SCANNING VOL. 37, 399–405 (2015) © Wiley Periodicals, Inc.
Correlation Between Frictional Force and Surface Roughness of Orthodontic Archwires SAMJIN CHOI,1 EUN-YOUNG HWANG,2 HUN-KUK PARK,1 AND YOUNG-GUK PARK2 1 2
Department of Biomedical Engineering, College of Medicine, Kyung Hee University, Seoul, Korea Department of Orthodontics, College of Dentistry, Kyung Hee University, Seoul, Korea
Summary: Lateral force microscopy measures the lateral bending of the cantilever depending on the frictional force acting between the tip and surface. The aim of this study was to investigate and compare the relationship between the surface roughness and frictional resistance of four archwire and bracket combinations consisting of the 0.016-inch NiTi and 0.019 0.025-inch stainless steel archwires interacting clinically with two representative self-ligating brackets, 1 active-type Clippy-C ceramic self-ligating brackets, 1 and passive-type Damon stainless steel self-ligating brackets, using the lateral force microscopy technique. A 0.016-inch NiTi archwire interacting with passive1 type Damon stainless steel self-ligating brackets showed the smoothest surface roughness and the lowest frictional resistance compared to other combinations. 1 The archwires interacting with passive-type Damon stainless steel self-ligating brackets showed significantly lower surface roughness and frictional resistance 1 than those interacting with active-type Clippy-C ceramic self-ligating brackets. The frictional force in the in vivo archwire and bracket system increased with increasing surface roughness of the archwire. This positive correlation suggests that surface roughness can be used as an evaluating marker for estimating the efficiency of orthodontic treatment, rather than the direct measurement of frictional force. SCANNING 37:399–405, 2015. © 2015 Wiley Periodicals, Inc. Contract grant sponsor: Korean Health Technology Research & Development Project by the Ministry of Health & Welfare. Contract grant sponsor: Republic of Korea; Contract grant number: HI14C2241. Conflict of interest: None Address for reprints: Young-Guk Park, D.M.D., Ph.D., Department of Orthodontics, College of Dentistry, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul 130-701, Republic of Korea. E-mail: [email protected] Received 24 February 2015; revised 20 April 2015; Accepted with revision 29 April 2015 DOI: 10.1002/sca.21225 Published online 27 May 2015 in Wiley Online Library (wileyonlinelibrary.com).
Key words: lateral force microscopy, frictional resistance, surface roughness, archwire-bracket system, self-ligating bracket
Introduction Lateral force microscopy (LFM) is an atomic force microscopy (AFM) technique that identifies relative differences in surface friction. It is one of several methods designed as an extension to the basic morphological mapping capabilities of scanning force microscopy. In particular, LFM is useful for classifying surface materials (Choi et al., 2007; Reitsma, 2007; Wang and Zhao, 2007; Prunici and Hess, 2008; Karhu et al., 2009). During scanning in contact mode, the cantilever bends not only vertically along the surface as a result of repulsive Van der Waals interactions, but also undergoes lateral deformation. Since this technique measures the lateral bending of the cantilever depending on the frictional force acting on the tip, this is also known as friction force microscopy. This technique has been used to identify the transitions between different components in polymer blends, composites, and other mixtures, identifying organic, and other contaminants on surfaces, delineating coverage by coatings, and other surface layers, and for chemical force microscopy using functionalized tips (Karhu et al., 2009). In orthodontics, tooth movement can be controlled by the friction between the wire and bracket. This friction results from the mechanical force applied to the tooth. The teeth and their surrounding structures respond to the force by a complex biologic cascade, and tooth movement takes places through the alveolar bone (Choi et al., 2012a). Friction is the force resisting the motion of solid surfaces or motional elements sliding against each other (Geminard and Bertin, 2010). Tooth movement comes about as the applied force goes beyond the friction induced by the interaction of orthodontic appliances. Frictional force between the wire and bracket increases with decreasing actual bone application to the tooth. This negative correlation decreases the efficiency of orthodontic treatments (Choi et al., 2012a).
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The main factor associated with the frictional force that determines the efficiency of orthodontic treatment (Table S1, Supporting Information) is the material of orthodontic appliances. In particular, the surface roughness of orthodontic appliance materials determines the superficial contact interaction and affects corrosion and biocompatibility. The frictional resistance between the wire and bracket has been indirectly measured by the surface roughness of orthodontic appliances using various tools. Profilometry is a fundamental technique for measuring surface roughness by scanning the topography in a line of a preselected area (Wichelhaus et al., 2005; Zinelis et al., 2005). However, one drawback is that it cannot measure the surface defects adjacent to the scanning line. In addition, this method may damage the surface of specimens during scanning (Choi et al., 2012a). Alternative methods for indirectly estimating surface roughness are scanning electron microscopy (SEM) and index scoring methods (Marques et al., 2010; Hosseinzadeh et al., 2013; Chng et al., 2014); however these techniques do not elucidate real-time changes and provide no quantitative information about the sample surfaces. On the other hand, AFM provides information regarding surface roughness and the overall surface of target materials. Our research group has reported that frictional resistance can be indirectly evaluated through the surface roughness calculated from the AFM image of clinically relevant orthodontic appliances (Lee et al., 2010a; Park et al., 2010; Choi et al., 2011; 2012a, 2012b). To the best of our knowledge, there have been no studies measuring the frictional resistance of clinically used orthodontic wires using the LFM technique. The objective of this study was to quantitatively investigate the in vivo frictional resistance on the wire surface according to four wire and bracket combinations with bicuspid-extraction treatment and anterior alignment, and to compare the indirect approach for measuring friction through contact-mode AFM topographical images—surface roughness—and a direct approach through contact-mode LFM frictional images—lateral force (Scheme 1).
collected from patients with upper anterior crowding, and the upper arch was used. The wire sections engaged with the brackets of teeth located on the lingual side about 1–2 mm from the adjacent teeth were included in this study. The 0.016-inch NiTi wires were applied for four weeks in the aligning stage. The 0.019 0.025-inch SS archwires (3M, Monrovia, CA) were collected from patients with first premolar-extraction treatment. Wire sections engaged with the brackets of the second premolars were cut. Orthodontic appliances were reactivated four times at 4-week intervals during enmasse retraction. All archwires were collected from patients seen in the Department of Orthodontics, Kyung Hee University School of Dentistry, Seoul, Korea.
Experimental Group
There were four experimental groups according to the combination of two archwires and two SLB systems 1 (Table I): Clippy-C CE-SLB þ 0.016-inch NiTi arch1 wire, Clippy-C CE-SLB þ 0.019 0.022-inch SS arch1 wires, Damon SS-SLB þ 0.016-inch NiTi archwire, and Damon1 SS-SLB þ 0.019 0.022-inch SS archwire. To expose the surface of the wires corresponding to the second premolar region for AFM-LFM analysis, each archwire was cut at the marked three sites with a precise cutter. Each of the cut wires was rinsed with physiologic saline and dried with an air syringe. The wires were then immobilized on mica with double-sided tape and fixed to face lingual-side up to undergo frictional interaction with the bracket slot (Fig. S2, Supporting Information).
AFM-LFM Measurements
Contact-mode AFM topographical-deflection and LFM frictional images of the four wire groups were
Methods Wire Preparation
Orthodontic 0.016-inch nickel-titanium (NiTi) archwires (n ¼ 15) and 0.019 0.025-inch stainless steel (SS) archwires (n ¼ 15) after orthodontic use were employed. The wires (n ¼ 5 for each type) were 1 interacted with active-type Clippy-C ceramic (CE)1 SLBs (Tomy, Tokyo, Japan) and passive-type Damon SS-SLBs (Ormco, Orange County, CA), as shown in Table I and Fig. S1 (Supporting Information). Asreceived NiTi and SS archwires were employed as the control group (n ¼ 5 for each type). All archwires were
Scheme 1. AFM topographical (Fig. 1A), LFM frictional (Fig. 1B), and AFM deflection (Fig. 1C) signals of the cantilever and the corresponding obtainable information.
Choi et al.: LFM analysis of AWs TABLE I
401
Specifications of the orthodontic appliances used in this study.*
Property Size (inch) Width (mm) Composition Ligature
Clippy-C1 SLB
Damon1 SLB
Circular wire
Rectangular wire
0.0220.028 2.65 Ceramic Active
0.0220.028 1.19 Stainless steel Passive
0.016
0.0190.025
NiTi
Stainless steel
*Bracket indicates the dimension and composition of a slot.
obtained using an NANOS N8 NEOS (Bruker, Herzogenrath, Germany) equipped with a 42.5 42.5 4-mm3 XYZ scanner and two Zeiss optical microscopes Epiplan 200 /500 (Carl Zeiss Inc., Standort G€ottingenVertrieb, Germany). External noise was eliminated by placing the AFM machine on an active vibration isolation table (Table Stable Ltd., Surface Imaging Systems, Herzogenrath, Germany) inside a passive vibration isolation table (Pucotech, Seoul, Korea). The wire surface was scanned in air with a size of 30 30 mm2, a resolution of 256 256 pixels, and a scan speed of 0.4 lines/s. LFM contact-mode frictional imaging was performed at room temperature and 35% relative humidity using a cantilever PPP-LFMR (NANOSENSORSTM, Neuchatel, Switzerland; Table S2, Supporting Information). The planification process was performed on all images. To identify the frictional and morphological changes in the surfaces of each archwire, four parameters (Table S3, Supporting Information) including mean values (Eq. S1), root-mean-square values (Eq. S2), peak-to-peak values (Eq. S3), and ten-point values (Eq. S4) were calculated using Scanning Probe Image Processor SPIPTM ver. 4.8.3 (Image Metrology, Hørsholm, Denmark). These values were represented as the average of three images per wire specimen.
Statistics
The quantitative data were expressed as the mean standard deviation. Statistical analysis was performed using a two-tailed Student’s t-test to compare relative
differences in surface roughness and frictional resistance between two groups. P-values less than 0.05 were considered statistically significant.
Results Figure 1 shows representative 30 30 mm2 contactmode AFM topographical images, LFM fractional images, and AFM deflection images of the surfaces of 1 a 0.016-inch NiTi wire interacting with the Clippy-C CE-SLBs. Each image clearly shows distinctive features according to operation principles. After clinical orthodontic treatment, the contact-mode AFM topographical images (Fig. 1(A)) and deflection images (Fig. 1(C)) clearly showed the nanostructure and edge of the wire 1 surface interacting with the Clippy-C CE-SLB, while the contact-mode LFM frictional image (Fig. 1(B)) showed the nanostructure as well as the presence of frictional resistance in the wire surface interacting with 1 the Clippy-C CE-SLBs. Figures 2 and 3 show representative contact-mode AFM topographical and LFM frictional images and their line profiles for a 0.016-inch NiTi wire surface interacting 1 1 with the Damon SS-SLBs and the Clippy-C CE-SLBs, respectively. The nanostructural findings of the contactmode AFM topographical images showed a different pattern compared to the LFM frictional images. The wires with sliding movement showed severe scratches caused by the fictional force between the bracket slots and wires. Contact-mode AFM topographical images showed only the morphological changes in the wire surface, while
Fig. 1. Comparison of the contact-mode AFM topographical image, LFM frictional image, and AFM deflection image for the 0.016 inch NiTi wire and Clippy-C1 CE-SLB combination. au; arbitrary unit. Sz, Fz, and Dz indicate the peak-to-peak values for the topographical, frictional, and deflection images, respectively. Scale bar¼5 mm.
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SCANNING VOL. 37, 6 (2015)
Fig. 2. Representative contact-mode AFM topographical image (A), LFM frictional image (B), and corresponding line profiles for the 0.016 inch NiTi wire and Damon1 SS-SLB combination. Scale bar¼5 mm.
contact-mode LFM frictional images showed the morphological changes as well as the presence of frictional resistance of the wire surfaces. Therefore, we could estimate position-to-position frictional information from the contact-mode LFM frictional images. From Table II, the mean surface roughness of a 0.016-inch wire interacting with the Damon1 SS-SLBs was smaller than 1 that with the Clippy-C CE-SLBs. The mean frictional
resistance of a 0.016-inch wire interacting with the Damon1 SS-SLBs was smaller than that of the Clippy1 C CE-SLBs. This change in the 0.016-inch NiTi wire showed a similar pattern to that of the 0.019 0.025-inch archwire; both mean surface roughness and frictional resistance of the 0.019 0.025-inch archwire interacting 1 with the Damon SS-SLBs were smaller than those of the 1 Clippy-C CE-SLBs. The change in the LFM-acquired
Fig. 3. Representative contact-mode AFM topographical image (A), LFM frictional image (B), and corresponding line profiles for the 0.016 inch NiTi wire and the Clippy-C1 CE-SLB combination. Scale bar¼5 mm.
Choi et al.: LFM analysis of AWs
403
TABLE II Quantitative analysis of frictional resistance and surface roughness according to the 0.016-inch NiTi wire and 0.0190.025-inch SS wire surfaces interactions with the Damon1 SS-SLBs and the Clippy-C1 CE-SLBs. Parameter
AFM-Sa (nm) AFM-Sq (nm) AFM-Sz (nm) AFM-S10z (nm) LFM-Fa (au) LFM-Fq (au) LFM-Fz (au) LFM-F10z (au)
0.016 inch NiTi archwires
0.0190.025 inches SS archwires
Damon1 SS-SLBs (n¼5)
Clippy-C1 CE-SLBs (n¼5)
Damon1 SS-SLBs P-value (n¼5)
56.4 10.6 70.8 14.4 532.1 127.6 510.0 133.2
73.6 21.4 93.0 30.0 755.2 157.6 666.8 166.9
N.S. N.S.
Correlation Between Frictional Force and Surface Roughness of Orthodontic Archwires SAMJIN CHOI,1 EUN-YOUNG HWANG,2 HUN-KUK PARK,1 AND YOUNG-GUK PARK2 1 2
Department of Biomedical Engineering, College of Medicine, Kyung Hee University, Seoul, Korea Department of Orthodontics, College of Dentistry, Kyung Hee University, Seoul, Korea
Summary: Lateral force microscopy measures the lateral bending of the cantilever depending on the frictional force acting between the tip and surface. The aim of this study was to investigate and compare the relationship between the surface roughness and frictional resistance of four archwire and bracket combinations consisting of the 0.016-inch NiTi and 0.019 0.025-inch stainless steel archwires interacting clinically with two representative self-ligating brackets, 1 active-type Clippy-C ceramic self-ligating brackets, 1 and passive-type Damon stainless steel self-ligating brackets, using the lateral force microscopy technique. A 0.016-inch NiTi archwire interacting with passive1 type Damon stainless steel self-ligating brackets showed the smoothest surface roughness and the lowest frictional resistance compared to other combinations. 1 The archwires interacting with passive-type Damon stainless steel self-ligating brackets showed significantly lower surface roughness and frictional resistance 1 than those interacting with active-type Clippy-C ceramic self-ligating brackets. The frictional force in the in vivo archwire and bracket system increased with increasing surface roughness of the archwire. This positive correlation suggests that surface roughness can be used as an evaluating marker for estimating the efficiency of orthodontic treatment, rather than the direct measurement of frictional force. SCANNING 37:399–405, 2015. © 2015 Wiley Periodicals, Inc. Contract grant sponsor: Korean Health Technology Research & Development Project by the Ministry of Health & Welfare. Contract grant sponsor: Republic of Korea; Contract grant number: HI14C2241. Conflict of interest: None Address for reprints: Young-Guk Park, D.M.D., Ph.D., Department of Orthodontics, College of Dentistry, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul 130-701, Republic of Korea. E-mail: [email protected] Received 24 February 2015; revised 20 April 2015; Accepted with revision 29 April 2015 DOI: 10.1002/sca.21225 Published online 27 May 2015 in Wiley Online Library (wileyonlinelibrary.com).
Key words: lateral force microscopy, frictional resistance, surface roughness, archwire-bracket system, self-ligating bracket
Introduction Lateral force microscopy (LFM) is an atomic force microscopy (AFM) technique that identifies relative differences in surface friction. It is one of several methods designed as an extension to the basic morphological mapping capabilities of scanning force microscopy. In particular, LFM is useful for classifying surface materials (Choi et al., 2007; Reitsma, 2007; Wang and Zhao, 2007; Prunici and Hess, 2008; Karhu et al., 2009). During scanning in contact mode, the cantilever bends not only vertically along the surface as a result of repulsive Van der Waals interactions, but also undergoes lateral deformation. Since this technique measures the lateral bending of the cantilever depending on the frictional force acting on the tip, this is also known as friction force microscopy. This technique has been used to identify the transitions between different components in polymer blends, composites, and other mixtures, identifying organic, and other contaminants on surfaces, delineating coverage by coatings, and other surface layers, and for chemical force microscopy using functionalized tips (Karhu et al., 2009). In orthodontics, tooth movement can be controlled by the friction between the wire and bracket. This friction results from the mechanical force applied to the tooth. The teeth and their surrounding structures respond to the force by a complex biologic cascade, and tooth movement takes places through the alveolar bone (Choi et al., 2012a). Friction is the force resisting the motion of solid surfaces or motional elements sliding against each other (Geminard and Bertin, 2010). Tooth movement comes about as the applied force goes beyond the friction induced by the interaction of orthodontic appliances. Frictional force between the wire and bracket increases with decreasing actual bone application to the tooth. This negative correlation decreases the efficiency of orthodontic treatments (Choi et al., 2012a).
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SCANNING VOL. 37, 6 (2015)
The main factor associated with the frictional force that determines the efficiency of orthodontic treatment (Table S1, Supporting Information) is the material of orthodontic appliances. In particular, the surface roughness of orthodontic appliance materials determines the superficial contact interaction and affects corrosion and biocompatibility. The frictional resistance between the wire and bracket has been indirectly measured by the surface roughness of orthodontic appliances using various tools. Profilometry is a fundamental technique for measuring surface roughness by scanning the topography in a line of a preselected area (Wichelhaus et al., 2005; Zinelis et al., 2005). However, one drawback is that it cannot measure the surface defects adjacent to the scanning line. In addition, this method may damage the surface of specimens during scanning (Choi et al., 2012a). Alternative methods for indirectly estimating surface roughness are scanning electron microscopy (SEM) and index scoring methods (Marques et al., 2010; Hosseinzadeh et al., 2013; Chng et al., 2014); however these techniques do not elucidate real-time changes and provide no quantitative information about the sample surfaces. On the other hand, AFM provides information regarding surface roughness and the overall surface of target materials. Our research group has reported that frictional resistance can be indirectly evaluated through the surface roughness calculated from the AFM image of clinically relevant orthodontic appliances (Lee et al., 2010a; Park et al., 2010; Choi et al., 2011; 2012a, 2012b). To the best of our knowledge, there have been no studies measuring the frictional resistance of clinically used orthodontic wires using the LFM technique. The objective of this study was to quantitatively investigate the in vivo frictional resistance on the wire surface according to four wire and bracket combinations with bicuspid-extraction treatment and anterior alignment, and to compare the indirect approach for measuring friction through contact-mode AFM topographical images—surface roughness—and a direct approach through contact-mode LFM frictional images—lateral force (Scheme 1).
collected from patients with upper anterior crowding, and the upper arch was used. The wire sections engaged with the brackets of teeth located on the lingual side about 1–2 mm from the adjacent teeth were included in this study. The 0.016-inch NiTi wires were applied for four weeks in the aligning stage. The 0.019 0.025-inch SS archwires (3M, Monrovia, CA) were collected from patients with first premolar-extraction treatment. Wire sections engaged with the brackets of the second premolars were cut. Orthodontic appliances were reactivated four times at 4-week intervals during enmasse retraction. All archwires were collected from patients seen in the Department of Orthodontics, Kyung Hee University School of Dentistry, Seoul, Korea.
Experimental Group
There were four experimental groups according to the combination of two archwires and two SLB systems 1 (Table I): Clippy-C CE-SLB þ 0.016-inch NiTi arch1 wire, Clippy-C CE-SLB þ 0.019 0.022-inch SS arch1 wires, Damon SS-SLB þ 0.016-inch NiTi archwire, and Damon1 SS-SLB þ 0.019 0.022-inch SS archwire. To expose the surface of the wires corresponding to the second premolar region for AFM-LFM analysis, each archwire was cut at the marked three sites with a precise cutter. Each of the cut wires was rinsed with physiologic saline and dried with an air syringe. The wires were then immobilized on mica with double-sided tape and fixed to face lingual-side up to undergo frictional interaction with the bracket slot (Fig. S2, Supporting Information).
AFM-LFM Measurements
Contact-mode AFM topographical-deflection and LFM frictional images of the four wire groups were
Methods Wire Preparation
Orthodontic 0.016-inch nickel-titanium (NiTi) archwires (n ¼ 15) and 0.019 0.025-inch stainless steel (SS) archwires (n ¼ 15) after orthodontic use were employed. The wires (n ¼ 5 for each type) were 1 interacted with active-type Clippy-C ceramic (CE)1 SLBs (Tomy, Tokyo, Japan) and passive-type Damon SS-SLBs (Ormco, Orange County, CA), as shown in Table I and Fig. S1 (Supporting Information). Asreceived NiTi and SS archwires were employed as the control group (n ¼ 5 for each type). All archwires were
Scheme 1. AFM topographical (Fig. 1A), LFM frictional (Fig. 1B), and AFM deflection (Fig. 1C) signals of the cantilever and the corresponding obtainable information.
Choi et al.: LFM analysis of AWs TABLE I
401
Specifications of the orthodontic appliances used in this study.*
Property Size (inch) Width (mm) Composition Ligature
Clippy-C1 SLB
Damon1 SLB
Circular wire
Rectangular wire
0.0220.028 2.65 Ceramic Active
0.0220.028 1.19 Stainless steel Passive
0.016
0.0190.025
NiTi
Stainless steel
*Bracket indicates the dimension and composition of a slot.
obtained using an NANOS N8 NEOS (Bruker, Herzogenrath, Germany) equipped with a 42.5 42.5 4-mm3 XYZ scanner and two Zeiss optical microscopes Epiplan 200 /500 (Carl Zeiss Inc., Standort G€ottingenVertrieb, Germany). External noise was eliminated by placing the AFM machine on an active vibration isolation table (Table Stable Ltd., Surface Imaging Systems, Herzogenrath, Germany) inside a passive vibration isolation table (Pucotech, Seoul, Korea). The wire surface was scanned in air with a size of 30 30 mm2, a resolution of 256 256 pixels, and a scan speed of 0.4 lines/s. LFM contact-mode frictional imaging was performed at room temperature and 35% relative humidity using a cantilever PPP-LFMR (NANOSENSORSTM, Neuchatel, Switzerland; Table S2, Supporting Information). The planification process was performed on all images. To identify the frictional and morphological changes in the surfaces of each archwire, four parameters (Table S3, Supporting Information) including mean values (Eq. S1), root-mean-square values (Eq. S2), peak-to-peak values (Eq. S3), and ten-point values (Eq. S4) were calculated using Scanning Probe Image Processor SPIPTM ver. 4.8.3 (Image Metrology, Hørsholm, Denmark). These values were represented as the average of three images per wire specimen.
Statistics
The quantitative data were expressed as the mean standard deviation. Statistical analysis was performed using a two-tailed Student’s t-test to compare relative
differences in surface roughness and frictional resistance between two groups. P-values less than 0.05 were considered statistically significant.
Results Figure 1 shows representative 30 30 mm2 contactmode AFM topographical images, LFM fractional images, and AFM deflection images of the surfaces of 1 a 0.016-inch NiTi wire interacting with the Clippy-C CE-SLBs. Each image clearly shows distinctive features according to operation principles. After clinical orthodontic treatment, the contact-mode AFM topographical images (Fig. 1(A)) and deflection images (Fig. 1(C)) clearly showed the nanostructure and edge of the wire 1 surface interacting with the Clippy-C CE-SLB, while the contact-mode LFM frictional image (Fig. 1(B)) showed the nanostructure as well as the presence of frictional resistance in the wire surface interacting with 1 the Clippy-C CE-SLBs. Figures 2 and 3 show representative contact-mode AFM topographical and LFM frictional images and their line profiles for a 0.016-inch NiTi wire surface interacting 1 1 with the Damon SS-SLBs and the Clippy-C CE-SLBs, respectively. The nanostructural findings of the contactmode AFM topographical images showed a different pattern compared to the LFM frictional images. The wires with sliding movement showed severe scratches caused by the fictional force between the bracket slots and wires. Contact-mode AFM topographical images showed only the morphological changes in the wire surface, while
Fig. 1. Comparison of the contact-mode AFM topographical image, LFM frictional image, and AFM deflection image for the 0.016 inch NiTi wire and Clippy-C1 CE-SLB combination. au; arbitrary unit. Sz, Fz, and Dz indicate the peak-to-peak values for the topographical, frictional, and deflection images, respectively. Scale bar¼5 mm.
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SCANNING VOL. 37, 6 (2015)
Fig. 2. Representative contact-mode AFM topographical image (A), LFM frictional image (B), and corresponding line profiles for the 0.016 inch NiTi wire and Damon1 SS-SLB combination. Scale bar¼5 mm.
contact-mode LFM frictional images showed the morphological changes as well as the presence of frictional resistance of the wire surfaces. Therefore, we could estimate position-to-position frictional information from the contact-mode LFM frictional images. From Table II, the mean surface roughness of a 0.016-inch wire interacting with the Damon1 SS-SLBs was smaller than 1 that with the Clippy-C CE-SLBs. The mean frictional
resistance of a 0.016-inch wire interacting with the Damon1 SS-SLBs was smaller than that of the Clippy1 C CE-SLBs. This change in the 0.016-inch NiTi wire showed a similar pattern to that of the 0.019 0.025-inch archwire; both mean surface roughness and frictional resistance of the 0.019 0.025-inch archwire interacting 1 with the Damon SS-SLBs were smaller than those of the 1 Clippy-C CE-SLBs. The change in the LFM-acquired
Fig. 3. Representative contact-mode AFM topographical image (A), LFM frictional image (B), and corresponding line profiles for the 0.016 inch NiTi wire and the Clippy-C1 CE-SLB combination. Scale bar¼5 mm.
Choi et al.: LFM analysis of AWs
403
TABLE II Quantitative analysis of frictional resistance and surface roughness according to the 0.016-inch NiTi wire and 0.0190.025-inch SS wire surfaces interactions with the Damon1 SS-SLBs and the Clippy-C1 CE-SLBs. Parameter
AFM-Sa (nm) AFM-Sq (nm) AFM-Sz (nm) AFM-S10z (nm) LFM-Fa (au) LFM-Fq (au) LFM-Fz (au) LFM-F10z (au)
0.016 inch NiTi archwires
0.0190.025 inches SS archwires
Damon1 SS-SLBs (n¼5)
Clippy-C1 CE-SLBs (n¼5)
Damon1 SS-SLBs P-value (n¼5)
56.4 10.6 70.8 14.4 532.1 127.6 510.0 133.2
73.6 21.4 93.0 30.0 755.2 157.6 666.8 166.9
N.S. N.S.
