Biology of orthodontic tooth movement

Presented by:
Alaa Abd Elsalam
Under supervision of:
Prof.Dr.Maher Fouda
Biology of tooth movement

Introduction
Orthodontic tooth movement is
a unique process where a solid
object (tooth) is made to move
through a solid medium (bone).
The ability of independent
movement of the teeth is unique
to humans in particular and
mammals In general as teeth
are not ankylosed to the bone.

Orthodontic treatment is possible due to the fact that
whenever a prolonged force is applied on a tooth, bone
remodeling occurs around the tooth resulting in its
movement.
Bone subject to pressure as a result of compression of
periodontal ligament resorbs while bone forms under
tensile force as a result of stretching of the periodontal
ligament.

Physiologic Tooth Movement
They are naturally occurring tooth movements.
. Physiologic tooth movements include :
A. Tooth eruption.
B. Migration or drift of teeth.
C. Changes in tooth position during mastication.

Tooth Eruption
Tooth eruption is the axial movement of the tooth
from its developmental position in the jaw to its final
position in the oral cavity.

Theories of tooth eruption
A. Blood pressure theory :
The tissue around the developing end of the root is highly
vascular, this vascular pressure is believed to cause the
axial movement.
B. Root growth:
The apical growth of roots results in an axially directed
force that brings about the eruption of the teeth .

C. Hammock ligament:
A band of fibrous tissue exists below the root apex and Is
rich in fluid droplets.
The developing root forces itself against this band of tissue,
which in turn applies an occlusally directed force on the
tooth.
D. Periodontal ligament traction:
The periodontal ligament is rich in fibroblasts that contain
contractile tissue.
The contraction of these periodontal fibers (mainly oblique
group of fibers) result in axial movement of the tooth.

Migration Or Drift Of Teeth
It is the minor changes in tooth position observed after
eruption of teeth.
In case of the maxillary dentition, it shows a natural tendency
to move in a mesial and occlusal direction.
As the teeth undergo occlusal and
proximal wear, they move in a mesial
and occlusal direction to maintain
inter-proximal and occlusal contact.

Tooth movement during mastication
The teeth and periodontal structures are subjected to
intermittent heavy forces which occur in cycles of one
second or less and may range from 1- 50 kilograms .
A tooth subjected to these heavy forces, exhibits slight
movement within its socket and subsequently returns to its
original position .

Histology Of Tooth Movement
The histological changes seen during tooth movement vary
according to the amount and duration of force applied, its
classified as:
A. Changes following application of mild force.
B. Changes following application of extreme force.

A.Changes Following Application Of Mild Force
When a force is applied to a tooth, areas of pressure
and tension are produced.
Changes on pressure side :
1. The periodontal ligament in the direction of the tooth
movement gets compressed to almost l/3rd of its original
thickness.
2. Increase in cellular proliferation within a few days.

3. Osteoclasts migrate into the PDL from blood vessels.
4. When the forces applied are within physiologic limits, the
resorption is seen in the alveolar plate immediately adjacent
to the ligament. This kind of resorption is called frontal
resorption.

Changes on tension side :
1. Stretching of PDL fibres the distance between the
alveolar process and the
tooth is widened.
2. Cellular proliferation of fibroblasts and osteoblasts.
3. Deposition of osteoid immediately adjacent to the lamina
dura.

4. Secondary remodeling changes take place elsewhere
to maintain the width or thickness of the alveolar
bone.
If a tooth is being moved in a labial direction, there is
compensatory deposition of new bone on the outer side of the
labial alveolar bony plate and a compensatory resorption on the
lingual side of the lingual alveolar bone .

A. Secondary remodeling changes seen following the
application of a bodily force in a lingual direction .
B. Secondary remodeling changes seen following the
application of a tipping force in a lingual direction .

B.Changes Following Application Of Extreme
Force
On the pressure side :
1. Capillary blood vessels are crushed resulting in death
of cells in PDL (hyalinization(.
2. In areas adjacent to the hyalinized sections of PDL cellular
proliferation occurs .
3. Resorption occurs deep to hyalinized area from cancellous
bone outwards toward lamina dura of PDL (undermining
resorption(.

On the tension side :
1. The periodontal ligament gets over-stretched leading
to tearing of the blood vessels and ischemia.
Thus there is a net Increase in osteoclastic activity as
compared to bone formation with the result that the tooth
becomes loosened in its socket.In addition ,pain and
hyperemia of the gigivae may occur due to application of
extreme forces during orthodontic tooth movement .

Diagram showing the effect
of applying an excessive
force
Areas of hyalinization (1(
Undermining resorption (2(
Direct resorption in areas where
force is less (3(

Optimum Orthodontic Force
It is the force which moves teeth most rapidly in the
desired direction, with the least possible damage to tissue
and with minimum patient discomfort.
the optimum force is equivalent to the capillary pulse
pressure which is 20-26 gm/ sq.cm of root surface area.

It has the following characteristics:
1. Produces rapid tooth movement.
2. Minimal patient discomfort .
3. The lag phase of tooth movement is minimal.
4. No marked mobility of the teeth being moved.
5. The vitality of the tooth and supporting periodontal
ligament is maintained.
6. Initiates maximum cellular response and Produces
direct or frontal resorption .

Phases Of Tooth Movement
Tooth movement progresses through three stages:
A. Initial phase:
1. Very rapid tooth movement is observed over a short
distance which then stops .
2. It represents displacement of the tooth in the periodontal
membrane space and probably bending of alveolar bone to
a certain extent.
3. The tooth movement in the initial phase is between 0.4 to
0.9 mm and usually occurs in a week's time.

B. Lag phase:
1. During this phase, little or no tooth movement occurs.
2. Characterized by formation of hyalinized tissue in the
periodontal ligament which has to be resorbed before further
tooth movement can occur.
3. If light forces are used, the area of hyalinization is small
and frontal resorption occurs.
4. If heavy forces are used, the area of hyalinization is large.
Resorption in this case is undermined and a longer lag period
occurs to eliminate the hyalinized tissue.

5. The lag phase usually extends for 2-3 weeks but may
at times be as long as 10 weeks.
C. Post lag phase:
1. After the lag phase, tooth movement progresses rapidly as
the hyalinized zone is removed and bone undergoes
resorption.

Theories Of Tooth Movement
A. Pressure tension theory by Schwarz (1932 ).
B. Blood flow theory by Bien (1966).
C. Bone bending piezoelectric theory by Farrar
(1876).

Reasons For More Rapid
Tooth Movement In Children
Physiological tooth movement is greatest when the
teeth are erupting.
The periodontal ligament is more cellular, and therefore
there are more cells available for resorption and remodeling
The alveolar bone has a greater proportion of osteoblasts
The cellular response in reaction to an applied force is quicker

The width of the periodontal ligament is increased in
newly erupted teeth, and so a greater force can be applied
before constriction of the blood vessels occurs.
Growth can be utilized.

Drugs And Tooth Movement
The rate of orthodontic tooth movement can be altered
by applying certain drugs locally or systemically.
A. Promoter drugs
These agents basically enhance bone resorption .
They couple with the secondary and primary inflammatory
mediators and enhance tooth movement .

They are :
1. Prostaglandin’s
2. Leucotriens
3. Cytokines
4. Vitamin d
5. Osteocalcin
6. Corticosteroids
Except vitamin d and corticosteroids the other above said
agents are not that much widely used in medical profession.

Since bone turn over rate will be more for those patients
under any of the above mentioned drugs, care should be
taken by utilizing low forces or by giving increased duration
between appliance activation appointments.
The duration of orthodontic treatment is usually 18 months,
this extended duration can be reduced by applying promoter
agents locally near the moving unit, (i.e. anteriors)

B.Suppressor agents
These agents basically reduce bone resorption .
1. Nonsteroidal anti-inflammatory agents -- they interfere
with archidonic acid metabolism, blocks production of
primary and or secondary messengers.
Since NSAIDs are freely available over the counter, patients
should be advised not to take these drugs during orthodontic
treatment, without the dentist’s knowledge.

2. Bisphosphonates – bind with calcium ions, promotes
apoptosis of working osteoclasts.
The bisphosphonate groups of drugs are economically more
in cost and not easily available over the counter, but they are
the drugs of choice for patients with osteoporosis.
A thorough medical history will definitely reveal whether the
patient is under such a treatment, caution should be taken while
taking up these patients for orthodontic treatment

At present orthodontic mini implants are used to aid in
anchorage, when compared to headgears which also aid
in anchorage these implants costs more. Moreover most
of the patients deny wearing headgears.
Alternatively the suppressor agents can be delivered
locally near the anchor unit (i.e. molars) to enhance
anchorage and retention.

Biology of orthodontic tooth movement

More Related Content

What's hot (20)

Similar to Biology of orthodontic tooth movement (20)

More from Maher Fouda (20)

Recently uploaded (20)

Biology of orthodontic tooth movement