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

www.indiandentalacademy.com
INTRODUCTION

www.indiandentalacademy.com
INTRODUCTION
• Orthodontic problems are the result of
mechanical forces, and their correction
depends on mechanical forces...
• Altering the balance of forces can arrest or
reverse progressive deformities during
growth, and it can correct many of t...
• Thus understanding of the fundamentals
of mechanics must be the starting point for
understanding orthodontics.

www.indi...
• The principles of force analysis are the
basic tools of the mechanical engineer, &
their application is universal.

www....
• In applying them to oral environment, one
combines engineering with dentistry,
which requires a mixed terminology that i...
BIOMECHANICS
Laws
&
Terminologies
www.indiandentalacademy.com
Laws & Terminologies

This chapter is divided into following parts:
• Couple

• Force
–
–
–

– Moment of couple
– Factors ...
Mechanical Forces
• The two broad classes of mechanical
force are:
– Static
– Dynamic

• At any moment the oral structures...
Force
Definition:
• an act upon a body that changes or tends
to change the state of rest or the motion of
that body.

www....
Magnitude of force
• Increasing the amount of force will
increase the amount of a free body
displacement.
• However, it is...
Point of Application
• Center of Mass
• Center of Gravity
• Center of Resistance

www.indiandentalacademy.com
Center of Mass:

Flash Player Movie

• Each body has a point in its mass, which
behaves as if the whole mass is
concentrat...
Back to Earth

www.indiandentalacademy.com
Center of Gravity:
• The same is called center of Gravity in an
environment where gravity is present.

www.indiandentalaca...
• The center of gravity of the tooth is located
more towards the crown of the tooth as
the mass of the tooth is concentrat...
Center of Resistance
• It is a point at which resistance to tooth
movement is concentrated.
• It is at the approximate mid...
Center of Resistance

Center of Resistance
Center of Gravity

www.indiandentalacademy.com
Where is the Center of resistance
of…
•
•
•

Single Tooth ?
Anterior Segment ?
Full Upper Dentition ?

Flash Player Movie
...
Moment
Is defined as a tendency to rotate

www.indiandentalacademy.com
Moment of force
• We can apply a force only on the exposed
part of the tooth, which is at a distance
from the center of re...
• In orthodontic terminology we refer to
moment as
– Rotation
– Tipping
– Torquing

Flash Player Movie
www.indiandentalaca...
Factors controlling the Moment:
• Moment (M)
• Force (F)
• Perpendicular Distance (d)

M=Fxd
www.indiandentalacademy.com
Center of Rotation

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Center of Rotation &
Center of Resistance
• Changing the point of force application
and its relation to the center of resi...
Couple
Two equal and opposite, non-collinear

forces

www.indiandentalacademy.com
Couple
• The two forces cancel out any tendency
for the center of resistance of the pencil to
move, but the moment created...
• If the two forces of the couple act on
opposite sides of the center of resistance ,
their effect is additive.
• However,...
A clinical example

Subtractive

Additive
www.indiandentalacademy.com
Explanation
Resultant moment = Fd1 + Fd2
F1

F1

d1

F1 x d1 = Fd1
d2

F2 x d2 = Fd2

F2

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d1
...
Factors controlling the Moment
of a Couple
• Moment (M)
• One of the forces (F1 or F2)
• Moment arm of the couple (d)

M= ...
Couple – Clinical point
• When the tooth is embedded within the
alveolar bone we cannot apply a couple
with one force on t...
• Irrespective of point of application of a
couple on a body or a tooth, the body will
experience a moment & it will rotat...
• Depending on the plane in which the
couple is acting, this rotation has been
called “rotation” (first order), “tipping”
...
• I am sure all of you already familiar with the
above mentioned points.
• I will assume that from now onwards you are
fam...
• Next we will cover– Moment to Force Ratio

• And I am sure many have this question:
– Which moment?
– Whether moment of ...
Moment-to-Force ratio
The ratio of counter-balancing moment
produced to net force that is applied to
a tooth.

www.indiand...
An example:
• In order to retract an incisor tooth we
apply a force on the crown of the tooth.
• This force tends to move ...
• An counter-clockwise moment can be
generated easily by applying a couple.
Note couple generates a moment
irrespective of...
• The two moments (i.e. the moment of
force and the moment of couple) cancel
out any tendency for the rotation of the
toot...
Bodily movement of a tooth requires a moment-toforce ratio of 8:1 or 10:1, depending on the length of
the root, BUT WHY?

...
Tooth Movement
Orthodontic Application
of
Moment to Force Ratio
www.indiandentalacademy.com
• As we have seen whenever a force is
applied at the crown of a tooth, a tendency
for the tooth to rotate, tip or torque (...
• The force at the
bracket is equivalent
to a force at the
center of resistance
plus a moment that
will cause the tooth
to...
• In addition to the
force applied, a
couple may also be
engaged intentionally
to partially correct,
completely correct, o...
• By varying the ratio of moment to force
applied to teeth, the quality of tooth
movement can be changed among
uncontrolle...
Uncontrolled Tipping
At the
BRACKET

At the
CENTER OF
RESISTANCE

NET
MOMENT

www.indiandentalacademy.com

Flash Player Mo...
Controlled Tipping
At the
BRACKET

At the
CENTER OF
RESISTANCE

NET
MOMENT

www.indiandentalacademy.com

Flash Player Movi...
Translation
At the
BRACKET

At the
CENTER OF
RESISTANCE

NET
MOMENT

ZER

www.indiandentalacademy.com

Flash Player Movie
Root Movement
At the
BRACKET

At the
CENTER OF
RESISTANCE

NET
MOMENT

www.indiandentalacademy.com

Flash Player Movie
Pure Rotation
At the
BRACKET

At the
CENTER OF
RESISTANCE

NET
MOMENT

www.indiandentalacademy.com

Flash Player Movie
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandentalacademy.com
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Copy of biomech 01 /certified fixed orthodontic courses by Indian dental academy

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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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Copy of biomech 01 /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. INTRODUCTION www.indiandentalacademy.com
  3. 3. INTRODUCTION • Orthodontic problems are the result of mechanical forces, and their correction depends on mechanical forces. • The force systems in the face can form or deform, and their conscious control is a continuing challenge in orthodontics. www.indiandentalacademy.com
  4. 4. • Altering the balance of forces can arrest or reverse progressive deformities during growth, and it can correct many of their effects even in the adult. www.indiandentalacademy.com
  5. 5. • Thus understanding of the fundamentals of mechanics must be the starting point for understanding orthodontics. www.indiandentalacademy.com
  6. 6. • The principles of force analysis are the basic tools of the mechanical engineer, & their application is universal. www.indiandentalacademy.com
  7. 7. • In applying them to oral environment, one combines engineering with dentistry, which requires a mixed terminology that is partly foreign to each discipline: BIOLOGY + MECHANICS _______________ BIO-MECHANICS www.indiandentalacademy.com
  8. 8. BIOMECHANICS Laws & Terminologies www.indiandentalacademy.com
  9. 9. Laws & Terminologies This chapter is divided into following parts: • Couple • Force – – – – Moment of couple – Factors controlling the moment of couple Direction Magnitude Point of application (Center of Resistance) • Moment to Force ratio • Moment – Moment of force – Factors controlling the moment of force – Center of rotation – Center of rotation and type of tooth movement www.indiandentalacademy.com
  10. 10. Mechanical Forces • The two broad classes of mechanical force are: – Static – Dynamic • At any moment the oral structures can be considered to be in a state of static balance. www.indiandentalacademy.com
  11. 11. Force Definition: • an act upon a body that changes or tends to change the state of rest or the motion of that body. www.indiandentalacademy.com
  12. 12. Magnitude of force • Increasing the amount of force will increase the amount of a free body displacement. • However, it is unclear how force magnitude is related to the rate of tooth movement, which is biologically controlled phenomenon. www.indiandentalacademy.com
  13. 13. Point of Application • Center of Mass • Center of Gravity • Center of Resistance www.indiandentalacademy.com
  14. 14. Center of Mass: Flash Player Movie • Each body has a point in its mass, which behaves as if the whole mass is concentrated at that single point, which we call it the center of Mass in a gravity-free environment. www.indiandentalacademy.com
  15. 15. Back to Earth www.indiandentalacademy.com
  16. 16. Center of Gravity: • The same is called center of Gravity in an environment where gravity is present. www.indiandentalacademy.com
  17. 17. • The center of gravity of the tooth is located more towards the crown of the tooth as the mass of the tooth is concentrated more coronally www.indiandentalacademy.com
  18. 18. Center of Resistance • It is a point at which resistance to tooth movement is concentrated. • It is at the approximate midpoint of the embedded portion of the root. www.indiandentalacademy.com
  19. 19. Center of Resistance Center of Resistance Center of Gravity www.indiandentalacademy.com
  20. 20. Where is the Center of resistance of… • • • Single Tooth ? Anterior Segment ? Full Upper Dentition ? Flash Player Movie Center of Resistance www.indiandentalacademy.com
  21. 21. Moment Is defined as a tendency to rotate www.indiandentalacademy.com
  22. 22. Moment of force • We can apply a force only on the exposed part of the tooth, which is at a distance from the center of resistance. • Therefore with a single force in a typical clinical situation we invariably create a moment, called as moment of force. www.indiandentalacademy.com
  23. 23. • In orthodontic terminology we refer to moment as – Rotation – Tipping – Torquing Flash Player Movie www.indiandentalacademy.com Flash Player Movie Flash Player Movie
  24. 24. Factors controlling the Moment: • Moment (M) • Force (F) • Perpendicular Distance (d) M=Fxd www.indiandentalacademy.com
  25. 25. Center of Rotation www.indiandentalacademy.com
  26. 26. Center of Rotation & Center of Resistance • Changing the point of force application and its relation to the center of resistance of the tooth will create: Uncontrolled tipping Controlled tipping Root Movement www.indiandentalacademy.com Bodily Movement Center of Rotation at infinity
  27. 27. Couple Two equal and opposite, non-collinear forces www.indiandentalacademy.com
  28. 28. Couple • The two forces cancel out any tendency for the center of resistance of the pencil to move, but the moment created by the two forces does not cancel each other. • The pencil therefore, rotates about its center of resistance regardless of the point of application of the couple. www.indiandentalacademy.com
  29. 29. • If the two forces of the couple act on opposite sides of the center of resistance , their effect is additive. • However, if they are on the same side of the center of resistance, their effect is subtractive. www.indiandentalacademy.com
  30. 30. A clinical example Subtractive Additive www.indiandentalacademy.com
  31. 31. Explanation Resultant moment = Fd1 + Fd2 F1 F1 d1 F1 x d1 = Fd1 d2 F2 x d2 = Fd2 F2 www.indiandentalacademy.com d1 d2 F2
  32. 32. Factors controlling the Moment of a Couple • Moment (M) • One of the forces (F1 or F2) • Moment arm of the couple (d) M= F1 x d OR M= F2 x d www.indiandentalacademy.com F1 F1 d d F2 F2
  33. 33. Couple – Clinical point • When the tooth is embedded within the alveolar bone we cannot apply a couple with one force on the crown and the other force on the root. • We can apply a couple only on the exposed part of the tooth. www.indiandentalacademy.com
  34. 34. • Irrespective of point of application of a couple on a body or a tooth, the body will experience a moment & it will rotate around it’s center of resistance. Stick.swf www.indiandentalacademy.com
  35. 35. • Depending on the plane in which the couple is acting, this rotation has been called “rotation” (first order), “tipping” (second order), or “torque” (third order) in orthodontics. www.indiandentalacademy.com
  36. 36. • I am sure all of you already familiar with the above mentioned points. • I will assume that from now onwards you are familiar with terminologies such as, – Force – Moment of a force – Couple – Moment of a couple www.indiandentalacademy.com
  37. 37. • Next we will cover– Moment to Force Ratio • And I am sure many have this question: – Which moment? – Whether moment of force or moment of couple? www.indiandentalacademy.com
  38. 38. Moment-to-Force ratio The ratio of counter-balancing moment produced to net force that is applied to a tooth. www.indiandentalacademy.com
  39. 39. An example: • In order to retract an incisor tooth we apply a force on the crown of the tooth. • This force tends to move the center of resistance of the tooth, however it also creates a moment of force (clockwise). F F = Force d = distance (X) F x d(X) = M(X) www.indiandentalacademy.com M(X)
  40. 40. • An counter-clockwise moment can be generated easily by applying a couple. Note couple generates a moment irrespective of center of resistance of the tooth. F = Force (X) d = distance F(X) x d = M(X) www.indiandentalacademy.com M(X)
  41. 41. • The two moments (i.e. the moment of force and the moment of couple) cancel out any tendency for the rotation of the tooth, thereby allowing the force to move the center of resistance of the tooth. www.indiandentalacademy.com
  42. 42. Bodily movement of a tooth requires a moment-toforce ratio of 8:1 or 10:1, depending on the length of the root, BUT WHY? 20 mm 10 mm M : F 10 : 1 www.indiandentalacademy.com M : F 20 : 1
  43. 43. Tooth Movement Orthodontic Application of Moment to Force Ratio www.indiandentalacademy.com
  44. 44. • As we have seen whenever a force is applied at the crown of a tooth, a tendency for the tooth to rotate, tip or torque (a moment) is also created. www.indiandentalacademy.com
  45. 45. • The force at the bracket is equivalent to a force at the center of resistance plus a moment that will cause the tooth to tip. www.indiandentalacademy.com
  46. 46. • In addition to the force applied, a couple may also be engaged intentionally to partially correct, completely correct, or over-correct this tendency. www.indiandentalacademy.com
  47. 47. • By varying the ratio of moment to force applied to teeth, the quality of tooth movement can be changed among uncontrolled tipping, controlled tipping, translation and root movement. www.indiandentalacademy.com
  48. 48. Uncontrolled Tipping At the BRACKET At the CENTER OF RESISTANCE NET MOMENT www.indiandentalacademy.com Flash Player Movie
  49. 49. Controlled Tipping At the BRACKET At the CENTER OF RESISTANCE NET MOMENT www.indiandentalacademy.com Flash Player Movie
  50. 50. Translation At the BRACKET At the CENTER OF RESISTANCE NET MOMENT ZER www.indiandentalacademy.com Flash Player Movie
  51. 51. Root Movement At the BRACKET At the CENTER OF RESISTANCE NET MOMENT www.indiandentalacademy.com Flash Player Movie
  52. 52. Pure Rotation At the BRACKET At the CENTER OF RESISTANCE NET MOMENT www.indiandentalacademy.com Flash Player Movie
  53. 53. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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