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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 13  |  Issue : 4  |  Page : 199-207

Microscopic study of surface roughness of four orthodontic arch wires


1 Department of Orthodontic, Faculty of Dentistry, Tanta University, Tanta City, Egypt
2 Department of Dental Biomaterial, Faculty of Dentistry, Tanta University, Tanta City, Egypt

Date of Submission26-Aug-2016
Date of Acceptance27-Oct-2016
Date of Web Publication14-Dec-2016

Correspondence Address:
Atia A Yousif
Department of Orthodontic, Faculty of Dentistry, Tanta University, Tanta 31511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-8574.195714

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  Abstract 

Aim/purpose
Comparative evaluation of surface roughness of stainless steel (SS), nitinol (NiTi), titanium molybdenum alloy (TMA) and copper nitinol (Cu NiTi) orthodontic arch wires before and after clinical use to find the smoothest wire surface best used in orthodontic sliding mechanics.
Materials and methods
Surface roughness of 40 arch wires divided into four groups (group 1: 10 SS arch wires, group 2: 10 NiTi arch wires, group 3: 10 TMA arch wires and group 4: 10 Cu NiTi arch wires) were measured at five different points for each wire before and after its clinical use in oral cavity for 4 weeks using atomic force microscope and optical digital microscope. All obtained data was statistically tested.
Results
SS arch wires had the smoothest surface (average roughness: 17.38 μm for new wires and 104.1 μm for used wires) and Cu NiTi arch wires had the roughest surface (average roughness: 221.12 μm for new wires and 499 μm for used wires) with high significant differences between both groups either new or used arch wires (P < 0.001). High significant difference was found between new and used wires for all groups. NiTi wires had greater surface roughness (average roughness: 211.8 μm for new wires and 313.8 for used wires) than TMA wires (average roughness: 138.5 μm for new wires and 221.2 μm for used wires).
Conclusion
SS orthodontic arch wires exhibited the least amount of surface roughness and advocated to be used in sliding mechanics to minimize the friction during orthodontic tooth movements.

Keywords: atomic force microscope, digital microscope, surface roughness


How to cite this article:
Yousif AA, Abd El-Karim UM. Microscopic study of surface roughness of four orthodontic arch wires. Tanta Dent J 2016;13:199-207

How to cite this URL:
Yousif AA, Abd El-Karim UM. Microscopic study of surface roughness of four orthodontic arch wires. Tanta Dent J [serial online] 2016 [cited 2018 Jun 21];13:199-207. Available from: http://www.tmj.eg.net/text.asp?2016/13/4/199/195714


  Introduction Top


When sliding biomechanics are used with fixed appliances, the main force that contrasts tooth movement is the frictional force developed by the interaction of the bracket slot and the orthodontic wire. As the efficiency of fixed appliance therapy depends on the fraction of force delivered with respect to the force applied, high frictional forces resulting from the interaction between the bracket and the guiding arch wire affect treatment outcomes and duration. So during orthodontic treatment with fixed appliances, frictional forces should be kept to a minimum so that lower levels of force can be applied to obtain an optimal biological response for effective tooth movement. The surface properties, such as roughness, hardness, and topography of orthodontic arch wires may affect the sliding mechanics by influencing the coefficient of friction. Surface properties also determine the aesthetics of dental products as well as corrosion potential and biocompatibility.

The surface roughness of orthodontic arch wires may be measured using several methods, including laser spectroscopy, contact-surface profilometry, and atomic force microscopy (AFM) [1,2]. Bourauel et al. [3] compared the surface roughness of different wires by using these three techniques. They stated that the results of these three methods generally correspond well.

AFM (scan rate: 1 Hz, nonconductive silicon nitride probe using Proscan 1.8 software and IP 2 software) has many advantages, such as the production of topographical three-dimensional (3D) images in real space with a very high resolution. The samples do not require any special treatment, such as metallization, and the AFM can provide quantitative values for the investigated parameters. The most important AFM drawback is the small scan size, which, in association with the slow velocity of scanning, often impedes a complete analysis of the sample. Thus AFM is considered a promising technique for the evaluation of surface qualities of dental materials [4-6].

The AFM provides a 3D profile on a nanoscale, by measuring forces between a sharp probe (radius <10 nm) and surface at very short distance (0.2-10 nm probe-sample separation). The probe is supported on a flexible cantilever and the AFM tip gently touches the surface and records the small force between the probe and the surface. The use of digital microscope based on the increasing demand for nondestructive and noninvasive techniques has enhanced new methods of analysis, based on optical methods [7].

So this study was designed to compare the surface roughness of 0.016"×0.022" [stainless steel (SS), nitinol (NiTi), titanium molybdenum alloy (TMA), copper nitinol (Cu NiTi)] arch wires using AFM and optical digital microscope (Scope Capture Digital Microscope, Guangdong, China) before and after their clinical use in oral cavity for 4 weeks.


  Materials and methods Top


In this study 40 orthodontic arch wires 0.016"×0.022" [SS (G and H Orthodontics, Franklin, Indiana, USA), NiTi (American Ortho United Kingdom, Bucks, UK), TMA (Ormco, Orange, California, USA) and Cu NiTi (Ormco, Orange)] 10 arch wires for each group were tested for surface roughness at five different points for each wire before and after clinical use in oral cavity for 4 weeks using AFM (Thermo-Microscope) [Figure 1] and optical digital microscope [Figure 2] [8]. All patients in this study were informed and written consents were assigned from them regarding using the old wires that were discarded and replaced by another one. This research has been conducted in full accordance with the World Medical Association Declaration of Helsinki
Figure 1: Atomic force microscope (AFM)

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Figure 2: Scope Capture Digital Microscope (Guangdong, China)

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Standardization for atomic force microscope

The new wires were hold by hand untouched and cleaned by distilled water then dried by air jet oil free. For used wire before removal of the wire from the patient mouth the areas of the wire opposite to the anterior brackets (3M Unitek, Monrovia, California, USA) were marked with permanent marker and the wire was removed untouched cleaned with distilled water and dried with oil free air jet and scanned for surface roughness at the marked area.

Standardization for optical digital microscope

  • Similar to AFM
  • Fixation of the distance between wire and microscopic lens
  • Fixation of the amount of magnification for all specimens
  • The measurement was repeated for each wire at five different points opposite the wire-bracket contact and the mean of these five measurements were taken to increase the accuracy and reliability of measurement.
To avoid the influence of the brackets on the results a similar brackets were used for all patient from one supplier 3M Unitek. The selected type of the brackets had zero degree tips and zero degree torque (standard edge wise brackets) to avoid the effect of different degrees of tip and torque in preadjusted brackets. Also all brackets used with 22 slots.

Atomic force microscope

AFM (model: Autoprobe cp-research head; Thermo-Microscope) was used the scan area: 50 × 50 μm 2 and number of data points: 256 × 256 at scan rate: 1 Hz. The AFM was operated in contact mode using nonconductive silicon nitride probe using Proscan 1.8 software for controlling the scan parameters and IP 2.1 software for image analysis [Figure 1].

Atomic force microscope measures

  • Roughness average (Ra): The arithmetic average of the absolute values of the measured height deviations from the mean surface taken within the evaluation area
  • Root mean square (rms) roughness (Rq): The root mean square average of the measured height deviations from the mean surface taken within the evaluation area
  • Maximum area peak height (Rp): The maximum height in the evaluation area with respect to the mean surface as shown in [Figure 3]
  • Maximum area valley depth (Rv): The minimum height in the evaluation area with respect to the mean surface as shown in [Figure 4]
  • Area peak-to-valley height (Rp-v): The vertical distance between the maximum height and the maximum depth in the evaluation area, and it is given by the following equation:
Rp-v = Rp + RV
Figure 3: Maximum area peak height (Rp)

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Figure 4: Maximum area valley depth (Rv)

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Optical digital microscope

Specimens were photographed using USB Digital microscope with a built-in camera connected with an IBM compatible personal computer using a fixed magnification of ×200.The images were recorded with a resolution of 1280 × 1024 pixels per image. Digital microscope images were cropped to 350 × 400 pixels using Microsoft office picture manager to specify/standardize area of roughness measurement. The cropped images were analyzed using WSxM software [9]. Within the WSxM software, all limits, sizes, frames and measured parameters are expressed in pixels. Therefore, system calibration was done to convert the pixels into absolute real world units. Calibration was made by comparing an object of known size (a ruler in this study) with a scale generated by the software [Figure 2].

Subsequently, a 3D image of the surface profile of the specimens was created. Three 3D images were collected for each specimen, both in the central area and in the sides at area of 10 × 10 μm 2 . WSxM software was used to calculate average of surface roughness (Ra) of the average heights of every specimen, expressed in μm, which can be assumed as reliable indices of surface roughness [4].

Statistical analysis

All the statistical tests were carried out with the SPSS 17 (SPSS Inc., Chicago, Illinois, USA) software using analysis of variance and Tukey's test (P ≤ 0.05 significance level).


  Results Top


Atomic force microscope results

For all wires a highly significant difference was found between new and used wires [Figure 5] with lowest surface roughness for new SS wire (17.38 average roughness) and highest surface roughness for used Cu NiTi wire (499 average roughness) [Table 1] and [Table 2]).
Figure 5: Two-dimensional, three-dimensional and histogram obtained from atomic force microscope of different new and used wires. Cu NiTi, copper nitinol; NiTi, nitinol; St St, stainless steel; TMA, titanium molybdenum alloy

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Table 1 Comparison of new and used wires regarding different roughness parameters obtained from atomic force microscope


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Table 2 Comparison of stainless steel, nitinol, titanium molybdenum alloy and copper nitinol wires regarding different roughness parameters obtained from atomic force microscope


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Optical digital microscope results

For all wires used in this study surface roughness was increased after clinical use with significant difference between new wire and used wire [Figure 6] [Figure 7] [Figure 8]. The new SS arch wire showed the least amount of surface roughness (0.0743) and the used Cu NiTi arch wire showed the highest surface roughness (1.124). SS arch wires showed the smoothest surface followed by TMA wire then NiTi wire and lastly Cu NiTi wire recorded the highest value for surface roughness [Table 3].
Figure 6: Comparison of new and used wires regarding different roughness parameters obtained from atomic force microscope. Cu NiTi, copper nitinol; NiTi, nitinol; St St, stainless steel; TMA, titanium molybdenum alloy

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Figure 7: Digital microscope pictures and 3d surface pictures of different arch wires. Cu NiTi, copper nitinol; NiTi, nitinol; St St, stainless steel; TMA, titanium molybdenum alloy

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Figure 8: Surface roughness of different arch wires before and after its clinical use. Cu NiTi, copper nitinol; NiTi, nitinol; St St, stainless steel; TMA, titanium molybdenum alloy

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Table 3 Showing surface roughness of different arch wires before and after its clinical use


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When different wires were compared a highly significant difference (P ≤ 0.001) was found between SS arch wire and (NiTi, TMA and Cu NiTi) also a highly significant difference was found between TMA wire and Cu NiTi wire for both new and used wires [Table 4].
Table 4 The level of significance between different arch wires


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When the result of AFM compared with that of optical digital microscope a nonsignificant differences was obtained between both methods which ensures that both methods are effective in determination of surface roughness of orthodontic arch wires.


  Discussion Top


From the clinical point of view the less surface roughness the easier and faster the sliding of the tooth along the arch wire with little force as the force consumed in friction will be kept at minimal level. A good wire must maintain this surface smoothness over the whole period of its use as the chemical composition of the oral cavity may deteriorate the surface characters of the wire rendering it very rough over the period of its use this consuming apart of the force planned to move the tooth to overcome frictional force which is considered of major importance from clinical orthodontic view.

The AFM is considered the most appropriate tool for measuring surface topography because it can provide 3D information on surface morphology [10].

Also optical digital microscope is considered a good method for measuring surface roughness due to the increasing demand for nondestructive and noninvasive techniques has enhanced new methods of analysis, based on optical methods [7].

The results showed that the least rough wire was the SS wire. It has been demonstrated that SS shows the lowest frictional coefficient and the lowest sliding resistance, when used in passive configuration, because of its combination of low roughness, high hardness, and high strength this came in accordance with D'Anto and colleagues [11,12].

A similar results to the results of the present study was obtained by several previous studies [13-16] which reported that frictional losses in orthodontic force was lowest when SS wires are employed and increase in the following order: cobalt-chrome alloys, nickel-titanium alloys, and b-titanium.

In the present study TMA wire showed less roughness than NiTi wire these findings came in contrast with several studied who reported that TMA wire were the roughest [17,18]. These data are consistent with those from the study of Doshi and Bhad-Patil [19] which showed higher values of surface roughness for TMA, but they are in contrast with the results of Kusy et al. [20] in which NiTi wires were considered the roughest.

The significantly high AFM roughness for NiTi wires may be attributed in part to the crystallographic structure of the products. Nickel-titanium alloys exhibit a phase transformation from the Martensite to the austenite structure at a given transformation temperature [21,22]. The transformation of the alloy composition of the wires starts between room temperature and the application temperature of 37°C [23]. Concomitant with dramatical changes the of wire-surface structure.

An important factor that influences the surface topography of orthodontic wires is, therefore, the production technique. Also frictional force between wires and brackets is considered a harmful factor that influences the normal movement of the teeth during sliding mechanics [24]. Many studies [25-28] confirm that a correlation exists between surface roughness and friction, but tooth orthodontic movement is a very complex process, correlated with a number of critical factors. In fact, Prososki et al. [29] and Ghafari [30] found that low wire-surface roughness is not a sufficient condition for low frictional coefficients.

In the present study Cu NiTi wire showed the greatest surface roughness these findings came in accordance with Gravina et al. [31] and Fischer-Brandies et al. [32] who proved that Cu NiTi 35°C wires by Ormco presented not only very visible drawing marks and slots seen under any degree of magnification, but also microcavities formed due to pullout of particles of NiTi, which could generate a higher coefficient of attrition.

Comparing the results from surface roughness measurements with studies on frictional forces between different orthodontic arch wires and brackets [15,33] that showed the interaction between the different mechanical parameters is rather complex and not yet solved. For example, b-titanium wires generated the highest frictional losses in most investigations. This is in contrast with the results of this study and earlier studies on surface roughness as the b-titanium wires can be arranged in the group of wires with a medium roughness [20]. Consequently, frictional losses cannot directly be deduced from the roughness of a certain orthodontic arch wire.


  Conclusion Top


Both techniques (AFM and optical digital microscope) showed similar and reliable findings. SS orthodontic arch wires exhibited the least amount of surface roughness and advocated to be used in sliding mechanics to minimize the friction during orthodontic tooth movements.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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