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1. TISSUE REACTIONS
IN
ORTHODONTICS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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2. INTRODUCTION
•
Orthodontic Appliances have been in use for a
very long time. Since then the mode of action of
appliances have been the same. Appliances have
been fabricated and used in various designs to
apply a therapeutic force which would move teeth
through the bone to their intended positions.
•
Irrespective of the type of appliance - a spring, an
arch wire or an elastic the mechanical-biological
transduction and the following tissue changes of
the periodontium are generally the same. This
presentation deals with the tissue changes in the
periodontium and the biology of tooth movement.

3. HISTOLOGY OF THE SUPPORTING
STRUCTURES
PERIODONTAL LIGAMENT
GINGIVA
ALVEOLAR BONE

4. PERIODONTAL LIGAMENT
0.25mm wide cellular and
vascular connective tissue rich
in fibres connecting the root
surface to the alveolar bone
wall
The fibres are : Principle
fibres, Elastic fibres and
indifferent fibre plexus
Principle fibres are made of
collagen and form the basis of
the attatchment apparatus
Principle fibres are divided into
Apical, Oblique,Horizontal and
Alveolar crestal fibres.

5. PERIODONTAL LIGAMENT
Collagen fibres are synthesised from fibroblasts.
Fibroblasts synthesise Tropocollagen fibril molecules which are later
organised into fibres and fibre bundles.
The collagen turnover rate is higher than any other tissue in the body- 3
to 23 days. The collagen turnover rate in the gingiva is also high but
comparitively slower than the PDL.

6. PERIODONTAL LIGAMENT
Elastic fibres are: Oxytalan
and Eluanin.
They are immature Elastin
fibres.
Oxytalan fibres run vertically
parallel to the root surface
and get embedded coronally
into the cementum.
Oxytalan fibres control the
vascularity of the Periodontal
ligament as they intermingle
with the blood vessels.

7. PERIODONTAL LIGAMENT
•
CELLS:
Fibroblasts
Mesenchymal cells
Epithelial cell rests
Defence cells

8. PERIODONTAL LIGAMENT
Fibroblasts are stellate
shaped cells with
interconnecting peripheral
processes.
They are responsible for the
synthesis and destruction of
the collagen fibres and the
extracellular matrix.
Thus they are responsible for
the tissue turn over.

9. PERIODONTAL LIGAMENT
Mesenchymal cells form the reserve for
all connective tissue cells like
fibroblasts, osteoblasts and osteoclasts.
Their number decreases with age.
Osteoblasts and Osteoclasts are seen
lining the socket wall.
Mesenchymal cells form the reserve for
all connective tissue cells like
fibroblasts, osteoblasts and osteoclasts.
Their number decreases with age.

10. PERIODONTAL LIGAMENT
The extracellular matrix is made of
Glycosaminoglycans which hold the tissue fluid within
itself and is responsible for the viscoelastic properties
of the PDL.

11. GINGIVA
Parts of the Gingiva:
Free Gingiva,
Attached Gingiva,
Interdental Papilla.

12. GINGIVA
Composition:
65% Connective
tissue fibres.
5% Fibroblasts.
35% Nerves,
Vessels and
Matrix.

13. GINGIVA
Collagen in the Gingiva has
two types of arrangements:
Bundles and Networks.
The Bundles are:
Dentogingival
Dentoperiosteal
Transseptal
Circular

14. GINGIVA
Collagen
composition:
90% Type I
Collagen
8% Type II
Collagen
2% Type IV,V,VI &
VII Collagen

15. GINGIVA
Collagen fibre Bundles:
Gingival collagen has a high turnover rate but not as high as the
PDL.
However the rate of turnover of the transseptal fibres is similar
to that of the PDL.

16. GINGIVA
• Connective tissue matrix:
Proteoglycans: similar to Glycosaminoglycans found in the
PDL.
Glycoproteins:
Fibronectin and Laminin: Extracellular multiadhesive
proteins necessary for cell migration, differentiation and
healing.
SPARC(Secreted Protein Acidic and Rich in Cysteine) or
Osteonectin: A Calcium binding protein which disrupts CellECM interactin and found at sites of cell migration,
proliferation and morphogenesis.

17. ALVEOLAR BONE
Parts of the alveolar
bone:
Alveolar bone
proper
Cancellous bone
Outer cortical plate

18. ALVEOLAR BONE
Cells of the Alveolar Bone:
Osteoblasts
Osteoclasts
Osteocytes
Osteoprogenitor cells

19. ALVEOLAR BONE
Osteoblasts:
Bone forming cells
Derived from Osteoprogenitor cells
Later mature to form Osteocytes

20. ALVEOLAR BONE
Osteoclasts:
Bone resorbing
cells
Haemopoetic in
origin derived from
monocyte
precursors
Multinucleated with
ruffled border

21. OSTEOCLASTS

22. TISSUE RESPONSE TO NORMAL
FORCES
•
The periodontal ligament is a fluid filled chamber with porous walls of
limited permeability. The PDL thus acts as a shock absorber within
physiological limits due to it’s viscoelastic properties.
•
During masticatory function teeth meet force values between 2kg to
50kg of very short duration may be 1 second or less. During this time
the tooth is not displaced within the PDL but the PDL acts as a shock
absorber and transfers the forces to the alveolar bone producing bone
bending.
•
But however if a similar amount of force is applied for a longer time the
tooth moves within the PDL space with excursion of the extracellular
fluid into the marrow spaces resulting in close approximation of the
root surface with the alveolar bone proper resulting in pain.
•
The PDL is well adapted to physiological forces and maintain the
integrity of the arches. But when a therapeutic force is applied for a
long duration of time the physiological limit is crossed and tooth
movement takles place.

23. REACTION OF THE PERIODONTAL LIGAMENT
TO PHYSIOLOGICAL FORCES
TIME IN SECONDS
REACTION
<1
PDL fluid incompressible
Alveolar bone bends
Peizoelectricity
1 to 2
PDL fluid expressed
Tooth moves within the PDL
space
3 to 5
PDL fluid squeezed out
Tissues compressed
Pain

24. TISSUE RESPONSE TO ORTHODONTIC
FORCES
• Tissue reaction to Orthodontic forces depends on the following
factors
Force magnitude
Force duration
Morphology of the supporting structures
• As the tooth is being moved through a biological medium using
a force the basic laws of physics donot hold good. Higher forces
donot produce faster tooth movement nor do lighter forces
cause slower tooth movement.

25. FORCE DISTRIBUTION
• Orthodontic forces applied on a tooth are not
evenly distributed through the Root surface.
Force distribution for each type of tooth
movement -Tipping,Translation,Rotation,
Intrusion and Extrusion are different.
• Force distributions are represented by a
Loading diagram.

26. FORCE DISTRIBUTION DURING
TIPPING
Only one half of the PDL surface
area is loaded.
Concentration of pressure in limited
areas- beneath the alveolar crest
and near the apical third of the root.
Tensile forces present opposite to
areas of pressure.
force value decreases from the
loaded areas towards the region of
the centre of rotation and reaches a
value of zero at the centre of
rotation
Force value:35 to 60g.

27. FORCE DISTRIBUTION DURING
BODILY MOVEMENT
PDL area is uniformly
loaded.
Two times more force
is required than tipping
as the area loaded is
two times more.
A uniform area of
pressure on one side
and a uniform area of
tension on the other
side is seen.
Force value: 70 to 120g

28. FORCE DISTRIBUTION DURING
TORQUING
Initially the pressure area is located close to
the middle region of the root due to the
variation in thickness of the PDL.
Later a uniform area of pressure is seen along
the surface of the root.
Force value: 50 to 100g.

29. FORCE DISTRIBUTION DURING
ROTATION
Force can be distributed over the entire PDL
area.
Larger forces can be applied.
Usually two pressure areas and two areas of
tension are seen.
Force value: 35 to 60g

30. FORCE DISTRIBUTION DURING
EXTRUSION
Ideally should produce no areas of
compression.
Force value: 35 to 60g.

31. FORCE DISTRIBUTION DURING
INTRUSION
Light force is required
as it is concentrated
in a very small area.
Force value: 10 to
20g.

32. TISSUE REACTIONS IN THE
PERIODONTAL LIGAMENT
The tooth alone does not move but so does it’s attachment
apparatus. Tooth movement is basically a periodontal ligament
phenemenon and all tissue reactions are mediated through the
periodontal ligament.
The role of the periodontal ligament is explained by the PressureTension theory which is the classical theory of tooth movement.
Other theories that explain tooth movement are the Peizoelectric
theory and Streaming potential which are concerned with
Bioelectricity..
The role of the periodontal ligament will be explained in relation to
the Pressure tension theory.

35. FRONTAL RESORPTION AND
UNDERMINING RESORPTION.

36. RESPONSE TO A SUSTAINED
THERAPEUTIC FORCE
Light force:
TIME
RESPONSE
Less than 1 sec
Alveolar bone bending and
peizoelectric signals are
generated
1 to 2 sec
PDL fluid expressed
Tooth moves within the PDL
space
3 to 5 sec
Vascular changes
Fibres and cells mechanically
distorted
Minutes
Blood flow altered
Oxygen tension altered
PG and cytokines released

37. RESPONSE TO A SUSTAINED
THERAPEUTIC FORCE
Light force:
TIME
RESPONSE
Hours
Metabolic changes
Chemical messengers alter cellular
activity
Cellular enzymes released
4 Hours
Cellular differentiation detectable in
the PDL
2 Days
Tooth movement begins as bony
socket is remodelled

38. RESPONSE TO A SUSTAINED
THERAPEUTIC FORCE
Heavy force:
TIME
RESPONSE
< 1 sec
Alveolar bone bending and peizo
electricity
1 to 2 sec
Tooth moves within the PDL space
3 to 5 sec
Blood vessels totally occluded
Minutes
Blood flow totally cut off to the
compressed area

39. RESPONSE TO A SUSTAINED
THERAPEUTIC FORCE
Heavy force:
TIME
RESPONSE
Hours
Cell death in compressed area
3 to 5 days
Cell differentiation in adjacent
marrow spaces
7 to 14 days
Undermining resorption removes the
lamina dura adjacent to compressed
PDL and tooth movement occurs

40. TOOTH MOVEMENT AND TISSUE
CHANGE
Tooth movement can be divide
into three phases : Initial tooth
movement, Lag phase and Post
lag phase
Initial tooth movement is due to
movement of the tooth within the
PDL space
Lag phase is the period during
which the hyalinised area is
cleared up
Post lag phase is the period of
frontal resorption

41. TRANSDUCTION OF MECHANICAL
FORCE INTO BIOLOGICAL SIGNALS.
•
Many transduction mechanisms have been studied:
cAMP dependent second messenger system
Prostaglandin E dependent second messenger system
Other Eicosanoids
Phosphatidylinositol pathway
Cytoskeletal-Matrix interaction
Neuropeptides

42. cAMP DEPENDENT MECHANISM
Mechanical forces cuse cell
membrane pertubrations which
cause an influx of Calcium ions
The influx of Calcium ions
causes production of cAMP
cAMP stimulates differentiation
of osteoblasts and osteoclasts
from osteoprogenitor cells
cAMP appears only 4 to 6
hours after application of
sustained force

43. PROSTAGLANDIN E DEPENDENT
SECOND MESSENGER SYSTEM
Prostaglandins are derived from cell
membrane phospholipids called
Arachinodic acid
They are produced by the
cyclooxygenase pathway which
produce inflammatory mediators. A
pathway that is blocked by common
NSAID’s
The pathway is stimulated by a
mechanical disturbance of the cell
membranes
Prostaglandin E which is then produced
can stimulate Osteoclasts after 48
hours and later stimulate the
osteoblasts . So first a wave of
resorption is seen followed by a wave
of bone deposition.
Prostaglandins can also stimulate
Inteleukin1 which later stimulates the
cAMP mechanism
QuickTime™ and a GIF decompressor are needed to see this picture.

44. OTHER EICOSANOIDS
Recent studies have shown
that tooth movement cannot be
explained by the role of cAMP
and PGE alone.
QuickTime™ and a GIF decompressor are needed to see this picture.
Other second messengers like
leukotrienes which are also
metaboluites of Arachidonic
acid are now known to play a
role. PGE and Leukotrienes
belong to the same family of
compounds called
Eicosanoids.

45. CYTOSKELETAL-MATRIX
INTERACTION

46. Phosphatidylinositol Pathway

47. NEUROPEPTIDES
Experiments have shown that cAMP levels can
be increased not only by mechanical stimuli but
also by endogenous chemical stimulus
Neuropeptides like Substance P, Vasoactive
intestinal polypeptide and Calcitonin gene
relared polypeptide are released from sensory
nreve endings in the PDL.
Substance P bind to osteoblast cell receptors
and also cause vasodilation

48. TISSUE RESPONSE OF THE
GINGIVA
Gross gingival changes are seen after closure of an extraction space or after rotation
or excessive labial movement.
After space closure accumulation of gingival tissue and enlargement of the interdental
papilla is seen due to retraction and compression of the gingival tissues of the
extraction space.
At the mesial surface of the orthodontically retracted tooth a triangular red patch is
seen. This is the Reduced enamel epithelium that has peeled off.
After space closure vertical invaginations and clefts are formed by both the epithelium
and connective tissue on the Buccal and lingual aspects.

49. ULTRASTRUCTURAL CHANGES
Studies done by Transmission Electron microscopy have shown that there is an increase in the
diameter of collagen fibres in areas of pressure and tension.
Degraded collagen fibres are seen in areas of compressed papillae.
There is an increase in the number and size of elastic fibre on the pressure side.
Fewer elastic fibres are seen on the tension side.
After tooth movement there is an increase in interstitial matrix content, collagen and elastic
fibres.
A pappillary epithelial hyperplasia is seen in the extraction space after space closure.
The transseptal fibres in the extraction space are coiled and compressed and have a football
shape.
Stretched supracrestal fibres are not responsible for relapse but it is the increase in Elastic
fibres and ground substance in the region of compressed areas that are responsible for

50. CHANGES IN THE
ALVEOLAR BONE

51. ALVEOLAR
BONE
NORMAL BONE
TURNOVER

52. CHANGES IN THE
ALVEOLAR BONE
RESORPTION FRONT

53. CHANGES IN THE
ALVEOLAR BONE
Apposition front

54. SIGNALLING MECHANISM IN BONE

55. CHANGES IN THE ALVEOLAR
BONE
Bone resorption and deposition are always coupled. Uncoupling of
resorption and deposition takes place during tooth movement. IL-1 is
responsible for uncoupling
Bone resorption is the limiting factor of tooth movement
There are two waves of bone resorption. The first wave of resorption is
from precursor cells present within the PDL. The second wave is from
precursor cells from the blood vessels
Always osteoclasts are stimulated first followed by osteoblast

56. CHANGES IN THE ALVEOLAR
BONE
After 93% of appliance activity is over a second wave of bone
remodelling is seen. - BIPHASIC BONE REMODELLING.
Bone has STRAIN MEMORY which is created by mechanical
distortion of it’s extracellular matrix. So cells are stimulated even after
the mechanical stimulus is removed.
Short exposures to mechanical signals can stimulate substantial
amounts of bone remodelling.
Cyclic or pulsating forces can produce tooth movement similar to
those produced by continuous forces.

57. SERUM MARKERS AND OTHER
BIOMOLECULES
Serum markers of Osteoblast activity:
Osteocalcin
Alkaline phosphatase
Serum markers of Osteoclast activity:
Acid Phosphatase

58. BIOMOLECULES STIMULATING
BONE CELLS
Stimulating Osteoclasts:
Interleukin-1
Tumor Necrosis Factor - alpha
Metabolites of VitaminD
Stimulating Osteoblasts:
Tumor Growth Factor - beta
Insulin like Growth factor - I
Platelet Derived Growth Factor

59. WAVES OF BONE ACTIVITY
PERIODS OF DELAY
INITIAL 7 DAYS
CELL ACTIVITY
Increased in number of osteoclasts
Increased serum acid phosphatase
Increased serum alkaline phosphatase
and osteocalcin
DAYS 10 to 14
No resorption
Increased Osteoblast bone
formation
DAYS 14 TO 18
Tooth movement
Resorption
Inhibition of formation
18th DAY

60. PEIZOELECTRICITY AND
STREAMING POTENTIAL
Peizoelectricity is a phenomenon common to all crystalline
structures. When any crystalline structure undergoes stress
induced deformation a current is produced within the crystalline
structure due to displacement of the electrons within it. The
alveolar bone can also be considered as a huge crystal of
hydroxyapatite molecules and peizoelectric currents induced in
them by forces - physiological or therapeutic. As the alveolar bone
bends concave areas become electropositive and resorption takes
place whereas convex areas become electronegative and bone
deposition takes place.

61. CLINICAL IMPLICATIONS
Force duration
Differential anchorage
Differential force philosophy
Adult Orthodontics
Relapse

62. FORCE DURATION
Intermittent force
Interrupted force
Continuous light force

63. INTERMITENT FORCE
Force levels decrease abruptly to zero when the appliance is
removed by the patient.- RA, Headgear, Elastics

64. INTERRUPTED FORCE
Force levels decline to zero between activations

65. CONTINUOUS LIGHT FORCE
Force maintained at some appreciable fraction of the original
from one appointment to the next

66. FORCE DURATION
A force duration of atleast 4 hours is required to produce second
messengers
In humans clinical experience has shown that atleast 6 hours of
sustained force is necessary
Continuous forces produce the most efficient tooth movement
Interrupted forces give enough time for tissues to regenerate and
reorganize
In case heavy forces are used, which most often happens undermining
resorption would take atleast 7 to 14 days so appliances are not to be
reactivated within 3 weeks

67. DIFFERENTIAL ANCHORAGE
Anchorage potential of a tooth may vary according to the
density of the alveolar bone and the cross section of the
root
The volume of osseous tissue that should be removed is
a tooths anchorage value
Maxillary molars have lesser anchorage value than
mandibular molars
Thin cortices and trabeculae of maxillary alveolar
bone
Bone formed during mesial movement of the molar is
more dense in the mandible

68. DIFFERENTIAL FORCE
PHILOSOPHY
Storey and Smith first
studied the effects of
force variation in
orthodontics
The concept was later
adopted by Begg into
his Light arch wire
technique

69. ADULT ORTHODONTICS
Due to Bone loss the PDL area decreases so the same force will
cause higher Pressure
So the absolute force magnitude used should be less
The centre of resistance is more apically located so the moment of
any force would increase. Thus the countermoment magnitude
should be increased. Overall the M:F ratio is increased
Decreased blood flow and decreased vascularity of the PDL provide
an explanation for the insufficient source of progonitor cells
Cortical bone becomes more dense and the cancellous bone
changes from a trabecular pattern to a network
Initial forces should be low as the immediate pool of cells available
is less.
Light continuous intrusive force to be maintained if marginal bone
loss is seen

70. RELAPSE
Stretched gingival fibres play a
major role
Increased Oxytalan fibres and
ECM in compressed areas are
also a reason
Gingival fibres take 232 days to
totally remodel
Rotation corrections and
closure of spaces have a high
relapse rate

71. CONCLUSION
Tissue reactions in Orthodontics form the basis of our
clinical procedures - How much force? and What type
of Force? A sound knowledge of the tissue reactions is
necessary to know how we really move teeth through
bone.
Though most of the research done is based on animal
studies the use of these results in a clinical setting
seem promising. The use of NSAID’s like indomethacin
to inhibit tooth movement and locally administered
Prostaglandins to accelerate tooth movement in
humans can be tried. With improved histological
techniques and better research methods used, our
knowledge of the tissue reactions will improve.

72. Thank you
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