Frictional resistances in combinations with effects

stainless steel bracket-wire of vertical deflections

Randall H. Ogata, DDS, MS, a Ram S. Nanda, DDS, MS, PhD, b Manville G. Duncanson, Jr., DDS, PhD, c Pramod K. Sinha, BDS, DDS, MSfl and G. Fr~ins Currier, DDS, MSD, MEd e Oklahoma City, Okla.

This research evaluated the effects of different bracket-wire combinations and second-order deflections on kinetic friction. Thirteen different brackets, six with 0.018 × 0.025 inch slots and seven with 0.022 × 0.028-inch slots were evaluated with six different sizes and shapes of stainless steel orthodontic wire, i,e., 0.016, 0.016 x 0.022, 0.017 x 0.025, 0.018, 0.018 x0.025 and 0.019 x 0.026 inch for four second order deflections of 0.00, 0.25, 0.50, and 0.75 mm. The wires were ligated into the brackets with elastomeric modules. Bracket movement was implemented by means of an Instron universal testing instrument (RMO, Denver, Colo.), and frictional forces were measured by a tension load cell and recorded on an X-Y recorder (Hewlett-Packard, Anaheim, Calif.). Second-order deflection was created by a specially designed and machined testing apparatus that allowed two alternate pairs of the four total brackets to be offset in increments of 0.25 mm. The kinetic frictional force increased for every bracket-wire combination tested as the second-order deflection increased. Friction also increased with an increase in wire size, whereas rectangular wires produced greater friction than round wires. Bracket designs that limited the force of ligation on the wire generated less friction at low second-order deflections (0.00 and 0.25 mm). (Arn J Orthod Dentofac Orthop 1996;109:535-42.)

S l i d i n g mechanics in orthodontic treat- ment involve the relative movement of brackets over an arch wire. This type of movement generates fric- tional forces that must be overcome to elicit peri- odontal response for tooth movement. Understand- ing the frictional forces between the brackets and the wires is essential for adequate tooth movement and optimum biologic response. The most desirable and ideal situation is one in which little or no friction exists at the bracket-wire interface.

The effects of deflection on bracket-wire fric- tion have been investigated by Peterson et al. 1 Increased angulation between bracket and wire produced greater frictionJ These investigators var- ied the bracket-wire angulation from 0 ° to 15 ° in a single bracket system that tested both stainless

From the University of Oklahoma Health Sciences Center College of Dentistry. This report is based on a thesis submitted to the Graduate College, University of Oklahoma Health Sciences Center, in partial fulfillment of the requirements for the degree of master of science. aGradnate student. UProfessor and Chair, Department of Orthodontics. ~Professor and Chair, Department of Dental Materials. eAssistant Professor, Department of Orthodontics. eProfessor, Department of Orthodontics. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/96/$5.00 + 0 8/1/60324

steel and nitinol wires. Frank and Nikolai 2 found that frictional resistance increased in a nonlinear manner with increased bracket angulation. In ad- dition, they found that as the force of ligation increased the frictional resistance increased. Kapila et al. a and Angolkar et al. 4 found that round wires generated less friction than rectangular wires and that friction increased with increased wire size. Vaughan et al., 5 using the same testing apparatus as Kapila et al. 3 and Angolkar et al. 4 demonstrated that sintered stainless steel brackets generated 40% less friction than cast stainless steel brackets. Sev- eral orthodontic manufacturing companies have recently introduced new bracket designs intended to reduce the amount of friction generated at the bracket-wire interface. These brackets need evalu- ation, because the clinician needs to know the range of frictional forces expected in various bracket-wire combinations. Yet, there is a lack of information in the literature on the effects of second-order deflection on the kinetic frictional force. The purpose of this investigation was to evaluate the effects of different bracket-wire com- binations and second-order deflections on kinetic friction. The effect of the bracket design and the manufacturing process on frictional resistance was also studied.

535

536 Ogata et aL American Journal of Orthodontics and Dentofacial Orthopedics May 1996

Fig. 1. Testing apparatus with four RS-S-018 brackets in place and 0.016 x O.025-inch stainless steel orthodontic wire ligated in place at maximum (0.75 mm) second-order deflection.

Fig. 2. Sintered stainless steel brackets, from right to left: R-S-022, RS-S-022, and U-S-022.

MATERIALS AND METHODS

This study measured the kinetic frictional forces developed between maxillary first premolar brackets with 0.018 x 0.025-inch and 0.022 x 0.028-inch slots tested with resilient stainless steel wire (Tru-Chrome, Rocky Mountain Orthodontics [RMO], Denver, Colo.) of vari- ous cross-sectional sizes and shapes. All wires were ligated into the brackets with elastomeric ligatures (J-176 ligature ringlets, RMO, Denver, Colo.). All tests were conducted on a Instron universal testing instrument (Model 1135, Instron Corp., Canton, Mass.) with the data being plotted on a X-Y recorder (Model 7005B, Hewlett-Packard, Anaheim, Calif.). Second-order deflec- tions were created by using a specially designed testing apparatus that allowed two pairs of brackets, four total, to be offset from 0.00 mm to a maximum of 0.75 mm in increments of 0.25 mm. (See Fig. 1.)

Data Collection

Data were gathered on 13 bracket types (six 0.018 × 0.025-inch and seven 0.022 × 0.028-inch slots) and six wire shapes and sizes (0.016 inch, 0.016 × 0.022 inch, 0.017 x 0.025 inch, 0.018 inch, 0.018 × 0.025 inch

and 0.019 × 0.026 inch). Four different second-order deflection settings (0.00, 0.25, 0.50, and 0.75 mm) were examined for each bracket-wire combination. A sample size of 10 wires was tested for each bracket-wire-deflec- tion combination. Each wire was tested across the four deflection settings, then a new wire and set of brackets would be placed in the apparatus and the process re- peated. The data were collected in two sets, one for 0.018 × 0.025-inch slot brackets and one for 0.022 × 0.028-inch slot brackets. The brackets were initially grouped by manufacturing process. Fig. 2 illustrates the 0.022 × 0.028-inch edgewise brackets produced with the sintering process, i.e, RMO Mini-Taurus (R-S-022), RMO Mini-Taurus Synergy (RS-S-022) (RMO, Denver, Colo.) and Unitek Mini Twin (U-S-022) (3M Unitek, Monrovia, Calif.). Fig. 3 shows the 0.022 × 0.028-inch edgewise brackets produced with casting methods, i.e., American Friction Free (A-022) (American Orthodon- tics, Sheboygan, Wis.), GAC Shoulder (G-022) (GAC, Central Islip, N.Y.), and Ormco Mini Diamond (0-022) (Ormco, Glendora, Calif.). Fig. 4 illustrates the TIP Tip-Edge (TP-022) (TP Orthodontics, LaPorte, Ind.) which is a cast bracket, currently available only in an 0.022-inch slot.

American Journal of Orthodontics and Dentofacial Orthopedics Ogata et al. 537 Volume 109, No. 5

Fig. 3. Cast stainless steel brackets, from right to left: A-022, G-022, and 0-022.

The testing apparatus held four brackets so that the bracket slots were oriented vertically. Two brackets were attached to the fixed half, and two brackets were at- tached to the sliding half of the test apparatus. A straight, 5-inch segment of orthodontic wire was fixed onto the brackets with elastomeric ligatures. The testing apparatus allowed for the brackets to be off-set, deflect- ing the wire in increments of 0.25 mm by the use of a built-in millimetric slide-rule. Bracket movement was implemented by the Instron at a rate of 0.02 inch per minute for 2 minutes for each deflection evaluated. The kinetic frictional forces generated as the brackets moved along the wire were measured by the tension load cell and plotted on the X-Y recorder. The area of the plot where this curve leveled off was recorded as the friction generated for that bracket-wire-deflection combination. Deflection was increased in 0.25 mm increments up to a maximum of 0.75 mm of second-order deflection for each wire evaluated. A new set of brackets and wire was then placed in the testing apparatus and the process repeated.

Statistical Analysis

The means and standard deviations of the frictional forces were calculated for each specific bracket-wire- deflection combination. The data were analyzed with one-factor repeated measure analyses of variance with contrasts between repeated measures used to determine whether specific deflections generated significantly dif- ferent mean frictional forces. Increases in kinetic fric- tional forces were all tested at the same level of signifi- cance, i.e., p < 0.05.

RESULTS 0.018 x O.025-inch Slot Brackets

The mean kinetic frictional forces generated by all 0.018 × 0.025-inch brackets are shown in Table I for three wire sizes and four different second- order deflections. For all but one of the bracket- wire combinations tested, there were statistically significant increases between the mean kinetic fric- tional forces as deflection increased.

Sintered stainless steel brackets. As the degree of second-order deflection increased, the mean ki-

Fig. 4. Cast stainless steel, combination bracket: TP-022. Slot design has two 20 ° wedges removed from each side to allow slot to vary from 0.022 to 0.028 inch.

netic frictional forces increased significantly for every bracket-wire combination tested, except the R-S-018 brackets with 0.016-inch wires. At low deflections, these combinations did not generate significant increases in kinetic frictional forces when comparing 0.00 and 0.25 mm second-order deflections.

Cast stainless steel brackets. As the degree of second-order deflection increased, the mean ki- netic frictional forces increased significantly for every bracket-wire combination tested.

0.022 x O.028-inch Slot Brackets

The mean kinetic frictional forces generated by all 0.022 x 0.028-inch brackets are illustrated in Table II for six wire sizes and four different sec- ond-order deflections. For the majority of the bracket-wire combinations tested, there were sig- nificant increases between the mean kinetic fric- tional forces as deflection increased. In the three

538 Ogata et al. American Journal of Orthodontics and Dentofacial Orthopedics May 1996

Table I . Means and standard deviations (gins) for all 0.018 x O.025-inch slot brackets tested with three different sizes and shapes of stainless steel orthodontic wire over different second-order deflections, (n = 10")

0.018 x O.025-inch brackets

Means and standard deviations (gins)

Cast edgewise Sintered edgewise

G-O18 0-018 R-S-O18 RS-S-O18 U-S-O18

67.5 29.2 397.5 30.1 389.2** 36.6 1.2 3.2 530.0 58.9 271.0 20.5 707.0 25.3 636.5 84.9 0.0 0.0 689.5 101.7 622.5 184.5 928.0 49.5 610.5 75.9 68.7 58.1 746.5 49.0 237.0 41.4 432.0 24.2 469.6** 57.1 55.3 19.0 592.0 57.6 754.0 31.9 925.0 49.9 965.0 55.4 39.5 20.6 835.0 103.8

1238.5 117.6 1237.0 102.1 762.5 83.5 215.0 108.7 1174.5 70.3 480.5 50.2 648.5 35.7 678.2 74.6 222.8 36.7 753.0 69.3

1583.5 73.1 1490.5 91.8 1578.5 115.3 637.0 68.9 1193.0 127.0 2323.5 98.1 1821.0 142.7 1586.5 174.9 920.3 204.2 1881.0 130.4 767.5 55.3 854.0 36.0 874.6 95.1 407.0 53.2 934.0 69.0

2430.0 77.0 2001.0 107.5 2223.0 156.0 1497.0 186.6 1624.0 154.0 4441.5 66.0 2386.0 137.0 2486.0 283.7 1744.5 328.6 2512.0 161.8

Deflection

A-018

Mean { SD

0.00 nun 0.016 2.6 5.0 16 x 22 142.5 44.6 17 x 25 188.5 33.7

0.25 mm 0.016 151.6 26.0 16 x 22 559.5 29.8 17 x 25 766.5 45.0

0.50 mm 0.016 361.4 40.0 16 x 22 1220.0 60.3 17 x 25 1530.5 38.4

0.75 mm 0.016 558.6 56.5 16 x 22 1976.5 74.0 17 x 25 2451.0 293.3

*RS-S-018 brackets were evaluated with a n = 20 for 0.016 and 0.017 x 0.025-inch wires. **Indicates that there was no significant difference (p < 0.05) between the means of this specific bracket-wire combination across 0.00 and 0.25 mm of second-order deflection. All other interactions were significant at p < 0.05.

instances where there were no significant increases, all occurred between 0.00 and 0.25 mm of second- order deflection.

Sintered stainless steel brackets. As the degree of second-order deflection increased, kinetic frictional forces increased significantly for every bracket-wire combination tested, except the RS-S-022 brackets with 0.016-inch and 0.018-inch wires between 0.00 and 0.25 mm of second-order deflection.

Cast stainless steel brackets. As the degree of second-order deflection increased, kinetic frictional forces increased significantly for every bracket-wire combination tested, except the A-022 brackets with 0.016-inch wires between 0.00 and 0.25 mm of second-order deflection.

Cast combination bracket. As second-order de- flection increased, the mean kinetic frictional forces increased significantly for every wire size tested with TP-022 brackets.

The TP-022 brackets at low deflections gener- ated forces between those of the cast brackets that restricted ligation and the cast brackets ligated conventionally. However, as deflections increased, the frictional resistance generated by TP-022 brackets did not increase as rapidly as the edgewise brackets.

DISCUSSION

Investigators have indicated that the proper magnitudes of force during orthodontic treatment will result in optimal tissue response and rapid tooth movement. Storey and Smith 6 developed the concept of optimal forces required for maximum rate of tooth movement with a range of 180 to 240 gm being recommended for permanent canine re- traction. Other relationships between orthodontic forces and tooth movement have been proposed. Quinn and Yoshikawa 7 concluded that the rate of tooth movement increased as forces increased up to a certain point, after which, increases in force produced no appreciable increases in movement. During mechanotherapy involving movement of the bracket relative to the wire, friction at the bracket- wire interface may prevent the attainment of opti- mal force levels in the supporting tissues. Hence, an understanding of forces required to overcome friction is important so that the appropriate mag- nitude of force can be used to produce optimal biologic tooth movement.

The variables implicated as contributing to bracket-wire frictional forces include bracket de- sign, manufacturing process, slot size, wire alloy type, wire size and shape, method of ligation and

American Journal of Orthodontics and Dentofacial Orthopedics Volume 109, No. 5 Ogata et al. 5 3 9

force of ligation, as well as salivary lubrica- tion. 1'a5'811 As the majority of these variables are under the control of the clinician, careful selection of appropriate brackets, wires, and ligatures may be used to control the relative rates of tooth move- ment and to enhance or reduce anchorage.

Previous investigations on bracket-wire friction have found that as wire size increases so does the frictional force between bracket and wire. J'2'8'9 The experimental design of some previous studies pro- vided information for frictional forces generated at fixed bracket wire angulations ranging from 0 ° to 15°. 1'2'8 The frictional forces determined by keeping a fixed second-order bracket-wire deflection system were not likely to be representative of the in vivo dynamic changes in wire-bracket relationships. The clinical situation often requires leveling of deflec- tions in a series of bracketed teeth, not just a single bracket. In the clinical management of the patient requiring maximum anchorage protection, com- plete leveling of an arch before using sliding me- chanics, is necessary. Leveling reduces the forces required for retraction of the teeth, because the forces required for overcoming frictional resistance will be decreased.

In this study, the mean kinetic frictional force generally increased as wire size increased. In addi- tion, it was noted that rectangular wires generated greater frictional forces than round wires. Further, as deflection increased, the frictional forces gener- ated did not increase in a linear manner, which is in agreement with the findings of Frank and Nikolai. 2

In recent years, bracket design and manufactur- ing have become more sophisticated, incorporating new design features and new processing methods in the production of brackets. The effect of changes in deflection and wire sizes on the mean kinetic fric- tional force generated in the current study will be discussed for several variables.

Effect of Deflection on Frictional Forces

As second-order deflection increased, frictional resistance increased for every bracket-wire combi- nation evaluated in the current study. This increase was statistically significant for the majority of deflec- tion increases across each wire size and shape being evaluated. However, as second-order deflection in- creased between 0.00 to 0.25 mm, frictional forces did not significantly increase for every bracket-wire combination. Frictional increases appeared in two phases. With lower deflections, a smooth sliding phase appeared in which friction increased in ap- proximately a linear manner. However, as deflection

Fig, 5. Facial and mesial views of RS-S-022 bracket demon- strating bumps on slot walls and floor and how force of ligation would be held off of wire. Arrows point to these bumps.

increased, a binding phase occurred in which the friction increased at a much greater rate and was not necessarily linear. The point at which this binding occurred was different for each bracket-wire combi- nation but generally occurred at about 0.75 mm of second-order deflection.

Effect of Bracket Design on Frictional Forces

New bracket designs have been introduced that restrict the amount of force placed on the wire by the ligature. These designs generated lower mean frictional forces at second-order deflections of 0.00 and 0.25 mm than conventionally ligated brackets. The three bracket types that could be ligated in this manner were A-018/022, G-018/022, and RS- S-018/022. These new bracket designs generated lower frictional forces than brackets ligated in a conventional manner. RS-S brackets have six wings, with three on each side of the bracket slot. (See Fig. 5.) The lateral wings may be included in ligation for correction of rotation of teeth. For testing in this experiment, only the center wings were ligated. This method of tying reduced binding created by the pressure of ligation in this bracket.

540 Ogata et al. American Journal of Orthodontics and Dentofacial Orthopedics May 1996

The effect of the design of the new brackets, when ligated with the wire, limits the force on the wire with the result that the normal component of frictional force was markedly reduced. The results of this study confirmed the findings of an earlier investigation 3 that the conventional brackets de- signs that permit full force of the ligation to bear on the arch wire produced greater frictional resis- tance. This was evident from the data concerning small diameter wires at 0.00 mm or low second- order deflections. In comparison, the newly de- signed brackets revealed lower values of frictional resistance. With new bracket designs, higher mea- surements of friction largely reflected a greater degree of second-order deflection.

The frictional forces recorded for the RS-S brackets were lower for all sizes of wire-bracket combinations at every level of second-order deflec- tion, even when compared with the other new design brackets of A-018/022 and G-018/022. This difference may be attributed to the additional de- sign features in these brackets. They have bumps on the bracket walls and bracket floor, which re- duce the surface area in contact with the wires, and helped reduce the friction at the bracket-wire in- terface.

The TP-022 brackets have a design in which 20 ° wedges were cut out of the bracket slot on diago- nally opposite corners. These brackets were de- signed largely for the practitioners of the Begg technique, where teeth are first tipped and later uprighted with auxiliary springs. With this bracket design, when a tooth tips on retraction, the binding of the wire at the edges of the bracket is greatly minimized. The result of this design is that fric- tional resistances are greatly reduced. However, the results of this bracket cannot be compared on the same plane with those of the other brackets in this study, which were designed to seek bodily move- ment as far as possible.

Effect of Manufacturing Process on Frictional Forces

The three bracket types that were sintered, or metal injection molded (MIM), in their manufac- ture were R-S-018/022, RS-S-018/022, and U-S- 018/022. Comparisons of the frictional forces produced by stainless steel orthodontic wires in sintered and cast stainless steel brackets have indi- cated that the wires in the sintered brackets pro- duced 38% to 44% less frictional resistance than cast brackets. 5 The differences in frictional forces

between the two types of brackets may be attrib- uted to the surface texture of the bracket. The scanning electron micrographs of the sintered brackets demonstrated a smoother bracket surface afforded by the sintering process. 5 Sintering allows each individual bracket to be premolded in a smooth streamlined manner. The stainless steel particles are then compressed in a contoured, smooth, rounded shape as opposed to casting pro- cedures where the milling or cutting processs may leave sharp angular brackets that are more bulky and rough. This study showed that as second-order deflections increased the sintered brackets began to generate lower frictional resistances as com- pared with cast edgewise brackets. (See Tables I and II.)

Effect of Wire Shape and Size on Frictional Forces

The findings of this study are in agreement with earlier reports 35 that frictional forces increase not only with larger diameter wires, but with rectangu- lar wires. Larger wires increase the bracket-wire interface that will affect the frictional forces.

In the bracket-wire-deflection combinations that generated the lowest kinetic frictional force, the fol- lowing factors contributed to reduce the magnitude of frictional forces. First, lower second-order deflec- tions (0.00 and 0.25 ram) contributed to lower fric- tional forces. Second, smaller wire sizes (0.016 and 0.016 × 0.022 inch) generated lower frictional forces. Third, brackets that restricted the force of ligation (A-018/022, G-018/022, and RS-S-018/022) generated less frictional resistance than convention- ally ligated brackets.

In the bracket-wire-deflection combinations that produced the greatest kinetic frictional forces, most of the higher frictional forces were recorded for larger degrees of second-order deflection (0.50 and 0.75 ram) and larger rectangular wires.

Clinical Significance

On the basis of the information gathered from this study, several points of clinical significance can be identified. To reduce friction during tooth move- ment, complete leveling of the arch is an important factor. New bracket designs and bracket types will further help to reduce the amount of friction gen- erated. Bracket designs that restrict the force of ligation will allow the clinician to level the arch or retract teeth without this constant force. Since sintered brackets 5 reduced friction 40%, these bracket types would be advantageous in leveling

American Journal of Orthodontics and Dentofacial Orthopedics Ogata et aL 541 Volume 109, No. 5

Table I I . Means and s tandard deviat ions (gins) for all 0.022 x 0.028-inch slot brackets tes ted with six

d i f ferent sizes and shapes o f stainless s teel o r thodon t i c wires over d i f ferent s econd-o rde r deflections,

0.022 x O. 028-inch brackets

Means and standard deviations (gins)

Cast edgewise Sintered edgewise Combination

G-022 0-022 R-S-022 RS-S-022 U-S-022 TP-022

Mean SD Mean I SD Mean I SD Mean SD Mean I SD Mean I SD

95.0 13.9 481.0 44 .2 463.5 53.5 0.0" 0.0 384.5 29 .9 292.5 19.2 188.0 16.4 732.5 25 .6 680.0 51.3 0.0 0.0 646.5 87 .5 574.5 29.0 205.0 15.8 747.5 25 .6 645.0 30.4 0.0 0.0 705.5 20 .5 732.0 58.9 132.0 25.8 549.0 51 .3 361.5 42.4 0.0" 0.0 436.5 16 .2 362.0 37.3 233.0 13.6 821.0 30 .0 700.0 76.6 0.0 0.0 803.0 49 .1 612.5 24,5 246.0 16.0 1060.0 80 .3 848.5 40.6 0.0 0.0 908.5 95 .0 737.5 35.1 117.5 17.4 529.0 46 .9 487.0 58.7 0.0" 0.0 430.0 31 .6 326.5 26.5 282.5 10.1 842.0 35 ,3 734.0 48.9 6.5 4.1 714.5 57 .6 607.0 18.0 441.5 27.6 868.0 31 .7 733.0 40.6 11.0 5.7 808.0 39 .2 761.5 49.4 177.5 28.5 605.0 49 .6 408.5 40.6 1.5" 3.4 498.5 17 .8 442.0 69,8 515.0 10.0 1131.0 94 .4 852.0 122.7 12.0 5.9 895.0 69 .5 814.5 24.9 592.5 25.0 1830.0 36.1 1044.0 55.6 30.5 18.2 993.5 97 .3 799.5 29.9 247.5 14.2 665.0 52 .3 550.0 64.8 29.0 12.4 384.5 27 .8 383.0 25.4 653.0 22.0 1355.0 45 .3 905.0 44 .0 151.5 24.8 1061.5 99 .4 657.0 23.6

1017.5 55.8 1468.0 45.0 1032.0 68 .2 254.5 28.9 1063.0 75 .2 806.5 21.2 403.0 23.9 830.5 64 .4 596.5 23.7 97.5 8.2 620.5 33 .0 480.5 54.7

1221.5 32.1 1616.0 121.3 1621.5 272.1 234.0 21.1 1136.5 80.4 1009.5 73.4 1380.5 73.2 2499.5 54.4 1889.0 136.0 373.0 62.7 1432.0 104.2 1055.0 59.1 398.5 18.3 824.5 58 .0 713.5 79 .1 110.5 23.7 734.0 36 .5 450.0 34.8

1190.0 48.0 1934.0 74.1 1336.0 87 .5 459.0 41.6 1280.0 78 .3 857.5 29.8 1929.0 60.7 1990.5 89.2 1609.0 98 .3 755.5 32.3 1546.0 160.2 962.0 43.1 710.5 29.4 1081.5 87 .2 873.0 58 .9 313.5 53.8 787.0 35 .3 527.0 45.8

2224.5 75.9 2741.0 182.6 2532.4 468.9 866.0 51.2 1815.5 190.9 1276.0 77.3 3051.5 64.9 3468.5 61.7 2680.0 224.0 1217.5 146.9 2247.0 171.3 1514.0 138.3

(n = 10)

A-022

Deflection Mean SD

0.00 mm 0.016 89.0* 8.1 16 x 22 174.5 13.2 17 x 25 192.5 12.3

0.018 106.5 9.1 18 x 25 246.0 28.2 19 × 26 257.5 37.2

0.25 mm 0.016 91.0" 7.7 16 x 22 195.0 13.1 17 x 25 213.0 7.5

0.018 117.5 9.2 18 x 25 266.5 28.2 19 x 26 356.0 58.6

0.50 mm 0.016 113.5 6.7 16 x 22 291.0 23.5 17 x 25 409.0 11.0

0.018 185.0 9.1 13 x 25 589:0 56.4 19 x 26 997.0 183.8

0.75 mm 0 . 0 1 6 236.5 14.2 16 x 22 786.0 86.0 17 x 25 1067.5 54.0

0.018 475.0 16.3 13 x 25 1383.0 50.5 19 x 26 1600.5 117.5

*Indicates tha~ there was no significant difference (p < 0.05) between the means of this specific bracket-wire combinations across 0.00 and 0.25 mm of second-order deflections. All other interactions were significant at p < 0.05.

and re t rac t ion of teeth. T h e select ion of var ious

wire shapes and sizes will also allow the cl inician to

regula te the a m o u n t o f friction. T h e advances in

bo th b racke t design and manufac tu r ing offer

g rea te r flexibility in reduc ing fr ic t ional res is tance

dur ing sliding mechanics .

A l imi ta t ion to this study would be the inter-

p re t a t ion of this in vi t ro study to any in vivo

si tuation. Wi th any tes t ing si tuation, it is impossible

to r e p r o d u c e the exact s i tuat ion one might encoun-

te r in the mouth . T h e r e f o r e the re la t ive fr ict ional

forces ob ta ined in this study are m o r e m e a n i n g f u l

w h e n c o m p a r e d with each other, as opposed to an

actual force va lue tha t might be m e a s u r e d clinically

on a pat ient . In addi t ion, this study only eva lua ted

stainless s teel brackets and wires, fu ture research

may inc lude d i f fe ren t b racke t or wire mater ia ls .

CONCLUSIONS

1. Kinet ic f r ic t ional force increased as second-

o rde r def lect ions increased for all bracket-

wire combina t ions tested.

2. Fr ic t ional forces t ended to be g rea te r for

rec tangular wires as c o m p a r e d with round

wires.

3. Fr ic t ional forces t e n d e d to increase with an

increase in wire size.

4. The RS-S brackets g e n e r a t e d consistent ly

low fr ic t ional forces that have b e e n attrib-

u ted to the un ique design of these brackets.

5. Bracke t designs that res t r ic ted the force of

l igat ion f rom being p laced on the arch wire,

such as A-018/022, G-018/022, and RS-S-

018/022 brackets gene ra t ed lower kinet ic

542 Ogata et al. American Journal of Orthodontics and Dentofacial Orthopedics May 1996

frictional forces as compared with bracket designs that did not restrict the ligation force at second-order deflections of 0.00 and 0.25 mm.

REFERENCES

1. Peterson L, Spencer R, Andreasen GF. Comparison of frictional resistance of nitinol and stainless steel wires in edgewise brackets. Quint Inter Digest 1982;13:563-71.

2. Frank CA, Nikolai RJ. A comparative study of frictional resistance between orthodontic bracket and arch wire. AM J ORTHOD 1980;78:593-609.

3. Kapila S, Angolkar PV, Duncanson Jr MG, Nanda RS. Evaluation of friction between edgewise stainless steel brackets and orthodontic wires for four alloys. AM J ORTHOD DENTOFAC ORTHOP 1990;98:117-26.

4. Angolkar PV, Kapila S, Duncanson Jr MG, Nanda RS. Evaluation of friction between ceramic brackets and ortho- dontic wires of four alloys. AM J ORTHOD DENTOFAC ORTHOP 1990;98:499-506.

5. Vaughan JL, Duncanson Jr MG, Nanda RS, Currier GF. Relative kinetic frictional forces between sintered stain-

less steel brackets and orthodontic wire. AM J ORTHOD DENTOFAC ORTHOP 1995;107:20-7.

6. Storey F, Smith R. Force in orthodontics and its relation to tooth movement. Aust Dent J 1952;56:11-8.

7. Quinu RB, Yoshikawa DK. A reassessment of force magni- tude in orthodontics. AM J ORTHOD 1985;88:252-60.

8. Andreasen GF, Quevedo FR. Evaluation of frictional forces in the 0.022" × 0.028" edgewise bracket in vitro. J Biomech 1970;3:151-60.

9. Riley JL, Garrett SG, Moon PC. Frictional forces of ligated plastic and metal edgewise brackets. J Dent Res 1979;58:A21.

10. Stanndard JG, Gau JM, Hanna M. Comparative friction of orthodontic wires under dry and-wet conditions. AM J ORTHOD 1986;89:485-91.

11. Baker KL, Nieberg LG, Weimer AD, Hanna M. Frictional changes in force values caused by saliva substitution. AM J ORTHOD DENTOFAC ORTHOP 1987;91:316-30.

Reprint requests to: Dr. Ram Nanda University of Oklahoma Health Sciences Center College of Dentistry P.O. Box 36901 Oklahoma City, OK 73190

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