanohybrid composites have higher fracture resistance when compared with other composites (i.e., hybrids, microhybrids, and microfills). They can be easily used at posterior applications (Doctor Spiller, 2015). In addition to the advantages as explained above, there are many other advantages of using nanohybrids. At application of nanohybrids, there is the need for minimal removal of tooth structure. Adding nanohybrids to defective segments needs no extra preparation. This is why patients like to keep the concept of protecting the natural tooth structure. Direct application of nanohybrid composites can result cost savings from 50% to 80% when provided in lieu of dental crowns. These applications eliminate the expense of dental laboratory fees and dental crown buildup. With nanohybrids, it is not an error to say that (1) the composite

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restorations can be finished in one visit and (2) selection of color matching is possible. Because of the superpolishing ability of nanohybrid composites, minimal dental plaque formation is expected. This is good for young patients because implants may not be necessary because of patients’ age and economy. Premise (Kerr Dental, USA) and Herculite Ultra (Kerr Dental, USA) are the leading brand names of nanohybrids (LeBlanc, 2009).

8.5.2 OTHER NANOMATERIALS MIXED WITH DENTAL COMPOSITES It is known that around the applied dental restorative material which is applied close to mucosa, dental plague can easily accumulate. Some companies add different bacteria-static materials beside the silica, zirconia fillers. This component is usually used as nanosilver. However, quaternary ammonium PEI (QPEI) has very strong bactericidal activity against most pathogens (Beyth et al., 2012). HA has been introduced, adding as a filler in composites to improve the material properties in adhesives and has also been added to root canal sealer materials at the nanometer scale. However, so far there is no report of the use of nano-HA in adhesive composite resins (Leitune et al., 2013).

8.5.3 FUTURE PREDICTIONS It is believed that the use of amalgam will decline, while the use of restorative dental composite resin grows (this statement was made as recently as 2013) (Radz, 2013). It is also claimed that one day the use of amalgam will stop. Nanodentistry is realizing that it has huge potential for the future. It includes nanotechnology and biomimetics which refers to human-made processes, substances, devices, or systems that imitate nature (Upadhyay, 2013; Techtarget, 2015; Lainovi´c et al., 2012). At this point it is to be said that, before nanodental applications, there are many social issues of public acceptance, regulations, human safety, ethics, and many others which must be handled first before application in the molecular biological level. There is a very large global population that needs high-quality dental care. There are also time and financial resources, scientific resources, specific advances, and human need required (Nagpal et al., 2011) for the future of nanotechnology not only in dentistry but also in all other areas. The toxic potential of nanoparticles is still not very well known. Scientists are reporting that they have the possibility of accessing the cell structure (Zimmerli et al., 2010).

8.6 NANOTECHNOLOGY IN PERIODONTICS Periodontology or periodontics is a branch of dentistry that is concerned with supporting structures of teeth, together with diseases and conditions that affect them (Wictionary, 2015). The supporting tissues are known as the periodontium,

8.6 Nanotechnology in Periodontics

consisting of gingiva (gums), alveolar bone, cementum, and the periodontal ligament. Periodontal diseases are the most common chronic inflammatory diseases affecting the supportive periodontal tissues, causing not only tooth loss but also reflections in the individual systemic condition of the patient (Cullinan and Seymour, 2013). Therefore, it is crucial to introduce treatment strategies for preventing or managing periodontal diseases, including diagnosis and treatment. With the help of the applications including such technology in dentistry, and periodontics in particular, creating a perfect oral health will not be an unreachable dream for humans. Nanotechnology in periodontics can be explained under two main headings as: 1. Nanotechnology in periodontal diagnosis; 2. Nanotechnology in periodontal treatment. If disease is described as a trait or an individual attribute then diagnosis should be defined as the clinician’s faith in the person who has the attribute (Temple et al., 2001). The way that clinicians make the proper diagnosis as well as proper treatment requires understanding of the exact tissue changes. Some nanodiagnostic materials, which are usually associated with oral cancer diagnosis, include nanoscale cantilevers, which are engineered to attach cancer-associated molecules, quantum rods, which bind to tumoral tissues make the cancer cells trackable by glowing brightly under ultraviolet light, and nanosensors, which detect salivary biomarkers for oral cancer (Gau and Wong, 2007). Besides these nanomaterials, a nanotechnologic lab-on-a-chip device not only helps detecting molecules associated with the extent and severity of periodontitis on the small sample volumes but also diminishes the reagent cost as well (Herr et al., 2007; Christodoulides et al., 2007).

8.6.1 PERIODONTAL TREATMENT PROCEDURES Periodontal treatment procedures consist of three phases: nonsurgical (phase I), surgical (phase II) and supportive periodontal treatment (phase III). Phase I therapy includes the patient’s oral hygiene applications and the clinician’s interventions, such as elimination of the microbial etiologic factors with mechanical instrumentation on the tooth and root surfaces together with releasing of predisposing factors. Phase II therapy is the surgical phase of the periodontal treatment, including resective and/or regenerative approaches. Phase III includes patient’s recall visits in certain time intervals in order to maintain and improve the results of periodontal treatments. Nanotechnologic improvements emerged into both nonsurgical and surgical parts of these treatment modalities. Specific microorganisms which are responsible for various kinds of periodontal infections require local or systemic antimicrobial administrations for treatment of these diseases (Slots, 2002). Periodontal drug-delivery systems were investigated for controlled drug release using some kinds of nanostructures including hollow spheres, core-shell structures, nanotubes, and nanocomposites (Kong et al., 2006; Caruso et al., 1998; Kohli and Martin, 2003; LeGeros et al., 2003; Murugan

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and Ramakrishna, 2004; Park et al., 2005; Ravi Kumar, 2000; Wang et al., 2002). Another material that demonstrated successfully reduction of the periodontal inflammation consisted of triclosan-loaded nanoparticles (Kohli and Martin, 2003; LeGeros et al., 2003; Murugan and Ramakrishna, 2004; Park et al., 2005; Ravi Kumar, 2000; Wang et al., 2002; Pinon-Segundo et al., 2005). In an experimental animal study, nanostructured 8.5% doxycycline gel was found to be successful in periodontal surface protection following treatment of periodontal infection (Botelho et al., 2010). Also, commercially available tetracycline-loaded microspheres (Arestin®) are used in periodontal pockets for local antimicrobial therapy (Paquette et al., 2004). A different antimicrobial treatment approach, photodynamic therapy, is used for eliminating complete microbial strains during periodontal treatment (Gursoy et al., 2013). Photodynamic therapy is based on a rationale including combination of a photosensitizer material to a target cell, activation by light with adequate wavelength and creation of a toxicity effect to the related cell (Malik et al., 2010). A new photosensitizer, indocyanine-greenloaded nanospheres demonstrated a similar photodynamic effect under 805-nm wavelength diode laser radiation (Nagahara et al., 2013). Nanodentistry exerts itself in surgical regenerative periodontal therapies by proposing various biomaterials which are aimed to be used for periodontal tissue engineering. Alveolar bone shows a composite-like structural property including organic content (collagen) with inorganic content (HA). Nanostructured bone materials like nanocomposites can mimic this composite-like characteristic of alveolar bone with their self-assembly property in order to achieve perfect periodontal regeneration. Various kinds of nanocomposite bone replacement biomaterials have been produced with different trademarks and compositions, such as: Ostium® (Osartis GmbH, Germany), VITOSSO® (OrthovitaInc, USA), NanOSS® (Angstrom Medica, USA), and Bonegen-TR® (BiolokInt, USA) (Kanaparthy and Kanaparthy, 2011). These nanocomposite biomaterials are produced containing one or more from HA, tricalcium phosphate (TCP), and calcium sulfate materials. Elangovan et al. (2013) demonstrated calcium phosphate (CaP) nanoparticles as potentially good vehicles (nanovectors) delivering the target genes to fibroblasts for the purpose of periodontal regeneration in vitro. Besides bone replacement or bone-inducing nanocomposite biomaterials and nanovectors identified for the use of regenerative periodontal treatment response, biodegradable nanofiber hemostatic agents, silk nanofiber wound dressings, nanocrystalline silver particles-containing antimicrobial wound dressings (Acticoatt, UK), nanosized stainless steel crystal-containing nanoneedles (RK 91 needlest, AB Sandvik, Sweden) are presented for surgical periodontal treatment approaches (Kanaparthy and Kanaparthy, 2011). Another field of surgical periodontal treatment is dental implant implications for the treatment of tooth loss. Nanostructured materials including metals, polymers, carbon fibers, ceramics, and composites improve osteoblast adhesion and calcium/phosphate mineral deposition resulting in enhancement of the osseointegration capability of dental implants (Kanaparthy and Kanaparthy, 2011; Colon et al., 2006; Meyer et al., 2006.)

8.7 Nanotechnology in Orthodontics

Surface modifications in order to enhance the osseointegration ability of the dental implants are the current trends of their production. Creation of nanoscale features at the implant surface include various methods: (1) physical methods like ion beam deposition and compaction of nanoparticles through self-assembly of monolayers; (2) chemical methods including acid etching, peroxidation, alkali treatment (NaOH), and anodization; (3) nanoparticle deposition (colloidal particles, discrete crystallines); and (4) lithography and contact printing technique (Goldman et al., 2014; Thakral et al., 2014).

8.6.2 FUTURE ASPECTS OF NANOTECHNOLOGY IN PERIODONTICS The growing interest in nanodentistry may lead to nanotechnologic improvements creating micron-sized dental robots called nanorobots. These nanoscaled robots may be controlled by a dentist using a computer transmitting orders with local sensors or acoustic signals. These nanorobots with cell penetration ability may be used in local anesthesia and analgesia by affecting the sense transfer on the nerve; in dentin hypersensitivity by occluding dentinal tubules with native logical nanomaterials; as a dentifrice patrolling all over the tooth surface; for metabolizing dental biofilm into harmless and odorless together with calculus debridement; as a part of a targeted releasing system delivering novel vaccines, antibiotics, and drugs with reduced side effects (Patil et al., 2008; Hemalatha et al., 2014; Kanaparthy and Kanaparthy, 2011). Furthermore, nanotweezers which will make cell surgery possible will be produced in the near future (Kanaparthy and Kanaparthy, 2011). All of these possibilities in the future of nanodentistry will give us a chance to reach the target of perfect oral health reconstruction.

8.7 NANOTECHNOLOGY IN ORTHODONTICS A combination of nanomaterials and nanorobots has started being used in diverse fields including medicine. It is obviously to see that the applications of nanotechnology will improve rapidly in different areas of dentistry (Oh et al., 2014), such as orthodontics, which is one of the most important parts of dentistry. Nanoorthodontics is providing not only new solutions, such as better tools for diagnosis and management of orthodontic problems, but also better methods with the aid of nanotechnology. Small structures and systems of nano-orthodontics can be classified as follows (Maheshwari et al., 2014): 1. Orthodontic nanocomposites, 2. Nanotechnologic enamel remineralizing agents, 3. Nanocoated orthodontic archwire, 4. Nanotechnologic orthodontic brackets, 5. Orthodontic nanorobots and furtherance.

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8.7.1 ORTHODONTIC NANOCOMPOSITES Basically, nanocomposites and nanoionomers are biomaterials developed by nanoparticle technology. Nanosized filler particles have been added to composite matrix and glass ionomer cements. Techniques of nanoparticle technology including flame pyrolysis, flame spray pyrolysis, and sol gel processes can be used while preparing nanofillers (Maheshwari et al., 2014). It is clear that application of nanofillers into orthodontic composites changes the mechanical properties of materials. Nanofillers with small dimensions provide more filler load and reduce the PS. This reduction increases the bond strength of orthodontic composites or orthodontic attachments such as brackets or bands. One of the most important problems for orthodontic mechanics is bond failure due to daily activities such as chewing or biting. Bond failure causes longer treatment time, chair time, and of course financial expense. Improved bond strength means better treatment conditions and incomes. Today, some nanotechnological products like silver nanoparticles are added to the orthodontic composites to solve the problems mentioned above or antimicrobial problems. From the antimicrobial problems point of view, nano-zincoxide and nano-chitosan particles are added to the orthodontic composites to improve antibacterial effectiveness. The effectiveness of these composites is tested at different levels of these particles. In clinical conditions, placement of orthodontic mechanics into the mouth increases the risk of caries due to the difficulty of providing adequate oral hygiene and changes of microflora, especially, white spot lesions around the brackets. That is why, in order to reduce risk of caries during orthodontic treatment, nanocomposites with antimicrobial effects are preferred (Mirhashemi et al., 2013).

8.7.2 NANOTECHNOLOGIC ENAMEL-REMINERALIZING AGENTS Enamel-remineralizing agents like nano-HA have been developed with nanotechnogical advancements. Calcium nanophosphate crystals are used to improve the properties of remineralizing agents (Maheshwari et al., 2014). Demineralization of the enamel surface of teeth can be seen during orthodontic treatment. Successful remineralization of the enamel surface reduces the risk of caries and prevents unwanted side effects.

8.7.3 NANOCOATED ORTHODONTIC ARCHWIRE Nanotechnological developments lead to coating the archwire surface with metal nanoparticles. This process of coating of the archwire surface with Ni film reduces the friction of the archwire surface. Orthodontic wires can be coated with inorganic fullerene-like tungsten disulfide nanoparticles. These nanoparticles possess a dry lubricatory effect on archwire surface and have an ability to reduce the friction forces on orthodontic mechanics (Redlich et al., 2008; Sivaramakrishnan and Neelakantan, 2014).

8.7 Nanotechnology in Orthodontics

FIGURE 8.1 Representation of straight wire technique.

FIGURE 8.2 Effects of friction forces.

Sandvik nanoflex is a newly developed stainless steel archwire. This archwire has more strength than conventional wires and possesses better properties like good deformability, better corrosion resistance, and a good surface finish (Patel et al., 2014; Robert and Freitas, 2010; Dalai et al., 2014). Different techniques are used and different mechanical solutions are considered to correct the orthodontic malocclusions. One of them is a straight wire technique and mechanics and McLaughlin-Bennett-Trevisi (MBT) prescription brackets and archwires (see Figure 8.1). At both the beginning of the treatment on the leveling and alignment phase and the end of the treatment on the space closure phase, friction is an important factor, so that successful treatment outcome is directly affected by the level of friction force (see Figure 8.2). Lower friction force provides a fast treatment process, saves money and is less timeconsuming. Lower friction can also help to prevent unwanted side effects of

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orthodontic treatment like loss of anchorage and root resorption. Light force can be used in the lower friction conditions (Sivaramakrishnan and Neelakantan, 2014; Bhat et al., 2013).

8.7.4 NANOTECHNOLOGIC ORTHODONTIC BRACKETS When hard alumina nanoparticles are added to polysulfane, like UC3M, the product possesses high strength, lower friction, and high biocompatibility. Orthodontic brackets are a most important part of orthodontic mechanics, because they play a very important role in orthodontic treatment, by carrying the archwire forces to the teeth. They also include adequate tip and torque values. Consequently, their design is very important in the success of the orthodontic treatment. Brackets are used from beginning to the end of the active orthodontic treatment. That is, their strength, friction, corrosion resistance, and biocompatibility are essential factors to be taken into account.

8.7.5 ORTHODONTIC NANOROBOTS AND FURTHERANCE Nanorobots are probably the most important subject of nanotechnology and will change the process of different applications like orthodontic treatment. Diameters of nanorobots are between 0.5 and 3 μm and the sizes of their components are between 1 and 100 nm (Dalai et al., 2014). A nanorobot consists of two main parts: 1. A biocompatible glycocalyx-coated diamondoid material with molecular sorting rotors; 2. A robot arm. Other parts are a camera, pay load, capacitor, and a swimming tail. Carbon is the main element of nanorobots and other elements like sulfur, hydrogen, nitrogen, oxygen, fluoride, and other lightweight elements can be added to the nanorobots due to functional specialty (Dalai et al., 2014; Bhat et al., 2013; Kumar et al., 2011). Adequate power can be supplied to nanorobots using local glucose and oxygen or external acoustic energy. Computers can be connected to nanorobots via broadcast-type acoustic signaling or an onboard preprogrammed nanocomputer can control the nanorobot (Boomi and Prabu, 2013). These very small machines can reach the correct cells by checking cells’ specific antigens. When nanorobots finish their work they can exit from the human body with different paths like excretory channels, or scavenger systems can remove nanorobots (Dalai et al., 2014; Babel and Mathur, 2011). In the future, these nanotechnologic nanorobots, which will be named orthodontic nanorobots, will be used in orthodontic treatment. Nanorobots can be added to the mouthwash or toothpastes and they can clean the tooth surface from unwanted microorganisms during the day time and this function can reduce the risk of caries (Ozak and Ozkan, 2013). By considering the main functional parameter, it is recollected that the major drug for orthodontic treatment is force that produces the tooth

8.8 Nanotechnology in Endodontics

movement and sometimes skeletal changes. These processes include very complex cellular activities produced by different body systems, such as the immune, blood, skeletal, and muscle systems. Due to the fact that orthodontic nanorobots can be programmed, they manipulate the periodontal tissues like periodontal ligament, cementum, alveolar bone, and gingiva and provide faster and comfortable orthodontic movements (Patel et al., 2014; Chandki et al., 2012; Freitas Jr., 2000; Jan et al., 2014). These nanorobots can also change the shape and size of bones and cartilages of the orthodontic area, such as the maxillary bone or temporomandibular condyle cartilage. They can also affect and change the size and shape of the soft tissues like lips or attached gingiva (Kohli and Martin, 2003). Nanorobots can also use the nanomaterials as skeletal tissues (Bozec and Horton, 2006). It is obvious that these future plans can be enhanced easily. All types of orthodontic corrections will be corrected in minutes or hours with orthodontic nanorobots (Sivaramakrishnan and Neelakantan, 2014).

8.8 NANOTECHNOLOGY IN ENDODONTICS Recently bioengineered tooth has been successfully generated from pig tooth bud tissue or rat-cultured tooth bud cells seeded on polyglycolic acid/poly(lacticco-glycolic acid) PGA/PLGA and grown in the omenta (Young et al., 2002; Duailibi et al., 2004). Finally, the development of immune-compatible off-the-shelf stem cells will make the pulp therapy for dentin pulp regeneration in endodontic treatment a potential reality (Nakashima, 2005). Although modern protocols for the treatment of pulp diseases and apical periodontitis guarantee high success rates, a new, ideal therapy approach in endodontic therapy is the induction of healthy tissue and replacement of diseased or necrotic pulp tissue (Upadhyay, 2013). The anti-inflammatory effects of biologically active nanostructured multilayer films on fibroblasts are studied. Melanocortin peptidecontaining films (which can stimulate human pulp fibroblasts in order to modulate pulpal inflammation) are the first reported as a new active biomaterial for endodontic regeneration (National Nanotechnology Initiative, 2015). In this section, nanotechnology in endodontics is simply considered under three subheadings.

8.8.1 NANOPARTICLES AS ANTIMICROBIAL AGENTS Bacteria are the main reason for endodontic disease. Nanoparticles display higher antibacterial activity because of their high surface area, polycationic or polyanionic nature that gives rise to several possible applications in various fields. Both the treatment of bacterial biofilms and wound-healing processes benefit from antimicrobial properties and biocompatibility of nanoparticles. These disinfect the canal by the antibacterial action of the intracanal drugs (Shrestha et al., 2009).

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The disinfection can be achieved by cleaning the root canal system prior to sealing. These fillings disinfect any antibacterial effect. Mostly, antimicrobial endodontic sealers which are biocompatible are used in the disinfection of root canal systems. For this purpose, different nanoparticles of biocompatible polymers have been used. In a recent study, quaternized polyethylenimine nanoparticles which are stable, nonvolatile and exhibit antibacterial properties, have been used. The effect of these sealers on the proliferation of RAW264.7 macrophage and L-929 fibroblast cell lines and on the production of tumor necrosis factor-α from macrophages have been examined (Abramovitz et al., 2012). In another recent study of the group, the quaternized polyethylenimine nanoparticles incorporate antibacterial properties to the endodontic sealers (Abramovitz et al., 2012; Kesler et al., 2013). Various different polymeric nanocomposites have been utilized for this purpose. Due to its versatile antibacterial property and biocompatibility, chitosan nanoparticle composites can be employed for treatment of dentinal tubule infection (Yao et al., 2013; Shrestha and Kishen, 2012). High-intensity focused ultrasound can be used as a potential method to deliver antibacterial chitosan nanoparticles into dentinal tubules to improve root canal disinfection (Shrestha et al., 2009).

8.8.2 NANOTECHNOLOGY-BASED ROOT-END SEALANT Nanomaterial-enhanced retrofill polymers provide superior strength and contour to the tooth structure. Bioaggregate, white nanoparticle ceramic cement is a newgeneration filling material, composed primarily of calcium silicate, calcium hydroxide, and HA (Sasalawad et al., 2014). Since the 1980s, CaPs have been used for bone substitution and repair purposes (Jarcho et al., 1979) among which the stoichiometrically adjusted HA and β-TCP are stable CaP phases at high temperature and can be easily converted into ceramics by sintering. β-TCP is known to be bioabsorbable and replaced by bone, whereas HAs constitute nondegradable materials. β-TCP is mainly used as a bioceramic to guarantee the biodegradability, whereas HA is also being processed for other biomaterial uses, such as the coating of metallic prostheses where a mechanical improvement is needed as an osteoconductive bone repair material or a composite ceramic polymer (Eichert et al., 2008). The latter also shows excellent bone bonding abilities (De Groot et al., 1987; Bonfield, 1988). The association of these two high-temperature CaPs allows a controlled resorption rate and has been shown to offer good biological properties (Daculsi et al., 2003; Legeros, 2002). In the last two decades, in order to understand the formation of biological apatites and their properties, various synthetic HA powders have been produced from pure chemicals, with different chemical techniques, such as precipitation under different conditions, solid/solid reaction at high temperature, hydrolysis of other CaPs, and hydrothermal methods. As a consequence of these techniques, the composition of the substituents can be easily determined (Eichert et al., 2008). Sol gel processes still raise some problems (Liu et al., 2002).

8.9 Conclusions

• •

Long time needed for preparation of the sol; Other CaP phases depending on aging time and temperature.

Hydrothermal methods, on other hand, are complex methods which require high-pressure systems (Rocha et al., 2005). An improvement has been made with the development of CaP cements (Brown and Chow, 1987). These are able to strengthen the material in a living body and most can be injected. Despite their poor mechanical properties they offer numerous advantages and can be used for several applications. HA is one of the most commonly used CaP materials in medicine and dentistry. The biocompatibility of HA is closely related to its similarity to bone and dental tissues. However, due to its inferior mechanical properties, the use of HA as an endodontic material is limited. This has led to investigation of modified structures of calcium-phosphatebased biomaterials with improved mechanical and biological properties (Huan and Chang, 2009; Khshaba et al., 2011; Ma et al., 2011; Willershausen, 2013; Damas et al., 2011; Hakki et al., 2013). Accelerated Portland cement (APC) has been obtained by the sol gel method using the white mineral trioxide aggregate and CaCl2 (as an accelerator). APC had rapid setting but lowered compressive strength in comparison to the mineral aggregate. The decrease in the compressive strength has been attributed to the CaCl2 in the binding system. Moreover, as the amount of CaCl2 used is increased up to 10% wt., formation of a new hydrate phase, that is, calcium hydroxyl chloride, can be observed enhancing the biocompatibility and cytotoxicity of APC specimens (Voicu et al., 2012).

8.8.3 FUTURE ASPECTS OF NANOTECHNOLOGY IN ENDODONTICS In terms of endodontics, nanotechnology will not only improve the mechanical properties but also make a profound improvement in the biological properties of a material. It is not too far away that nanodentistry will succeed in maintaining near-perfect dental health with the help of nanomaterials, nanorobotics, and biotechnology.

8.9 CONCLUSIONS Nanotechnology can be applied in almost all fields of human activity. As Feynman, a Nobel-Prize-winning physicist explained briefly the important point of view with the following words: “Concept of nanotechnology is an inevitable development in the progress of science.” Particularly, nanotechnology has made progress in the fields of medicine and dentistry. The field of nanotechnology has tremendous potential, which, if harnessed efficiently, can bring out significant benefits such as improved health and better use of natural resources (Mohan et al., 2013). Actually, it may be concluded that among these, the most

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substantial contribution of nanotechnology to dentistry is the enhancement in tooth restoration with nanocomposites. As final words, the combination of philosophies of science and art will come together in this scene. In nanotechnology, someone will imagine it and then someone will do it. As an example, Jules Gabriel Verne imagined the moon trip and Neil Armstrong and other scientists did it.

ACKNOWLEDGEMENTS The work has been funded by PN-II-PT-PCCA-2013-4-0891 project “Innovative dental products with multiple applications LavEndo” funded by UEFISCDI.

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