This document discusses the role of friction in orthodontic sliding mechanics. It begins by introducing friction and its impact on tooth movement efficiency. It then explores the physics of friction and the variables that affect friction during orthodontic treatment, including properties of archwires, brackets, ligation methods, and biological factors. Materials that have been introduced to reduce friction are also mentioned. The document provides details on factors influencing friction and the formulas used to calculate frictional forces.

1. JERUN JOSE
3RD MDS
DEPT. OF ORTHODONTICS
ROLE OF FRICTION IN SLIDING
MECHANICS

2. CONTENTS
 INTRODUCTION
 PHYSICS
 VARIABLES AFFECTING FRICTION
 RECENTLY INTRODUCED MATERIALS TO
REDUCE FRICTION
 CONCLUSION
 REFERENCE

3. INTRODUCTION
 Friction is the force that resists against the
movement of one surface in relation to another
and that acts on the opposite direction of the
desired movement
 The friction present during orthodontic sliding
mechanics represents a clinical challenge to the
orthodontists because high levels of friction may
reduce the effectiveness of the mechanics,
decrease tooth movement efficiency and further

4. Friction and sliding mechanics
 Orthodontic tooth movement during space
closure may be performed with two different types
of mechanics. The first is the “Segmented Arch
Mechanics” (SAM), which consists in bending
loops on stainless steel (SS) or titanium
molybdenum (TMA) wires.
 SAM is also called “frictionless mechanics”
because the brackets and tubes do not slide
along the archwire.

5.  The other space closure mechanics used in
Orthodontics is the Sliding Mechanics (SM),
which involves the actual sliding of brackets and
tubes along the wire.

6.  When two surfaces slide one over the other, two
force components are created: Frictional Force
(FF), tangent to the Contacting Surface (CS) and
Normal Force (N), perpendicular to the FF and to
the CSMariana Ribeiro Pacheco, Dental Press J Orthod. 2012

7.  Kusy and Whitley divided friction into three
components: (1) classic friction, static and kinetic,
due to contact of the wire with the bracket
surface; (2) binding, created when the tooth tips
or the wire flexes so that there is contact between
the wire and the corners of the bracket; and (3)
notching, when permanent deformation of the
wire occurs at the wire-bracket corner interface
Kusy RP, Whitley JQ. Influence of archwire and bracket dimensions on
sliding mechanics: derivations and determinations of the critical contact
angles for binding. Eur J Orthod. 1999

8.  Only classical friction is imporatnt because
binding and notching are non existent.
 There are two types of FF: Static Friction (SF)
and Kinetic Friction (KF)

9.  SF is the smallest force needed to initiate a
movement between two solid bodies that were
static in relation to each other.
 Kinetic friction is the force that resists against the
sliding movement of a solid object against
another at a constant speed.

10.  SF is always greater than KF since it is harder to
change a body from its inertial situation than to
maintain it moving.
 When an orthodontist tries to slide a tooth along the
archwire, the tooth is subjected to an alternate
movement of tipping and uprighting, thus moving in a
sequential number of small and consecutive
movements.
 Therefore, SF is more important than KF during space

11.  The application of the retraction force during
space closure with SM generates a moment on
the tooth’s crown that causes an initial crown
tipping and later root uprighting.
 This moment is determined by the location of the
point of force application in relation to the center
of resistance of the tooth or group of teeth.

12.  A number of successive crown tippings and root
uprightings take place in the same plane of space
towards the direction of the applied force.
 When the tooth inclines, the orthodontic wire
binds against the edge of the bracket slot
(“binding effect”), increasing friction and further
restricting OTM.

13.  Greater frictional forces mean that an increased
number of tipping and uprighting must take place.
 Thus, friction should be minimized to achieve a
more efficient sliding movement of the tooth along
the arch wire

14.  When the orthodontic wire slides through the
bracket slot and the tubes, some resistance to
sliding always takes place at the bracket/wire
interface.
 This phenomenon is observed during leveling and
alignment, space closure and even during torque
expression at the end of treatment

15.  A percentage of the orthodontic force applied to
the teeth is lost as static friction and the rest is
transferred to the tooth and its periodontium,
generating the actual OTM.
 Kojima e Fukui evaluated the influence of friction
on OTM using the finite element method and
reported that approximately 60% of the
orthodontic force applied to a tooth is lost as SF.

16.  Thus, the biological tissue response to the
mechanical stimulus takes place only if the force
is strong enough to overcome SF
 Therefore, higher levels of friction during sliding
mechanics require the application of higher
orthodontic forces and may compromise the
amount of OTM obtained as well as complicate
anchorage control.

18. Physics -friction
 In the late 15th century, Leonardo Da Vinci
proposed the two basic laws of sliding friction.
 Frictional resistance to sliding is,
1. Proportional to the load
2. Independent of the area of the sliding interfaces

19.  Amontons-Coulomb Laws
 Experimental verification by Amontons and Coulomb, in
1699 and 1781, respectively
 Amontons' First Law: The force of friction is directly
proportional to the applied load.
 Amontons' Second Law: The force of friction is
independent of the apparent area of contact.
 Coulomb's Law of Friction: Kinetic friction is independent
of the sliding velocity

20.  Coulomb’s friction law was not applicable at an
extremely low sliding velocity.
 the frictional forces between SS brackets and
wires increased with the decrease of sliding
velocity
Angle Orthod. 2014

21.  Static friction (occurring instantaneously up to the
onset of sliding) and kinetic friction (occurring
continuously after the onset of sliding)

23.  static frictional resistance (fs) is equal to the normal
force or load (F) multiplied by a coefficient of static
friction
fs=µs× F
 The kinetic frictional resistance is equal to the normal force
or load (F) multiplied by a coefficient of kinetic friction
fk = µk × F

24. The classic Amontons-Coulomb laws relate static
and kinetic friction as follows:
 µs and µk are independent of F and ∑0
 µs and µk are materials dependent; and
 usually µk< µs

26. Bowden-Tabor Microscopic Interpretation
Schematic depiction of a variety of asperity configurations

27. Contributions of Bowden and Tabor
 1. The effective area of contact ∑ eff between
solids is independent of the nominal surface area
∑0, and is determined only by normal force F
(load)
 2. A microscopic consideration of dry friction
accounts for shearing of interlocking and/or
adhered asperities

28.  3. The elastic-plastic properties of localized point
contacts between microscopically irregular
surfaces are a key feature of dry friction

29. Static Coefficient as a Function of
Time
 the static coefficient of friction varies as a
function of increasing time t before the onset of
sliding.
 The observation is that the longer a mass M is at
rest on a flat surface S (or an archwire at rest on
a bracket) the greater the resistance to pulling
force f parallel to the contact surface of nominal
area ∑0.

30.  When plastic deformation occurs at the level of
the softer asperities, the frictional force f becomes
a function of shear stress localized to
point contacts among surface asperities of mass
M and surface S.
 So frictional force

31. Kinetic Coefficient as a Function
of Velocity
 Constancy of the kinetic frictional coefficient k is
dependent on maintenance of a steady sliding
velocity VC
 Different materials exhibit unique kinetic frictional
characteristics as a function of velocity {ie, µk (V)}.

33. The Stick-Slip Phenomenon
 A single stick-slip cycle involves a stick state
associated with elastic loading of the system,
followed by a sudden slip corresponding to stress
relaxation

34.  Stick-slip motion, as observed over a broad
velocity range in frictional sliding, can potentiate
consequences resulting in noise (chatter), energy
loss (friction), surface damage (wear), and
component failure (breakage).

35. Formula for frictional force
 The coefficient of friction at the archwire-bracket
interface was calculated using the appropriate
formula,
where P is frictional resistance, F = equivalent force
acting at a distance,W= bracket slot width, h = 12
mm, and µ= coefficient of friction.
Tidy DC. Frictional forces in fixed appliances. Am J Orthod Dentofacial Ortho
1989;54:249–254

36. Variables influencing Friction
during OTM
 Mechanical/Physical
 Biological
Friction: An Overview
P. Emile Rossouw, SEMINARS IN
ORTHODONTICS-2003

37. 1.Physical/mechanical factors
i) Archwire properties:
a) material
b) cross sectional shape/size
c) surface texture
d) stiffness

38. ii) Bracket to archwire ligation
a) ligature wires
b) elastomerics
c) method of ligation.

39. iii) Bracket properties:
a) Material
b) surface treatment
c) manufacturing process
d) slot width and depth
e) bracket design
f) bracket prescription (first-order/in-out;second-
order/toe-in; third-order/torque).

40. iv) orthodontic appliances:
a) interbracket distance
b) level of bracket slots between teeth
c) forces applied for retraction

41. 2. Biological factors such as:
a) Saliva
b) Plaque
c) acquired pellicle
d) Corrosion
e) food particles

42. Physical /mechanical factors
Bracket properties
a) Material
 Metal brackets present lower friction coefficients
than ceramic and plastic brackets and they are
considered the golden standard to perform sliding
mechanics
 Plastic brackets showed lower values of friction
than polycrystalline ceramic brackets

43.  At high ligation forces (500 g), the
monocrystalline brackets had the highest level of
friction whereas at lower levels there was no
difference in the friction levels when compared
with the polycrystalline brackets

44.  Omana and coworkers found difference in
crystalline structure did not produce any
significant reduction in friction, moreover, they
also found injection molded ceramic brackets had
less friction than other ceramic brackets.
Omana HM, Moore RN, Bagby MD. Frictional properties of metal and
ceramic brackets. J Clin Orthod. 1992

45.  The insertion of a metal slot in ceramic brackets
has showed relatively good success to reduce the
levels of SF on this type of esthetic orthodontic
brackets.
 Ceramic brackets with metal slots did show lower
levels of SF than pure ceramic brackets

46.  Their levels of SF remained higher than those
registered with metal brackets
 This difference may be due to the different
ceramic and metal expansion coefficients, or to
the presence of a gap between the ceramic
bracket body and the metal slot

47. Bracket Width and Interbracket Width
 Wide brackets demonstrate increased friction at
small second order tip, whereas narrow brackets
do not bind until twenty degrees of tip.
 Greater interbracket width allows the longer
lengths of wire between brackets larger amounts
of deflection, thus greater flexibility

48.  Frank and Nikolai found interbracket distance to
have little effect on frictional resistance.

49. Arch wire properties
 In general, increasing wire size or cross-sectional
shape (round or rectangular) for a constant
bracket size increased the frictional resistance at
binding and nonbinding angulations.

50.  Cacciafesta et al evaluated the amount of friction
related to the most commonly alloys used in
orthodontic archwire manufacture: Stainless steel
(SS), nickel-titanium (NiTi) and TMA. 0.016-in,
0.017 x 0.025-in and 0.019 x 0.025-in wires were
tested
 The results showed that SF increases when
thicker wires of the same alloy were tested
 TMA wires presented higher frictional resistance
than SS and NiTi wires of same diameterEvaluation of friction of stainless steel and esthetic self-ligating
brackets in various bracket archwire combinations. Am J Orthod
Dentofacial Orthop. 2003;

51.  In sliding mechanics, stainless steel wires
generally showed the least friction followed by
cobalt- chromium (Elgiloy), nickel-titanium, and
beta-titanium (TMA).
 Friction appears to depend primarily on the
vertical dimension of the wire, thus the frictional
resistance of a 0.016 inch wire is not much
different than a 0.016 * 0.022 inch wire
Friction: Validation of Manufacturer’s Claim
Kevin Mendes and P. Emile Rossouw, SEMINARS IN
ORTHODONTICS-2003

52. Bracket to archwire ligation
 Steel or elastic ligatures may contribute differently
to friction increase depending on how they are
used.
 Steel ligatures influence resistance to sliding
according to the intensity of the ligation.
 They can generate higher amounts of SF than
elastic ligatures if they are tightly used.

53.  if they are loosely inserted, small gaps between
the wire and the bracket slot remain present and
smaller SF values may be registered.
 Loosely tied stainless steel ligatures generally
produced negligible friction in both dry and wet
situations

54.  The amount of SF may also vary depending on
the type of elastic ligature used to ligate the
archwire to the brackets.
 Hain et al reported that elastic ligatures with
decreased surface roughness generated lower
amounts of friction
Hain M, Dhopatkar A, Rock P. The effect of ligation method on friction in
sliding mechanics. AJODO 2003

55.  Elastic ligatures tied as the number 8
generated increased levels of SF with all ligatures
tested.

56.  The use of small and medium elastomeric
ligatures determines a 13–17% decrease in static
friction compared with large ligatures.
 Silicone- lubricated modules can reduce static
friction by 23–34% with respect to the small and
medium nonlubricated elastomeric ligatures and
by 36–43% compared with nonlubricated large
Angle Orthod -2005

57. Biological factors
 When human saliva is present, frictional forces and
coefficients may increase, decrease, or not change
depending on the arch wire alloy tested.
 The greatest differences between dry and wet states
occurred with TMA archwire, in which the kinetic
coefficients of friction in the wet state were reduced to
50% of the values in the dry state.
 At this point they were comparable to nickel-titanium
but still higher than stainless steelAsian Journal of Oral Health & Allied Sciences - Volume 1, Issue 1, Jan-
Mar 2011

58.  Saliva can cause increase in friction in elastomeric
modules, but does not cause any significant
difference in friction when stainless steel or Teflon
coated stainless steel ligatures are used.
 Baty et al., has noted that when extended and
exposed to an oral environment, elastomeric
materials absorb water and saliva, permanently stain,
and suffer a breakdown of internal bonds that leads to
permanent deformation.
 They also experience a rapid loss of force due to
stress relaxation, resulting in a gradual loss of
effectiveness.
Aparna et al,Effects of Different Ligature Materials on Friction in
Sliding Mechanics, Journal of International Oral Health 2015

60.  Studies have shown that debris accumulation on
the wire surface increases roughness and
generates higher levels of friction.
 Recent studies have demonstrated that self-
ligating brackets favor a higher colonization of
Streptococcus mutans and accumulate more
biofilm compared with conventional brackets with
steel wire ligation

61.  Self-ligating and conventional brackets showed a
significant increase in debris and friction after
intraoral exposure for 8 weeks.
 Accumulation of debris was higher for self-
ligating brackets.
Debris and friction of self-ligating and conventional orthodontic brackets
after clinical use
Angle orthodontist-2015

62. Orthodontic appliance
Bracket prescription
 Increasing torque when using SLBs causes an
increase in friction, since contact between the
bracket slot wall and the wire edge becomes
greater; the design of brackets influences static
friction
Angle Orthod. 2014;

63.  With increase in tip friction also increase
Ajodo -2004

64. Manufacturing process

65.  Evaluated surface rougness

67.  The correspondence between all three methods
is in the range of 20 per cent, except for the wires
SSA and NSA(GAC sentalloy,neosentalloy )
 The roughness of these two products is affected
by the application temperature, which alters their
microstructure and, thus, their external
topography
Christoph et al, Europian journal of orthodontics-1998

68. Sliding Velocity
 The friction of cobalt chromium wire decreased
with increasing sliding velocity
 The coefficient of friction increased for Beta-
titanium (TMA) with increasing sliding velocity
possibly because of “cold welding.
Seminars in orthod-2003

69. Recently introduced orthodontic
materials to reduce friction
 The main technological innovations that have
been tried to create low-friction orthodontic
materials could be divided in design innovations
and surface treatments
 Among the various attempts to change the
bracket design to reduce friction, the use of self-
ligating brackets (SLB) has been the most tested.

70.  SLB present a clip incorporated to its buccal
surface that locks the wire within the slot and
transforms the bracket in a tube-like device, thus
eliminating the need for elastic or steel ligatures.

72.  There were no significant differences between the
amounts of friction registered when passive and
active SLB where tested with round wires
 However, when heavier rectangular wires were
implemented active SLB showed more resistance
to sliding than passive SLB
Pacheco MR, Oliveira DD, Smith-Neto P, Jansen WC. Evaluation of friction in
selfligating brackets subjected to sliding mechanics: an in vitro study. Dental
Press J Orthod. -2011

73.  There were no evidence to support that SLB
brackets generate significantly less friction than
conventional brackets in the following clinical
situations: (1) when rectangular stainless steel
wires were used; (2) with marked dental tipping or
torquing and (3) when treating complex
malocclusions.Ehsani et al .Frictional resistance in selfligating orthodontic
brackets and conventionally ligated brackets. A systematic review.
Angle Orthod. 2009

74. Ligature material and design
 A polyurethane elastic ligature-SLIDE
 This ligature combined to a conventional
bracket forms a tube-like structure.
 significant lower resistance to sliding with the
Slide® ligature than with conventional elastic
ligatures
Baccetti T, Franchi L. Friction produced by types of elastomeric
ligatures in treatment mechanics with the preadjusted appliance.
Angle Orthod. 2006

75. Metafasix® (Super Slick Elastic Modules)
 Consisting of a water resistant polymeric coating,
thus making the elastic ligature extremely slippery
in the presence of saliva.
 Hain et al reported approximately 60% of friction
reduction when these elastic ligatures were used
Hain M, Dhopatkar A, Rock P. The effect of ligation method on
friction in sliding mechanics. Am J Orthod Dentofacial Orthop.
2003

76. Surafce coated wires/ion implantation
 Burstone and Farzin-Nia showed that ion implantation
increases archwire hardness, reduces flexibility, and
improves surface finish
 Nitrogen Ion implanted β-titanium orthodontic archwires
(honeydew and purple).
 The ion implanted TMA has also been known as “low-
friction” and is offered in different colors
Youssef et al .Titanium Nitride and
Nitrogen Ion Implanted Coated Dental
Materials .
Coatings -2012

77.  Ion implantation produces no sharp interface.
 Does not alter wire dimension, mechanical
properties
 Depth, distribution of implantaion can be
controlled by varying the ion dosage and energy.
Burstone CJ, Farzin-Nia F. Production of low friction
and coloured TMA by Ion implantation. JCO. 1995

78. Bioforce iongurad
 NiTi wire on which 3-micron nitrogen coating that
is produced by ion bombardment of the wire
surface.
 Reduced friction
Viazis A D; Atlas of advanced
orthodontics

80. Before sliding
After
Uncoated TMA Purple Honey dew
Comparative Evaluation of Frictional Properties, Load Deflection Rate and
Surface Characteristics of Different Coloured TMA Archwires - An Invitro Study,
JCDR-2015

81.  Diamond-like carbon (DLC) surface coating of SS
and NiTi orthodontic wires have been suggested
to decrease static frictional force
 These ions were incorporated to the surface of
wire during the manufacturing process, increasing
the wire hardness and significantly reducing SF
when compared to the conventional orthodontic
wiresMuguruma T, Iijima M, Brantley WA, Mizoguchi I. Effects of a diamond-
like carbon coating on the frictional properties of orthodontic wires.
Angle Orthod. 2011

82.  WC/C (tungsten carbide)coated archwires with
their thin nature and smooth surface showed low
frictional properties when compared with
uncoated and TiAlN coated archwires making it
ideal for space closure stage of orthodontic
mechanics, when sliding mechanics is used.
Angle orthodontist-
2012

83. CONCLUSION
 Friction cannot be eliminated from materials.
Therefore, the clinician should be aware of the
characteristics of the orthodontic appliance that
contribute to friction during sliding mechanics and
the extent of the amount of force expected to be
lost to friction. This will help allow efficient
reproducible results to be achieved.

84. REFERENCES
 Mariana Ribeiro Pacheco, Dental Press J Orthod.
2012
 Kusy RP, Whitley JQ. Influence of archwire and
bracket dimensions on sliding mechanics:
derivations and determinations of the critical contact
angles for binding. Eur J Orthod. 1999
 Friction: An Overview P. Emile Rossouw,
SEMINARS IN ORTHODONTICS-2003

85.  Omana HM, Moore RN, Bagby MD. Frictional
properties of metal and ceramic brackets. J Clin
Orthod. 1992
 Evaluation of friction of stainless steel and
esthetic self-ligating brackets in various bracket
archwire combinations. Am J Orthod Dentofacial
Orthop. 2003;
 Hain M, Dhopatkar A, Rock P. The effect of
ligation method on friction in sliding mechanics.

86.  Asian Journal of Oral Health & Allied Sciences -
Volume 1, Issue 1, Jan-Mar 2011
 Effects of Different Ligature Materials on Friction
in Sliding Mechanics, Journal of International Oral
Health 2015
 Debris and friction of self-ligating and
conventional orthodontic brackets after clinical
use .Angle orthodontist-2015

87.  Christoph et al, Europian journal of orthodontics-1998
 Pacheco MR, Oliveira DD, Smith-Neto P, Jansen WC.
Evaluation of friction in selfligating brackets subjected
to sliding mechanics: an in vitro study. Dental Press J
Orthod. -2011
 Ehsani et al .Frictional resistance in selfligating
orthodontic brackets and conventionally ligated
brackets. A systematic review. Angle Orthod. 2009

88.  Baccetti T, Franchi L. Friction produced by types of
elastomeric ligatures in treatment mechanics with the
preadjusted appliance. Angle Orthod. 2006
 Hain M, Dhopatkar A, Rock P. The effect of ligation
method on friction in sliding mechanics. Am J Orthod
Dentofacial Orthop. 2003
 Youssef et al .Titanium Nitride and Nitrogen Ion
Implanted Coated Dental Materials .Coatings -2012

89.  Burstone CJ, Farzin-Nia F. Production of low friction
and coloured TMA by Ion implantation. JCO. 1995
 Comparative Evaluation of Frictional Properties, Load
Deflection Rate and Surface Characteristics of
Different Coloured TMA Archwires - An Invitro Study,
JCDR-2015
 Muguruma T, Iijima M, Brantley WA, Mizoguchi I.
Effects of a diamond-like carbon coating on the
frictional properties of orthodontic wires. Angle
Orthod. 2011

90.  Viazis A D; Atlas of advanced orthodontics
 Krishnan V, Ravikumar KK, Sukumaran K, Kumar KJ.
Invitro evaluation of physical vapor deposition coated
beta titanium orthodontic archwires. Angle Orthod.
2012
 Yumi Yanase; Hideki Ioi; Masato Nishioka; Ichiro
Takahashi Effects of sliding velocity on friction An in
vitro study at extremely low sliding velocity
approximating orthodontic tooth movement.AO-2014

91.  Baker KL, Nieberg LG, Weimer AD, Hanna M.
Frictional changes in force values caused by
saliva substitution. Am J Orthod Dentofacial
Orthop 1987;91(4):316-20
 Tidy DC. Frictional forces in fixed appliances. Am
J Orthod Dentofacial Orthop. 1989;54:249–254