Introduction to Orthodontics Fifth Year

1. 15th Lecture
Biology of Tooth
Movement-I

2. Outlines
•
•
•
•
April 28, 2012
Clinical consideration of the periodontium:
Periodontal Ligament:
Mechanisms of Orthodontic tooth
movement:
Tissue Reaction To Tooth Movement:
Physiologic Tooth Movement:
a) Resorptive bone wall
b) Depository bone wall
Dr. Ahmed Basyouni
2

3. Outlines
Orthodontic Tooth Movement
(OTM):
a) Dentoalveolar tissue reaction:
i. Pressure side:
ii. Tension side:
b) Hyalinization
April 28, 2012
Dr. Ahmed Basyouni
3

4. Fact
Orthodontic treatment is based on this fact:
Orthodontic treatment is possible, by
applying appropriate forces to move teeth
through the alveolar bone.
Accurate and precise control of tooth
movement can be achieved with proper use of
mechanics and knowledge of subsequent tissue
response.
April 28, 2012
Dr. Ahmed Basyouni
4

5. Clinical consideration of the periodontium
• Periodontium is a major factor influencing tooth
movement during orthodontic treatment.
It includes:
a) Gingiva
b) Alveolar bone
c) Periodontal ligament
d) Cementum
April 28, 2012
Dr. Ahmed Basyouni
5

6. Periodontal Ligament
• Periodontal ligament (PDL) is the connective tissue
surrounds the root and attaches it to the alveolar bone.
It consists of Cells, fibers, ground substance & normal width
0.5 mm .
Functions:
1. Formative
2. Supportive
3. Protective
4. Nutritive
5. Sensory
April 28, 2012
Dr. Ahmed Basyouni
6

7. Mechanisms of Orthodontic tooth movement
Modeling and remodeling of the alveolar bone caused
by Two basic cellular processes:
a) Osteoblastic activity (bone formative)
b) Osteoclastic activity (bone resorptive)
These two cellular activities remove bone from
one place and add it to another, to make characteristic
size and shape of each bone for everyone.
The DNA encoded information in each cell
nucleus or sometimes external (environmental ) could
direct cell activities to produce changes in size and
shape that occur during growth.
April 28, 2012
Dr. Ahmed Basyouni
7

8. Mechanisms of Orthodontic tooth movement
Orthodontic Tooth Movement (OTM) causes:
a) Pressure side: cell replication is decreased as a
result of vascular constriction.
b) Tension side: cell replication is increased, bec. Of
stimulation afforded by stretching of the fiber
bundles of the PDL.
April 28, 2012
Dr. Ahmed Basyouni
8

9. Periodontal and Other Tissue Reaction To
Tooth Movement
I.
II.
Physiologic Tooth Movement:
a) Resorptive bone wall
b) Depository bone wall
Orthodontic Tooth Movement (OTM):
a) Dentoalveolar tissue reaction
i. Pressure side
ii. Tension side
b) Hyalinization
April 28, 2012
Dr. Ahmed Basyouni
9

10. Periodontal and Other Tissue Reaction To Tooth Movement
I. Physiologic Tooth Movement:
Growth of the craniofacial complex in vertical,
sagittal and transverse dimensions causes positional
changes of the teeth in all three planes of space.
a) Resorptive bone wall:
Alveolar bone resorption occurs on the side
toward which tooth is moving, same time,
reconstruction of ligament support between tooth and
bone is taking place.
April 28, 2012
Dr. Ahmed Basyouni
10

11. Physiologic Tooth Movement:
a) Resorptive bone wall:
Microscopically, osteoclasts present in
scattered resorptive lacunae on alveolar bone
wall. After a while, resorption stop and
Howship’s Lacunae will be occupied by other
cells depositing new layers of bone to which
new periodontal fibrils become embedded.
April 28, 2012
Dr. Ahmed Basyouni
11

12. Physiologic Tooth Movement:
b) Depository bone wall:
Alveolar bone deposition occurs on the side
opposite the direction to which tooth is moving,
together with rearrangement of the periodontal fibers.
April 28, 2012
Dr. Ahmed Basyouni
12

13. Periodontal and Other Tissue Reaction To Tooth Movement
II. Orthodontic Tooth Movement (OTM):
OTM is a biologic response of periodontal tissues
to applied forces. Orthodontic forces are much
heavier than natural forces responsible for
physiologic migration .
Histochemical changes and cellular response
depend on:
1. Force intensity
2. Force duration
3. Force direction
April 28, 2012
Dr. Ahmed Basyouni
13

14. Periodontal and Other Tissue Reaction To Tooth Movement
Orthodontic Tooth Movement (OTM):
The ideal force is one which induces a
pressure in the periodontal ligament not
exceeding the capillary blood pressure i.e.
not more than 32 mmHg.
April 28, 2012
Dr. Ahmed Basyouni
14

15. April 28, 2012
Dr. Ahmed Basyouni
15

16. Periodontal and Other Tissue Reaction To Tooth Movement
Orthodontic Tooth Movement (OTM)
a) Dentoalveolar tissue reaction:
A distinct pressure and tension zone is developed on
either side of the tooth after force application.
Bone modification is not restricted only to resorption and
apposition around tooth in the periodontal space but also,
seen in marrow spaces and under periosteum on external
surfaces of the alveolar processes.
This mechanism shows that, tooth is not simply moved
through bone, but supporting structures move with a tooth
into a new position as a response to change in its
environment.
April 28, 2012
Dr. Ahmed Basyouni
16

17. Periodontal and Other Tissue Reaction To Tooth Movement
Orthodontic Tooth Movement (OTM)
i. Pressure side:
Periodontal cells have differentiated into
specialized cells (Osteoclasts) which are responsible
for resorption of the alveolar bone wall.
In young individuals, resorption process may
begin as soon as 12 hours after force application.
The periodontal width on pressure side has been
initially decreased due to mechanical compression of
the periodontal ligament, then greatly increased in
order to allow space for high cellular activity and
proliferation of vascular structures.
April 28, 2012
Dr. Ahmed Basyouni
17

18. Orthodontic Tooth Movement (OTM)
i. Pressure side:
A chain of osteoclasts is seen along the alveolar
wall. Fibrous supporting apparatus on pressure side is
reconstructed by almost complete breakdown of the
old fibers and formation of new fibrous elements.
The vascular system provides many of the
undifferentiated cells that are responsible for
reconstructional changes.
April 28, 2012
Dr. Ahmed Basyouni
18

19. Orthodontic Tooth Movement (OTM) i.
Pressure side:
Effects of LIGHT forces on the periodontium:
•
Light, continuous forces
– Osteoclasts formed
– Removing lamina dura
– Tooth movement begins
– This process is called “FRONTAL
RESORPTION”.
April 28, 2012
Dr. Ahmed Basyouni
19

20. Orthodontic Tooth Movement (OTM) i.
Pressure side:
•
“Frontal resorption” because it occurs
between the root and the lamina dura.
April 28, 2012
Dr. Ahmed Basyouni
20

21. Orthodontic Tooth Movement (OTM)
i. Pressure side:
April 28, 2012
Dr. Ahmed Basyouni
21

22. Periodontal and Other Tissue Reaction To Tooth Movement
Orthodontic Tooth Movement (OTM)
ii. Tension side:
Cellular increase occurs after 30 to 40 hours following
application of an orthodontic force.
Stretched fibers on tension side is seen to be reconstructed by
changes of the original fibrils.
New unmineralized osteoid material is laid down around
stretched fibers close to alveolar bone wall produced by
osteoblasts. Mineralization of the osteoid starts in the deepest
layers.
April 28, 2012
Dr. Ahmed Basyouni
22

23. Orthodontic Tooth Movement (OTM)
ii. Tension side:
April 28, 2012
Dr. Ahmed Basyouni
23

24. Periodontal and Other Tissue Reaction To Tooth Movement
Orthodontic Tooth Movement (OTM)
b) Hyalinization
Hyalinization occurs when heavy applied forces
presses tooth too hard against the alveolar bone wall.
Periodontal membrane responds with local
degeneration and sterile necrosis. In humans, it takes
1 to 2 days for a hyalinized zone to develop. Tooth is
not capable of movement until this hyalinized tissue
is removed.
April 28, 2012
Dr. Ahmed Basyouni
24

25. Periodontal and Other Tissue Reaction To Tooth Movement
Orthodontic Tooth Movement (OTM)
b) Hyalinization
Elimination of hyalinized zone occurs by two
mechanisms:
1. Resorption of the alveolar bone by
osteoclasts.
2. Invasion of cells and blood vessels from
periphery of compressed zone by
which necrotic tissue is removed.
April 28, 2012
Dr. Ahmed Basyouni
25

26. Orthodontic Tooth Movement (OTM)
b) Hyalinization
• Effects of HEAVY forces on the
periodontium
• Heavy, continuous forces cause
– Blood supply to PDL occluded
– Aseptic necrosis
– PDL becomes “hyalinized” –
“HYALINIZATION”
– This process is called “UNDERMINING
RESORPTION”.
April 28, 2012
Dr. Ahmed Basyouni
26

27. Orthodontic Tooth Movement (OTM)
b) Hyalinization
“Undermining resorption” because it occurs on the
underside of lamina dura, not between lamina
dura and the root.
April 28, 2012
Dr. Ahmed Basyouni
27

28. FRONTAL
RESORPTION
Phase 3
Phase 2
Phase 1
Time (Arbitrary Unit)
UNDERMINGING
RESORPTION
Tooth movement (mm)
Tooth movement (mm)
Orthodontic Tooth Movement (OTM)
b) Hyalinization
Phase 3
Phase 2
Phase 1
Time (Arbitrary Unit)
Frontal resorption facilitates orthodontic tooth movement, whereas
undermining resorption impedes orthodontic tooth movement.
April 28, 2012
Dr. Ahmed Basyouni
28

29. Summary
•
•
•
•
April 28, 2012
Clinical consideration of the periodontium:
Periodontal Ligament:
Mechanisms of Orthodontic tooth
movement:
Tissue Reaction To Tooth Movement:
Physiologic Tooth Movement:
a) Resorptive bone wall
b) Depository bone wall
Dr. Ahmed Basyouni
29

30. Summary
Orthodontic Tooth Movement
(OTM):
a) Dentoalveolar tissue reaction:
i. Pressure side:
ii. Tension side:
b) Hyalinization
April 28, 2012
Dr. Ahmed Basyouni
30

31. April 28, 2012
Dr. Ahmed Basyouni
31