Keywords

1 Introduction to Nanotechnology

Richard Feynman first proposed the idea of nanotechnology in his famous speech “There’s Plenty of Room at the Bottom” [1]. It attempts to use molecular engineering to create nano machineries that can produce nano materials. Under “Definition of Nanotechnology,” an early NNI document (National Science and Technology Council [NSTC], 2000) claimed that the ability to operate at the molecular level, atom by atom, to develop enormous structures with fundamentally new molecular organization is the essence of nanotechnology. The behavior of structural features in the range of 10−9 to 10−7 (1–100 nm) exhibits significant alterations when compared to the behavior of isolated molecules of approximately 1 nm (10−9) or of bulk materials. We will be able to organize atoms in any way we like, thanks to nanotechnology, which will allow us to effectively and completely control the structure of matter [2, 3].

Nanomedicine is a brand-new area that has emerged as a result of developments in the applications of nanotechnology in medicine [4]. According to Robert A. Freitas Jr., who first proposed this idea in 1993, this notion entails using nanostructures and nanodevices to observe, manage, and treat the biological systems of the human body at the molecular level [5]. The pharmaceutical business, where many medications are hydrophobic in nature and only sparsely or weakly soluble in aqueous solutions, is one of the most straightforward applications of nanotechnology. Due to the enormous increase in surface area, shrinking a pharmaceutical down to the nanoparticle size range can enable more of the drug to go into the solution [6]. Dental treatments using designed nano materials can improve therapeutic and preventative outcomes.

2 Nano Dentistry

The most recent advances in nanotechnology research and development can be used to improve and upgrade conventional dental materials and equipment. In order to create regenerative materials, nano fillers, nano composites, nano impression materials, target-oriented antimicrobial mouthwashes, implants, and drug-enclosing nanoparticles, various synthesis approaches, including bottom up, top down, functional, and biomimetic approaches, can be used in nano dentistry. A thorough grasp of the tooth’s structure and environment, as well as expertise in the material, synthesis process, and synthesis technique, are necessary for the development of nano dental products. Since ancient times, dental biomaterials made of metals, ceramics, resins, and polymers have been created and further modified [7]. Polymers can be made from both synthetic and natural (plant- and animal-based) materials [8]. To improve the mechanical and optical properties of polymers, some uncommon materials, such as carbon nanotubes (CNT), graphene oxide, and nanodiamonds, can be used in place of traditional glass or carbon fibers [9] (Figs. 1 and 2).

Fig. 1
A framework with nanoparticles used in dentistry at the center. It is surrounded by antimicrobial nanoparticles at the top, reinforcement nanoparticles on the right, therapeutic nanoparticles at the bottom, and regenerative nanoparticles on the left.

Classes of nano materials used in dentistry

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Fig. 2
A flow diagram. The applications from left to right are diagnostic tools, restorative therapy, hypersensitivity treatment, dental implants and teeth replacement therapy, preventive and regenerative, orthodontic treatment, and endodontic treatment.

Applications of nanoparticles in dentistry

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3 Applications in Diagnosis

For the prevention or treatment of oral disorders caused by biofilms, a thorough understanding of bacterial adhesion—the primary factor in bacterial colonization and pathogenesis—as well as bacterial nano mechanics is necessary [10]. The ability of bacteria to cling to individuals of the same or other species as well as to various substrates, such as teeth and implants, has been well documented [11, 12]. AFM offers a breakthrough in the characterization of bacteria as well as the measurement of their adhesion to various substrates [13, 14], because of its capacity to directly interact with imaging live cells without affecting their morphology and properties [15]. A real-time, highly sensitive scanning of a living bacterial cell was made possible with nanomechanical biosensors and an AFM cantilever [16]. Additionally, details on the characteristics of the membrane molecules [17] and the elasticity of a cell [18] are made available.

4 Application of Nano Dentistry in Conservative and Restorative Treatment of Teeth

The primary treatment needed in the oral cavity is caries management. To preserve the tooth’s structural and cosmetic integrity, an appropriate restorative material has to be used to fill the tooth. After a tooth is lost, it is restored using a bridge, an implant, and a crown. Nanoparticles can be added to filling materials and implants to improve them. The material must be close to the tooth structure and adhere to it in order for the restoration of a carious tooth to be successful. Micro gaps, leaks, and ultimately filling failure are caused by compromised adhesion or intersurface integrity [19, 20]. For enhanced defense, mineral deposition, and sealing of exposed collagen fibers in prepared teeth, the use of nano fillers or nano gels has been tried [21]. Reactive nanogels [22], zirconia (20–50 nm) [23], HA (20–70 nm) [24], colloidal silica (5–40 nm) or barium aluminosilicate nanofillers (400 nm) [25], and bioactive calcium/sodium phosphosilicate [21] are some examples of nano materials. Self-healing adhesives that can patch up microscopic or nanoscale cracks without compromising the strength of resin-dentin connections have also been developed [26]. They contain nano capsules that are packed with healing agents, and the presence of a break in the resin matrix typically causes the nano capsules to burst and release their contents. The durability of the resin-dentin interface has also been improved by using nano-controlled molecular interaction between the resin monomer and HA that is still present in the hybrid layer [27]. In comparison to fine size fillers, nano fillers offer superior adherence, biocompatibility, and durability. Many scientific organizations are using hydroxyapatite (HA), the primary inorganic mineral component of teeth, to create nano composites. To serve as an inorganic component of nano composites, Chung et al. created a physiological component mixture using HA and chitosan nanoparticles [28]. By creating HP-gelatin/curcumin nanocomposites, antimicrobial properties against Escherichia coli, Staphylococcus aureus, and Streptococcus mutans were introduced into filler materials [29]. Various natural polymers have been employed in investigations to alter the organic nanocomposites’ organic component characteristics [30]. The strongest antibacterial HA/CuO/TiO2 nanocomposites were created by Imani et al. The strong Quality by Design principle assisted in the manifestation of development [31]. A difficult challenge to incorporate Ag NPs, graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs), and graphene oxide nanoribbons (GONRs) in HA nanocomposites was recently undertaken by Balu et al. The team investigated how the amount of carbon affected the final hardness of the nanocomposites. Additionally, a bio strain was used to assess the Ag NPs activity (E. coli and S. aureus bacteria). Lidocaine was made available as a model drug release by the created nanocomposite [32].

As a supplementary material in the creation of nanocomposites, other synthetic polymers have been investigated. Poly Methyl Methacrylate Nanocomposites have improved mechanical properties as compared to HA nanocomposites [33]. Mallakpour et al. developed multi-component nanocomposites (Polyvinylpyrrolidone/L-leucine Amino Acid, Functionalized Mg-Substituted Fluorapatite Nanocomposites) using ultrasonic waves as an energy source [34]. Microwaves [35,36,37], photons [38] and their combinations [39] are other energy sources that have been used by various research groups to create nano composites.

Open tubules are brushed with highly concentrated GNPs to prevent pain and suffering in dentinal hypersensitivity, and laser irradiation is used to encourage the aggregation of nanoparticles to cover the exposed tubules [40]. Additionally, dental nanorobots provide a rapid and effective treatment for dentin hypersensitivity by accurately and selectively occluding the tubules with biological materials in a matter of minutes [4].

5 Applications in Endodontics Treatment

The innermost, most important, and vascular component of a tooth is the dental pulp, which is made up of nerve fibers and blood vessels. The area of dentistry known as endodontics deals with periodontal tissues and dental pulp. When an infection penetrates the dentin and enamel to reach the pulp, pulp treatment is necessary. Cleaning and preparing root canals that contain pulp tissues for an appropriate filling and sealing material is the focus of endodontics. The following qualities should be present in an ideal root-end filling material: a hermetic seal, non-resorb ability, non-toxicity, non-carcinogenicity, biocompatibility, and dimensional stability [41,42,43]. None of the materials in existence satisfies every requirement. To sanitize root canals, root canal sealers contain a number of nanoparticles, including zinc oxide and chitosan alone or in combination. The flow characteristics of the sealers were unaffected, but they improved the antibacterial action, as evidenced by a notable decrease in Enterococcus faecalis adhering to treated dentin [44]. It was possible to retain the inhibitory impact of a chitosan-modified root canal sealer on biofilm growth at the sealer-dentin interface by first treating the surface of root canal dentin with phosphorylated chitosan [45]. Metal oxides, including magnesium oxide nanoparticles, show promised antibacterial activity in both in vitro and ex vivo tests and may be employed as a possible root canal irrigant. Magnesium oxide nanoparticles (5 mg/L) show a statistically significant long-term benefit in the removal of E as compared to the usual NaOCl solution (5.25%). Faecalis adhered to the dentin of the root canal [46].

Nano materials that aim to regenerate pulp tissue could improve endodontic treatment by preserving the health of the pulp and, by extension, the structural integrity of the tooth. Dentin Odontoblast (located at the edge of the pulp) stem cells have also been investigated for this purpose; however, the clinical setup showed a futile response [47, 48]. Hanafy et al. investigated two widely used dental biomaterials, namely mineral trioxide aggregate (MTA) and nano-HA, as odontogenic differentiation promotors. The results showed significantly higher and upregulated expression of the odontotomy differentiation-specific genes, namely OPN, RUNX2, OCN, and Collagen1, in the treatment group compared to the control group [49]. Another strategy to keep the pulp healthy and keep the infection outside the vascular area is pulp capping. Li et al. suggested a combination of micro-nano bioactive glasses with biocompatible, osteogenesis-sensitizing characteristics. Dental pulp capping using Ca–Zn–Si-based micro nanospheres (Zn doped). The results were positive, showing increased antibacterial effects and increased macrophage stimulation to decrease proinflammatory indicators, followed by dentin remineralization via sensitization of dental pulp cells [50]. Drug-encapsulated liposomes were suggested by Sinjari et al. as a very sophisticated nanotechnological method for restoring the homeostasis of dental pulp stem cells. In terms of 2-hydroxyethyl methacrylate, the treatment was able to help restore cell proliferation and reduce inflammation markers [51]. Kim et al. have suggested an RGD peptide conjugated dendrimer-based medication delivery system for dental pulp differentiation following severe dental injury. Higher mineralization and odontogenic potential were very positive findings [52]. With a very small number of tests, Elgendy and Fayyad investigated natural scaffolds, such as propolis and chitosan, for tooth restoration and discussed their potential for endodontic treatment because of their high biocompatibility and capacity for tissue restoration [53]. In a similar vein, Tondnevis et al. suggested creating a dental tissue scaffold utilizing polymers and the freeze-drying method that contains nano-HA or Nano-Fluro HA/Chitosan scaffold. Results showed that chitosan was helpful in significantly increasing cell proliferation [54]. These experiments demonstrated the chitosan NPs’ potential for use in dental endodontics. The role of eggshell-derived porous nano-HA and CMC (Carboxy Methylcellulose) composite was recently reported in a laboratory study by Baskar et al., which demonstrated their impact on dental bioactivity and cell proliferation using the significantly increased levels of VEGF and dentine sialo phosphoprotein [55]. The development and testing of amoxicillin-loaded nanodiamond Gutta-percha composite (NDGP-AMC) for use in root canal procedures produced encouraging results [56]. Gelatin [57,58,59], collagen [60], silk [59], and other natural fibers and polymers have also been investigated in nano dentistry.

6 Applications in Orthodontic Treatment

To realign teeth, force must be applied in the desired direction and interfacial stability must exist between the tooth surface, bracket, arch wire, and ligatures, among others [61]. Better holding and stability are prevented by the frictional forces between the arch wire and the brackets, which can also lengthen the course of treatment and have an impact on the final result. These components are covered with Fullerene, such as Molybdenum and tungsten disulfide NPs, to lessen this friction [61]. Also, nanotechnology can help in maintaining better oral hygiene, better anchorage, and lesser enamel demineralization during orthodontic treatment by several coatings like elastomeric ligatured supported NPs (Benzocaine and Ag) [62], nanocomposites (Ag NPs with ZnO, chlorhexidine) of adhesive types/bands [63], gold NPs in orthodontic adhesives [64], silver NPs [65], TiO2 NPs [66], and copper oxide NPs [67].

7 Applications in Prosthodontic Treatment

Patients are increasingly more likely to seek out rehabilitation therapy as a result of greater awareness of and interest in quality-of-life enhancement. Nanotechnology is now a component of materials for crown, bridge, and implants used in restorative dentistry as a result of progress in research aimed at improving tooth replacement. The qualities of currently employed materials, including ceramics, impression materials, denture bases, and different forms of prosthodontic cement, have also been greatly improved by nanotechnology. Polymethylmethacrylate (PMMA) polymers are mostly used in removable prosthodontic appliances such as complete dentures, partial dentures, and detachable maxillofacial prostheses. Chlorinated polyethylene, poly(methyl methacrylate), poly(urethane), poly(vinyl chloride), and poly(dimethyl-siloxane) (PDMS—silicone elastomers) have all been employed in the production of maxillofacial prosthesis [68]. Although PMMA has strong biocompatibility, aesthetics, processability, and reparability, it has the drawbacks of being weak, having a low fracture resistance, behaving radiopacitively, and having microbial adherence [69,70,71]. Well-dispersed nano-ZrO2 particles can increase the strength, modulus, and ductility while TiO2 nanoparticles strengthened the mechanical behavior of PMMA. Particles of Ag TiO2 and Fe2O3 considerably lessen C’s adhesion. albicans made of PMMA that have no impact on growth or metabolism [72,73,74]. It can aid in treating pathological conditions such as denture stomatitis brought on by Candida albicans adhering to the denture base materials [75]. Due to their sophisticated mechanical and physical qualities, silicone elastomers have been employed in the production of dental prosthesis for a long time [76]. They are also non-toxic, chemically resistant, and biocompatible. PDMS [77, 78] and silicone rubber are the most preferred types [79,80,81]. In recent studies, various filler nanoparticles (NPs) have been added to silicone rubbers to enhance their physical and mechanical properties through [82]. The silicone matrix is most frequently reinforced using silica NPs as fillers [82, 83]. Silicone elastomers’ mechanical and physical properties would vary depending on the concentration of silica NPs present [82, 84]. Additionally, silicone elastomers are supported by polyhedral oligomeric silsesquioxanes (POS), a nano (1.5 nm) silica cage, and metal nanoparticles (NPs) to enhance their tensile strength and other physical characteristics. Fixed prosthesis can use nano materials, nanocomposites, and nano coatings. Cytotoxicity brought on by the leaching of organic monomers can be resolved by nanocomposites built on nanofiller technology. To increase flexural strength and hardness, 3-methacryloxypropyl-tri-methoxy-silane was applied to silica particles to create zirconia-silica nanoparticles. Nanotechnology offers new opportunities and promises for enhancing the adherence and endurance of implants. In addition to calcium phosphate, silica-based NPs, polyvinyl alcohol, and carbon nanotubes were employed to create nanocomposites and occasionally scaffolds for enhancing mechanical strength and tissue regeneration [85]. The most recent developments in research on the uses of nanometals, nanoceramics, nanoresins, and other nano materials in prosthodontics have been reviewed. This research clearly demonstrates that many properties of materials used in prosthodontics, such as modulus elasticity, surface hardness, polymerization shrinkage, and filler loading, can be significantly improved after their scales were reduced from micron-size into nano size by nanotechnology.

8 Application in Dental Implants

Nanostructure-modified titanium implants encourage osteogenic differentiation and could have a better bio-integration into the alveolar bone [86]. The flat surface of titanium implants can be anodized to create nanotubular structures with a diameter of less than 100 nm [87]. The physicochemical characteristics of surfaces [88], as well as the spacing and diameter of nanotubes, can be controlled by altering variables including voltage, current density, and the chemistry of the electrolyte. Long nano tube arrays (10 m) and pillar-like nanostructures with adjustable sizes are also deposited by anodization on titanium surfaces [89]. On Titanium, Ti6Al4V, Cr–Co–Mo alloys, and Tantalum, nano pit networks (pit diameter 20–100 nm) can be successfully created by combining strong acids or bases with oxidants. According to a study, treatment with HCl produces superior outcomes than those with H2SO4 and Na2S2O8 [90]. Acid etching can be used in conjunction with other procedures, such as grit blasting, to remove contaminants on implant surfaces by blasting residues. The titanium dental implants’ osseointegration could be hampered by the grit blasting residue. But compared to an acid-etched surface, the nanostructured Ti surface created by physical vapor deposition had a surface area increase of up to 40% and a stronger osseointegration. Additionally, to improve bone regeneration, HA nanocrystals [91] and calcium-phosphorus NPs [92] can be used to treat or modify the implant surface. A wide range of distinctive nanostructures, including octahedral bipyramids, nano flowers, nano needles, nano rods, and meso-porous nano scaffolds, have been produced on titanium using a combination of hydrothermal treatments (tuning concentration, temperature, reaction medium composition, and time duration) and sodium hydroxide [93]. Early bone healing and improved mechanical interlocking with bone result from the deposition of discrete 20–40 nm nanoparticles on a dual acid-etched implant surface. Niobium oxide and diamond-like carbon nano topographies have been produced on titanium and other substrates with the aid of a mixture of chemical vapor deposition and the sol–gel method, improving the bioactivity of implantable metals. Other current techniques for creating a nanostructured dental implant surface include laser technology and coatings made of ultraviolet (UV) photo functionalized (picometer to nanometer) TiO2 [94].

9 Applications Preventive Therapy

Anticaries DNA vaccine’s immunogenicity has been improved by the use of customized delivery vehicles, such as anionic liposomes in chitosan/DNA nanoparticle complexes. In order to permit the release of the vaccine in a pH-dependent way, the surface charge of the delivery vehicle may also be pH-dependent. All in vitro research up to this point has suggested that nanotechnology may be able to stop the progression of early caries lesions in their surface but not deeper layers. A local application of a nanostructured doxycycline gel has been employed in an experimental periodontal disease model to stop bone loss. With their continuous and quick movement (1–10 m/s) across the supra and subgingival surfaces, nanorobots (dentifrobots) mouthwash or toothpaste left on the occlusal surfaces of teeth continually remove the organic residues and prevent the calculus accumulation. When eaten, these nanorobots can be safely deactivated [95]. A number of oral health care products, including liquids and pastes containing nano-appetite for managing biofilm at the tooth surface and goods including nano materials for remineralizing early submicrometric sized enamel defects, have been developed using biomimetic techniques. On the tooth surface, bacteria form biofilms that lead to dental cavities. Nanocomposite surface coatings can minimize bacterial adhesion, prevent pathogenic effects, and make the tooth surface easier to clean. The apatite nanoparticle-containing toothpaste can be employed as biofilm management nano materials and as a method for remineralizing enamel lesions that are smaller than sub-micrometers [96,97,98]. However, these oral nanoparticle preventive medications are still in the research phase, and further in-depth research is required before they can be used in clinical settings. Several nanoparticles, like zinc oxide, silver, and polyethyleneimine, can be incorporated into dental composites or dental adhesives to give antibacterial nano treatment. This inhibits the growth of germs through a variety of ways. The bacterial cell membrane is disrupted, sugar metabolism and active transport are both inhibited, reactive oxygen species are produced, magnesium ions necessary for the enzymatic activity of oral biofilms are displaced, electron transport across the bacterial membrane is disturbed, and DNA replication is prevented [99, 100].

10 Applications in Regenerative Therapy

Different types of nano-calcium phosphates, including dicalcium phosphate anhydrous, tetra calcium phosphate, monocalcium phosphate monohydrate, and carbonate hydroxyapatite, have been employed as Ca- and PO-releasing fillers for remineralization in recurrent caries [101, 102]. Similar to other medical fields, tissue engineering in dentistry has been used to integrate scaffold matrices with the regeneration abilities of stem cells, which are mostly derived from dental tissues such as dental pulp, periodontal ligament (PDL), and alveolar bone. These scaffolding materials have been significantly improved thanks to nanotechnology in tissue engineering, creating special 3D matrix conditions for cells and tissues. A native tissue architecture can be developed using a bottom up method, giving an engineered construct the mechanical properties of enamel and dentin [103]. The dental tissues’ nanoarchitecture is used to create electro spun nanofibers, self-assembling peptides, and phase-separation matrices. The development of nanofibrous scaffolds as matrices for the regeneration of dental tissues, such as the dentin-pulp complex, enamel, PDL, cementum, alveolar bone, and temporomandibular joint, has been widespread [104, 105].

11 Conclusion

Nano dentistry attracts patients to dentistry because it is cost-effective, saves time, and prevents psychological trauma. More patient-centered research will aid in the advancement of nanotheranostics that are both effective and cost-effective. Despite the numerous irrefutable gaps that limit its clinical exploration, revolutionary nanotechnology has enhanced conventional dentistry. Research in the field of nano dentistry still lags behind other areas of biological study. Prior to the application of nanotechnology on a large scale, fundamental molecular engineering methods, mass production techniques, and the simultaneous coordination of many nanorobots must be overcome. Nanotechnology advancements are shaping the future of healthcare administration. They have the potential to produce significant benefits, such as improved health, more efficient use of natural resources, and less environmental pollution. Nanotechnology will profoundly alter dentistry, healthcare, and human life. However, social issues of public acceptance, ethics, regulation, and human safety must be addressed prior to the incorporation of molecular nanotechnology into the modern medical and dental arsenal.