Biomechanics in Orthodontics

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5. With all the changes in appliances that
have occurred during the past 100 years,
have the basic principles changed???
No, we still exert forces to move teeth in
desired directions.
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Physics has not changed
What does the 21st century have
in store for orthodontics?

6. Though, Orthodontics is one
of the oldest branch of
dentistry and the first
specialization of dentistry
How the appliances
worked?????????
Why it didn’t work in some
patients????
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8. “Role of forces is analogous to role of drugs
in medicine.”
Drugs act on specific cells, in orthodontics
moments and forces act on specific cells.
Side effects from drugs are inevitable and must
be managed, side effects due to mechanics
also are inevitable and must be managed.
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The basic building block in mechanics & analogous to role
of drugs in medicine

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imbalanc
e
Balanced
!!

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Sliding
mechanics

12. Active tie-backs consist of an elastic module and ligature
tie combination.

13. Introduction
Branch of physics concerned
with the behavior of bodies
when subjected to forces.
is the application of
mechanical principles on
living organisms.
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Mechanics
Biomechanic
s

14. The basic building block in mechanics is the
application of force.
A force is defines as a vector with both
magnitude and direction.
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Both the ball
and boy are in
equilibrium
If we want to
move anyone, we
need to apply
force

15. Some basic
terminologies…….
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Each body has a point in its mass, which behaves as
if the whole mass is concentrated at a single point,
which is the centre of mass in a gravity free
environment.
Centre of mass:
Any force through
this point, will cause
body to translate
Object’s : Balance point

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Same point is called Center of Gravity in an environment
where gravity is present.

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Centre of resistance
In a restrained body;
a point analogous to
the center of mass is
used : center of
resistance.

20. Cres can be described in all the 3 planes.
Cres - Single tooth, units of teeth, dental arch,
jaws
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long axis ,between one third
and one half of the root
length apical to the alveolar
crest
Is between the
roots, 1 or 2 mm
apical to the
furcation.

21. The position of the center of
resistance varies with:
root length
alveolar bone height.
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22. Force through Cres –
Translation.
Problem is that Cres
is half way in the root,
and the only portion
which is visible to us
is the crown.
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??????

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Sliding
mechanics

24. Active tie-backs consist of an elastic module and ligature
tie combination.

25. What if force is
elsewhere????
 Whenever we apply
a force, an
equivalent force is
felt at Cres.
 Rotate as the force
is acting away from
Cres.

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Its damn
easy,
Its hardly
moving

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D M
D
Moment can occur in all 3 planes rotation, tipping ,
torquing -
If force is not acting at Cres, then a moment is created.

28. Moment – rotate – point
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Centre of rotation:
Point about which a body
appears to have rotated as
determined from its initial to
final position.
Can be at the center of
resistance, apical or incisal to
Cres or at infinity.
Its position will determine the
type of tooth movement.

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Sliding
mechanics

30. Active tie-backs consist of an elastic module and ligature
tie combination.

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Uncontrolled
tipping
Controlled
tipping
Translation Root
movement
Lies at infinity
Slightly apical to
center of
resistance
Apex of root
Incisal edge

32. On the exposed crown, if we apply force, we
will cause uncontrolled tipping or controlled
tipping.
What if I want to move tooth bodily or move
only the root ?????
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Couple

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Couple
Couple consists of two
parallel forces that are
equal in magnitude,
opposite in sense and do
not share a line of action.

34. Can couple cause any
change????
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It does not produce any
translation, only rotation.
The resultant force is
zero. BUT, the
resultant moment of a
couple is not zero; it is a
pure moment.

35. How can we use moments
?????
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Uncontrolled
tipping
Counter moment
Controlled
tipping

36. Counter moment????
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Moment of couple / Moment of
force

37. Depending on the magnitude of counter moment
applied, type of tooth movement varies.
Translatio
n
Root
movement

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Sum of Forces = 0
Sum of Moments = 0
imbalanc
e

39. Determinate systems - there is couple at one
end and only force at the other end, there will
be only point contact.
When we tie the wire into bracket at both the
ends, a statically indeterminate system is
created.
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40. HIGH PULL HEADGEAR
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LINE OF FORCE THROUGH THE CENTER OF RESISTANCE OF BOTH THE
MAXILLA AND THE MAXILLARY DENTITION

41. HIGH PULL HEADGEAR
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MAXILLA
MAXILLAR
YDENTITI
ON

42. HIGH PULL HEADGEAR
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MAXILLA
MAXILLARY
DENTITION

43. CASE
REPORT
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44. Pretreatment: Suhas, 13yr c/o forwardly placed upper front
teeth & also highly placed corner teeth.
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45. Class Molar Relation
U & L anterior crowding
highly placed upper
canines
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46. U .014 NiTi & L .0175 Co ax wire
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47. U .016 Aus Sp+
L .014 NiTi with
anterior biteplane
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48. U .016” Aus Sp+ & L .014” Aus
Sp+
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49. U/L 16×22 SS with class II
elastics
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50. U/L 17×25 SS with class II
elastics
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51. U/L 19×25
SS with Spee
& class II
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52. U/L 16×22 Braided arch wire with
short class II elastics
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53. Post treatment
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54. Post
treatment
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