Mechanics of orthodontic tooth movement

1. MECHANICS OF
TOOTH
MOVEMENTS
PRESENTED
IRA SOLANKI
(FINAL BDS)

2. CONTENTS
 Introduction
 Force
 Stress and strain
 Couple
 Centre of resistance
 Moment
 Centre of rotation
 Types of tooth movements
 Types of force

3. Introduction
 Mechanics is defined as that branch of
engineering science that describes the
effect of force on a body.

5. CLINICAL
CELLULAR
STRESS-STRAIN
LEVEL OF ACTIVITY
The response of a tooth to an applied force can be at 3 le

18. Types Of Tooth Movement-
 The prime motive of orthodontic treatment
is to move the teeth into more favourable
and corrected positions.
 The teeth undergoes a variety of
movements in all the 3 planes of space
i.e. sagittal, coronal and transverse.

19.  Tooth movements in the oral cavity can be
listed as follows-
1. Tipping
2. Bodily movement
3. Intrusion
4. Extrusion
5. Torquing
6. Uprighting

20. Tipping
 Tipping is a simple type of tooth
movement where a single force is applied
to the crown, which results in movement
of the crown in the direction of the force
and the root in the opposite direction
 Controlled tipping
 Uncontrolled tipping

21.  Bodily Movement- If the
line of action of an
applied force passes
through the centre of
resistance of a tooth, all
the points on the tooth will
move an equal distance
in the same direction
signifying a bodily
displacement or
translation.
 Intrusion- bodily
displacement of tooth
along its long axis in an
apical direction.
 Extrusion- bodily
displacement of the tooth
along its long axis in an

22.  Rotation- labial and
lingual movements of a
tooth around its long axis.
 Torquing- reverse tipping
characterised by lingual
movement of the root.
 Uprighting- the crowns of
certain teeth will be tipped
in a mesio-distal direction
with the roots tipped in the
opposite way. Tipping
these roots back to get a
parallel orientation is
termed uprighting.

23.  In more specific approach the tooth
movements can be classified basically into
three-
1. PURE TRANSLATION- It occurs when all
points on the tooth move an equal distance
in the same direction. This is brought about
when the line of action of an applied force
passes through the centre of resistance of
a tooth. It can be of 3 types- intrusion
- extrusion
- bodily movement

24.  PURE ROTATION-
A displacement of the body, produced by a
couple, characterised by the centre of
rotation coinciding with the centre of
resistance i.e. the movement of points of the
tooth along the area of circle, with the centre
of resistance being the centre of the circle.
1. Transverse rotation- e.g. Tipping and
tourquing
2. Long-axis rotation- e.g. rotation of the
tooth around its long axis.

25.  GENERALISED ROTATION-
Any movement that is not pure translation or
rotation can be described as a combination
of both translation and rotation and can be
termed generalised rotation.

26. Types of forces
 Continuous- force maintained at
some appreciable fraction of the
original from one patient visit to
the next.
 Interrupted- force level decline
to zero between activations.
Both continuous & interrupted forces
can be produced by fixed appliance
that are constantly present.
 Intermittent- force level declines
abruptly to zero intermittently,
when an orthodontic appliance
or elastic attached to a fixed
appliance is removed by the pt.,
& then return to the original level
some time later.
Intermittent forces are produced by all pt.-
activated appliances such as removable
plates, headgear, & elastics.

27. THANK YOU