Dr. ZUBER AHAMED NAQVI
Objectives

 Physiologic tooth movement
 Histology of tooth movement
 Optimum orthodontic force
 Phases of tooth movement
 Force , Couple and moment
 Center of Resistance
 Center of Rotation
 Types of tooth movement
 Anchorage

 Physiologic tooth movement
 Naturally occuring tooth movements that takes place
during and after tooth eruption.
A. Tooth eruption
B. Migration or drift of teeth.
C. Change in tooth position during mastication.
Tooth eruption
 Blood pressure theory

 Hammock Ligament theory
 Periodontal ligament traction theory
Migration or drift of teeth
Direction- mesial and occlusal.

--------proximal and occlusal wear of teeth.
Tooth movement during mastication
The tissue fluid present in the periodontal space, being incompressible ,
prevent major displacement of tooth within the socket.
Forces are transmitted through the tissue fluids to the alveolar bone.
Histology of tooth movement

Force
Pressure
In the direction of tooth movement
Bone resorption
Tension
In the opposite direction of tooth
movement
Bone deposition
Histologic changes
a. Mild forces
b. Heavy forces
Histological changes following
application of mild forces

Pressure side
 PDL compressed
 Increase in vascularity
 Mobilization of cells such
as fibroblasts and
osteoclasts
 Osteoclast line up along
socket wall
 Bone resorption
 Frontal resorption
Tension side
 PDL stretch
 Increase in vascularity
 Mobilization of cells such as
fibroblasts and osteoblasts
 Osteoid laid down by
osteoblast in PDL
immediately adjacent to the
lamina dura
 Osteoid matures to form
woven bone.
Histological changes following application of
heavy forces

Pressure side
 Crushing or total compression of
PDL
 Root approximates the lamina
dura
 Occlusion of blood vessels
 Regressive changes- hyalinization
 Bone cannot resorb in frontal
portion.
 Bone resorption in adjacent
marrow spaces and in the
alveolar plate below, behind and
above the hyalinized zone
 Undermining resorption
Tension side
 PDL overstretched
 Tearing of blood vessels
 Ischemia

 Net effect of extreme heavy forces
 Net increase in osteoclastic activity as compared to
bone formation.
 Increased tooth mobility.
 Pain and hyperemia of gingiva.
 Root resorption.
Optimum orthodontic
force

 The force which moves the teeth most rapidly in the
desired direction, with the least possible damage to tissue
and with minimum patient discomfort.
 High enough to stimulate cellular activity without completely
occluding blood vessels in the PDL” (Proffit et al. 2000).
 Oppenheim and Schwartz
 Optimum force is equivalent to the capillary pulse
pressure, which is 20-26 gm / sq. cm of root surface area.
Force Types

Light, continuous forces


Never declines to zero.

Interrupted forces
Force levels decline to zero between
activations

Intermittent forces


Force levels decline to abruptly.
Phases of tooth movement

 Phase 1- Initial phase
 phase 2- lag phase
 Phase 3- post lag phase
Couple and moment

Couple
Two forces of opposite directions and with non-overlapping
points of application.
Brings about pure rotation.

Moment
 can be defined as rotational potential of
force with respect to a specific axis.
 Moment = magnitude of force X distance ( perpendicular distance from the
 center of resistance of the body to the line of action of the force)
Biomechanics of Tooth
Movement






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
Center of Resistance --“that point on the tooth when a single force is
passed through it, would bring about it’s
translation along the line of action of the force”.
Single rooted teeth- 6th-tenth of distance between
apex of tooth and crest of alveolar bone
Multirooted teeth- below furcation.
Center of Rotation --- The point around which a
body appears to have rotated, as determined
from it’s initial and final positions.
Controlled crown tipping-----------------root apex
Translation------------------------------------- infinity.
Types of tooth movement

 Tipping
 Bodily movement
 Intrusion
 Extrusion
 Torquing
 Uprighting
Anchorage



Graber –
“ the nature and degree of resistance to displacement offered by
an anatomic unit for the purpose of effecting tooth movement”.
Sources of anchorage
 Intra oral




Teeth
Alveolar bone
Basal jaw bone
Musculature
 Extra oral
 Cranium
 Back of
neck
 Facial bones
According to manner of force applicationSimple anchorage
Stationary anchorage
Reciprocal anchorage
Classification
( Moyers )

According to jaws involved
Intramaxillary
intermaxillary
According to site of Anchorage
Intraoral
Extraoral muscular
According to number of Anchorage units
Single or primary anchorage
Compound anchorage
Multiple or reinforced anchorage
Simple anchorage


The manner and application of force is such that it tends
to change the axial inclination of the tooth or teeth that
form the anchorage unit in the plane of space in which
the force is being applied.
Stationary anchorage

 The manner and application of force is
such tends to displace the anchorage
unit bodily in the plane of space in
which the force is being applied.
 Reciprocal anchorage
 Both units move equal distance.
 Exemplified by closing a diastema between two
central incisors.
Intra maxillary anchorage

 All the anchorage units are situated
within the jaw.
 Intermaxillary anchorage
Anchorage unit and the teeth
being moved are not situated in
the same jaw.
 Reinforced anchorage
More than one type of resistance
unit is utilized .
 Anchorage classification- ( Ravindra Nanda)

 Group A anchorage 75% or more of extraction space is used for
anterior retraction.
 Group B Equal movement of posterior and anterior teeth
to close extraction space.
 Group C 75% or more of extraction pace closure is
achieved through mesial movement of posterior
teeth.
Temporary anchorage devices

 Useful in patients who have
lost multiple teeth or hypodontia.
 Micro implants
 According to method of placing the implant
 Self tapping method- drilling required.
 Self drilling method – no pre drilling required.
 Miniplates
References

 Contemporary orthodontics- 4th edition: William R.
Proffit.
 Orthodontics : The art and Science- 4th edition: S.I.
Bhalaji