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

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wire at one or both of its contact points with the edge of the slot, known as mechanical notching, can occur, further adding to the resistance to sliding. 70,94 In a clinical study, this damage to the archwire was found to be related to the design of the orthodontic bracket. 95 The main effect of archwire-notching on friction is the creation of “obstacles” that impede relative wire-slot sliding. 96 It appears that notching may be a function of the materials in contact. Kusy et al. 30 found that ceramic brackets cause more notching than stainless steel brackets. Similarly, Articolo’s group 96 found that notching of archwires was three times more prevalent and severe with ceramic brackets than with stainless steel brackets. Third-Order Torque The term “third-order torque” in orthodontics pertains to the rotational control and movement of a tooth crown or root faciolingually. This type of tooth movement can occur subsequent to twisting a square or rectangular archwire along its longitudinal axis, required to place it into the slot of a crown-attachment. In this process, two contact forces acting on the occlusal and gingival walls of the slot by partial archwire deactivation create a third-order 30
couple, resulting in the delivery in the faciolingual plane of torsional forces to the tooth. 97,98 The preadjusted edgewise appliance is designed with a specific amount of slot-/pre-torque for each tooth in the arch to aid in achieving optimal crown- and root- positioning. Theoretically, this torque will be expressed when a full-size archwire is allowed to deactivate completely over time after being seated in the slot of a properly placed bracket. When a rectangular wire not completely filling the slot is engaged, a certain amount of rotation around the longitudinal axis of the wire can occur before the occlusogingival clearance within the slot becomes zero and third-order rotational forces are transmitted to the crown-attachment. This clearance-angle is known as “slop” or “play,” and its magnitude is primarily dependent on the shape and dimensions of the wire and slot, as well as the amount of edge-bevel in the wire cross-section. 99-101 The difference between the appliance- torque and this clearance-angle gives the effective torque, the estimated amount of third-order torque that the bracket-wire combination will express after deactivation of the wire. 98 Because most orthodontic treatment is undertaken with less than full-size archwires, some preadjusted brackets include accentuated torque in the 31
Page 1 and 2: THE EFFECTS OF THIRD-ORDER TORQUE A
Page 3 and 4: of torque, all five attachment sets
Page 5 and 6: COMMITTEE IN CHARGE OF CANDIDACY: A
Page 7 and 8: 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: added. Similarly, Bunkall 15 noted
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 and 76: increased to only five degrees. The
Page 77 and 78: tension on one edge of the wire and
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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