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 Table of Contents  
Year : 2021  |  Volume : 8  |  Issue : 3  |  Page : 176-181

Comparison of frictional resistance of different esthetic archwires in different esthetic brackets in dry and wet fields: An in vitro study

Department of Orthodontics and Dentofacial Orthopedics, Indira Gandhi Institute of Dental Sciences, Sri Balaji Vidyapeeth, Puducherry, India

Date of Submission27-Mar-2021
Date of Acceptance29-May-2021
Date of Web Publication23-Aug-2021

Correspondence Address:
Jinsa Nakasseril Joseph
Department of Orthodontics and Dentofacial Orthopedics, Indira Gandhi Institute of Dental Sciences, Sri Balaji Vidyapeeth, Puducherry - 605 007
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrr.jdrr_50_21

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Introduction: The patient's desire toward achieving an esthetically pleasing face has not only increased the demand for orthodontic therapy but also necessitates the need for an esthetic appearance during the treatment period which led to the introduction of tooth-colored ceramic brackets and archwires. Materials and Methods: The experimental research was done using esthetic brackets (polycrystalline ceramic brackets with and without metal slot and monocrystalline brackets) and stainless steel archwires (uncoated, Teflon coated, epoxy coated, and rhodium coated) in both dry and wet fields. Two typhodont models were selected onto which the above-mentioned brackets were bonded and frictional resistance was evaluated using Instron machine for each of the archwire-bracket combinations in dry and wet fields. Results: The uncoated stainless steel (SS) wires showed less friction when compared to esthetic-coated SS wires. The frictional resistance was least for wet field when compared with dry field for all the groups and subgroups. It was also found that frictional resistance was minimum for Teflon-coated wires in polycrystalline ceramic bracket with metal slot (wet field) and maximum for rhodium-coated wires in monocrystalline brackets (dry field). Conclusion: Polytetrafluorethylene/Teflon-coated archwire and ceramic bracket with metal slot could be preferred as the esthetic archwire and bracket material of choice, respectively, due to their low frictional properties.

Keywords: Artificial saliva, brackets, ceramic, friction

How to cite this article:
Joseph JN, Ammayappan P, Sankar H, Yashwant V A, Alexander L. Comparison of frictional resistance of different esthetic archwires in different esthetic brackets in dry and wet fields: An in vitro study. J Dent Res Rev 2021;8:176-81

How to cite this URL:
Joseph JN, Ammayappan P, Sankar H, Yashwant V A, Alexander L. Comparison of frictional resistance of different esthetic archwires in different esthetic brackets in dry and wet fields: An in vitro study. J Dent Res Rev [serial online] 2021 [cited 2022 Dec 1];8:176-81. Available from: https://www.jdrr.org/text.asp?2021/8/3/176/324417

  Introduction Top

Orthodontics is a specialty of dentistry that deals with the diagnosis and correction of malocclusion and associated problems with special emphasis on augmenting the facial esthetics, acquiring a functional occlusion and attaining structural balance for the patient. Majority of patients undergo orthodontic treatment for esthetic reasons while rest of them seek to improve their masticatory efficiency, speech, and self-confidence.[1] Because of the longer duration of treatment, esthetic appearance of orthodontic appliance is also a major concern for patients, particularly among adolescents. Since the introduction of ceramic brackets made of aluminum oxide in 1986, they have become the most popular esthetic appliances. Monocrystalline and polycrystalline are the most common variants of ceramic brackets in use. The combination of ceramic brackets and esthetic archwires received maximum acceptance among patients in terms of appealing orthodontic treatment. Esthetic archwires can be composite, optiflex, or coated archwires.[2] Coated archwires refers to coating of tooth colored or esthetically acceptable materials on to metallic archwires such as nickel-titanium, stainless steel (SS), or titanium‒molybdenum alloy wires. Tooth movement in orthodontics depends on sliding mechanics which implies to the sliding of archwire along the bracket slot. Sliding movement will produce frictional force, which is the resistance between the wire and bracket slot. For tooth movement to occur the applied force should be high enough to exceed this frictional resistance. Ceramic brackets have the disadvantage of higher frictional resistance and surface roughness which can potentially impede the tooth movement. Several measures have been adopted to alleviate resistance, such as metal slots and use of Teflon-coated wires. Several studies done in the wet medium have concluded that the human saliva, due to its lubricant action lowers the frictional resistance up to 50%.[3] However, in vitro studies using wet and dry medium have shown mixed results. Previous literature has focused on the comparison of esthetic wires in different bracket combinations, but there is a dearth in research with respect to rhodium-coated wires. This study aims at finding the arch wire – bracket combination with low frictional values in a simulated typodont model. This could be advantageous clinically since reduced friction acting between newer esthetic archwire and bracket can reduce the treatment duration.

  Materials and Methods Top

The study was designed as an in vitro prospective comparative study. The physical tests for this in vitro study were performed at Central Institute of Plastics Engineering and Technology (C. I. P. E. T), Cochin, Kerala, and Indira Gandhi Institute of Dental Sciences, Puducherry. The study was approved by the Institutional Ethics Committee (IEC reference no: IGIDSIEC2018NRP42PGJIODO).

This study involved four SS archwires of 0.019 × 0.025 inch dimensions, which consisted of one uncoated and three-coated esthetic archwires. The coated archwires consisted of polytetrafluorethylene (PTFE) coated, epoxy coated, and rhodium coated. Three ceramic bracket systems of 0.022 Slot MBT were used in this study, namely ceramic bracket with metal slot, ceramic brackets without metal slot, and monocrystalline brackets [Figure 1]. The esthetic archwires were procured from different manufacturers since none of the manufacturers had all the esthetic wires in their catalog. Details are mentioned in [Supplementary Table 1] and [[Supplementary Table 1].
Figure 1: Armamentatrium - Jig and brackets mounted on typhodont model

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Each wire was tested in each of the bracket systems, making a total of 12 groups in dry field and a total of 12 subgroups in wet field. Wet field was demonstrated using mucin based artificial saliva (Wet Mouth – ICPA) that was equally and evenly spread with a dropper on top of archwire and brackets.

Ceramic brackets with and without metal slot and monocrystalline brackets were bonded on to two maxillary typhodonts on incisors, canines, and second premolars on both the quadrants using cyanoacrylate adhesive (Fevikwik) with the help of bracket positioner in a straight line so as to allow 0.019 × 0.025 archwire to pass through it passively [Figure 2]. The archwire was secured to the bracket slot with the help of clear elastomeric modules. Each group was evaluated for frictional resistance by subjecting the bracket wire combinations to Instron Universal Testing Machine (TINIUS OSLEN) [Figure 3]. The typhodonts were mounted tightly on the jig using screws, such that the typhodont-jig assembly remained stable while performing the experiment. This was then mounted to the upper clamp of the Instron Universal testing machine. The wire sample was held onto the lower clamp of the testing machine. The lower clamp of the machine was determined to move at a speed of 5 mm/min, keeping the upper clamp with typhodont – jig assembly stable. The wire was cut and fixed in such a way that it extends mesial to the central incisor bracket of opposing quadrant. The wires were drawn from the distal most end till the arch wire reaches the mesial end of the bracket of the central incisor on the working side. In this study, arch wires were made to slide onto brackets to simulate the clinical scenario of en-masse retraction.
Figure 2: Wires ligated onto the brackets-ceramic bracket with metal slot

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Figure 3: Friction test using instron

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The methodology has been illustrated in the consort diagram [Figure 4].
Figure 4: Flow chart depicting the study methodology

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The readings of frictional analysis were recorded in Newton (N) on a digital computer with a graphical illustration for both the dry and wet conditions. The statistical analyses were performed using the computer software IBM® SPSS® 24.0.0 (Chicago, Illinois, USA).

Sample size calculation

A pilot study was conducted to estimate the sample size and the mean (standard deviation [SD]) frictional resistance was found to be 3 (0.57) N. Assuming the expected population SD to be 0.57, with 95% confidence interval and an acceptable error of 5%, the calculated sample size for the study was 5. This sample size was calculated using the following formula:[4]

Statistical analysis

Descriptive statistics were calculated for the groups. According to Shapiro–Wilk test, all groups were normally distributed. One-way analysis of variance (ANOVA) and multiple Bonferroni test were used to evaluate the results. The significance level was predetermined as 0.05.

  Results Top

The study results are summarized in [Table 1]. In our study, SS wires (control group) in polycrystalline ceramic brackets with metal slot in wet medium-delivered minimum frictional resistance (3N). Among coated archwires, Teflon-coated wires exhibited least frictional resistance, whereas among the brackets, polycrystalline ceramic bracket with metal slot delivered minimum frictional characteristics irrespective of the type of archwire used. On the other hand, rhodium-coated archwires in monocrystalline brackets (dry field) delivered maximum frictional resistance (21.7N). In this study, wet medium was found to have less frictional resistance than dry medium among all archwire – bracket combinations. The mean frictional resistance between the groups was compared using the one-way ANOVA and was found to be statistically significant for both dry and wet fields. On multiple comparison using Bonferroni test, subgroups A with D, subgroups H with K, and groups H with K showed no statistically significant difference (P > 0.05), whereas all the other groups showed statistically significant difference (P < 0.05).
Table 1: Frictional resistance of various archwires in polycrystalline ceramic bracket with and without metal slot and monocrystalline brackets in dry field and wet field

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  Discussion Top

The demands of the patients undergoing orthodontic therapy are not only limited to having an exquisite appearance posttreatment but also during the course of the treatment. This had paved way for the introduction of tooth-colored brackets, which marked the beginning of a new era in the field of orthodontics. Among the tooth-colored brackets, (ceramic, plastic, and composite brackets), it was found that ceramic brackets exhibited better esthetics and hardness when compared with the remaining brackets.[5] However, these brackets failed to bring out satisfying treatment outcomes owing to their high frictional properties.[6] Polycrystalline ceramic brackets with metal slot and polycrystalline ceramic brackets without metal slot were used in this study, since they were proved to have comparatively high fracture toughness, thereby permitting the usage of different rectangular SS wires of 0.019 × 0.025 inch dimension.[7] With the intention of reducing the frictional resistance, a newer design of ceramic brackets was introduced that involved incorporation of metallic slots.[8] This modification in structure combined both the esthetic property of ceramic brackets and clinical efficiency of metallic brackets.[9]

In this study, frictional resistance of different esthetic coated archwires in different esthetic bracket systems was compared with the control group of uncoated archwires in both dry and wet fields. SS wires of 0.019 × 0.025 inch dimension were utilized for testing in the three bracket systems. This dimension and material were preferred since it is the most widely used largest dimension of archwire by the majority of orthodontists for the purpose of retraction. Clinically, the most common method of ligating the archwire to bracket is by means of clear elastomeric modules, and hence, it was included in this study. This study involved the use of clear elastomeric modules to secure every archwire-bracket combination, in order to exclude the impact of ligating method on the frictional properties. Experimental studies for the determination of friction in the wet medium was performed either by using human saliva or salivary substitutes such as artificial saliva.[10] Thus, in our study, mucin-based artificial saliva was used for the purpose of lubrication in the wet medium and they were found to reduce friction than the dry medium. Lubricant acts to decrease the strength as well as the number of bridges developed within the asperities of sliding surfaces. Mucin-based artificial saliva was preferred for this study since no significant difference in the lubrication characteristics were observed between mucin-based artificial saliva and natural saliva. Kusy et al. determined that saliva played a great role in affecting frictional characteristics by reducing it to 50% than in the dry medium.[3]

In this study, a cross head speed of 5 mm/min was used for pulling the archwires. This was taken as the standard speed because according to Taylor and Ison[11] there was no significant difference in frictional values while using speeds from 0.5 to 50 mm/min. This helped to reinforce our study by keeping the cross speed more precise to quantify the frictional resistance by means of Instron.

Evaluation of frictional resistance of uncoated and coated wires in polycrystalline ceramic bracket with and without metal slot and monocrystalline bracket in dry and wet fields indicated that uncoated wires have least frictional resistance when compared with coated wires in the three bracket types. Among the coated archwires, Teflon-coated wires exhibited least frictional properties in both dry and wet medium. This proves that PTFE-coated wires and ceramic bracket with metal slot are considered to be the most preferred choice of arch wire – bracket combination with minimum frictional resistance among the experimental groups in dry and wet fields. PTFE is an anti-adherent material that exhibits good mechanical stability as well as excellent chemical inertia. It is manufactured through sintering procedure and exists as two forms: classical PTFE which is not microporous (Teflon) and expanded PTFE (ePTFE) that is microporous. ePTFE is composed of oriented microfibrils which are held together by solid junctions. No other modifications of PTFE were used and only classical PTFE wires were used as a part of this study.

Since Teflon has low coefficient of friction, archwires coated with Teflon aid in decreasing the resistance to sliding.[12] According to Abbas et al, Teflon-coated (PTFE) archwires arch wires delivered minimum frictional resistance among all the esthetic archwires because of their smooth surface characteristics, whereas rhodium-coated wires possess greater surface roughness, thereby contributing toward an increased frictional resistance.[13] Ceramic bracket with metal slot exhibited least frictional resistance and monocrystalline brackets showed maximum frictional resistance regardless of the type of wire placed in the bracket slot in both dry and wet fields. Even though, monocrystalline brackets possess smoother surfaces than polycrystalline brackets, literature proposes that higher frictional characteristics of these brackets could be attributed to the hard and sharp edges present at the intersection between the walls and base of bracket slot with external surface of bracket.[14]

The clinical significance of friction is that it will dampen the net force applied on the tooth from active components such as loop, elastic, or spring. Bracket archwire combination with high frictional values (e.g.,: monocrystalline brackets and rhodium-coated wires) require greater amount of force to move a tooth when compared with those having low frictional values (ceramic bracket with metal slot and SS wires).[15] Careful and precise selection of archwire and bracket with reduced coefficient of friction is necessary to optimize treatment.[16]

The present study can be summarized by stating that PTFE/Teflon-coated archwire in ceramic bracket with metal slot (wet medium) delivered the least amount of frictional resistance. The reason could be attributed to the smoother surface exhibited by Teflon-coated wires when compared with the other coated wires. Furthermore, the presence of metal slot in ceramic brackets was advantageous in reducing the friction while maintaining the esthetic appearance. It was also observed that frictional values were more in dry medium than wet medium for all the groups. This could be due to the lubricating action of artificial saliva and various authors have supported the theory that saliva aids in reducing friction by forming a layer on the SS arch wire and brackets. The combination of rhodium archwire and monocrystalline bracket exhibited highest frictional resistance in both dry and wet fields because of the high surface roughness of rhodium arch wires as well as sharp and hard edges of monocrystalline brackets.


This study did not take into consideration factors such as saliva, occlusal forces, and acquired pellicle since it was carried out in vitro.

  Conclusion Top

  1. The uncoated wires delivered least frictional resistance than the coated arch wires in both dry and wet fields
  2. PTFE-coated archwires delivered least resistance to friction, whereas rhodium-coated archwires exhibited maximum frictional resistance than the other coated wires in ceramic bracket with and without metal slot and monocrystalline bracket among all the groups and subgroups
  3. Wet field demonstrated less frictional resistance than their corresponding groups in dry field
  4. The ceramic bracket with metal slot delivered significantly less frictional resistance when compared with ceramic bracket without metal slot and monocrystalline bracket, irrespective of the archwires used in all the groups and subgroups.

Hence, it can be concluded that PTFE/Teflon-coated archwire and ceramic bracket with metal slot could be preferred as the archwire and bracket material of choice, respectively, owing to their low frictional characteristics.

Ethical clearance

The study was approved by the institute ethics committee.

Protocol No. IGIDSIEC2018NRP42PGJIODO, dated 14.12.2018.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

[TAG:2]Supplementary Tables[TAG:2]

  References Top

Jayachandar D, Dinesh SP. Factors affecting patient's desire for seeking orthodontic treatment. Int J Ortho Rehab 2016;7:89.  Back to cited text no. 1
Singh DP. Esthetic archwires in orthodontics – A review. J Oral Hyg Health 2016;4:1-4.  Back to cited text no. 2
Kusy RP, Whitley JQ, Prewitt MJ. Comparison of the frictional coefficients for selected archwire-bracket slot combinations in the dry and wet states. Angle Orthod 1991;61:293-302.  Back to cited text no. 3
Ryan TP. Methods of determining sample sizes. In: Sample Size Determination and Power (Wiley Series in Probability and Statistics). John Wiley & Sons, Inc., Hoboken, NJ, USA; 2013. p. 17-55.  Back to cited text no. 4
Karamouzos A, Athanasiou AE, Papadopoulos MA. Clinical characteristics and properties of ceramic brackets: A comprehensive review. Am J Orthod Dentofacial Orthop 1997;112:34-40.  Back to cited text no. 5
Jena AK, Duggal R, Mehrotra AK. Physical properties and clinical characteristics of ceramic brackets: A comprehensive review. Trends Biomater Artif Organs 2007;20:101-15.  Back to cited text no. 6
Johnson G, Walker MP, Kula K. Fracture strength of ceramic bracket tie wings subjected to tension. Angle Orthod 2005;75:95-100.  Back to cited text no. 7
Sukh R, Singh GK, Tandon P, Singh GP, Singh A. A comparative study of frictional resistance during simulated canine retraction on typodont model. J Orthod Sci 2013;2:61-6.  Back to cited text no. 8
Kusy RP. Ongoing innovations in biomechanics and materials for the new millennium. Angle Orthod 2000;70:366-76.  Back to cited text no. 9
Stannard JG, Gau JM, Hanna MA. Comparative friction of orthodontic wires under dry and wet conditions. Am J Orthod 1986;89:485-91.  Back to cited text no. 10
Taylor NG, Ison K. Frictional resistance between orthodontic brackets and archwires in the buccal segments. Angle Orthod 1996;66:215-22.  Back to cited text no. 11
Farronato G, Maijer R, Carìa MP, Esposito L, Alberzoni D, Cacciatore G. The effect of Teflon coating on the resistance to sliding of orthodontic archwires. Eur J Orthod 2012;34:410-7.  Back to cited text no. 12
Abbas AA, Faisal AA. The effect of wire dimension, type and thickness of coating layer on friction of coated stainless-steel arch wires. Int J Med Res Health Sci 2018;7:115-21.  Back to cited text no. 13
Saunders CR, Kusy RP. Surface topography and frictional characteristics of ceramic brackets. Am J Orthod Dentofacial Orthop 1994;106:76-87.  Back to cited text no. 14
Tselepis M, Brockhurst P, West VC. The dynamic frictional resistance between orthodontic brackets and arch wires. Am J Orthod Dentofacial Orthop 1994;106:131-8.  Back to cited text no. 15
Guerrero AP, Guariza Filho O, Tanaka O, Camargo ES, Vieira S. Evaluation of frictional forces between ceramic brackets and archwires of different alloys compared with metal brackets. Braz Oral Res 2010;24:40-5.  Back to cited text no. 16


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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