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

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educing the torquing efficiency and causing errors in torque-expression. 64 In contrast, a “passive” ligating mechanism does not reduce the depth of the slot and places no inherent normal force on the archwire. These systems have one of two basic designs. The passive-slide design utilizes a sliding “door” that closes the slot, effectively transforming the bracket into a tube. 67 Another passive ligation design features a nickel-titanium alloy “C-clip” mechanism lateral to each of the mesial and distal tie-wings 72 ; an archwire that is snapped into the bracket-slot may remain passive in the lumens of the clips. The claimed benefit of these passive self-ligation systems is reduced friction with all wire sizes, resulting in faster tooth movement. 73 With the absence of a lingually directed force against the archwire, however, some critics argue that the inability to control torque could be a problem. 41 For this reason, passive self- ligating brackets are manufactured with a faciolingual slot-dimension as small as 0.027 inches, instead of the traditional 0.028 inches minimum. In orthodontics, friction arises when there is contact and a tendency for mesiodistal sliding of an archwire relative to the slot. When a small rectangular wire not completely filling the slot is engaged, some amount of 54
unconstrained rotation around the longitudinal axis of the wire can occur. If and when the occlusogingival clearance within the slot becomes zero, third-order rotational forces are created to be transmitted to the crown-attachment through direct contact with the slot. Moore, Harrington, and Rock 61 measured friction in two different brackets with predetermined tip and torque. The group discovered a significant increase in friction in the presence of active, third-order torque. Using an Instron testing machine, Sims and colleagues 44 also evaluated friction produced with wires sliding through bracket-slots positioned to input specific torque values. They reported that, with torsion, the self- ligating Activa bracket (‘A’ Company, San Diego, CA) showed consistently less resistance to sliding than the two conventionally ligated brackets. Apparently no studies have been published to date that compare friction across categories of self-ligating brackets when third-order positioning is controlled. The purpose of this study was to determine the effect of wire- slot torque on friction in 0.022-inch crown-attachment sets that included self-ligating brackets with a 0.019- x 0.025- inch stainless steel archwire engaged. The effect of the design of the various ligating mechanisms on kinetic 55
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 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: self-ligating bracket systems to ma
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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