Original Article
Effects of third-order torque on frictional force of self-ligating brackets Takeshi Mugurumaa; Masahiro Iijimab; William A. Brantleyc; Karamdeep S. Ahluwaliad; Naohisa Kohdaa; Itaru Mizoguchie ABSTRACT Objective: To investigate the effects of third-order torque on frictional properties of self-ligating brackets (SLBs). Materials and Methods: Three SLBs (two passive and one active) and three archwires (0.016 3 0.022-inch nickel-titanium, and 0.017 3 0.025-inch and 0.019 3 0.025-inch stainless steel) were used. Static friction was measured by drawing archwires though bracket slots with four torque levels (06, 106, 206, 306), using a mechanical testing machine (n 5 10). A conventional stainlesssteel bracket was used for comparison. Results were subjected to Kruskal-Wallis and MannWhitney U-tests. Contact between the bracket and wire was studied using a scanning electron microscope. Results: In most bracket-wire combinations, increasing the torque produced a significant increase in static friction. Most SLB-wire combinations at all torques produced less friction than that from the conventional bracket. Active-type SLB-wire combinations showed higher friction than that from passive-type SLB-wire combinations in most conditions. When increasing the torque, more contact between the wall of a bracket slot and the edge of a wire was observed for all bracket types. Conclusions: Increasing torque when using SLBs causes an increase in friction, since contact between the bracket slot wall and the wire edge becomes greater; the design of brackets influences static friction. (Angle Orthod. 0000;00:000–000.) KEY WORDS: Friction; Self-ligating brackets; Archwire; SEM
INTRODUCTION Frictional force (resistance to sliding) between the bracket and the wire (archwire) during tooth movement is one of the primary issues in clinical orthodontics, and if the frictional force can be decreased, the efficiency of tooth movement can be improved.1 Friction during clinical tooth movement depends on the size and shape of the wire,2 the bracket type,3–6 the bracket and wire materials,7 the angulation of the wire relative to the bracket,8 the type of ligation, 2 whether the environment is wet or dry,9 and whether a surface coating is present.10–12 The origin of the self-ligating bracket (SLB) concept can be traced back to the Russell Lock edgewise attachment described by Stolzenberg.13–15 Since the SPEED appliance was introduced by Hansen in the early 1980s,16 various SLBs, such as the Damon (Ormco, Glendora, Calif) and In-Ovation (DENTSPLY GAC, Bohemia, NY), have been introduced commercially and acquired popularity.15,17 The basic advantages of SLBs involve the elimination of certain utilities or materials such as elastomeric modules, along with the process or tools associated with their application, and the slide or clip opening-closing system of SLBs
Instructor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan. b Associate Professor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan. c Professor, Division of Restorative, Prosthetic and Primary Care Dentistry, College of Dentistry, The Ohio State University, Columbus, Ohio. d Assistant Professor, Department of Orthodontics and Dentofacial Orthopedics, Jaipur Dental College, Jaipur, India. e Professor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan. Corresponding author: Dr Masahiro Iijima, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Kanazawa 1757, Ishikari-tobetsu, Hokkaido 061-0293, Japan (e-mail: [email protected]) a
Accepted: March 2014. Submitted: November 2013. Published Online: April 16, 2014 G 0000 by The EH Angle Education and Research Foundation, Inc. DOI: 10.2319/111913-845.1
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Table 1. Self-ligating Brackets and Conventional Bracket and Archwires Used in the Present Study Bracket Passive type Passive type Active type
Wire
Conventional type 0.016 3 0.022 inch 0.017 3 0.025 inch 0.019 30.025 inch
Damon Q SmartClip In-Ovation R Mini Uni-Twin Nitinol Super Elastic Stainless-steel archwire Stainless-steel archwire
Ormco 3M Unitek Dentsply GAC 3M Unitek 3M Unitek 3M Unitek 3M Unitek
increases chair-side efficiency due to elimination of the ligaturing process.5,6 Other advantages claimed by bracket manufacturers, such as increased patient comfort, improved oral hygiene, superior patient cooperation and acceptance, less chair time, shorter treatment time, and enhanced expansion of arches, have interested orthodontists. However, there is no evidence for some of these claimed advantages.6 Although previous in vitro studies reported that SLBs had lower friction,18,19 randomized clinical trials investigating the efficiency of orthodontic treatment using SLBs have shown inconsistent results.5,6 In various treatment stages, the contact state between the bracket and wire should largely influence the frictional properties of a multibracket system, and few research groups have studied the effects of second-order angulation on frictional properties of SLBs.9,19 Only the study by Chung et al.20 has described the effects of third-order torque on frictional properties of SLBs, and limited information is currently available on this issue. It is important to understand the frictional characteristics of the SLBs in detail to demonstrate their clinical performance, and systematic in vitro studies may be required. The purpose of this in vitro study was to investigate the frictional properties in SLBs with different designs (two passive types and one active type) under different third-order bracket torques. The contact state between the bracket with different designs and the wire was studied using a scanning electron microscope (SEM). We hypothesized that design of the bracket and the torque values do not affect friction. MATERIALS AND METHODS This study used three different SLBs, two passive types (Damon Q, Ormco; SmartClip, 3M Unitek, Monrovia, Calif) and one active type (In-Ovation R, DENTSPLY GAC International), three wires (nickeltitanium with 0.016 3 0.022-inch cross-section dimensions [Nitinol Super-Elastic, 3M Unitek] and stainless steel [Stainless Steel, 3M Unitek] with 0.017 3 0.025inch and 0.019 3 0.025-inch cross-section dimensions). A conventional stainless-steel bracket (Mini Uni-Twin, 3M Unitek) was used for comparison Angle Orthodontist, Vol 00, No 0, 0000
Figure 1. Photographs of three self-ligating brackets and the conventional bracket used in the present study. (a) Damon Q. (b) SmartClip. (c) In-Ovation R. (d) Mini Uni-Twin.
(Table 1; Figure 1). Considering that different thirdorder torque values affect friction, the use of brackets with 0u built-in torque eliminates the influence of original torque, and such brackets were chosen for the present study, although their type (teeth) was different (Damon Q for mandibular canine, SmartClip for maxillary canine, In-Ovation R for maxillary canine, Uni-Twin for standard canine). All four bracket products were clinically popular 0.022-inch types. Friction Test The static frictional force generated with each bracket-wire combination was measured under dry conditions and at room temperature (25uC) using a custom-fabricated friction-testing device attached to a universal testing machine (EZ Test, Shimadzu, Kyoto, Japan), as shown in Figure 2.12 Each bracket was bonded to a stainless-steel plate that could provide four different bracket torques (0u, 10u, 20u, and 30u) and 0u angulation with the aid of a bracket-mounting device (Figure 2) that employed a nonfiller adhesive resin (Superbond, Sun Medical, Shiga, Japan). The stainless-steel plate with the bracket was attached to the friction-testing device, and a 5-cm segment of wire obtained from the posterior straight portions of nickeltitanium or stainless-steel wires was then fixed to each SLB or ligated to the conventional bracket using a 0.010-inch-diameter ligature wire (Preformed Ligature Wire, Ormco) or an elastomeric module (AlastiK Easyto-Tie Ligatures, 3M Unitek), except that the SLBs were tested in a closed position. The upper end of the wire was fixed with a grip that was attached to the load cell, and the lower end of the wire was fixed to a 150-g weight. The distance from the grip to the center of the bracket slot was adjusted to 16.5 mm. Each wire was drawn through the bracket slot at a cross-head speed of 10 mm/min for a distance of 5 mm. The static frictional force was determined from load-displacement curves.1 The sample size for each bracket-wire combination was 10. Observation of Bracket-Wire Combination Specimens by SEM To observe the cross-section views of the wirebracket contacts, each combination with a different
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FRICTIONAL FORCE OF SELF-LIGATING BRACKETS
Figure 2. Friction testing system (a, b) Custom-fabricated frictional testing device attached to universal testing machine. (c, d) Bracket-mounting device. (e) Stainless-steel plate that could apply third-order torque to the bracket. A, grip; B, bracket-wire combination specimen; C, stainlesssteel plate; D, weight (150 g); E, angle measurement device.
bracket torque was first encapsulated in epoxy resin (EpoFix, Struers, Copenhagen, Denmark). After 24 hours, the encapsulated specimens were cut mesiodistally with a slow-speed water-cooled diamond saw (Isomet, Buehler, Lake Bluff, Ill) and polished using silicon carbide abrasive paper and a diamond suspension (particle sizes of 3 mm and 1 mm, respectively) and final slurry of 0.05 mm alumina particles. All specimens were sputter coated with pure gold and examined by an SEM (S-3500N, Hitachi, Tokyo, Japan) operating at 20 kV. Statistical Analysis A statistical analysis was performed using SPSS Statistics (version 20.0J for Windows, IBM, Armonk, NY). The static frictional force values were not homogenous (Levene test), and a Kruskal-Wallis test was applied to determine whether a significant difference existed among the bracket-wire combina-
Figure 3. Static frictional forces measured at four different bracket torques for the three self-ligating brackets and the conventional bracket with the nickel-titanium wire and the stainless-steel wires.
tions. The Mann-Whitney U-test was then used for two independent bracket-wire combinations, and the Bonferroni correction was applied (P , .0050 or P , .0083). RESULTS Tables 2 and 3 and Figures 3 and 4 show the frictional forces measured at four different bracket torques (0u, 10u, 20u, and 30u) for the three SLBs (Damon Q, SmartClip, and In-Ovation R) and the conventional bracket (Mini Uni-Twin) ligated by two different methods (ligature wire [L] or elastomeric module [E]), with the nickel-titanium wire (0.016 3 0.022 inch) and the stainless-steel wires (0.017 3 0.025 inch and 0.019 3 0.025 inch). In most bracketwire combinations, increasing the torque from 0u to 10u, 20u, or 30u produced an increase in static frictional force (Table 2). All SLB–nickel-titanium wire combina-
Figure 4. Static frictional forces for the three self-ligating brackets and the conventional bracket with the nickel-titanium wire and the stainless-steel wires. DQ indicates Damon Q; SC, SmartClip; IO, InOvation R; MU(L), Mini Uni-Twin ligated with ligature wire; MU(E), Mini Uni-Twin ligated with elastomeric module. Angle Orthodontist, Vol 00, No 0, 0000
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Table 2. Frictional Forces Measured at Four Different Bracket Torques for the Three Self-ligating Brackets and the Conventional Bracket With the Nickel-Titanium Wire and the Stainless-Steel Wiresa Friction Force, gf Torque 0u Wire .016 3 .022 nickel-titanium
.017 3 .025 stainless steel
.019 3 .025 SS
Bracket Damon Q SmartClip In-Ovation R Mini Uni-Twin Mini Uni-Twin Damon Q SmartClip In-Ovation R Mini Uni-Twin Mini Uni-Twin Damon Q SmartClip In-Ovation R Mini Uni-Twin Mini Uni-Twin
Median
(E) (L)
(E) (L)
(E) (L)
0.89 1.27 1.02 126.06 237.08 1.27 1.27 33.78 93.81 179.22 1.40 0.89 61.57 171.95 207.13
Torque 10u IQR
b
0.76–1.21 1.08–1.47 0.76–1.72 119.43–137.60 199.16–265.89 1.08–1.47 0.83–1.27 28.87–40.85 88.78–102.86 164.17–218.86 0.83–1.78 0.51–1.21 58.38–67.24 149.39–186.93 175.45–263.85
b b c b b b b b b b b b b
Median 0.51 0.89 12.24 184.31 251.49 1.27 41.94 49.07 135.49 196.04 2.80 77.12 175.90 220.13 309.74
b
c c c b c c c b c c c c c
IQR 0.51–1.15 0.51–1.02 11.66–12.62 177.69–211.46 141.29–322.29 1.27–1.91 33.01–47.35 46.65–52.01 122.94–144.35 159.65–253.14 2.04–3.51 65.13–102.42 142.25–204.71 183.49–225.74 288.01–361.49
a The Kruskal-Wallis test was applied to determine whether significant differences existed among the bracket-wire combinations. The MannWhitney U-test was then used for two independent bracket-wire combinations, and the Bonferroni correction was applied (P , .0083). IQR indicates interquartile range. Identical letters indicate that mean values were not significantly different.
tions for all torque values produced less frictional force than that from the conventional bracket (Table 3). The active SLB–nickel-titanium wire combinations showed higher static friction than the passive SLB–nickeltitanium wire combinations, except at 0u of torque. The active SLB–stainless-steel wire combinations showed higher static friction than the passive SLB–stainlesssteel wire combinations, except at 30u of torque for the 0.019 3 0.025-inch stainless-steel wire. Some Mini Uni-Twin (L)–wire combinations showed higher static friction than Mini Uni-Twin (E)–wire combinations.
The SEM photomicrographs are shown in Figures 5 to 8, for a representative specimen of each crosssectioned bracket-wire combination. Each SLB showed a different appearance for the contact area. In comparing passive SLBs, the SmartClip bracket-wire combination specimens exhibited relatively less contact between the bracket slots and wires compared with the corresponding Damon Q bracket specimens. The clips of the In-Ovation R bracket (active SLB) contacted the wire surfaces for all wire sizes and torque conditions. When there was an increase in torque or wire size,
Table 3. Frictional Forces for the Three Self-ligating Brackets and the Conventional Bracket With the Nickel-Titanium Wire and the StainlessSteel Wiresa Friction Force, gf Damon Q Wire .016 3 .022 nickel-titanium
.017 3 .025 stainless steel
.019 3 .025 stainless steel
Torque 0u 10u 20u 30u 0u 10u 20u 30u 0u 10u 20u 30u
a
Median 0.89 0.51 1.53 4.59 1.27 1.27 16.19 456.20 1.40 2.80 195.91 1282.42
SmartClip IQR
b b b b b b b b b b b b
0.76–1.21 0.51–1.15 1.34–1.72 4.08–5.03 1.08–1.47 1.27–1.91 13.96–21.41 441.54–475.19 0.83–1.78 2.04–3.51 177.88–227.52 1095.18–1402.49
Median 1.27 0.89 1.40 1.15 1.27 41.94 42.70 347.72 0.89 77.12 250.60 784.16
b b b c b c c c b c b c
IQR 1.08–1.47 0.51–1.02 1.08–1.98 0.83–1.53 0.83–1.27 33.01–47.35 39.39–45.31 332.17–370.09 0.51–1.21 65.13–102.42 233.96–275.00 668.62–821.83
The Kruskal-Wallis test was applied to determine whether significant differences existed among the bracket-wire combinations. The MannWhitney U-test was then used for two independent bracket-wire combinations, and the Bonferroni correction was applied (P , .0050). IQR indicates interquartile range. Identical letters indicate that mean values were not significantly different. Angle Orthodontist, Vol 00, No 0, 0000
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FRICTIONAL FORCE OF SELF-LIGATING BRACKETS Table 2. Extended Friction Force, gf Torque 20u
Torque 30u
Median 1.53 1.40 16.19 244.99 622.28 16.19 42.70 219.11 255.44 298.01 195.91 250.60 935.97 714.95 669.95
IQR
c
1.34–1.72 1.08–1.98 14.59–17.53 212.29–262.39 600.36–701.37 13.96–21.41 39.39–45.31 185.84–240.46 226.06–295.72 275.64–353.91 177.88–227.52 233.96–275.00 918.64–1280.76 657.33–766.83 630.82–753.38
d d d c c d d c d d d d d
IQR
P Value
4.08–5.03 0.83–1.53 22.56–29.32 217.58–265.06 545.29–862.17 441.54–475.19 332.17–370.09 416.36–559.63 695.19–805.83 728.40–914.18 1095.18–1402.49 668.62–821.83 988.17–1177.71 959.43–1125.83 890.28–967.14
.000 .090 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
Median 4.59 1.15 24.60 244.09 814.75 456.20 347.72 483.60 721.32 866.63 1282.42 784.16 1108.30 1009.14 952.29
greater contact of the bracket slot wall and the wire edge was observed for all bracket types. DISCUSSION To investigate the effects of third-order torque of some popular SLBs, this study examined the static frictional forces and obtained SEM images of the cross-sectioned SLB-wire combinations to reveal the contact areas. It has been found that the bracket design is a highly important factor for friction. The present observation that increasing the torque had a highly significant influence on the static friction in most bracket–stainless-steel wire combinations suggests that tipping of teeth in labiolingual or buccolingual
d
e d d d d e e d e e d e e
directions is an important factor influencing the efficiency of initial orthodontic alignment using SLBs. The SLB–nickel-titanium wire combinations for all torque values produced less frictional force than that from the conventional bracket, suggesting that the tooth alignment capability using nickel-titanium wire with SLBs might be superior to use of conventional stainless-steel brackets. Except for combinations with relatively large wire size (0.019 3 0.025-inch stainless-steel), each SLB–stainless-steel wire combination at all torque conditions (0u, 10u, 20u, and 30u) showed less frictional force than that found with conventional bracket-wire combinations. This observation is in agreement with previous studies.18–20 Thus, the present in vitro results suggest that
Table 3. Extended Friction Force, gf In-Ovation R Median 1.02 12.24 16.19 24.60 33.78 49.07 219.11 483.60 61.57 175.90 935.97 1108.30
b c c d c c d b c d c b,d
Mini Uni-Twin (E) IQR
0.76–1.72 11.66–12.62 14.59–17.53 22.56–29.32 28.87–40.85 46.65–52.01 185.84–240.46 416.36–559.63 58.38–67.24 142.25–204.71 918.64–1280.76 988.17–1177.71
Median 126.06 184.31 244.99 244.09 93.81 135.49 255.44 721.32 171.95 220.13 714.95 1009.14
c d d e d d d,e d d d d b,d
Mini Uni-Twin (L) IQR
119.43–137.60 177.69–211.46 212.29–262.39 217.58–265.06 88.78–102.86 122.94–144.35 226.06–295.72 695.19–805.83 149.39–186.93 183.49–225.74 657.33–766.83 959.43–1125.83
Median 237.08 251.49 622.28 814.75 179.22 196.04 298.01 866.63 207.13 309.74 669.95 952.29
c d e f e d e d d e d d
IQR
P Value
199.16–265.89 141.29–322.29 600.36–701.37 545.29–862.17 164.17–218.86 159.65–253.14 275.64–353.91 728.40–914.18 175.45–263.85 288.01–361.49 630.82–753.38 890.28–967.14
.000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
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Figure 5. Scanning electron microscope photographs of cross-sectioned Damon Q bracket and each wire combination. (a–d) 0.016 3 0.022-inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless-steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u.
the SLBs produce less frictional force during anterior retraction. In addition, the use of heavy (stainless-steel) archwires may not be preferred during anterior retraction with sliding mechanics, and sufficient alignment using a nickel-titanium archwire with large cross-section dimensions is required before the anterior retraction stage. The classification of SLBs into active and passive types has been described by two previous articles.15,17 Both articles note that active SLBs usually have a sliding spring clip, which encroaches on the slot from the labial aspect and reduces the slot size in the horizontal dimension, potentially placing an active
force on the archwire. In contrast, passive SLBs have a slide that opens and closes vertically, thereby creating a passive labial surface that lacks the ability to encroach upon the slot and store force by deflection of a metal clip.15 A previous study21 showed that passive SLBs exhibit lower friction than active SLBs, and it was suggested that the wire-binding effect of active SLBs might be higher than passive SLBs. Similarly, the present study showed that passive SLBs have less static friction than active SLBs, and SEM observations of cross-sectioned bracket-wire specimens showed that passive SLBs have relatively loose contact between bracket slots and wires compared with active SLBs. An
Figure 6. Scanning electron microscope photographs of cross-sectioned SmartClip bracket and each wire combination. (a–d) 0.016 3 0.022inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u. Angle Orthodontist, Vol 00, No 0, 0000
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Figure 7. Scanning electron microscope photographs of cross-sectioned In-Ovation R bracket and each wire combination. (a–d) 0.016 3 0.022inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless-steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u.
additional consideration is that the sliding spring clip of an active SLB encroaches on the slot, facilitating contact between the slot and edge of the wire. However, this study showed that the Damon Q bracket (passive SLB) with 30u torque and 0.019 3 0.025-inch stainlesssteel wire produced higher friction than the In-Ovation R bracket (active SLB). The reason for this inconsistency may be distortion of the clip, which requires further study for verification. In the present study, all wires did not show any permanent deformation after the friction test, even when 30u torque was imposed on the 0.019 3 0.025inch stainless-steel heavy wire. The reason for this is
that a relatively long distance from the grip to the bracket was used (16.5 mm) for the friction testing, and this value is greater than the distance between adjacent brackets bonded to a patient’s teeth under clinical conditions. CONCLUSIONS N Increasing the third-order torque experienced by SLBs produces an increase in static friction. N The SLBs produce less static friction than conventional brackets, and passive SLBs produce less friction than active SLBs.
Figure 8. Scanning electron microscope photographs of cross-sectioned Mini Uni-Twin bracket and each wire combination. (a–d) 0.016 3 0.022inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless-steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u. Angle Orthodontist, Vol 00, No 0, 0000
8 N The extent of contact between the bracket and edge of the wire may be influential for static friction. REFERENCES 1. Burrow SJ. Friction and resistance to sliding in orthodontics: a critical review. Am J Orthod Dentofacial Orthop. 2009;135: 442–447. 2. Bazakidou E, Nanda RS, Duncanson MG Jr, Sinha P. Evaluation of frictional resistance in esthetic brackets. Am J Orthod Dentofacial Orthop. 1997;112:138–144. 3. Redlich M, Mayer Y, Harari D, Lewinstein I. In vitro study of frictional force during sliding mechanics of ‘‘reduced-friction’’ brackets. Am J Orthod Dentofacial Orthop. 2003;124:69–73. 4. Miles PG, Weyant RJ, Rustveld L. A clinical trial of Damon 2TM vs conventional twin brackets during initial alignment. Angle Orthod. 2006;76:480–485. 5. Harradine N. Self-ligating brackets increase treatment efficiency. Am J Orthod Dentofacial Orthop. 2013;143: 10–18. 6. Fleming PS, O’Brien K. Self-ligating brackets do not increase treatment efficiency. Am J Orthod Dentofacial Orthop. 2013;143:11–19. 7. Saunders CR, Kusy RP. Surface topography and frictional characteristics of ceramic brackets. Am J Orthod Dentofacial Orthop. 1994;106:76–87. 8. Frank CA, Nikolai RJ. A comparative study of frictional resistances between orthodontic bracket and arch wire. Am J Orthod. 1980;78:593–609. 9. Thorstenson GA, Kusy RP. Effect of archwire size and material on the resistance to sliding of self-ligating brackets with second-order angulation in the dry state. Am J Orthod Dentofacial Orthop. 2002;122:295–305. 10. Kusy RP, Tobin EJ, Whitley JQ, Sioshansi P. Frictional coefficients of ion-implanted alumina against ion-implanted
Angle Orthodontist, Vol 00, No 0, 0000
MUGURUMA, IIJIMA, BRANTLEY, AHLUWALIA, KOHDA, MIZOGUCHI
11.
12.
13. 14. 15.
16. 17. 18.
19.
20.
21.
beta-titanium in the low load, low velocity, single pass regime. Dent Mater. 1992;8:167–172. Wichelhaus A, Geserick M, Hibst R, Sander FG. The effect of surface treatment and clinical use on friction in NiTi orthodontic wires. Dent Mater. 2005;21:938–945. Muguruma T, Iijima M, Brantley WA, Mizoguchi I. Effects of a diamond-like carbon coating on the frictional properties of orthodontic wires. Angle Orthod. 2011;81:143–150. Stolzenberg J. The Russell attachment and its improved advantages. Int J Orthod Dent Child. 1935;21:837–840. Harradine NWT. Current products and practices self-ligating brackets: where are we now? J Orthod. 2003;30:262–273. Pandis N, Miles PG, Eliades T. Efficiency and treatment outcome with self-ligating brackets. In: Eliades T, Pandis N, eds. Self-ligation in Orthodontics. Oxford, UK: Wiley-Blackwell; 2009:69–84. Berger JL. The SPEED system: an overview of the appliance and clinical performance. Semin Orthod. 2008;14:54–63. Rinchuse DJ, Miles PG. Self-ligating brackets: present and future. Am J Orthod Dentofacial Orthop. 2007;132:216–222. Cacciafesta V, Sfondrini MF, Ricciardi A, Scribante A, Klersy C, Auricchio F. Evaluation of friction of stainless steel and esthetic self-ligating brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop. 2003; 124:395–402. Cordasco G, Giudice AL, Militi A, Nucera R, Triolo G, Matarese G. In vitro evaluation of resistance to sliding in self-ligating and conventional bracket systems during dental alignment. Korean J Orthod. 2012;42:218–224. Chung M, Nikolai RJ, Kim KB, Oliver DR. Third-order torque and self-ligating orthodontic bracket-type effects on sliding friction. Angle Orthod. 2009;79:551–557. Huang TH, Luk HS, Hsu YC, Kao CT. An in vitro comparison of the frictional force between archwires and self-ligating brackets of passive and active types. Eur J Orthod. 2012;34: 625–632.
Effects of third-order torque on frictional force of self-ligating brackets Takeshi Mugurumaa; Masahiro Iijimab; William A. Brantleyc; Karamdeep S. Ahluwaliad; Naohisa Kohdaa; Itaru Mizoguchie ABSTRACT Objective: To investigate the effects of third-order torque on frictional properties of self-ligating brackets (SLBs). Materials and Methods: Three SLBs (two passive and one active) and three archwires (0.016 3 0.022-inch nickel-titanium, and 0.017 3 0.025-inch and 0.019 3 0.025-inch stainless steel) were used. Static friction was measured by drawing archwires though bracket slots with four torque levels (06, 106, 206, 306), using a mechanical testing machine (n 5 10). A conventional stainlesssteel bracket was used for comparison. Results were subjected to Kruskal-Wallis and MannWhitney U-tests. Contact between the bracket and wire was studied using a scanning electron microscope. Results: In most bracket-wire combinations, increasing the torque produced a significant increase in static friction. Most SLB-wire combinations at all torques produced less friction than that from the conventional bracket. Active-type SLB-wire combinations showed higher friction than that from passive-type SLB-wire combinations in most conditions. When increasing the torque, more contact between the wall of a bracket slot and the edge of a wire was observed for all bracket types. Conclusions: Increasing torque when using SLBs causes an increase in friction, since contact between the bracket slot wall and the wire edge becomes greater; the design of brackets influences static friction. (Angle Orthod. 0000;00:000–000.) KEY WORDS: Friction; Self-ligating brackets; Archwire; SEM
INTRODUCTION Frictional force (resistance to sliding) between the bracket and the wire (archwire) during tooth movement is one of the primary issues in clinical orthodontics, and if the frictional force can be decreased, the efficiency of tooth movement can be improved.1 Friction during clinical tooth movement depends on the size and shape of the wire,2 the bracket type,3–6 the bracket and wire materials,7 the angulation of the wire relative to the bracket,8 the type of ligation, 2 whether the environment is wet or dry,9 and whether a surface coating is present.10–12 The origin of the self-ligating bracket (SLB) concept can be traced back to the Russell Lock edgewise attachment described by Stolzenberg.13–15 Since the SPEED appliance was introduced by Hansen in the early 1980s,16 various SLBs, such as the Damon (Ormco, Glendora, Calif) and In-Ovation (DENTSPLY GAC, Bohemia, NY), have been introduced commercially and acquired popularity.15,17 The basic advantages of SLBs involve the elimination of certain utilities or materials such as elastomeric modules, along with the process or tools associated with their application, and the slide or clip opening-closing system of SLBs
Instructor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan. b Associate Professor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan. c Professor, Division of Restorative, Prosthetic and Primary Care Dentistry, College of Dentistry, The Ohio State University, Columbus, Ohio. d Assistant Professor, Department of Orthodontics and Dentofacial Orthopedics, Jaipur Dental College, Jaipur, India. e Professor, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan. Corresponding author: Dr Masahiro Iijima, Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Kanazawa 1757, Ishikari-tobetsu, Hokkaido 061-0293, Japan (e-mail: [email protected]) a
Accepted: March 2014. Submitted: November 2013. Published Online: April 16, 2014 G 0000 by The EH Angle Education and Research Foundation, Inc. DOI: 10.2319/111913-845.1
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Table 1. Self-ligating Brackets and Conventional Bracket and Archwires Used in the Present Study Bracket Passive type Passive type Active type
Wire
Conventional type 0.016 3 0.022 inch 0.017 3 0.025 inch 0.019 30.025 inch
Damon Q SmartClip In-Ovation R Mini Uni-Twin Nitinol Super Elastic Stainless-steel archwire Stainless-steel archwire
Ormco 3M Unitek Dentsply GAC 3M Unitek 3M Unitek 3M Unitek 3M Unitek
increases chair-side efficiency due to elimination of the ligaturing process.5,6 Other advantages claimed by bracket manufacturers, such as increased patient comfort, improved oral hygiene, superior patient cooperation and acceptance, less chair time, shorter treatment time, and enhanced expansion of arches, have interested orthodontists. However, there is no evidence for some of these claimed advantages.6 Although previous in vitro studies reported that SLBs had lower friction,18,19 randomized clinical trials investigating the efficiency of orthodontic treatment using SLBs have shown inconsistent results.5,6 In various treatment stages, the contact state between the bracket and wire should largely influence the frictional properties of a multibracket system, and few research groups have studied the effects of second-order angulation on frictional properties of SLBs.9,19 Only the study by Chung et al.20 has described the effects of third-order torque on frictional properties of SLBs, and limited information is currently available on this issue. It is important to understand the frictional characteristics of the SLBs in detail to demonstrate their clinical performance, and systematic in vitro studies may be required. The purpose of this in vitro study was to investigate the frictional properties in SLBs with different designs (two passive types and one active type) under different third-order bracket torques. The contact state between the bracket with different designs and the wire was studied using a scanning electron microscope (SEM). We hypothesized that design of the bracket and the torque values do not affect friction. MATERIALS AND METHODS This study used three different SLBs, two passive types (Damon Q, Ormco; SmartClip, 3M Unitek, Monrovia, Calif) and one active type (In-Ovation R, DENTSPLY GAC International), three wires (nickeltitanium with 0.016 3 0.022-inch cross-section dimensions [Nitinol Super-Elastic, 3M Unitek] and stainless steel [Stainless Steel, 3M Unitek] with 0.017 3 0.025inch and 0.019 3 0.025-inch cross-section dimensions). A conventional stainless-steel bracket (Mini Uni-Twin, 3M Unitek) was used for comparison Angle Orthodontist, Vol 00, No 0, 0000
Figure 1. Photographs of three self-ligating brackets and the conventional bracket used in the present study. (a) Damon Q. (b) SmartClip. (c) In-Ovation R. (d) Mini Uni-Twin.
(Table 1; Figure 1). Considering that different thirdorder torque values affect friction, the use of brackets with 0u built-in torque eliminates the influence of original torque, and such brackets were chosen for the present study, although their type (teeth) was different (Damon Q for mandibular canine, SmartClip for maxillary canine, In-Ovation R for maxillary canine, Uni-Twin for standard canine). All four bracket products were clinically popular 0.022-inch types. Friction Test The static frictional force generated with each bracket-wire combination was measured under dry conditions and at room temperature (25uC) using a custom-fabricated friction-testing device attached to a universal testing machine (EZ Test, Shimadzu, Kyoto, Japan), as shown in Figure 2.12 Each bracket was bonded to a stainless-steel plate that could provide four different bracket torques (0u, 10u, 20u, and 30u) and 0u angulation with the aid of a bracket-mounting device (Figure 2) that employed a nonfiller adhesive resin (Superbond, Sun Medical, Shiga, Japan). The stainless-steel plate with the bracket was attached to the friction-testing device, and a 5-cm segment of wire obtained from the posterior straight portions of nickeltitanium or stainless-steel wires was then fixed to each SLB or ligated to the conventional bracket using a 0.010-inch-diameter ligature wire (Preformed Ligature Wire, Ormco) or an elastomeric module (AlastiK Easyto-Tie Ligatures, 3M Unitek), except that the SLBs were tested in a closed position. The upper end of the wire was fixed with a grip that was attached to the load cell, and the lower end of the wire was fixed to a 150-g weight. The distance from the grip to the center of the bracket slot was adjusted to 16.5 mm. Each wire was drawn through the bracket slot at a cross-head speed of 10 mm/min for a distance of 5 mm. The static frictional force was determined from load-displacement curves.1 The sample size for each bracket-wire combination was 10. Observation of Bracket-Wire Combination Specimens by SEM To observe the cross-section views of the wirebracket contacts, each combination with a different
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FRICTIONAL FORCE OF SELF-LIGATING BRACKETS
Figure 2. Friction testing system (a, b) Custom-fabricated frictional testing device attached to universal testing machine. (c, d) Bracket-mounting device. (e) Stainless-steel plate that could apply third-order torque to the bracket. A, grip; B, bracket-wire combination specimen; C, stainlesssteel plate; D, weight (150 g); E, angle measurement device.
bracket torque was first encapsulated in epoxy resin (EpoFix, Struers, Copenhagen, Denmark). After 24 hours, the encapsulated specimens were cut mesiodistally with a slow-speed water-cooled diamond saw (Isomet, Buehler, Lake Bluff, Ill) and polished using silicon carbide abrasive paper and a diamond suspension (particle sizes of 3 mm and 1 mm, respectively) and final slurry of 0.05 mm alumina particles. All specimens were sputter coated with pure gold and examined by an SEM (S-3500N, Hitachi, Tokyo, Japan) operating at 20 kV. Statistical Analysis A statistical analysis was performed using SPSS Statistics (version 20.0J for Windows, IBM, Armonk, NY). The static frictional force values were not homogenous (Levene test), and a Kruskal-Wallis test was applied to determine whether a significant difference existed among the bracket-wire combina-
Figure 3. Static frictional forces measured at four different bracket torques for the three self-ligating brackets and the conventional bracket with the nickel-titanium wire and the stainless-steel wires.
tions. The Mann-Whitney U-test was then used for two independent bracket-wire combinations, and the Bonferroni correction was applied (P , .0050 or P , .0083). RESULTS Tables 2 and 3 and Figures 3 and 4 show the frictional forces measured at four different bracket torques (0u, 10u, 20u, and 30u) for the three SLBs (Damon Q, SmartClip, and In-Ovation R) and the conventional bracket (Mini Uni-Twin) ligated by two different methods (ligature wire [L] or elastomeric module [E]), with the nickel-titanium wire (0.016 3 0.022 inch) and the stainless-steel wires (0.017 3 0.025 inch and 0.019 3 0.025 inch). In most bracketwire combinations, increasing the torque from 0u to 10u, 20u, or 30u produced an increase in static frictional force (Table 2). All SLB–nickel-titanium wire combina-
Figure 4. Static frictional forces for the three self-ligating brackets and the conventional bracket with the nickel-titanium wire and the stainless-steel wires. DQ indicates Damon Q; SC, SmartClip; IO, InOvation R; MU(L), Mini Uni-Twin ligated with ligature wire; MU(E), Mini Uni-Twin ligated with elastomeric module. Angle Orthodontist, Vol 00, No 0, 0000
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Table 2. Frictional Forces Measured at Four Different Bracket Torques for the Three Self-ligating Brackets and the Conventional Bracket With the Nickel-Titanium Wire and the Stainless-Steel Wiresa Friction Force, gf Torque 0u Wire .016 3 .022 nickel-titanium
.017 3 .025 stainless steel
.019 3 .025 SS
Bracket Damon Q SmartClip In-Ovation R Mini Uni-Twin Mini Uni-Twin Damon Q SmartClip In-Ovation R Mini Uni-Twin Mini Uni-Twin Damon Q SmartClip In-Ovation R Mini Uni-Twin Mini Uni-Twin
Median
(E) (L)
(E) (L)
(E) (L)
0.89 1.27 1.02 126.06 237.08 1.27 1.27 33.78 93.81 179.22 1.40 0.89 61.57 171.95 207.13
Torque 10u IQR
b
0.76–1.21 1.08–1.47 0.76–1.72 119.43–137.60 199.16–265.89 1.08–1.47 0.83–1.27 28.87–40.85 88.78–102.86 164.17–218.86 0.83–1.78 0.51–1.21 58.38–67.24 149.39–186.93 175.45–263.85
b b c b b b b b b b b b b
Median 0.51 0.89 12.24 184.31 251.49 1.27 41.94 49.07 135.49 196.04 2.80 77.12 175.90 220.13 309.74
b
c c c b c c c b c c c c c
IQR 0.51–1.15 0.51–1.02 11.66–12.62 177.69–211.46 141.29–322.29 1.27–1.91 33.01–47.35 46.65–52.01 122.94–144.35 159.65–253.14 2.04–3.51 65.13–102.42 142.25–204.71 183.49–225.74 288.01–361.49
a The Kruskal-Wallis test was applied to determine whether significant differences existed among the bracket-wire combinations. The MannWhitney U-test was then used for two independent bracket-wire combinations, and the Bonferroni correction was applied (P , .0083). IQR indicates interquartile range. Identical letters indicate that mean values were not significantly different.
tions for all torque values produced less frictional force than that from the conventional bracket (Table 3). The active SLB–nickel-titanium wire combinations showed higher static friction than the passive SLB–nickeltitanium wire combinations, except at 0u of torque. The active SLB–stainless-steel wire combinations showed higher static friction than the passive SLB–stainlesssteel wire combinations, except at 30u of torque for the 0.019 3 0.025-inch stainless-steel wire. Some Mini Uni-Twin (L)–wire combinations showed higher static friction than Mini Uni-Twin (E)–wire combinations.
The SEM photomicrographs are shown in Figures 5 to 8, for a representative specimen of each crosssectioned bracket-wire combination. Each SLB showed a different appearance for the contact area. In comparing passive SLBs, the SmartClip bracket-wire combination specimens exhibited relatively less contact between the bracket slots and wires compared with the corresponding Damon Q bracket specimens. The clips of the In-Ovation R bracket (active SLB) contacted the wire surfaces for all wire sizes and torque conditions. When there was an increase in torque or wire size,
Table 3. Frictional Forces for the Three Self-ligating Brackets and the Conventional Bracket With the Nickel-Titanium Wire and the StainlessSteel Wiresa Friction Force, gf Damon Q Wire .016 3 .022 nickel-titanium
.017 3 .025 stainless steel
.019 3 .025 stainless steel
Torque 0u 10u 20u 30u 0u 10u 20u 30u 0u 10u 20u 30u
a
Median 0.89 0.51 1.53 4.59 1.27 1.27 16.19 456.20 1.40 2.80 195.91 1282.42
SmartClip IQR
b b b b b b b b b b b b
0.76–1.21 0.51–1.15 1.34–1.72 4.08–5.03 1.08–1.47 1.27–1.91 13.96–21.41 441.54–475.19 0.83–1.78 2.04–3.51 177.88–227.52 1095.18–1402.49
Median 1.27 0.89 1.40 1.15 1.27 41.94 42.70 347.72 0.89 77.12 250.60 784.16
b b b c b c c c b c b c
IQR 1.08–1.47 0.51–1.02 1.08–1.98 0.83–1.53 0.83–1.27 33.01–47.35 39.39–45.31 332.17–370.09 0.51–1.21 65.13–102.42 233.96–275.00 668.62–821.83
The Kruskal-Wallis test was applied to determine whether significant differences existed among the bracket-wire combinations. The MannWhitney U-test was then used for two independent bracket-wire combinations, and the Bonferroni correction was applied (P , .0050). IQR indicates interquartile range. Identical letters indicate that mean values were not significantly different. Angle Orthodontist, Vol 00, No 0, 0000
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FRICTIONAL FORCE OF SELF-LIGATING BRACKETS Table 2. Extended Friction Force, gf Torque 20u
Torque 30u
Median 1.53 1.40 16.19 244.99 622.28 16.19 42.70 219.11 255.44 298.01 195.91 250.60 935.97 714.95 669.95
IQR
c
1.34–1.72 1.08–1.98 14.59–17.53 212.29–262.39 600.36–701.37 13.96–21.41 39.39–45.31 185.84–240.46 226.06–295.72 275.64–353.91 177.88–227.52 233.96–275.00 918.64–1280.76 657.33–766.83 630.82–753.38
d d d c c d d c d d d d d
IQR
P Value
4.08–5.03 0.83–1.53 22.56–29.32 217.58–265.06 545.29–862.17 441.54–475.19 332.17–370.09 416.36–559.63 695.19–805.83 728.40–914.18 1095.18–1402.49 668.62–821.83 988.17–1177.71 959.43–1125.83 890.28–967.14
.000 .090 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
Median 4.59 1.15 24.60 244.09 814.75 456.20 347.72 483.60 721.32 866.63 1282.42 784.16 1108.30 1009.14 952.29
greater contact of the bracket slot wall and the wire edge was observed for all bracket types. DISCUSSION To investigate the effects of third-order torque of some popular SLBs, this study examined the static frictional forces and obtained SEM images of the cross-sectioned SLB-wire combinations to reveal the contact areas. It has been found that the bracket design is a highly important factor for friction. The present observation that increasing the torque had a highly significant influence on the static friction in most bracket–stainless-steel wire combinations suggests that tipping of teeth in labiolingual or buccolingual
d
e d d d d e e d e e d e e
directions is an important factor influencing the efficiency of initial orthodontic alignment using SLBs. The SLB–nickel-titanium wire combinations for all torque values produced less frictional force than that from the conventional bracket, suggesting that the tooth alignment capability using nickel-titanium wire with SLBs might be superior to use of conventional stainless-steel brackets. Except for combinations with relatively large wire size (0.019 3 0.025-inch stainless-steel), each SLB–stainless-steel wire combination at all torque conditions (0u, 10u, 20u, and 30u) showed less frictional force than that found with conventional bracket-wire combinations. This observation is in agreement with previous studies.18–20 Thus, the present in vitro results suggest that
Table 3. Extended Friction Force, gf In-Ovation R Median 1.02 12.24 16.19 24.60 33.78 49.07 219.11 483.60 61.57 175.90 935.97 1108.30
b c c d c c d b c d c b,d
Mini Uni-Twin (E) IQR
0.76–1.72 11.66–12.62 14.59–17.53 22.56–29.32 28.87–40.85 46.65–52.01 185.84–240.46 416.36–559.63 58.38–67.24 142.25–204.71 918.64–1280.76 988.17–1177.71
Median 126.06 184.31 244.99 244.09 93.81 135.49 255.44 721.32 171.95 220.13 714.95 1009.14
c d d e d d d,e d d d d b,d
Mini Uni-Twin (L) IQR
119.43–137.60 177.69–211.46 212.29–262.39 217.58–265.06 88.78–102.86 122.94–144.35 226.06–295.72 695.19–805.83 149.39–186.93 183.49–225.74 657.33–766.83 959.43–1125.83
Median 237.08 251.49 622.28 814.75 179.22 196.04 298.01 866.63 207.13 309.74 669.95 952.29
c d e f e d e d d e d d
IQR
P Value
199.16–265.89 141.29–322.29 600.36–701.37 545.29–862.17 164.17–218.86 159.65–253.14 275.64–353.91 728.40–914.18 175.45–263.85 288.01–361.49 630.82–753.38 890.28–967.14
.000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
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Figure 5. Scanning electron microscope photographs of cross-sectioned Damon Q bracket and each wire combination. (a–d) 0.016 3 0.022-inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless-steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u.
the SLBs produce less frictional force during anterior retraction. In addition, the use of heavy (stainless-steel) archwires may not be preferred during anterior retraction with sliding mechanics, and sufficient alignment using a nickel-titanium archwire with large cross-section dimensions is required before the anterior retraction stage. The classification of SLBs into active and passive types has been described by two previous articles.15,17 Both articles note that active SLBs usually have a sliding spring clip, which encroaches on the slot from the labial aspect and reduces the slot size in the horizontal dimension, potentially placing an active
force on the archwire. In contrast, passive SLBs have a slide that opens and closes vertically, thereby creating a passive labial surface that lacks the ability to encroach upon the slot and store force by deflection of a metal clip.15 A previous study21 showed that passive SLBs exhibit lower friction than active SLBs, and it was suggested that the wire-binding effect of active SLBs might be higher than passive SLBs. Similarly, the present study showed that passive SLBs have less static friction than active SLBs, and SEM observations of cross-sectioned bracket-wire specimens showed that passive SLBs have relatively loose contact between bracket slots and wires compared with active SLBs. An
Figure 6. Scanning electron microscope photographs of cross-sectioned SmartClip bracket and each wire combination. (a–d) 0.016 3 0.022inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u. Angle Orthodontist, Vol 00, No 0, 0000
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Figure 7. Scanning electron microscope photographs of cross-sectioned In-Ovation R bracket and each wire combination. (a–d) 0.016 3 0.022inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless-steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u.
additional consideration is that the sliding spring clip of an active SLB encroaches on the slot, facilitating contact between the slot and edge of the wire. However, this study showed that the Damon Q bracket (passive SLB) with 30u torque and 0.019 3 0.025-inch stainlesssteel wire produced higher friction than the In-Ovation R bracket (active SLB). The reason for this inconsistency may be distortion of the clip, which requires further study for verification. In the present study, all wires did not show any permanent deformation after the friction test, even when 30u torque was imposed on the 0.019 3 0.025inch stainless-steel heavy wire. The reason for this is
that a relatively long distance from the grip to the bracket was used (16.5 mm) for the friction testing, and this value is greater than the distance between adjacent brackets bonded to a patient’s teeth under clinical conditions. CONCLUSIONS N Increasing the third-order torque experienced by SLBs produces an increase in static friction. N The SLBs produce less static friction than conventional brackets, and passive SLBs produce less friction than active SLBs.
Figure 8. Scanning electron microscope photographs of cross-sectioned Mini Uni-Twin bracket and each wire combination. (a–d) 0.016 3 0.022inch nickel-titanium wire. (e–h) 0.017 3 0.025-inch stainless-steel wire. (i–l) 0.019 3 0.025-inch stainless-steel wire. (a, e, i) Wire torque at 0u. (b, f, j) Wire torque at 10u. (c, g, k) Wire torque at 20u. (d, h, l) Wire torque at 30u. Angle Orthodontist, Vol 00, No 0, 0000
8 N The extent of contact between the bracket and edge of the wire may be influential for static friction. REFERENCES 1. Burrow SJ. Friction and resistance to sliding in orthodontics: a critical review. Am J Orthod Dentofacial Orthop. 2009;135: 442–447. 2. Bazakidou E, Nanda RS, Duncanson MG Jr, Sinha P. Evaluation of frictional resistance in esthetic brackets. Am J Orthod Dentofacial Orthop. 1997;112:138–144. 3. Redlich M, Mayer Y, Harari D, Lewinstein I. In vitro study of frictional force during sliding mechanics of ‘‘reduced-friction’’ brackets. Am J Orthod Dentofacial Orthop. 2003;124:69–73. 4. Miles PG, Weyant RJ, Rustveld L. A clinical trial of Damon 2TM vs conventional twin brackets during initial alignment. Angle Orthod. 2006;76:480–485. 5. Harradine N. Self-ligating brackets increase treatment efficiency. Am J Orthod Dentofacial Orthop. 2013;143: 10–18. 6. Fleming PS, O’Brien K. Self-ligating brackets do not increase treatment efficiency. Am J Orthod Dentofacial Orthop. 2013;143:11–19. 7. Saunders CR, Kusy RP. Surface topography and frictional characteristics of ceramic brackets. Am J Orthod Dentofacial Orthop. 1994;106:76–87. 8. Frank CA, Nikolai RJ. A comparative study of frictional resistances between orthodontic bracket and arch wire. Am J Orthod. 1980;78:593–609. 9. Thorstenson GA, Kusy RP. Effect of archwire size and material on the resistance to sliding of self-ligating brackets with second-order angulation in the dry state. Am J Orthod Dentofacial Orthop. 2002;122:295–305. 10. Kusy RP, Tobin EJ, Whitley JQ, Sioshansi P. Frictional coefficients of ion-implanted alumina against ion-implanted
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12.
13. 14. 15.
16. 17. 18.
19.
20.
21.
beta-titanium in the low load, low velocity, single pass regime. Dent Mater. 1992;8:167–172. Wichelhaus A, Geserick M, Hibst R, Sander FG. The effect of surface treatment and clinical use on friction in NiTi orthodontic wires. Dent Mater. 2005;21:938–945. Muguruma T, Iijima M, Brantley WA, Mizoguchi I. Effects of a diamond-like carbon coating on the frictional properties of orthodontic wires. Angle Orthod. 2011;81:143–150. Stolzenberg J. The Russell attachment and its improved advantages. Int J Orthod Dent Child. 1935;21:837–840. Harradine NWT. Current products and practices self-ligating brackets: where are we now? J Orthod. 2003;30:262–273. Pandis N, Miles PG, Eliades T. Efficiency and treatment outcome with self-ligating brackets. In: Eliades T, Pandis N, eds. Self-ligation in Orthodontics. Oxford, UK: Wiley-Blackwell; 2009:69–84. Berger JL. The SPEED system: an overview of the appliance and clinical performance. Semin Orthod. 2008;14:54–63. Rinchuse DJ, Miles PG. Self-ligating brackets: present and future. Am J Orthod Dentofacial Orthop. 2007;132:216–222. Cacciafesta V, Sfondrini MF, Ricciardi A, Scribante A, Klersy C, Auricchio F. Evaluation of friction of stainless steel and esthetic self-ligating brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop. 2003; 124:395–402. Cordasco G, Giudice AL, Militi A, Nucera R, Triolo G, Matarese G. In vitro evaluation of resistance to sliding in self-ligating and conventional bracket systems during dental alignment. Korean J Orthod. 2012;42:218–224. Chung M, Nikolai RJ, Kim KB, Oliver DR. Third-order torque and self-ligating orthodontic bracket-type effects on sliding friction. Angle Orthod. 2009;79:551–557. Huang TH, Luk HS, Hsu YC, Kao CT. An in vitro comparison of the frictional force between archwires and self-ligating brackets of passive and active types. Eur J Orthod. 2012;34: 625–632.
