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2. One of the most common methods of translating
a tooth orthodontically - sliding mechanics.
Mesiodistal tooth movement - by guiding a
tooth along a continuous arch wire with the use
of an orthodontic bracket.
Disadvantage - friction - resist the movement.
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3. Friction is defined as a force that retards or
resists the relative motion of two objects in
contact, and its direction is tangential to the
common boundary of the two surfaces in
contact.
Frictional force - 2 sliding surfaces α to the
force - surfaces are pressed together.
Ffr = u × F. The value of u (the coefficient of
friction)
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4. Static Frictional forces - smallest force
needed to start a motion of solid surfaces
with respect to each other.
Kinetic frictional force - force needed to
resist the sliding motion of one solid
object over another at a constant speed.
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6. Ligation of arch wire to bracket.
Ligature wires.
Elastomerics.
Bracket.
Material.
Slot width and depth.
First order bend (in-out).
Second order bend (angulation).
Third order bend (torque).
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8. Static frictional force = coefficient of static
friction x resultant normal force;
Kinetic frictional force = coefficient of
kinetic friction x resultant normal force.
The coefficients of static and kinetic
friction, generally having magnitudes
between zero and one,
depend upon -relative roughness of the
contacting surfaces.
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9. Prososki etal (AJO-1991) states that surface
roughness influences friction most directly
when
dry, unlubricated sliding occurs or when only
meager lubrication is present.
geometry of roughness,
orientation of roughness features, and
relative hardness of the two contacting surfaces.
Friction tends to be highest for very rough or
very smooth surfaces.
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10. Sliding mechanics- biologic tissue response
and tooth movement - applied forces -
overcome the friction at the bracket-wire
interface.
High levels of bracket-wire friction may
result in
binding of the bracket little or no tooth
movement.
binding of an anterior tooth under retraction
loss of anchorage.
The most desirable and ideal situation, - little or
no friction - b/w bracket and wire.
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11. Proffit etalconsiders frictional resistance in
orthodontic appliance to be multifactorial,
It is α force with which the contacting
surfaces are pressed together
Affected by the nature of the surface at the
interface
Independent of the apparent area of contact
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12. role of asperities (limited number of small spots at
the peak of surface irregularities) - contributing
factor.
These elevated areas carry the entire load between
two surfaces and may undergo plastic deformation
with appropriate force.
Applied load determines the true contact area.
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13. coefficient of friction is
α shear strength of the junction &
1/ α yield strength of the material.
The interlocking of large and pointed asperities or
‘plowing’ of asperities into opposing surfaces -
friction.
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14. Arch wire:
Material:
Garner et al (AJO-1986) –
found significantly larger frictional force with
beta-titanium and nitinol when compared with
stainless steel.
Differences in surface smoothness - account for
the differences in friction.
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17. Drescher et al - SEM study - between diverse wire
materials.
SS and Elgiloy - smooth surface texture,
NiTi, TMA, - extensive surface roughness.
Surface texture - friction magnitude in edgewise
mechanics.
Effective force has to increase by twofold
(stainless steel) to sixfold (TMA) to overcome
bracket-to-wire friction.
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18. Tidy DC - fixed appliance in vitro to simulate
tooth movement in a previously aligned arch.
Nitinol and TMA (beta-titanium) >frictional
forces -2x & 5x – of SS.
SS arch wires may be used in preference to
nitinol or TMA arch wires to reduce the friction
in sliding mechanics.
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20. Kapila et al (AJO- 1990)-
greater magnitude and more frequent variation in
frictional forces per unit distance of bracket travel
with NiTi and ß-Ti wires than with SS or Co-Cr
wires.
Higher mean frictional forces - NiTi and ß-Ti
wires.
surface roughness of these alloys > SS or Co-Cr in
SS brackets
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21. Archwire Dimension:
Tidy found that wire dimension and slot size had
little effect on friction.
Vaughan etal - The frictional forces with
rectangular wire than with round wire, and
wire size frictional force.
Pizzoni - friction occurring in sliding mechanics
as being influenced by the bracket design, wire
material and wire cross section.
He concluded that round wires have lesser
friction than rectangular wires,
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22. Kapila et al(AJO 1990) -
Stainless steel, Co-Cr, and ß-Ti wires ↑ bracket-
wire friction with increase in wire size.
Increase in size of NiTi wires - no significant
effect on - friction between bracket and wire – in
0.018 inch narrow single br..
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23. Surface properties:
Ryan et al- (AJO 1997) - effects of ion
implantation on the rate of tooth movement.
ion-implanted wires - > movement than their
untreated counterparts.
The ion-implantation process - stress fatigue
and hardness of the material the friction.
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24. Brackets:
Drescher et al -study found narrow brackets to
intensify friction by enhancing tipping
movements. This implies a preference for the use
of medium or wide brackets in arch-guided tooth
movement, particularly in cases in which
excessive mesiodistal tooth translation is required
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25. Andreasen and Quevodo, - study to evaluate the
frictional forces in the 0.022 X 0.028” edgewise
bracket system.
Multiple round and rectangular SS wires,
brackets of three different widths,
four bracket wire angulations.
Tipping the bracket &larger wires - friction,
Bracket width & wet and dry conditions were
found to be insignificant
both wet
and dry
conditions
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26. Tidy studied the effect of load, bracket width, slot
size, arch wire size, and material.
The forces acting on the surface of the tooth root
were simulated by a single equivalent force
acting at the center of resistance of the root. The
couple produced by the two-point contact with
the arch wire counters the moment of this force
about the arch wire.
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28. The movable bracket was fitted with a 10 mm
power arm - weights - hung –force acting at the
center of resistance of the tooth root.
The length of the power arm - distance from the
slot to the center of resistance of a typical canine
tooth.
The movable bracket was suspended from the load
cell of the testing machine, while the baseplate
moved downward with the crosshead on which it
was mounted.
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30. Friction α applied load and
1/ α bracket width.
The friction was greatest for narrow brackets.
Wide brackets and stainless steel arch wires may be
used in preference to nitinol or TMA arch wires to
reduce the friction in sliding mechanics.
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31. Kapila et al.- investigated –
Frictional properties of Stainless steel (SS), cobalt-
chromium (Co-Cr), nickel-titanium (NiTi), and β-
titanium (β -Ti) wires of several sizes were tested in
narrow single (0.050-inch), medium twin (0.130-
inch) and wide twin (0.180-inch) stainless steel
brackets in both 0.018 and 0.022-inch slots.
frictional force - wider brackets
Due to the higher force of ligation - the greater
stretching of elastic ligatures on wider brackets.
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32. Vaughan et al –
Overall friction of sintered stainless steel brackets
40% to 45% < conventional cast stainless steel
brackets.
Pratten et al- frictional resistance of ceramic and
SS brackets + SS and NiTi wire.
Ceramic brackets frictional resistance than SS
brackets when used in combination with either SS
or NiTi arch wires.
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33. Dickson etal- experimental polycrystalline
ceramic bracket with a SS insert and compared -
conventional & SS bracket.
The exptl. bracket - frictional resistance and the
ceramic bracket - 0˚ angulation.
No sig. diff. between the two ceramic brackets at
10˚,
frictional resistance than SS bracket.
Stainless Steel insert slot - experimental bracket -
behave more like a stainless steel bracket rather
than a conventional ceramic bracket.
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34. Madhav.M and Jyothindra Kumar compared the
frictional properties and debonding
characteristics of gold inserted slot Luxi™
bracket system and stainless steel inserted
Clarity™ bracket system and compared them
with stainless steel Gemini™ bracket.
Metal inserted ceramic brackets - frictional
properties as good as stainless steel brackets.
Luxi™ - least kinetic friction
Clarity™ bracket - highest value, of the three
bracket systems evaluated for both 50 gms and
100 gms load.
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35. Ligation.
Edwards et al- ligation techniques - on the static
frictional resistance of stainless steel brackets and
archwires - dry and wet conditions.
No significant differences in frictional resistance
were found between conventionally tied
elastomeric modules and stainless steel ligatures.
Teflon-coated ligatures - lowest frictional forces.
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36. David etal- ( AO – 95) - static frictional resistances
between
Teflon- coated stainless steel and clear elastomeric
ligatures –with
SS, polycrystalline ceramic and single crystal ceramic
0.022-inch slot brackets,
SS and NiTi archwires, 0.018 inch and 0.016 × 0.022
inch.
Friction was measured in the dry state at bracket-
archwire angulations of 0, 5, 10, and 15 degrees.
Teflon-coated SS ligatures - friction than
elastomeric ligatures regardless of bracket type,
archwire type, or bracket-archwire angulation.
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37. Self ligation.
SPEED Appliance-
Spring-loaded,
Precision, Edgewise,
Energy, and Delivery,
all of which describe
features of the design.
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38. Berger (AJO – 1990) -
↓ force - required to move rectangular steel or
round braided arch wires - a standard distance -
self-ligation SPEED bracket < the elastomeric and
the steel-tie ligated "A"-Company and American
Orthodontics bracket systems.
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39. Activa brackets -fully
programmed
preadjusted brackets
that were introduced in
1986- Irwin Pletcher.
The arch wire -retained
- resilient clip -
retaining groove
gingival to the arch
wire.
The friction is <
elastomeric rings and
conventional brackets.www.indiandentalacademy.com
40. Shivapuja etal (AJO1994) –
Compared three self-ligating bracket systems to
conventional SS brackets and ceramic brackets +
polyurethane elastomeric and SS tie wire ligation.
Self-ligating bracket systems - frictional
resistance, chairtime for arch wire removal and
insertion.
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42. Saliva.
Stannard et al (AJO 1986)- compared the friction
of wires under dry and wet conditions.
artificial saliva - the coefficients of friction for
stainless steel, beta-titanium, and nickel-titanium
compared to dry conditions.
Thought to occur from atomic attraction
among ionic species.
Water and other polar liquids - adhesion or
attraction among polar materials and friction.
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43. Baker et al – (AJO 1987)- of force necessary
to move the teeth in a saliva medium as
compared to a dry medium.
Kusy et al –(AO 1991) - coefficients of friction
in the dry and wet (saliva) environment for
stainless steel, cobalt-chromium, nickel titanium,
and beta-titanium wires against either stainless
steel or polycrystalline alumina brackets.
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44. In the dry state - coefficients of friction -
stainless steel combinations
beta-titanium wire combinations.
In the wet state, -
stainless steel combinations - 0.05 over the dry
state.
beta titanium - 50% of the values in the dry
state.
Attributed to the adhesive and lubricious behavior
of the saliva.
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45. Tselepsis et al-(AJO 1994)- investigated frictional
resistance between brackets and arch wires for –
arch wire, brackets, angulation, and lubrication.
Lubrication significantly reduced the frictional
resistance (up to 60.5%) for both 0° and 10°
bracket-to-arch wire angulation
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46. Conclusion.
Friction has been a problem for orthodontists
ever. Many efforts have been made to
increase the efficiency of tooth moving
mechanics by reducing or eliminating the
friction, but to marginal success.
Orthodontist’s dream would be to move the
teeth in a frictionless system, effortlessly &
efficiently.
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