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INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

www.indiandeantalacademy.com
Orthodontic force
systems

www.indiandeantalacademy.com
Orthodontic force systems
BIOLOGY +MECHANICS =
BIOMECHANICS

www.indiandeantalacademy.com
Biomechanical concepts
Forces
Moments
Couples
Moment-to-Force ratios

www.indiandeantalacademy.com
Force
an act upon a body that changes or tends to
change the state of rest or the motion of that
body
Vectors , having bot...
Force
Point of application
Center of Mass
Center of Gravity
Center of Resistance

Each body has a point in its mass,
which...
Point of application of force in
relation to center of mass
Tipping

Force passing above or below the
center of mass of th...
Point of application of force in
relation to center of mass
Translation

Force passing through the center of
mass of of th...
Point of application of force in
relation to center of mass
Center of Resistance
Point at which the resistance to tooth mo...
Moments
Moment of the
force
Force applied at any
point other than
through the center of
resistance,in addition
to moving t...
Factors controlling the
moment

M=F x d
Either increasing the magnitude of the force
or applying the same force even furth...
Type of tooth movement

A-Uncontrolled tipping
B-Controlled tipping
C-Torque
D-translation or bodily movement
Center of re...
Couple
Moment of couple
Two forces equal in
magnitude and
opposite in direction
at a distance
Additive/Subtractive
A coupl...
Couple – Clinical point
We can apply couple
only on the exposed
part of the tooth
Depending on the plane
in which the coup...
Tooth movement
Equivalent force systems
Helps to predict the type of
tooth movement that will
occur with the appliance
act...
Center of resistance &center
of rotation
Point around which the
tooth rotates is called the
center of rotation

Can be at ...
Equivalent force system
cont…

the resulting force system describes the expected
tooth movement
by determining the equival...
Moment-to-Force ratio
The ratio of the counter-balancing moment produced
to the net force that is applied to a tooth will
...
Moment-to-Force ratio
Translation or bodily movement

www.indiandeantalacademy.com
Tooth movement
Thus by changing the ratio of the moment from the
applied couple(counter-balancing moment) to the force
app...
Tooth movement cont……
Controlled tipping
 M/F RATIO =7:1
 Center of rotation is at the
apex of the tooth
Translation
M/...
Tooth movement cont……
Root movement
 M/F RATIO = 13:1
 Center of rotation is at the
crown of the tooth and only
root mov...
Predicting orthodontic force
systems

To fully understand the response to
appliance activation the displacement at one
end...
Predicting orthodontic force
systems
Static equilibrium

 Physical laws of statics are governed by

Newtons laws of motio...
Predicting orthodontic force
systems
Static equilibrium cont…

Mesiodistal,buccolingual and
extrusion-intrusion forces in ...
Predicting orthodontic force
systems
Force system from intrusion arch in
equilibrium

www.indiandeantalacademy.com
Predicting orthodontic force
systems of unequal moments result in
The application
more complex force systems,and may occur...
Biomechanical classification
of orthodontic appliances
Equal and opposite force systems
One couple force systems
Two coupl...
Determinate Vs. Indeterminate
force systems
Determinate force systems
• moments and forces can readily be discerned
• E.g…...
Biomechanical classification
of orthodontic appliances
No couple
appliance system
• e.g..elastic band
stretched b/w two
po...
Biomechanical classification
of orthodontic appliances
One couple appliance system

• One end of the appliance
experiences...
One couple appliance system
Cantilever spring

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One couple appliance system
Auxiliary intrusion/extrusion arches

www.indiandeantalacademy.com
Two couple appliance system
Both ends of the appliance are engaged into
attachments(brackets or tubes).A couple is
thus ge...
Two couple appliance system
Force system
depends on wirebracket geometry

www.indiandeantalacademy.com
Two couple appliance system
Straight segment of
wire in misaligned
brackets

www.indiandeantalacademy.com
Two couple appliance system
“V” bend principle

www.indiandeantalacademy.com
Two couple appliance system
2x6 appliance can be used for molar
control

www.indiandeantalacademy.com
Two couple appliance system
Lingual arches as two couple system

www.indiandeantalacademy.com
How to predict?

It is sometimes beneficial not to
engage a straight wire into all of
the teeth in an arch

www.indiandean...
Conclusion
the choice of appliances and technique
used by practitioners varies radically among
individuals, but the fundam...
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandeantalacademy.com
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Ortho force systems /certified fixed orthodontic courses by Indian dental academy


The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078

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Ortho force systems /certified fixed orthodontic courses by Indian dental academy

  1. 1. www.indiandeantalacademy.com
  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandeantalacademy.com
  3. 3. Orthodontic force systems www.indiandeantalacademy.com
  4. 4. Orthodontic force systems BIOLOGY +MECHANICS = BIOMECHANICS www.indiandeantalacademy.com
  5. 5. Biomechanical concepts Forces Moments Couples Moment-to-Force ratios www.indiandeantalacademy.com
  6. 6. Force an act upon a body that changes or tends to change the state of rest or the motion of that body Vectors , having both magnitude and direction Magnitude light heavy Direction Pull Push www.indiandeantalacademy.com
  7. 7. Force Point of application Center of Mass Center of Gravity Center of Resistance Each body has a point in its mass, which behaves as if the whole mass is concentrated at that single point www.indiandeantalacademy.com
  8. 8. Point of application of force in relation to center of mass Tipping Force passing above or below the center of mass of the pencil www.indiandeantalacademy.com
  9. 9. Point of application of force in relation to center of mass Translation Force passing through the center of mass of of the pencil www.indiandeantalacademy.com
  10. 10. Point of application of force in relation to center of mass Center of Resistance Point at which the resistance to tooth movement is concentrated Depends on root length no. of roots Alv. bone support www.indiandeantalacademy.com
  11. 11. Moments Moment of the force Force applied at any point other than through the center of resistance,in addition to moving the center of resistance would create a moment “Rotation”,“Tipping”or Torquing www.indiandeantalacademy.com
  12. 12. Factors controlling the moment M=F x d Either increasing the magnitude of the force or applying the same force even further from the center of resistance increases the tendency for rotation www.indiandeantalacademy.com
  13. 13. Type of tooth movement A-Uncontrolled tipping B-Controlled tipping C-Torque D-translation or bodily movement Center of resistance of a tooth does not change ,only www.indiandeantalacademy.com the center of rotation changes
  14. 14. Couple Moment of couple Two forces equal in magnitude and opposite in direction at a distance Additive/Subtractive A couple applies a pure moment to a tooth www.indiandeantalacademy.com
  15. 15. Couple – Clinical point We can apply couple only on the exposed part of the tooth Depending on the plane in which the couple is acting, this moment has been called “ Rotation”(first order), “Tipping”(second order), “Torque”(third order) www.indiandeantalacademy.com
  16. 16. Tooth movement Equivalent force systems Helps to predict the type of tooth movement that will occur with the appliance activation by determining the force system at the center of resistance forces are replaced at the center of resistance; moment of force generated at the bracket is also placed at the center of resistance; Third.the applied moment is placed at the COR. Finally the applied moment and the moment of force are added to determine the net moment www.indiandeantalacademy.com
  17. 17. Center of resistance &center of rotation Point around which the tooth rotates is called the center of rotation Can be at the center of res.,at the root apex or at infinity www.indiandeantalacademy.com
  18. 18. Equivalent force system cont… the resulting force system describes the expected tooth movement by determining the equivalent force systems,it becomes apparent that achieving desired and predictable tooth movement requires an awareness of both applied forces and moments The relationship between the applied force system and the type of tooth movement can be described by the Moment-to-Force ratio www.indiandeantalacademy.com
  19. 19. Moment-to-Force ratio The ratio of the counter-balancing moment produced to the net force that is applied to a tooth will determine the type of tooth movement that will occur www.indiandeantalacademy.com
  20. 20. Moment-to-Force ratio Translation or bodily movement www.indiandeantalacademy.com
  21. 21. Tooth movement Thus by changing the ratio of the moment from the applied couple(counter-balancing moment) to the force applied, the center of rotation of the tooth can be varied to produce the type of tooth movement desired Uncontrolled tipping  M/F RATIO=0  Center of rotation just apical to center of rotation www.indiandeantalacademy.com
  22. 22. Tooth movement cont…… Controlled tipping  M/F RATIO =7:1  Center of rotation is at the apex of the tooth Translation M/F RATIO=10:1 the center of rotation is at infinity because no rotation occurs www.indiandeantalacademy.com
  23. 23. Tooth movement cont…… Root movement  M/F RATIO = 13:1  Center of rotation is at the crown of the tooth and only root movement occurs Pure rotation M/F RATIO = infinity center of rotation is coincident with center of resistance www.indiandeantalacademy.com
  24. 24. Predicting orthodontic force systems To fully understand the response to appliance activation the displacement at one end of the appliance has to be considered with the effects at the other Force systems by orthodontic appliance must be resolved separately To deduce how each tooth will be displaced as a result of activation ,the equivalent force systems acting at the centers of resistance must be assessed subsequently www.indiandeantalacademy.com
  25. 25. Predicting orthodontic force systems Static equilibrium  Physical laws of statics are governed by Newtons laws of motion  For any orthodontic appliance The sum of all forces present must equal zero The sum of all moments present must equal zero The sum of all forces and moments present must equal zero www.indiandeantalacademy.com
  26. 26. Predicting orthodontic force systems Static equilibrium cont… Mesiodistal,buccolingual and extrusion-intrusion forces in balance Two equal moments, system in balance Unequal moments, unbalanced system sum of these force systems=0,but system rotates clockwise www.indiandeantalacademy.com
  27. 27. Predicting orthodontic force systems Force system from intrusion arch in equilibrium www.indiandeantalacademy.com
  28. 28. Predicting orthodontic force systems of unequal moments result in The application more complex force systems,and may occur with bracket misalignment,eccentric “V”bends, gable bends or use of auxiliary space closing springs When applied moments are unequal “additional” forces must be present to oppose moment difference Being aware of the force system produced by an orthodontic appliance in equilibrium aids in the prediction of response to the treatment www.indiandeantalacademy.com
  29. 29. Biomechanical classification of orthodontic appliances Equal and opposite force systems One couple force systems Two couple appliance system www.indiandeantalacademy.com
  30. 30. Determinate Vs. Indeterminate force systems Determinate force systems • moments and forces can readily be discerned • E.g… one couple appliance system Indeterminate force system • Too complex for precisely measuring all forces and moments involved in the equilibrium • Only the direction of net moments and approx.. force levels can be determined • E.g… two couple appliance system www.indiandeantalacademy.com
  31. 31. Biomechanical classification of orthodontic appliances No couple appliance system • e.g..elastic band stretched b/w two points • Appliance is in equilibrium as the sum of forces and moments is zero www.indiandeantalacademy.com
  32. 32. Biomechanical classification of orthodontic appliances One couple appliance system • One end of the appliance experiences couple(bracket or tube) and other end is tied as a point contact(which can not produce a couple but only a simple force at that site) • E.g..cantilever spring activated to extrude a high maxillary canine and auxiliary intrusion or extrusion arches www.indiandeantalacademy.com
  33. 33. One couple appliance system Cantilever spring www.indiandeantalacademy.com
  34. 34. One couple appliance system Auxiliary intrusion/extrusion arches www.indiandeantalacademy.com
  35. 35. Two couple appliance system Both ends of the appliance are engaged into attachments(brackets or tubes).A couple is thus generated by the wire at either or both sites Statically indeterminate force system www.indiandeantalacademy.com
  36. 36. Two couple appliance system Force system depends on wirebracket geometry www.indiandeantalacademy.com
  37. 37. Two couple appliance system Straight segment of wire in misaligned brackets www.indiandeantalacademy.com
  38. 38. Two couple appliance system “V” bend principle www.indiandeantalacademy.com
  39. 39. Two couple appliance system 2x6 appliance can be used for molar control www.indiandeantalacademy.com
  40. 40. Two couple appliance system Lingual arches as two couple system www.indiandeantalacademy.com
  41. 41. How to predict? It is sometimes beneficial not to engage a straight wire into all of the teeth in an arch www.indiandeantalacademy.com
  42. 42. Conclusion the choice of appliances and technique used by practitioners varies radically among individuals, but the fundamental forces and moments they produce are universal. Appliance will always act according to the laws of physics Understanding the basic force systems helps achieving controlled tooth movement in a predictable manner www.indiandeantalacademy.com
  43. 43. Thank you For more details please visit www.indiandentalacademy.com www.indiandeantalacademy.com

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