Friction mechanics /certified fixed orthodontic courses by Indian dental academy

FRICTION
MECHANICS
www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education


FRICTION


It is a function of relative roughness of two
surfaces in contact.



Force that resists movement of one surface
past another and acts in direction opposite the
direction of movement.


CLASSIFICATION OF
RETRACTION MECHANICS
A] Based on wire configuration
Continuous arch mechanics
Segmented arch mechanics
B] Based on friction
Friction mechanics
Frictionless mechanics

C] Based on type of tooth movement
Tipping followed by uprighting
Translation
Based on mode of retraction
Cuspid retraction
En masse retraction
Based on Anchorage
Type A – Maximum Anchorage
Type B – Moderate Anchorage
Type C – Minimum Anchorage

INTRODUCTION
Two schools of thought of Retraction Mechanics
1.Seperate canine and incisor retraction
2.En masse retraction


Seperate canine and incisor retraction


En masse
Retraction


Sliding
Mechanics

Separate Canine
Retraction

Frictionless
Mechanics

En masse Space
closure


BIOMECHANICS OF SLIDING
MECHANICS


Friction plays an important role in sliding
space closure, hence the term ‘Friction
mechanics’.




E-link is the force component of the retraction
assembly and moment is produced by the
Archwire-bracket assembly




One moment rotates the tooth mesial out and other
causes the distal tipping of the crown.


The distal tipping contributes to the retraction by
causing binding of the arch wire, which in turn
produces moment that results in
distal root
movement.
WALKING MOVEMENT OF THE CANINE


WALKING MOVEMENT OF THE
CANINE

BINDING



As the tooth uprights, the moment decreases
until the wire no longer binds.



The crown then slides along the archwire
again distal crown tipping again causes
binding.



This process is repeated until the tooth is
retracted or the elastic force is dissipated.

MOMENT TO FORCE RATIO
DURING RETRACTION


The moment to force ratio is at its lowest during
the first few days after placement of E- chain
because the magnitude of force is at highest level.



As the teeth are retracted the moment to force ratio
improves because the elastic force dissipates and
the archwire bracket interaction due to crown
tipping produces a moment.



To optimize the use of sliding mechanics,
sufficient time must be allowed for the distal
rot movement to occur.



A common mistake is to change the elastic
chain too often, thus maintaining the high
force levels and moment to force ratio that
produces distal tipping only.


ADVANTAGES OF FRICTION
MECHANICS
1.

Complicated wire configuration is not
required

2.

Initial wire
consuming.

3.

Enhances patient comfort.

placement


is

less

time

DISADVANTAGES OF FRICTION
MECHANICS


Higher force levels.



Tendency to over activate elastic and spring
forces.


STEPS BEFORE RETRACTION
1.
2.
3.
4.
5.

Selection of the best bracket system
Proper bracket placement
Proper alignment of the teeth
Anchorage control
Retraction control


CANINE RETRACTION


Major cuspid retraction consists of controlled
tipping or translation of the canine when more
than 3mm of arch length per side is required.



Minor cuspid retraction consists of uncontrolled
tipping of the canine when 1-2 mm of arch length
per side is required.




It can be carried out with the help of lacebacks.


Minor cuspid retraction with
lacebacks




As the canine is
retracted the anterior
crowing unravels.

The lateral incisors
tend to move distally
due to the pull of
transeptal fibres.

CANINE RETRACTION WITH ‘J’
HOOK HEADGEAR


It involves extraoral anchorage so effective in
maximum anchorage cases



Involves use of headgear with a J hook
applying the force on the canine such that they
slide along the archwire.


EN MASSE SPACE CLOSURE
WITH SLIDING MECHANICS


In 1990s, a method of controlled space
closure was described using sliding
mechanics.



The MBT technique recommends following


ARCHWIRES


Rectangular .019/.025
steel wires with the .
022” slot.



This wire size has
good overbite control
while allowing free
sliding through the
buccal segment


ROLLER COASTER EFFECT


Clinical
example of
Roller Costar
Effect

SOLDERED HOOKS


0.7 brass hooks are preferred.



Soft SS 0.6 soldered hooks can be a useful
alternative.



The most common hook positions are 3638mm in Upper and 26mm in the Lower.


SOLDERED BRASS HOOK


ACTIVE TIEBACKS USING
ELASTOMERIC MODULES


Placement is not difficult.



Active tiebacks using elastomeric modules are
preferred for space closure.


Active tiebacks

Passive tiebacks


ACTIVE TIEBACKS

NiTi CLOSED COIL SPRINGS


ACTIVE TIEBACKS



1.
2.
3.
4.

ADVANTAGES
Convenient means of force application
DISADVANTAGES
Variation of efficiency of force delivery
High initial force levels
Degradation of force levels over a period of
time
Tendency to absorb moisture and accumulate
food debris and bacteria

NiTi COIL SPRINGS

1.

2.



ADVANTAGES
Efficient and relatively quick to close
extraction space owing to their continuous
force
No frequent activation required
DISADVANTAGES
Expensive

FORCE LEVELS


Active tiebacks are stretched their original size
during activation.



Without pre-stretching the force levels range
in between 200-300 gms.



If large spaces are to be closed NiTi coil
spring are used instead of Elastomeric module.

INHIBITORS OF SLIDING
MECHANICS


Inadequate leveling



When torque is being manifested in the
posterior segment



The ligature wire around the molar tube can
block the distal end of the wire

INHIBITORS OF SLIDING
MECHANICS


Any damage or compressed bracket binds with
the archwire and prevents sliding.



Soft tissue resistance due to its overgrowth in
extraction spaces.


PHYSICAL FACTORS
1. ARCH WIRE
 Material
 Cross sectional shape and size
 Surface texture
 Stiffness
2. LIGATION OF ARCHWIRE TO
BRACKET
 Ligature wires
 Elastomerics
 Method of ligation

PHYSICAL FACTORS
3. BRACKET
 Material
 Manufacturing process (cast or sintered SS)
 Slot width & depth
 Design of the bracket – Single / Double
width
 1st order ( in-out), 2nd order (angulations), 3 rd
order (inclinations) specifications.

PHYSICAL FACTORS
4. ORTHODONTIC APPLIANCE
 Inter-bracket distance
 Force levels
 Level of bracket slot between adjacent teeth


BIOLOGICAL FACTORS




Saliva
Plaque
Corrosion


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Friction mechanics /certified fixed orthodontic courses by Indian dental academy

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