Friction – etiology & management in straight wire technique /certified fixed orthodontic courses by Indian dental academy

Friction –
Etiology & Management
in SWA

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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.

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)

 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.

Several variables - directly or indirectly
contribute - friction – b/w - bracket & wire;
They are:
 Arch wire.
 Material.
 Cross-sectional shape/size.
 Surface texture.
 Stiffness.


 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).


 Orthodontic appliance.
 Interbracket distance.
 Level of bracket slots between adjacent teeth.
 Forces applied for retraction.
 Intraoral variable.





Saliva.
Plaque.
Acquired pellicle.
Corrosion.


 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.


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.

 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.

 Proffit etal considers 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

 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.

 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.

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.


SEM - SS

NiTi

Beta - Titanium


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.


 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.


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


 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,

 Kapila et al(AJO 1990) -

Stainless steel, Co-Cr, and ß-Ti wires ↑ bracketwire 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..


 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.

 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


 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.

both wet
and dry
conditions

 Tipping the bracket &larger wires -  friction,
 Bracket width & wet and dry conditions were

found to be insignificant


 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.


 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.


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.


 Kapila et al.- investigated –
 Frictional properties of Stainless steel (SS), cobalt-

chromium (Co-Cr), nickel-titanium (NiTi), and βtitanium (β -Ti) wires of several sizes were tested in
narrow single (0.050-inch), medium twin (0.130inch) 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.

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.


 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.

 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.

 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.

 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.

 Self ligation.
SPEED ApplianceSpring-loaded,
Precision, Edgewise,
Energy, and Delivery,
all of which describe
features of the design.


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.


 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.


 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.


 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.

 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.


 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.

 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

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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