Orthodontic tooth movement involves applying precise mechanical forces to the teeth to induce biological responses in the periodontal ligament that result in tooth movement. The proper application of biomechanical principles is necessary to control orthodontic treatment and increase efficiency. Optimal forces are light and continuous, applying just enough stress to stimulate cellular activity without damaging blood vessels in the periodontal ligament. Different force systems and levels can be used to produce various types of tooth movement, such as tipping, translation, rotation, and intrusion/extrusion.

1. Orthodontic
tooth
movement
Abdurrahman Mosaad
Orthodontics department
Armed forces medical complex – Kobry
al Qubba

2. I n t h e n a m e o f A l l a h , m o s t
g r a c i o u s , m o s t m e r c i f u l

3. # What is orthodontics :
= Orthodontics is the specialty of dentistry concerned
with the management and treatment
of malocclusion.
=In the majority of cases, a malocclusion does not in
itself represent a disease state, but rather a variation
from what is considered ideal

4. - Andrew’s keys for ideal occlusion

5. - The nature of orthodontic tooth movement :
= it has a bio – mechanic nature.
= solely based upon stress- strain occurs in the
PDL
environment
= the orthodontic tooth movement results from
forces delivered to the teeth

6. = the forces are delivered via orthodontic app.
Either fixed or removable
= PDL undergoes biological respond upon the
mechanical application of a force i.e to
achieve a
precise biological respond the mechanical
forces to be delivered should be precise

7.  = Knowledge of the mechanical principles
governing forces is necessary for the
control of orthodontic treatment
 = The proper application of biomechanics
principles increases treatment efficiency
through improved planning and delivery of
care

9. = Knowledge of the mechanical principles
governing forces is necessary for the control
of
orthodontic treatment
= The proper application of biomechanics
principles increases treatment efficiency
through improved planning and delivery of
care

10. 1 = center of
resistance.
- All objects have a
center of mass.
- This is the point
through which an applied
force must pass for a
free object to move
linearly without any
rotation,
- i.e., the center of mass
is an object’s “balance
point.”

11. analytic studies have
determined that the
center of resistance for
single-rooted teeth
with normal alveolar
bone levels is about
1/4 to 1/3 the distance
from the
cementoenamel
junction (CEJ) to the
root apex.

12. Location of the center of resistance depends on the alveolar
bone height and root length . = Locationof the center of
resistance with
alveolar bone loss
= witha shortened root

13. 2 - Forces
= they are actions applied to
bodies
= they equals ( mass X
acceleration) F =ma
= in clinical orthodontics its
unit is Grams
= forces has the
characteristics of vectors i.e
magnitude & direction
Note : the diagram shows that the
force vectors characteristics –
magnitude , point of origin &
direction

14. = 2 vectors could added by
placing one vector at the
head of the another i.e sum
of them called resultant
= a vector could be
resolved into components
along x , y & z axes

15. = Clinically the determination of the horizontal,
vertical, and transverse components of a force
improves the understanding of the direction of
tooth movement
= An important point of view that the orthodontic
tooth movement is not applied on the center of
rotation of the tooth as it is usually delivered
through the tooth crown

16. = as the orthodontic forces
are delivered through the
tooth crown they will not
produce a pure linear
movement ,, some rotational
movement will be present ,,
those rotational movements
are called Moment of the
force
= The moment of the force
is the tendency for a force to
produce rotation.

17. = Its direction is found by
following the line of action
around the center of resistance
toward the point of origin
=It is determined by multiplying
the magnitude of the force by
the perpendicular distance of
the line of action to the center of
resistance

18. = The importance of the moment of a force
is often not recognized in clinical
orthodontics, but awareness of it is needed
to develop effective and efficient appliance
designs

19. Clinical examples of moments of the forces

20. 3 – Couple
- A couple is
two parallel forces of equal
magnitude acting in opposite
directions and separated by a
distance (i.e. different lines of
action)
- The magnitude of a couple is
calculated by multiplying the
magnitude of force(s) by the
distance between them

21. Couples result in pure rotational
movement about the center of
resistance

22. c l i n i c a l e x a m p l e s o f c o u p l e s

23. 4 – Torque
= Torque is a common synonym for moment
(both moments of forces and of couples)
= Torque is erroneously described in terms of
degrees by many orthodontists.

24. = The appropriate unit for the applied torque is
gram/millimeters (force × distance). It is the
description of the moments that more accurately
describes the rotational components of a force
system and appliance design

25. Orthodontic wire bends
-1st order
-- 2nd order
-- 3rd order

29. # Anchorage
-Anchorage is the site
of delivery from which
force is exerted
- degree of resistance
to displacement
offered by an anatomic
unit for the purpose of
tooth movement.

30. # Classification of ortho. Anchorage
-acc. to manner of force application :
* simple * stationary * reciprocal
- according to jaws involved :
* intermaxillary * intramaxillary
- according to site :
* intraoral * extaraoral * muscular
- according to anchorage units :
* primary * compound *reinforced (multiple)

32. # anchorage planning :
-Increasing no. of teeth to be move requires
more anchorage
- teeth having more surface area requires more
anchorage
- bodly movement requires more anchorage
- prolonged tx. Plan requires more anchorage
- vertical growth pattern requires more
anchorage due to the less tonicity of muscles
- N.B. Good occlusion = Good anchorage

33. # Anchorage loss :
-Its is the unwanted tooth movements during
orthodontics that cause space loss
-Maximum anch.
* anch. Demand is very high
*not more than ¼ of ext space should be lost
* augmentation of anchor units is usually done
-Moderate anch.
* ¼ - ½ of ext space should be lost
- Minimum anch.
* more than ½ ext space could be lost

34. Maximum anch.

35. Moderate anch.

36. Minimum anch.

37. # Equivalent Force systems
= A useful method for
predicting the type of tooth
movement that will occur with
appliance activation is to
determine the equivalent force
system at the tooth’s center of
resistance
= The force system at the
center of resistance accurately
reflects the type of movement

38.  eg. Intrusion arch force system

39. # Types of tooth movement :
1 – tipping ( controlled & uncontrolled)
2 – translation ( bodily )
3 – root movement
4 - rotation
5 - intrusion & extrusion

40. -The relationship between the applied force
system and the type of movement can be
described by the moment/force ratio
-The movement that occurs is dependent on the
(moment/force ) ratio #and# the quality of the
periodontal Support

41. 1- Tipping :
* simplest orthodontic movement
* controlled occurs about the tooth apex
*uncontrolled occurs about CER
* Force needed is about 50 – 75 gm.

42. Controlled tipping

43. Uncontrolled tipping

44. 2- Translation :
* all PDL is uniformly loaded with the force
* Force needed is about 100 – 150 gm.

45. 3 – Rotation :
* needs high force
* occurs around the CER
* Force needed is about 50 – 100 gm.

46. 4 – Extrusion :
* needs to produce tension in the PDL
ligaments
* Force needed is about 50 gm.

47. 5 – Intrusion :
* forces are nearly at the apex
* needs minimum force application
* Force needed is about 15 – 25 gm.

49. 6- Root movement :
* usually expressed as torque
* the crown is held stationary and the root
moves
* CER is the bracket itself
* done by increasing the Moment/Force
ratio

50. Moment / Force ratios needed for different kinds of
tooth movement :
1 – tipping
* controlled 5 : 1
* uncontrolled 7 : 1
2 – translation 10 : 1
3 – root movement 12 : 1

51. Types of orthodontic forces acc. to Duration
- continuous
- interrupted
- intermitted

52. * Threshold --- 6 hrs per day.
* No tooth movement if forces are applied less
than
6 hrs/d.
* From 6 to 24 hrs/d, the longer the force is
applied, the more the teeth will move.

53. - Continuous force :
* achievable via fixed orthodontics
*Never declines to zero.

54. - Interrupted force :
* force starts heavy then decline to optimal
after that may reach zero .
*achievable via removable appliance.
* produces some kind of undermining
resorption .
* reactivated every specific time .

55. -Intermittent forces :
* declines to zero
* very high force 250 – 500 gm.( anch – dist )
* achievable via extraoral appliance
* needs at least 12 hrs/day to be effective
* 14 hrs/day is optimal

57. -Force level :
* Light, continuous forces are currently
considered to be most effective in inducing
tooth movement.
*Heavy forces cause damages and fail to move
the teeth.
N.B. Optimal force : “High enough to stimulate
cellular activity without completely occluding blood
vessels in the PDL”

59. Heavy Forces
* B.V of PDL is totally occluded ---
then
* causes cellular necrosis within the bone ---
then
* hyalinization i.e undermining resorption
occur
Phase 1
Phase 3
Phase 2
Tooth
movement
(mm)
Time (Arbitrary Unit)

60. Light, continuous forces
• Osteoclasts formed
• *Removing lamina dura.
*Tooth movement begins
*This process is called
“FRONTAL RESORPTION”.
( remodeling process )
Phase 3
Phase 2
Tooth
mov.
Time

64. -Phases of orthodontic tooth movement :-
* Displacement - no clinical movement
- instantaneous
* Delay – no clinical movement
- short ( partial B.Vs occ. ) or long
1-2
weeks ( more B.Vs occ. )
* Acceleration – rapid tooth displacement
- differs among individuals

65. Phase 1
Phase 3
Phase 2
Tooth
movement
(mm)
Time (Arbitrary Unit)

66. Orthodontic tooth movement adverse
effects :
* Pulp - transient inf. response , can cause
loss of vitality
- in cases of compromised tooth ,,
heavy
force ,, wrong mech.
* Root - usually repaired by cementum
during
rest periods
- resorption may occur up to 2 mm.
in
permanent cases
- At risk : thin roots ,, heavy force ,,

67. Material considerations :
1 – orthodontic wires
*material of the wire
* effect of increasing wire diameter
2 – orthodontic brackets
* edgewise vs pre-adjusted (roth)
* self ligating brackets
* size of slots
* interbracket distance
* torque of the brackets

69. Modulus of elasticity of the wire
force
deflection

70.  14’’ 50gm
 16’’ 85gm 71% increase
 18’’ 137gm 173% increase
Effect of increasing wire diameter
Percentage
increase
in
stiffness
100%
200%
300%
400%
Wire diameter
14’’ 16’’ 18’’ 20’’ 22’’

71. Torque selection of lower teeth brackets

72. Torque selection of upper teeth brackets

73. Finally :
Optimal force
is the lightest force that will move a
tooth to a desired position in the shortest
possible time without iatrogenic effects
So ,,, we should think optimal ,, it is
orthodontics so we ( work smarter not
harder ) 

74. Thank You 