Copy of biologic basis tooth movement /certified fixed orthodontic courses by Indian dental academy

Biologic basis of
Orthodontic Treatment
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Biologic basis of Orthodontic Treatment
 State

of equilibrium
 Classification of Orthodontic Forces
 Theories of Tooth Movement
 Types of Orthodontic tooth movement
 Orthopedic effects of Forces
 Iatrogenic effects of Orthodontic forces

 Why

do teeth not move under normal circumstances?

--- Equilibrium theory, which states that the forces
from the extraoral and the intraoral areas balance
each other, aided additionally by the periodontium.


THE BASIS OF ORTHODONTIC TOOTH MOVEMENT
ORTHODONTIC TREATMENT IS BASED ON THE PRINCIPLE
THAT IF PROLONGED PRESSURE IS APPLIED TO A TOOTH,
TOOTH MOVEMENT WILL OCCUR AS THE BONE REMODELS.
BONE IS SELECTIVELY REMOVED IN SOME AREAS AND
ADDED IN OTHERS.


THE TOOTH MOVES THROUGH THE BONE CARRYING
ITS ATTACHMENT APPARATUS WITH IT,AS THE
SOCKET OF THE TOOTH MIGRATES.
THIS

BONY

RESPONSE

IS

MEDIATED

BY

THE

PERIODONTAL LIGAMENT, TOOTH MOVEMENT IS
PRIMARILY A PERIODONTAL PHENOMENON.


Forces applied to the teeth can also affect the pattern of
bone apposition and resorption at sites distant from the
teeth, viz sutures of the maxilla and bony surfaces of the
TMJ
Thus, the biologic response to orthodontic treatment
includes not only the response of the PDL, but also the
growing areas distant from the dentition.


Theories of tooth movement
 Pressure-tension

theory
 Piezo-electric theory


 Pressure-tension

theory: This is the most accepted
theory. According to this theory, whenever
pressure and tension zones exist, chemical
messengers are released which will bring about
recruitment of osteoblasts and osteoclasts




a)
b)
c)

Pressure-tension theory: Can be divided into
three overlapping stages which include –
Alterations in Blood flow associated with
pressure
Formation and /or release of chemical mediators
Activation of cells

Alterations in Blood flow associated with pressure
a) Increasing pressure on the tooth results in
reduction of blood flow.
If the force application continues, a zone of sterile
necrosis results – Zone of Hyalinization


 The

second stage involves the release of chemical
messengers
--- Primary messengers: Cytokines, Prostaglandins
---- Secondary messengers: Cyclic AMP
Prostaglandin E2 has the property of stimulating
both osteoblastic as well as osteoclastic activity

After a delay of several days, cellular elements
from adjacent undamaged areas of PDL begin to
invade the necrosed area.
Osteoclasts appear within adjacent bone marrow
Spaces & begin an attack on the underside of the
Bone immediately adjacent to PDL—undermining
Resorption, since the attack is from the underside
Of lamina dura.

These osteoclasts arrive in two waves
-First wave-derived from local cell population
-Larger second wave-are brought in from distant
Areas via blood flow. These cells attack the adjacent
lamina dura removing bone in the process of
Frontal resorption.
Tooth movement begins thereafter.At the same
time,osteoblasts recruited from PDL form bone on
the tension side & begin remodeling activity.

Pressure-tension theory


a)
b)

Two types of resorption patterns are seen
whenever forces are applied to move teeth.
Frontal Resorption
Undermining resorption


a) Frontal Resorption: This is a favourable resorption
pattern which depends on:
-- Magnitude of force
-- Duration of force
In this type of resorption, Howship lacunae are seen
adjacent to the PDL in the frontal aspect of the
lamina dura.

b) Undermining resorption : This is a resorption
pattern seen whenever heavy forces are applied,
which compress the PDL beyond half its original
size.
Due to obstruction of the blood flow, osteoclasts
cannot be recruited onto the frontal aspect of the
lamina dura.

b) Undermining resorption :
Instead, a resorption wave is initiated from the
underside of the Lamina dura – known as
‘Undermining resorption’
Responsible for ‘jumpy’ pattern of tooth movement,
often seen with fixed appliances


The Piezo-electric theory




According to this theory, whenever stresses are
applied to bone, it deforms and bends.
Charges are produced on the inside and outside,
which stimulate either deposition or resorption


The Piezo-electric theory

a)
b)

Limitations:
Does not explain how the chemical mediators act
Piezo-electricity exists only for a short period.


Classification of Orthodontic forces
According to Schwarz :
a) First degree of efficiency:These are forces lower
than the threshold of stimulation to activate
Orthodontic tooth movement.
---Short duration and low force balanced by the
compensatory mechanisms



c) Third degree of Efficiency:
The forces in
this category tend to interrupt circulation in the
PDL (20-50 gm/sq.cm)



b) Second degree of efficiency:This refers to force
levels most effective in achieving Orthodontic
tooth movement. (Optimum Orhtodontic force).
Characterised by low but continuous forces
(roughly 15-20 gm/sq.cm over the compressed
PDL)



d) Fourth degree of Efficiency: The force levels in
this group are so excessive that they crush the
PDL between the tooth and the alveolar bone in
the areas of pressure. If continuous, they can
cause extensive, irreparable damage.




a)
b)
c)

According to Proffitt :
Continuous Forces
Interrupted forces
Intermittent forces


Factors affecting tooth movement
a)
b)
c)

Age of the patient and in turn, the viability of
supporting structures
Magnitude, duration and type of forces applied
Chemical agents – action of certain drugs


THE ORTHODONTIC FORCE DURATION IS CLASSIFIED1) CONTINUOUS –
2 ) INTERRUPTED3 ) INTERMITTENT-

Continuous and interrupted forces are produced by Fixed
appliances, while the intermittent forces are produced by
removable appliances


Factors affecting tooth movement
a)
b)
c)

Age of the patient and in turn, the viability of
supporting structures
Magnitude, duration and type of forces applied
Chemical agents


Types of Orthodontic tooth movement
a)
b)
c)
d)
e)

Tipping
Translation (Sagittal)
Intrusion
Extrusion
Rotation

EFFECTS OF FORCE MAGNITUDE
THE HEAVIER THE SUSTAINED PRESSURE,GREATER
SHOULD BE THE REDUCTION IN BLOOD FLOW THROUGH
COMPRESSED AREAS OF PDL,VESSELS ARE TOTALLY
COLLAPSED NO FURTHER BLOOD FLOWS.
WHEN LIGHT BUT PROLONGED FORCE IS APPLIED-

•Blood flow decreases
•Partially compressed PDL
•Tooth moves in the socket

Harmful effects of Orthodontic Forces
Heavy forces often result in extensive damage to the PDL
as well as root surfaces.
a) Crushing of the PDL – causing pain as well as mobility
b) Reversible resorption of bone
c) Apical Root Resorption


Orthopedic forces and their effects
a) On the maxilla – Maxillary growth stimulation
or restraint is facilitated because of the presence of sutures
in the naso-maxillary complex.


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Copy of biologic basis tooth movement /certified fixed orthodontic courses by Indian dental academy

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Copy of biologic basis tooth movement /certified fixed orthodontic courses by Indian dental academy