Introduction Fixed orthodontic appliances include a wide variety of archwires used as a means of delivering forces on teeth. The success of the orthodontic treatment may depend on the selection of the aligning archwires. An ideal aligning archwire should have a good formability, spring-back, stiffness biocompatibility, low friction, Join ability, and cost. The forces delivered by the archwires depend largely on the physical properties and dimensions of the wire material. The use of Nickel titanium (NiTi) archwires in orthodontics was first described by Andreasen and Hilleman. Since their development, improvements in their manufacturing and composition designed to enhance their properties have been introduced. NiTi archwires have many theoretical advantages over others in the initial alignment of the teeth.¹

Although orthodontic treatment has many recognized benefits including improvement in dental health, function appearance, and self-esteem, nevertheless orthodontic appliances can cause unwanted complications if adequate care is not taken during the treatment. 

Friction is one of the major factors present during retraction or alignment of teeth during orthodontic treatment. Minimizing the frictional forces between the orthodontic wire and brackets has the potential to increase the desired tooth movement and thus shorten treatment time. One of the methods to overcome high friction is the application of higher forces during treatment which results in undesirable anchorage loss. On the other hand, there are other methods of overcoming unwanted friction, including alteration of the bracket design or wire shape and size.²

The formation of white spot lesions (WSL) on the labial surface of the teeth is a common iatrogenic problem seen during and after fixed orthodontic treatment. Researchers have evaluated an array of compliant (oral hygiene maintenance, antibacterial mouth rinses, fluoride mouth rinses, fluoride dentifrices, or probiotic toothpaste) as well as noncompliant (fluoride varnish, using fluoride-containing adhesives, and fluoride releasing modules) methods for preventing the formation of WSL during fixed orthodontic treatment.³

Nanomaterials are materials with particle size in the range of 1–100 nm and due to their ultra-small sizes, large surface area to mass ratio and increased chemical reactivity, nanomaterials have superior physicochemical properties compared to their non-nanoscale counterparts.⁴ Nano materials are used in many areas of dentistry, such as conservative dentistry, endodontics, oral, and maxillofacial surgery, periodontics, orthodontics, and prosthetics².

The development of Nanotechnology gives better opportunities to both patient and orthodontist due to new physicochemical, mechanical and antibacterial properties of nanosized materials and can be used in coating orthodontic wires, elastomeric ligatures, and brackets, producing shape memory polymers and orthodontic bonding materials. Not only can we control biofilm formation, reduce bacterial activity, anticariogenic, increase the strength and durability of materials but also provides the desired tooth movement, shorten the treatment time.²

NPs used in orthodontic applications are generally integrated into orthodontic materials or applied as a special coating on the surface of these materials, both to increase antibacterial activity and to improve material surface properties². NPs can be categorized into three primary types based on their sources and mechanisms of action; inorganic NPs, organic NPs, and natural macromolecule compound NPs. Ag, Au ,Cuo,Zno,Tio₂,Sio₂are some of the inorganic nanoparticles. Chitosan, Curcumin, Quaternary ammonium compounds are organic nanoparticles⁵.

Chitosan is a natural polysaccharide that consists of multiple chains of N-acetyl-D-glucosamine obtained by the alkaline deacetylation of chitin. Chitin is the second most abundant natural polysaccharide after cellulose and is present in shells of insects, marine crustaceans, fungal cell walls, and planktons. Chitosan is active against a broad variety of microorganisms including fungi, algae, and bacteria. The high molecular weight chitosan is specifically more active against Gram positive bacteria and cationic chitosan interacts with the anionic cell membrane of microbes leading to leakage and disruption of the cell membrane³. Nathasha Mayma et al compared the antimicrobial property of nanochitosan coated and uncoated stainless steel (SS) brackets against Streptococcus mutans and Lactobacillus acidophilus and concluded that Chitosan exhibited short term antimicrobial property.^{3, 6}

Among the inorganic NPs, Silicon Dioxide (SiO2) have gained attention in the food, textile, automotive, and aviation industries and in the biological control of surfaces due to their hydrophobic properties, preventing the adherence of dirt and bacteria. These characteristics made such coatings to be acknowledged by self cleaning surfaces and the photocatalytic characteristic of these materials, which allows their use in several types of surfaces, including the oral environment⁷.

Stainless steel and superelastic Nickel-titanium (NiTi) archwires may be coated completely or just on their labial surface. However, in clinical situations, delamination, ditching, cracking, and discoloration have been observed. The partial or complete loss of the surface coating is called delamination which can lead to detrimental mechanical and esthetic properties. In addition, exposure to the oral environment and food stains lead to color instability of the coating material.⁸

In a clinical study conducted by Venkatesan et al., it was demonstrated that the TiO2 coating on NiTi archwires exhibited delamination and degradation and at the end of 1 month, the coating was found to have deteriorated by 60%. Long-term clinical studies evaluating the integrity of different types of nanocoatings are required⁹.

However, most of these advantages are based on in vitro testing methods, and in order for this advantage to be validated, these wires should be assessed clinically. Literature lacks studies on the coating loss and the alignment efficiency of organic and inorganic coated NiTi archwires. Thus the aim of the study is to evaluate and assess the frictional resistance, delamination and alignment efficiency of organic and inorganic coated NiTi archwires.

Aims and Objectives

Hypothesis  There is no difference between SiO2 and Chitosan nano coated NiTi arch wires.

Aim of the study  The aim of the study is to evaluate the frictional resistance , delamination and alignment efficiency of organic and inorganic nano coated Nickel titanium (NiTi ) arch wires.

Objectives of the study 

1.    To assess and compare changes in frictional resistance among organic nano coated (Chitosan), inorganic nano coated (Silicon dioxide) and non-coated Nickel titanium (NiTi) archwires before and after treatment period (3 months).

2.    To assess and compare delamination among organic nano coated(Chitosan) and inorganic nano coated (Silicon dioxide ) Nickel titanium (NiTi) arch wires.

3.    To evaluate and compare the alignment efficiency among organic nano coated (Chitosan) and inorganic nano coated (Silicon dioxide) and non coated Nickel titanium(NiTi) archwires.

Materials &Methods

Source of the subject  Patients visiting the Department of Orthodontics and dentofacial orthopaedics, Sibar Institute of dental sciences, Guntur.

Sample size   Sample size calculation was done using G power version 3.1.9.2. with effect size of 0.32, alpha error 0.05, power of the study 80%, number of groups 3, number of measurements 3, total sample size of 36 and 12 in each group.

Inclusion criteria 

Ø  Patients in the permanent dentition who require orthodontic treatment with Preadjusted edgewise appliance.

Ø  Moderate crowding of not more than 6 mm in the lower anteriors requiring 1^st premolar extraction.

Ø  Age group between 16-24 years.

Exclusion criteria 

Patients with the following reasons will be excluded from the study:

Ø  Unable to provide valid consent.

Ø  Craniofacial syndromes.

Ø  Teeth blocked out of the arch or ectopic teeth not allowing bracket placement and ligation at bond-up.

Ø  Hypodontia resulting in more than 1 tooth missing in any quadrant.

Materials used  

   0.016 inch Nickel Titanium archwire.(3M UNITEK )

   Silicon Dioxide (SiO₂ ) nanoparticles (Adnano )

   Chitosan nanoparticles ( HiMedia Laboratories Pvt Limited, Mumbai, India )

   Universal testing machine

   Colour scanner (Epson V750 )

A total of 36 subjects between 16-24 years who satisfy the inclusion and exclusion criteria and willing to participate in the study, with a lower anterior crowding of less than 6 mm ,as per Little’s irregularity index, requiring extraction of 1^st premolar will be randomly divided into three groups.

In each group, following the routine bonding procedures initial 0.016 NiTi wire will be placed for the alignment of anteriors.

In Group 1, conventional NiTi arch wires (Non coated ) will be used.

In Group 2, Silicon dioxide coated NiTi archwires will be used .

In Group 3, Chitosan coated NiTi archwires will be used.

The arch wire is religated at every 4 weeks interval and after a period of 3 months the 0.016 NiTi arch wires (Coated and Non coated) will be removed and subjected for evaluation of delamination, frictional resistance and alignment efficiency.

0.016 inch Nickel Titanium arch wires will be coated with Chitosan and SiO2 nanoparticles according to previous literature recommendations as follows 

Synthesis of SiO2 nanoparticles and coating on NiTi archwires

Surface coating of 0.016-in NiTi wires with SiO₂ nanoparticles will be done by sol –gel method. For synthesis the Tetraethyl orthosilicate, TEOS will be added to acetic acid, CH3COOH with distilled water as the solvent. The aging time in the experiments will be set to 2, 4 and 6 hours. The resulting colloidal sol then will be centrifuged and washed with ethanol and then it will be centrifuged again. Then, the resulting precipitate will be dried at 60 ⁰C for 1 day. The second parameter, the calcination temperature was varied between 600 ⁰C and 700 ⁰C at a holding time of 1 hour and 30 minutes in order to produce white silica nano powder.¹⁰ The coating procedure is a sol-gel thin film dip coating method, in which NiTi wires will be first cleaned under running water to prepare the surface for the coating procedure by removing the dust particles. The wires will be inserted into the bathtub containing the 100 ml of either SiO2 nanoparticle solution for 30 min, then they were removed from the tub and kept in a hanger and wires will be put in a colander, where they were painted with a solution of nanoparticle, and air-dried with the aid of a dryer for 2 min. Finally, they were placed in a hot air oven at 160⁰C for 3 min.¹¹

Synthesis of Chitosan nanoparticles and coating on NiTi archwires

The chitosan nanoparticles will be synthesized and coated by using the hydrothermal method. A solution of 0.5 g Chitosan in 30 ml distilled water will be prepared by continuous stirring for 30 min. Meanwhile 1.5 M solution of acetic acid solution will be prepared by mixing 60.05 g of acetic acid in 500 ml distilled water under stirring for the same duration. The acetic acid solution will be added dropwise to the chitosan solution under continuous stirring until the pH of the reactants becomes 10.9. This solution mixture will be transferred into Teflon lined sealed stainless-steel hydrothermal autoclave reactor along with NiTi archwires and kept in the hydrothermal oven at a temperature of 90°C for 8hours. The chitosan nanoparticle synthesized by the hydrothermal reaction will precipitate over the NiTi archwires as a uniform coating.¹²   

Frictional Resistance testing ⁷

To test the frictional resistance, wires will be tied to the orthodontic bracket slot with a gray-color modular elastic (GAC, Dentsply, USA) and changed in every experiment. The bracket used will be the Edgewise Slim (with zero torque and inclination) for upper central incisors (Morelli, Sorocaba, SP, Brazil) with an interwing size of 2.31 mm externally and 0.96 mm internally.  Protocol will be followed for control as well as coated wires before insertion of wires in patients mouth as well as after removal. The maximum static frictional force was measured in the universal testing machine set to run 5 mm of wire at 0.5 mm/min and cell load of 20N.      

The procedure will be explained to the patients who met the inclusion criteria, and they were invited to take part in the study. Informed consent will be obtained from the willing participants. Patients mandibular arches will be bonded with a preadjusted edgewise appliance, and the allocated archwires will be ligated to all teeth at bond –up. Patients will be instructed on oral hygiene measures and use of identical dentifrices and advised not to use any chewing gum, fluoridated mouthwash, or antibiotics during the period of the study. Patients will be recalled for every 4 weeks for 3 months and at 12 weeks after bond up for archwire removal. Coating loss of nanocoated inorganic and organic NiTi arch wires will be assessed and alignment efficiency will be evaluated.

Measurement of delamination⁸

To measure coating loss, each archwire will be placed against a green background and scanned using a color scanner (V750, Seiko Epson, Nagano, Japan). A resolution of 400 dpi will be used; this provides sufficient image quality to carry out the required measurements. The images  will be imported into AutoCAD 2014 software (Autodesk, San Rafael, Calif), and an arc will be drawn over the archwire using the “draw arc” tool. The archwire lengths and coating loss lengths will be obtained using the “arc dimension” tool. The measurements will be made at an increased magnification to minimize error. Coating loss will be determined using the following equation

                                                                      length of coating lost on archwire

                           % coating loss =          

                                                            total length of archwire

For coating loss measurements, a standardized photographic setup will be created to produce images of the wires. A digital single reflex lens camera (D2x, Nikon, Tokyo, Japan) with a 60-mm macro lens (Nikon), shutter speed of 1/125 of a second, and aperture of f/2.0 will be used throughout. The camera will be attached to an adjustable mount at a distance of 60 cm from the copy stand. A 45/0 geometry setup will be used with the object (archwire) at 0 to the detector (camera), with illumination from 2 lights at 45⁰ to the object. All photographs will be captured in “raw” format to prevent data loss and calibrated using a grey card (Fotowand, Sudwalde, Germany) with 17.68% € reflectance. The images will be opened in Photoshop Creative Suite 6 (Adobe Systems, San Jose, Calif). Coating loss measurements will be made using the L*a*b* slider tool.  Three measurements will be made for each archwire at randomly selected points, and the average of these values will be used. These will be then compared with the respective unused control archwire.

Measurement of alignment efficiency⁸

Alignment efficiency will be calculated by taking the difference in Little’s irregularity index.18 Measurements will be taken of contact point displacements between canine and canine for mandibular models on pretreatment and postintervention dental casts using digital calipers. The sums of the 5 readings will be taken per arch. Measurements will then be entered into an Excel spreadsheet. The difference between the 2 measurements will give us the reductions in irregularity and alignment efficiency.

Data will be subjected to statistical analysis using SPSS software version 23 (IBM Corp., Armonk, NY, USA) and results will be drawn.

Potential Risks and Benefits 

Risks - No additional risks involved.

Benefits - Nanoparticles improves the microbicidal properties, reduces friction and increases the strength of the material.

References

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