2. In the name of Allah , most
gracious , most merciful
3. # What is orthodontics :
= Orthodontics is the specialty of dentistry
with the management and treatment
of malocclusion.
concerned
=In the majority of cases, a malocclusion does not in
itself represent a disease state, but rather a variation
from what is considered ideal
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
8.
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
. = Location of the center of
resistance with
alveolar bone loss
= with a 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
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
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
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)
31.
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
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
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.
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.
48.
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
56.
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”
58.
59. Heavy Forces
Tooth movement (mm)
* B.V of PDL is totally occluded --then
* causes cellular necrosis within the bone --then
* hyalinization i.e undermining resorption
occur
Phase 3
Phase 2
Phase 1
Time (Arbitrary Unit)
60. •
•
Tooth mov.
Light, continuous forces
Osteoclasts formed
Phase 2
*Removing lamina dura.
*Tooth movement begins
Time
*This process is called
“FRONTAL RESORPTION”.
( remodeling process )
Phase 3
61.
62.
63.
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
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
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 )