The effects of third-order torque and self - Saint Louis University

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enters the slot asymmetrically, contacting a rectangular wire along either a gingival or occlusal edge. An engaged 0.019- x 0.025-inch archwire with zero torque would be expected to deflect the clip of either bracket. 76 A third- order rotation of the slot relative to the archwire, depending upon its sense, could potentially cause more or less deflection of the clip, thereby affecting the faciolingual normal forces exerted by the wire and the accompanying components of the frictional force system. The Time2 set generated larger frictional forces at +5 degrees than at -5 degrees of torque. When comparing frictional resistances at +10 degrees and -10 degrees of torque, both the Time2 and In-Ovation R brackets showed greater forces at the positive third-order angulation. This finding might be explained by the asymmetrical nature of the clip-designs. The Victory set also produced a larger mean frictional force at +10 degrees of torque than at -10 degrees. One possible explanation could be the occlusogingival asymmetry of the tie-wings of the Victory bracket design (Figure 3- 9); when viewed from a mesiodistal perspective, the occlusal tie-wing apparently extends farther facially than the gingival tie-wing, suggesting that the elastomeric module could have been lying across the wire with more 66
tension on one edge of the wire and/or the direction of the net normal force from the tie was skewed. Only the SmartClip set showed a significant increase in friction with every five-degree increase in torque (in either twist-direction). Because 5 degrees of third-order rotation from 0 degrees does not eliminate the wire-slot clearance with this bracket-wire combination, a possible reason for the observed increase in friction could be the contact of the nickel-titanium-alloy “C-clips” with the wire during testing. Any contact of the wire with the clips during sliding could have produced a notable contribution to frictional resistance; a previous orthodontic-materials study found nickel-titanium-alloy wire to have a relatively large kinetic frictional coefficient when paired with a stainless steel bracket. 18 Effect of Bracket Design At zero degrees of torque, the results of this study were similar to those from a previous research-effort 46 that evaluated friction in both self-ligating and traditionally ligated brackets. In the present study, with no torque imposed, mean frictional resistance was found to be significantly less from each of the four self-ligation sets when compared to that from the Victory set (brackets tied 67
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THE EFFECTS OF THIRD-ORDER TORQUE A
Page 3 and 4:
of torque, all five attachment sets
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COMMITTEE IN CHARGE OF CANDIDACY: A
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ACKNOWLEDGEMENTS The author wishes
Page 9 and 10:
LIST OF TABLES Table 2-1: Partial O
Page 11 and 12:
CHAPTER 1: INTRODUCTION The special
Page 13 and 14:
CHAPTER 2: REVIEW OF THE LITERATURE
Page 15 and 16:
surfaces. 6 The magnitudes of the c
Page 17 and 18:
Since the introduction to orthodont
Page 19 and 20:
that the application of the Amonton
Page 21 and 22:
archwires. At binding angulations,
Page 23 and 24:
A phenomenon known as “cold weldi
Page 25 and 26: of round wire with the slot created
Page 27 and 28: acket and the gold-lined Luxi brack
Page 29 and 30: and wire stiffness. As bracket widt
Page 31 and 32: ligation-friction relationship. The
Page 33 and 34: designs have been introduced to the
Page 35 and 36: otated tooth or a twisted rectangul
Page 37 and 38: to incisor irregularity after initi
Page 39 and 40: added. Similarly, Bunkall 15 noted
Page 41 and 42: couple, resulting in the delivery i
Page 43 and 44: Another factor that influences brac
Page 45 and 46: References 1. Stoner MM. Force cont
Page 47 and 48: 19. Kusy RP, Whitley JQ, Ambrose WW
Page 49 and 50: 37. Kusy RP, Whitley JQ, Mayhew MJ,
Page 51 and 52: 56. Khambay B, Millett D, McHugh S.
Page 53 and 54: 75. Tecco S, Festa F, Caputi S, Tra
Page 55 and 56: 93. Thorstenson GA, Kusy RP. Effect
Page 57 and 58: Tables Table 2-1: Partial Overview
Page 59 and 60: significantly less friction than th
Page 61 and 62: optimal clinical results. Fixed-app
Page 63 and 64: self-ligating bracket systems to ma
Page 65 and 66: unconstrained rotation around the l
Page 67 and 68: surface of a tooth-crown. The const
Page 69 and 70: 0.025-inch NuBryte Standard Arch st
Page 71 and 72: test-archwire in place and ligated,
Page 73 and 74: aseline values at 0 degrees of torq
Page 75: increased to only five degrees. The
Page 79 and 80: set, when the torque angle was incr
Page 81 and 82: with active, self-ligating sets. Th
Page 83 and 84: 11. Kusy RP, Whitley JQ. Effects of
Page 85 and 86: 33. Andreasen GF, Quevedo FR. Evalu
Page 87 and 88: 54. Downing A, McCabe JF, Gordon PH
Page 89 and 90: 76. Thorstenson GA, Kusy RP. Effect
Page 91 and 92: Table 3-2: Significance levels (α
Page 93 and 94: Table 3-4: Mean differences in fric
Page 95 and 96: Figure 3-3: Control of the third-or
Page 97 and 98: Figure 3-9: Victory bracket Figure
Page 99 and 100: Figure 3-12: Cross-section diagrams
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The effects of third-order torque and self - Saint Louis University

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