SCANNING VOL. 37, 414–421 (2015) © Wiley Periodicals, Inc.
Surface Ultrastructure and Mechanical Properties of Three Different White-Coated NiTi Archwires SEONG-HEE RYU,1 BYUNG-SUH LIM,1 EUN JOO KWAK,1 GI-JA LEE,2 SAMJIN CHOI,2 AND KI-HO PARK1 1 2
Department of Orthodontics, College of Dentistry, Kyung Hee University, Seoul, Korea Department of Biomedical Engineering, College of Medicine, Kyung Hee , University, Seoul, Korea
Summary: The recent trend in orthodontic treatment is to apply esthetic materials to orthodontic appliances with adequate clinical performance. The aim of this study was to investigate the ultrastructure (surface roughness) and mechanical properties (load-deflection curve) of three asreceived, white-coated superelastic nickel-titanium (NiTi) archwires using atomic force microscopy (AFM) and modified three-point bending test assessments, respectively. Three representative esthetic NiTi archwires were used, silver-platinum- and polymer-coated NiTi Natural Dany (Dany group), epoxy resin-coated Orthoforce UltraestheticTM (Ultra group), and Teflon1-coated Perfect (Perfect group). Uncoated metallic areas of each wire were used as controls. The diameter of the Perfect archwire was significantly larger than that of other archwires. The Dany and Ultra groups showed more deflection than the Perfect group. The hysteresis area of the Dany and Ultra groups showed approximately twoand fourfold increases compared to the control and the Perfect group. The Dany group (2037.5 527.3 nm) had the highest peak-to-peak surface roughness in the coated areas, followed by the Ultra group (811.1 407.5 nm) and the Perfect group (362.7 195.8 nm). However, reverse nanostructural changes in the surface roughness were observed in the uncoated metallic areas. The results suggested that the load-deflection properties and the
Contract grant sponsor: Ministry of Health & Welfare, Republic of Korea; Contract grant number: HI14C2241. Conflict of interest: The authors have no competing interests to declare. Address for reprints: Samjin Choi, Department of Biomedical Engineering, College of Medicine, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul 130-701, Republic of Korea E-mail: [email protected] Address for reprints: Ki-Ho Park, 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 8 April 2015; Accepted with revision 21 May 2015 DOI: 10.1002/sca.21230 Published online 30 June 2015 in Wiley Online Library (wileyonlinelibrary.com).
surface roughness of superelastic NiTi archwires were affected directly by the coating materials. Although the efficiency of orthodontic treatment was affected by various factors, when only considering the frictional force and mechanostructural properties, the epoxy resincoated Orthoforce UltraestheticTM archwires were the most effective for orthodontic treatment. SCANNING 37:414–421, 2015. © 2015 Wiley Periodicals, Inc. Key words: white coating, nickel-titanium archwires, load-deflection property, surface roughness
Introduction Recent trends in orthodontic treatment have emphasized materials with acceptable esthetics for patients and adequate clinical performance for clinicians (Elayyan et al., 2010), particularly for two representative fixed orthodontic materials, brackets and archwires. For brackets, composite and ceramic materials have been introduced (Russell, 2005) and metal-insert ceramic brackets were developed to produce less frictional force compared to conventional uncoated archwires (Dickson and Jones, ’96; Cacciafesta et al., 2003). In the archwires, three types of esthetic materials were introduced (Alavi and Hosseini, 2012); the esthetically transparent nonmetallic orthodontic wire Optiflex1, fiber-reinforced polymer archwire, and Teflon1 and epoxy resin coated archwires. Although Optiflex1 (Ormco Co., Glendora, CA) is coated with a silica core, silicone resin in the middle layer, and stain-resistant nylon in the outer layer, it did not show desirable mechanical properties (Talass, ’92; Lim et al., ’94). A fiber-reinforced polymer archwire developed by another research group (Imai et al., ’99) had an excellent appearance; however, it has not been clinically popular due to its brittle character (Lim et al., ’94; Kusy, 2002). Metallic archwires coated with polymer materials, such as Teflon1 and epoxy resin, have also been developed (Husmann et al., 2002; Elayyan et al., 2008). Tooth-colored nickel-titanium (NiTi) wire Woowa (Dany Harvest Co., Seoul, Korea) was recently
Ryu et al.: Mechanostructure of white-coated NiTi AWs
introduced in clinical orthodontics. This wire had a double-layered coating structure, an inner layer consisting of a silver and platinum coating, and an outer layer consisting of a special polymer coating (Iijima et al., 2012). In general, the frictional force between the archwire and bracket reduces the efficiency of orthodontic treatment (Choi et al., 2012a, 2012b). To develop a new material, the mechanical properties and surface characteristics of the orthodontic appliance as well as primary factors determining the friction should be considered for enhancing the efficiency of orthodontic treatment. The mechanical properties of orthodontic wires can be evaluated through load-deflection curve measurement via a three-point bending test (Elayyan et al., 2008). This is considered the most important parameter in determining the biological nature of tooth movement (Kapila and Sachdeva, ’89; Krishnan and Kumar, 2004). The advantage of this assessment is it is a clinic-friendly simulation for differentiating between the superelastic wires that lead to high reproducibility (Wilkinson et al., 2012). Alternatively, the surface roughness of orthodontic wires is an essential factor in determining the effectiveness of archwire-guided tooth movement (Bourauel et al., ’98; Choi et al., 2012a, 2012b). The surface quality of wires affects the area of surface contact and influences the corrosion behavior and biocompatibility of the archwires (Elayyan et al., 2008). Additionally, the surface topography can critically modify the esthetics, corrosion, and efficiency of the orthodontic components (Kusy et al., ’88). Variations in the surface roughness affect plaque accumulation (Wichelhaus et al., 2005). In particular, the surface roughness might modify the friction coefficient (Downing et al., ’94; Tselepis et al., ’94; Bazakidou et al., ’97). To the best of the authors’ knowledge, there have been no previous reports evaluating the mechanical properties and ultrastructure of various polymer-coated metallic archwires using a three-point bending test and atomic force microscopy (AFM) measurements except fiberreinforced polymer composite (FRPC) archwire-based
415
study. Therefore, the aim of this study was to investigate the effects of these various white coating materials on the surface roughness and load-deflection curve of commercially available orthodontic NiTi wires. Three-point bending tests and AFM assessments were used to evaluate the load-deflection properties and surface roughness, respectively.
Methods Materials
Three types of as-received white-coated NiTi archwires (n ¼ 15 per each), including NiTi Natural Dany (Dany BMT, Seoul, Korea), Orthoforce UltraestheticTM NiTi (G&H1 Wire Company, Greenwood, IN), and Perfect NiTi archwires (Hubit, Seoul, Korea) (Fig. 1) were investigated in this study. The Dany archwires (Dany group) had a double-layered coating structure, an inner layer consisting of a silver and platinum coating and an outer layer consisting of a special polymer coating. The UltraestheticTM archwires (Ultra group) were coated with epoxy resin. The Perfect archwires (Perfect group) were coated with Teflon1. Uncoated metallic areas for each white-coated NiTi archwire were used as controls.
Load-Deflection Characteristics
A modified three-point bending test using a simple device (Fig. 2) equipped with a digital caliper and a microscope (M2011 Dino-Lite Basic USB microscope, Dinolite, Taiwan) was conducted to examine the load and deflection properties in the bending wires (Choi et al., 2012b). The 0.022-in Clarity-SL bracket (3M Unitek, Monrovia, CA) with lower incisors was used as a supporting point. The anterior part of the archwire was used as the loading point for the three-point bending test. Two brackets of each group were bonded on both horizontal surfaces of the digital caliper using an instant
Fig 1. Three intact esthetic NiTi archwires. (A) Silver-platinum- and polymer-coated NiTi Natural Dany archwire (Dany BMT, Seoul, Korea), (B) epoxy resin-coated Orthoforce UltraestheticTM NiTi archwire (G&H1 Wire Company, Greenwood, IN), and (C) Teflon1coated Perfect NiTi archwire (Hubit, Seoul, Korea). Scale bar ¼ 10 mm.
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SCANNING VOL. 37, 6 (2015)
Fig 2. Modified three-point bending test device for evaluating the geometric configuration of orthodontic wires. Photos of a (A) modified three-point bending test device including the digital caliper and microscope and (B) the bending experiment. The wire was deflected downward vertically (red arrow). Scale bar ¼ 50 mm.
adhesive (Loctite 495, Henkel, Ireland). The mesial plane of each bracket base was aligned with the mesial plane of the caliper. Because the bracket base faced the floor, a three-point bending test in the buccolingual plane simulating the first-order wire deflection to the lingual side was performed. The interbracket distance was modulated by a digital caliper to 15 mm. For the threepoint bending experiment, the prepared wire samples were inserted and ligated into the brackets. The engaged NiTi wire was connected to the custom-made acrylic container at its half waypoint using a metal hook without a bracket. Each wire was first loaded and then unloaded. The load was increased in the container from 20 to 200 g at 20-g intervals and then decreased the load at 20-g intervals back to 20 g (Table S1, Supporting Information). The results of the bending test were presented as the average of five replicates using different 0.016-in wire samples (n ¼ 5 per group). All measurements were performed at room temperature (RT). The wires with straight in shape were used and the preformed archwire shapes were excluded. In order to estimate the geometric configuration of the wire, pictures were taken every moment with a microscope using a metal ruler for data compensation. Five clinicians measured the amount of vertical wire deflection using Motic Images Plus ver 2.0 (Motic China Group Co. Ltd, Xiamen, China).
Surface Ultrastructure
Tapping-mode AFM topographical images of the anterior part (coated areas) and the posterior part (uncoated areas) for three esthetic NiTi archwires were 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 ). External noise was eliminated by placing the AFM 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 512 512 pixels, and a scan speed of 0.6 lines/s. AFM tapping-mode topographical imaging was performed at RT and 35% relative humidity using a silicon cantilever with an integral pyramidal shaped tip (SICONG; Santa Clara, CA). The nominal tip radius and height were
Surface Ultrastructure and Mechanical Properties of Three Different White-Coated NiTi Archwires SEONG-HEE RYU,1 BYUNG-SUH LIM,1 EUN JOO KWAK,1 GI-JA LEE,2 SAMJIN CHOI,2 AND KI-HO PARK1 1 2
Department of Orthodontics, College of Dentistry, Kyung Hee University, Seoul, Korea Department of Biomedical Engineering, College of Medicine, Kyung Hee , University, Seoul, Korea
Summary: The recent trend in orthodontic treatment is to apply esthetic materials to orthodontic appliances with adequate clinical performance. The aim of this study was to investigate the ultrastructure (surface roughness) and mechanical properties (load-deflection curve) of three asreceived, white-coated superelastic nickel-titanium (NiTi) archwires using atomic force microscopy (AFM) and modified three-point bending test assessments, respectively. Three representative esthetic NiTi archwires were used, silver-platinum- and polymer-coated NiTi Natural Dany (Dany group), epoxy resin-coated Orthoforce UltraestheticTM (Ultra group), and Teflon1-coated Perfect (Perfect group). Uncoated metallic areas of each wire were used as controls. The diameter of the Perfect archwire was significantly larger than that of other archwires. The Dany and Ultra groups showed more deflection than the Perfect group. The hysteresis area of the Dany and Ultra groups showed approximately twoand fourfold increases compared to the control and the Perfect group. The Dany group (2037.5 527.3 nm) had the highest peak-to-peak surface roughness in the coated areas, followed by the Ultra group (811.1 407.5 nm) and the Perfect group (362.7 195.8 nm). However, reverse nanostructural changes in the surface roughness were observed in the uncoated metallic areas. The results suggested that the load-deflection properties and the
Contract grant sponsor: Ministry of Health & Welfare, Republic of Korea; Contract grant number: HI14C2241. Conflict of interest: The authors have no competing interests to declare. Address for reprints: Samjin Choi, Department of Biomedical Engineering, College of Medicine, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul 130-701, Republic of Korea E-mail: [email protected] Address for reprints: Ki-Ho Park, 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 8 April 2015; Accepted with revision 21 May 2015 DOI: 10.1002/sca.21230 Published online 30 June 2015 in Wiley Online Library (wileyonlinelibrary.com).
surface roughness of superelastic NiTi archwires were affected directly by the coating materials. Although the efficiency of orthodontic treatment was affected by various factors, when only considering the frictional force and mechanostructural properties, the epoxy resincoated Orthoforce UltraestheticTM archwires were the most effective for orthodontic treatment. SCANNING 37:414–421, 2015. © 2015 Wiley Periodicals, Inc. Key words: white coating, nickel-titanium archwires, load-deflection property, surface roughness
Introduction Recent trends in orthodontic treatment have emphasized materials with acceptable esthetics for patients and adequate clinical performance for clinicians (Elayyan et al., 2010), particularly for two representative fixed orthodontic materials, brackets and archwires. For brackets, composite and ceramic materials have been introduced (Russell, 2005) and metal-insert ceramic brackets were developed to produce less frictional force compared to conventional uncoated archwires (Dickson and Jones, ’96; Cacciafesta et al., 2003). In the archwires, three types of esthetic materials were introduced (Alavi and Hosseini, 2012); the esthetically transparent nonmetallic orthodontic wire Optiflex1, fiber-reinforced polymer archwire, and Teflon1 and epoxy resin coated archwires. Although Optiflex1 (Ormco Co., Glendora, CA) is coated with a silica core, silicone resin in the middle layer, and stain-resistant nylon in the outer layer, it did not show desirable mechanical properties (Talass, ’92; Lim et al., ’94). A fiber-reinforced polymer archwire developed by another research group (Imai et al., ’99) had an excellent appearance; however, it has not been clinically popular due to its brittle character (Lim et al., ’94; Kusy, 2002). Metallic archwires coated with polymer materials, such as Teflon1 and epoxy resin, have also been developed (Husmann et al., 2002; Elayyan et al., 2008). Tooth-colored nickel-titanium (NiTi) wire Woowa (Dany Harvest Co., Seoul, Korea) was recently
Ryu et al.: Mechanostructure of white-coated NiTi AWs
introduced in clinical orthodontics. This wire had a double-layered coating structure, an inner layer consisting of a silver and platinum coating, and an outer layer consisting of a special polymer coating (Iijima et al., 2012). In general, the frictional force between the archwire and bracket reduces the efficiency of orthodontic treatment (Choi et al., 2012a, 2012b). To develop a new material, the mechanical properties and surface characteristics of the orthodontic appliance as well as primary factors determining the friction should be considered for enhancing the efficiency of orthodontic treatment. The mechanical properties of orthodontic wires can be evaluated through load-deflection curve measurement via a three-point bending test (Elayyan et al., 2008). This is considered the most important parameter in determining the biological nature of tooth movement (Kapila and Sachdeva, ’89; Krishnan and Kumar, 2004). The advantage of this assessment is it is a clinic-friendly simulation for differentiating between the superelastic wires that lead to high reproducibility (Wilkinson et al., 2012). Alternatively, the surface roughness of orthodontic wires is an essential factor in determining the effectiveness of archwire-guided tooth movement (Bourauel et al., ’98; Choi et al., 2012a, 2012b). The surface quality of wires affects the area of surface contact and influences the corrosion behavior and biocompatibility of the archwires (Elayyan et al., 2008). Additionally, the surface topography can critically modify the esthetics, corrosion, and efficiency of the orthodontic components (Kusy et al., ’88). Variations in the surface roughness affect plaque accumulation (Wichelhaus et al., 2005). In particular, the surface roughness might modify the friction coefficient (Downing et al., ’94; Tselepis et al., ’94; Bazakidou et al., ’97). To the best of the authors’ knowledge, there have been no previous reports evaluating the mechanical properties and ultrastructure of various polymer-coated metallic archwires using a three-point bending test and atomic force microscopy (AFM) measurements except fiberreinforced polymer composite (FRPC) archwire-based
415
study. Therefore, the aim of this study was to investigate the effects of these various white coating materials on the surface roughness and load-deflection curve of commercially available orthodontic NiTi wires. Three-point bending tests and AFM assessments were used to evaluate the load-deflection properties and surface roughness, respectively.
Methods Materials
Three types of as-received white-coated NiTi archwires (n ¼ 15 per each), including NiTi Natural Dany (Dany BMT, Seoul, Korea), Orthoforce UltraestheticTM NiTi (G&H1 Wire Company, Greenwood, IN), and Perfect NiTi archwires (Hubit, Seoul, Korea) (Fig. 1) were investigated in this study. The Dany archwires (Dany group) had a double-layered coating structure, an inner layer consisting of a silver and platinum coating and an outer layer consisting of a special polymer coating. The UltraestheticTM archwires (Ultra group) were coated with epoxy resin. The Perfect archwires (Perfect group) were coated with Teflon1. Uncoated metallic areas for each white-coated NiTi archwire were used as controls.
Load-Deflection Characteristics
A modified three-point bending test using a simple device (Fig. 2) equipped with a digital caliper and a microscope (M2011 Dino-Lite Basic USB microscope, Dinolite, Taiwan) was conducted to examine the load and deflection properties in the bending wires (Choi et al., 2012b). The 0.022-in Clarity-SL bracket (3M Unitek, Monrovia, CA) with lower incisors was used as a supporting point. The anterior part of the archwire was used as the loading point for the three-point bending test. Two brackets of each group were bonded on both horizontal surfaces of the digital caliper using an instant
Fig 1. Three intact esthetic NiTi archwires. (A) Silver-platinum- and polymer-coated NiTi Natural Dany archwire (Dany BMT, Seoul, Korea), (B) epoxy resin-coated Orthoforce UltraestheticTM NiTi archwire (G&H1 Wire Company, Greenwood, IN), and (C) Teflon1coated Perfect NiTi archwire (Hubit, Seoul, Korea). Scale bar ¼ 10 mm.
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SCANNING VOL. 37, 6 (2015)
Fig 2. Modified three-point bending test device for evaluating the geometric configuration of orthodontic wires. Photos of a (A) modified three-point bending test device including the digital caliper and microscope and (B) the bending experiment. The wire was deflected downward vertically (red arrow). Scale bar ¼ 50 mm.
adhesive (Loctite 495, Henkel, Ireland). The mesial plane of each bracket base was aligned with the mesial plane of the caliper. Because the bracket base faced the floor, a three-point bending test in the buccolingual plane simulating the first-order wire deflection to the lingual side was performed. The interbracket distance was modulated by a digital caliper to 15 mm. For the threepoint bending experiment, the prepared wire samples were inserted and ligated into the brackets. The engaged NiTi wire was connected to the custom-made acrylic container at its half waypoint using a metal hook without a bracket. Each wire was first loaded and then unloaded. The load was increased in the container from 20 to 200 g at 20-g intervals and then decreased the load at 20-g intervals back to 20 g (Table S1, Supporting Information). The results of the bending test were presented as the average of five replicates using different 0.016-in wire samples (n ¼ 5 per group). All measurements were performed at room temperature (RT). The wires with straight in shape were used and the preformed archwire shapes were excluded. In order to estimate the geometric configuration of the wire, pictures were taken every moment with a microscope using a metal ruler for data compensation. Five clinicians measured the amount of vertical wire deflection using Motic Images Plus ver 2.0 (Motic China Group Co. Ltd, Xiamen, China).
Surface Ultrastructure
Tapping-mode AFM topographical images of the anterior part (coated areas) and the posterior part (uncoated areas) for three esthetic NiTi archwires were 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 ). External noise was eliminated by placing the AFM 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 512 512 pixels, and a scan speed of 0.6 lines/s. AFM tapping-mode topographical imaging was performed at RT and 35% relative humidity using a silicon cantilever with an integral pyramidal shaped tip (SICONG; Santa Clara, CA). The nominal tip radius and height were
