Biology Of Tooth Movement

1. BIOLOGYOFTOOTH

BIOLOGYOFTOOTH
MOVEMENTMOVEMENT
By:By:
Dr shabeel pnDr shabeel pn

2. IntroductionIntroduction
Orthodontic tooth movement is a Orthodontic tooth movement is a uniqueunique
process where a solid object (tooth) is made process where a solid object (tooth) is made
to move through a solid medium (bone). to move through a solid medium (bone).
Orthodontic treatment is possible due to the Orthodontic treatment is possible due to the
fact that fact that whenever a prolonged force is whenever a prolonged force is
applied on a tooth,bone remodelling applied on a tooth,bone remodelling
occurs around the tooth resulting in its occurs around the tooth resulting in its
movementmovement..

3. Bone subject to Bone subject to pressurepressure as a result of as a result of
compressioncompression of periodontal ligament of periodontal ligament
resorbsresorbs. While, bone . While, bone formsforms under under tensiletensile
force, as a result of force, as a result of stretchingstretching of of
periodontal ligament.The bony response is periodontal ligament.The bony response is
mediated by the mediated by the periodontal ligamentperiodontal ligament, ,
Tooth movement is primarily a periodontal Tooth movement is primarily a periodontal
ligament phenomenon.ligament phenomenon.

4. Structure of periodontal ligament:Structure of periodontal ligament:
The The PDLPDL occupies a space approximately occupies a space approximately 0.5mm 0.5mm
in width around all parts of roots. in width around all parts of roots.
Major component of the ligament are:-Major component of the ligament are:-
•Network of parallel Network of parallel collagenous fiberscollagenous fibers..
•Cellular elementsCellular elements along with vascular and along with vascular and
neural elements. neural elements.
•Tissue fluidsTissue fluids. .
 The cellular element and fluid play an The cellular element and fluid play an
important role in normal function and in important role in normal function and in
making orthodontic tooth movement possible.making orthodontic tooth movement possible.

5. I.Physiologic Tooth MovementI.Physiologic Tooth Movement
Naturally occurringNaturally occurring tooth movements that tooth movements that
take place during and after tooth eruptiontake place during and after tooth eruption. .
This include:This include:
A)A)Tooth EruptionTooth Eruption..
B)B)MigrationMigration or drift of teeth. or drift of teeth.
C)C)ChangesChanges in tooth position in tooth position during masticationduring mastication. .

6. TOOTH ERUPTION:TOOTH ERUPTION:
Tooth eruption is the Tooth eruption is the axial movementaxial movement of tooth from of tooth from
its development position in the jaw to its final position its development position in the jaw to its final position
in the oral cavity.in the oral cavity.
The following are some theories which explains the The following are some theories which explains the
eruption process.eruption process.
 a)a)Blood pressure theoryBlood pressure theory::
According to this theory,the tissue around According to this theory,the tissue around
the developing end of the root is highly vascular.This the developing end of the root is highly vascular.This
vascular pressure is believed to cause the axial vascular pressure is believed to cause the axial
movement of teeth.movement of teeth.

7. b)Root Growthb)Root Growth::
 According to this theory,the apical growth of According to this theory,the apical growth of
roots result in an axially directed force that brings about the roots result in an axially directed force that brings about the
eruption of teeth.eruption of teeth.
This theory was rejected because:This theory was rejected because:
The tooth moves at a greater distance than the root length.The tooth moves at a greater distance than the root length.
Onset of root growth and eruption do not coincide.Onset of root growth and eruption do not coincide.
Teeth without roots also erupt.Teeth without roots also erupt.
c)Hammock ligament theory:c)Hammock ligament theory:
 According to Sicher, a band of fibrous tissue According to Sicher, a band of fibrous tissue
exists below the root apex spanning from one side of alveolar exists below the root apex spanning from one side of alveolar
wall to other. This fibrous tissue appears to form a network wall to other. This fibrous tissue appears to form a network
below the developing root and is rich in fluid droplets.the below the developing root and is rich in fluid droplets.the
developing root forces itself against this band of tissue, which developing root forces itself against this band of tissue, which
in turn applies an occlusally directed force on tooth.in turn applies an occlusally directed force on tooth.

8. d)Periodontal traction theory:d)Periodontal traction theory:
This theory states that the This theory states that the
periodontal ligament is rich in fibroblasts periodontal ligament is rich in fibroblasts
that contain contractile tissue.The that contain contractile tissue.The
contraction of these periodontal fibers contraction of these periodontal fibers
(mainly the oblique group of fibers) results (mainly the oblique group of fibers) results
in axial movement of the tooth.in axial movement of the tooth.

9. B) B) Migration or drift of teeth:Migration or drift of teeth:
Refers to the minor changes in tooth position Refers to the minor changes in tooth position
observed after eruption .observed after eruption .
Human dentition shows a natural tendency to Human dentition shows a natural tendency to
move in a mesial & occlusal direction.move in a mesial & occlusal direction.
Usually a result of proximal and occlusal wear of Usually a result of proximal and occlusal wear of
teeth,teeth,
They move in a mesial and occlusal direction to They move in a mesial and occlusal direction to
maintain inter-proximal and occlusal contact.maintain inter-proximal and occlusal contact.

10. C)C)Tooth movement during mastication:Tooth movement during mastication:
During mastication ,the teeth and PDL During mastication ,the teeth and PDL
structures are subjected to intermittent structures are subjected to intermittent
heavy forces which occurs in cycles of heavy forces which occurs in cycles of
one second or less and may range from one second or less and may range from
1-50 kg based on the type of food 1-50 kg based on the type of food
being masticated.being masticated.

11. Physiologic response to heavy pressure Physiologic response to heavy pressure
against a toothagainst a tooth:-:-
<1 sec – PDL fluid incompressible, alveolar <1 sec – PDL fluid incompressible, alveolar

bone bends, piezoelectric effect.bone bends, piezoelectric effect.
1-2 sec – PDL fluid compressed, tooth moves 1-2 sec – PDL fluid compressed, tooth moves
within the PDL space.within the PDL space.
3-5 sec – PDL fluid squeezed out, tissue 3-5 sec – PDL fluid squeezed out, tissue
compressed, immediate pain.compressed, immediate pain.

12. II.Orthodontic Tooth MovementII.Orthodontic Tooth Movement
It is a pathological process from which the tissue It is a pathological process from which the tissue
recovers.recovers.
Histology of tooth movement:Histology of tooth movement:
Orthodontic movement bring about areas of pressure Orthodontic movement bring about areas of pressure
and tension around the tooth. The histologic changes and tension around the tooth. The histologic changes
seen during tooth movement vary according to the seen during tooth movement vary according to the
amount and duration of force applied. amount and duration of force applied.

14. Changes following application of Changes following application of
mild forces:mild forces:
Classically the movement of teeth has been Classically the movement of teeth has been
explained via the pressure:tension explained via the pressure:tension
hypothesis in which PDL tissues in hypothesis in which PDL tissues in
pressure side results in bone resurption , pressure side results in bone resurption ,
while placing the PDL tissues under tensile while placing the PDL tissues under tensile
force lead to bone deposition. force lead to bone deposition.

15. Changes on pressure side:Changes on pressure side:
 The PDL in direction of tooth movement gets The PDL in direction of tooth movement gets
compressed to almost 1/3rd of it’s original thickness. compressed to almost 1/3rd of it’s original thickness.
A marked increase in the vascularity of PDL on this A marked increase in the vascularity of PDL on this
side is observed due to increase in capillary blood side is observed due to increase in capillary blood
supply. supply.
This increase in blood supply helps in mobilization of This increase in blood supply helps in mobilization of
cells such as fibroblasts and osteoclasts. cells such as fibroblasts and osteoclasts.
 Osteoclasts are bone resorbing cells that lie in Osteoclasts are bone resorbing cells that lie in
Howship’s lacunae .Howship’s lacunae .
when forces applied are within physiologic limits,the when forces applied are within physiologic limits,the
resorption is seen in alveolar plate immediately resorption is seen in alveolar plate immediately
adjacent to the ligament.This kind of reorption is adjacent to the ligament.This kind of reorption is
called frontal resorption.called frontal resorption.

16. Changes on tension side:Changes on tension side:
PDL stretchedPDL stretched
Distance between alveolar process & tooth Distance between alveolar process & tooth
is widened.is widened.
Increased vascularity.Increased vascularity.
Mobilization of fibroblasts & osteoblasts.Mobilization of fibroblasts & osteoblasts.
Osteoid is laid down by osteoblast in PDL Osteoid is laid down by osteoblast in PDL
immediately adjacent to lamina dura.immediately adjacent to lamina dura.
Lightly calcified bone mature to form woven Lightly calcified bone mature to form woven
bone.bone.

17. Secondary remodelling changes:Secondary remodelling changes:
 Bony changes also takes place Bony changes also takes place
elsewhere to maintain the width or thickness of elsewhere to maintain the width or thickness of
alveolar bone.These changes are called secondary alveolar bone.These changes are called secondary
remodeling changes.remodeling changes.
For egFor eg:-:-If a tooth is being moved in a lingual direction If a tooth is being moved in a lingual direction
there is compensatory deposition of new bone on the there is compensatory deposition of new bone on the
outerside of the lingual alveolar bony plate and also a outerside of the lingual alveolar bony plate and also a
compensatory resorption on the labial side of the compensatory resorption on the labial side of the
labial alveolar bone. labial alveolar bone.
This is to maintain the thickness of the This is to maintain the thickness of the
supporting alveolar process .supporting alveolar process .

19. Change following application of extreme Change following application of extreme
forces:forces:
On the pressure sideOn the pressure side :- :-
Root closely approximates the lamina dura .Root closely approximates the lamina dura .
Compresses the PDL and leads to occlusion of Compresses the PDL and leads to occlusion of
blood vessels. blood vessels.
The PDL is hence deprived of its nutritional The PDL is hence deprived of its nutritional
supply leading to regressive changes called supply leading to regressive changes called
hyalinization .hyalinization .
Underminig/Rearward resorption occurs in the Underminig/Rearward resorption occurs in the
adjacent marrow spaces and alveolar plate below, adjacent marrow spaces and alveolar plate below,
behind & above the hyalinized zone.behind & above the hyalinized zone.

20. On the tension side:-On the tension side:-
Over stretched PDL .Over stretched PDL .
Tearing of blood vessels & ischaemia.Tearing of blood vessels & ischaemia.
Extreme forces applied net increase in Extreme forces applied net increase in
osteoclastic activity and tooth loosened in osteoclastic activity and tooth loosened in
socket. socket.

22. Optimum orthodontic force:Optimum orthodontic force:
Is one which moves teeth most rapidly in the desired Is one which moves teeth most rapidly in the desired
direction ,with the least possible damage to tissue and direction ,with the least possible damage to tissue and
with minimum patient discomfort. with minimum patient discomfort.
SchwarzSchwarz proposed the classic concept of the optimal proposed the classic concept of the optimal
force. He defined optimal continuous force as the force. He defined optimal continuous force as the
force leading to a change in tissue pressure ,that force leading to a change in tissue pressure ,that
approximated the capillary vessel & blood approximated the capillary vessel & blood
pressure.Thus preventing their occlusion in the pressure.Thus preventing their occlusion in the
compressed PDL. compressed PDL.
Below the optimal level cause no reaction in PDL. Below the optimal level cause no reaction in PDL.
Forces exceeding optimal level would lead to areas of Forces exceeding optimal level would lead to areas of
tissue necrosis ,preventing frontal bone resorption. tissue necrosis ,preventing frontal bone resorption.

23. Schwarz’sSchwarz’s definition was slightly modified definition was slightly modified
by by OppenheimOppenheim who advocated the use of who advocated the use of
lightest force capable of bringing about lightest force capable of bringing about
tooth movement.tooth movement.
OppenheimOppenheim and and SchwarzSchwarz following following
extensive studies state that the optimum extensive studies state that the optimum
force is equivalent to the capillary pulse force is equivalent to the capillary pulse
pressure which is 20-26gm/sq.cm of root pressure which is 20-26gm/sq.cm of root
surface area. surface area.

24. From a clinical point of From a clinical point of
view,Optimum orthodontic force has view,Optimum orthodontic force has
the following characteristics:the following characteristics:
Produce rapid tooth movement.Produce rapid tooth movement.
Minimal patient discomfort.Minimal patient discomfort.
The lag phase of tooth movement is The lag phase of tooth movement is
minimal.minimal.
No marked mobility of the teeth being No marked mobility of the teeth being
moved. moved.

25. From a histological point of view the From a histological point of view the
use of optimum force has the use of optimum force has the
following characteristics:-following characteristics:-
The vitality of the tooth and supporting The vitality of the tooth and supporting
PDL is maintained.PDL is maintained.
 Initiates maximum cellular response.Initiates maximum cellular response.
 Produces direct or frontal resorption Produces direct or frontal resorption

26. Hyalinization:Hyalinization:
Form of tissue degeneration characterized by Form of tissue degeneration characterized by
formation of a clear, eosinophilic homogenous formation of a clear, eosinophilic homogenous
substances substances
Denotes a compressed and locally Denotes a compressed and locally
degenerated PDL. degenerated PDL.
Reversible process. Reversible process.
Occurs in almost all forms of orthodontic Occurs in almost all forms of orthodontic
tooth movement but the areas are wider when tooth movement but the areas are wider when
the force applied is extreme.the force applied is extreme.

27. Changes observed during formation Changes observed during formation
of hyalinized zone are: of hyalinized zone are:
Gradual shrinkage of PDL fibres.Gradual shrinkage of PDL fibres.
Cellular structures become indistinctCellular structures become indistinct
Collagenous tissues gradually unite into a more or Collagenous tissues gradually unite into a more or
less cell free mass.less cell free mass.
changes also occur in the ground substance.changes also occur in the ground substance.
break down of blood vessel walls leading to break down of blood vessel walls leading to
spilling of their contents.spilling of their contents.
Osteoclasts are formed after a period of Osteoclasts are formed after a period of
20-30 hrs.20-30 hrs.

28. The presence of hyalinised zone indicates The presence of hyalinised zone indicates
that the ligament is non-functional and that the ligament is non-functional and
therefore bone resorption cannot therefore bone resorption cannot
occur.The tooth is hence not capable of occur.The tooth is hence not capable of
further movement until the local damaged further movement until the local damaged
tissue has been removed and the adjacent tissue has been removed and the adjacent
alveolar bone resorbs .alveolar bone resorbs .

29. Elimination of hyalinised tissue Elimination of hyalinised tissue
2 mechanism:-2 mechanism:-
2.2.By osteoclasts differentiating in the peripheral By osteoclasts differentiating in the peripheral
intact PDL membrane and in the adjacent intact PDL membrane and in the adjacent
marrow spaces. marrow spaces.
3.3.Invasion of cells and blood vessels from the Invasion of cells and blood vessels from the
periphery of the compressed zone by which periphery of the compressed zone by which
necrotic tissue is removed. The invading cells necrotic tissue is removed. The invading cells
penetrate the hyalinized tissue and eliminate penetrate the hyalinized tissue and eliminate
unwanted fibrous tissue by enzymatic action unwanted fibrous tissue by enzymatic action
and phagocytosis.and phagocytosis.

30. Forces & HyalinizationForces & Hyalinization
Greater the forces wider is the area of Greater the forces wider is the area of
hyalinization. Thus larger areas of the ligament hyalinization. Thus larger areas of the ligament
becomes functionless ,thereby showing larger becomes functionless ,thereby showing larger
areas of rearward resorption areas of rearward resorption
If lighter forces are used,the hyalinised zone is If lighter forces are used,the hyalinised zone is
smaller and a larger area of functioning smaller and a larger area of functioning
ligament is available and frontal resorption ligament is available and frontal resorption
predominates. predominates.
The location and extend of hyalinised tissue The location and extend of hyalinised tissue
largely depends upon nature of tooth largely depends upon nature of tooth
movement.movement.

31. A-A-TippingTipping –close to –close to
alveolar crestalveolar crest
B-B-ExcessiveExcessive forceforce
during tipping-two during tipping-two
areas,one on apical areas,one on apical
region and other in region and other in
marginal area.marginal area.
C-C-BodilyBodily-closer to -closer to
middle portion of rootmiddle portion of root

32. Phases of tooth movementPhases of tooth movement
Burstone categorize the stages as:-Burstone categorize the stages as:-
Initial phaseInitial phase
Lag phaseLag phase
Post lag phasePost lag phase

33. Initial phase:Initial phase:
Rapid tooth movement is observed over a short Rapid tooth movement is observed over a short
distance which then stops. distance which then stops.
Represents displacement of tooth in PDL Represents displacement of tooth in PDL
membrane space and probably bending of membrane space and probably bending of
alveolar bone .alveolar bone .
Both light and heavy forces displace the tooth to Both light and heavy forces displace the tooth to
same extent .same extent .
Between 0.4 to 0.9mm usually occurs in a weeks Between 0.4 to 0.9mm usually occurs in a weeks
time.time.
Both light & heavy forces displace the tooth to the Both light & heavy forces displace the tooth to the
same extent during this phase.same extent during this phase.

34. Lag phase:Lag phase:
Little or no tooth movement occurs .Little or no tooth movement occurs .
Formation of hyalinized tissue .Formation of hyalinized tissue .
Extent upto 2-3 weeks . Extent upto 2-3 weeks .

35. Post lag phase:Post lag phase:
Tooth movement progresses rapidly as the Tooth movement progresses rapidly as the
hyalinized zone is removed and bone undergoes hyalinized zone is removed and bone undergoes
resorption .resorption .
Osteoclasts are found over a larger surface area .Osteoclasts are found over a larger surface area .

37. Theories of tooth movement:Theories of tooth movement:
1.1.Pressure tension theory by Schwarz.Pressure tension theory by Schwarz.
(classic theory)(classic theory)
2.2.Fluid dynamic theory by Bien/ blood flow Fluid dynamic theory by Bien/ blood flow
theory: theory:
3.3.Bone bending & piezoelectric theory: Bone bending & piezoelectric theory:

38. Pressure tension theory by Schwarz.Pressure tension theory by Schwarz.
(classic theory) (classic theory)
Schwarz(1932) - author of this theory .Schwarz(1932) - author of this theory .
According to him ,whenever a tooth is According to him ,whenever a tooth is
subjected to an orthodontic force it results subjected to an orthodontic force it results
in areas of pressure and tension .in areas of pressure and tension .
Areas of pressure show bone resorption Areas of pressure show bone resorption
while areas of tension show bone while areas of tension show bone
deposition. deposition.

39. Fluid dynamic theory by Bien/ Fluid dynamic theory by Bien/
Blood flow theoryBlood flow theory
According to this theory tooth movement According to this theory tooth movement
occurs as a result of alternations in fluid occurs as a result of alternations in fluid
dynamics in PDL located in periodontal dynamics in PDL located in periodontal
ligament space. ligament space.
PDL space contains a fluid system made up of PDL space contains a fluid system made up of
interstitial fluid, cellular elements , blood interstitial fluid, cellular elements , blood
vessels and viscous ground substances in vessels and viscous ground substances in
addition to PDL fibres. addition to PDL fibres.
It is a confined space and passage of fluid in & It is a confined space and passage of fluid in &
out of this space is limited. out of this space is limited.

40. The contents of PDL creates a unique The contents of PDL creates a unique
hydrodynamic condition resembling a hydraulic hydrodynamic condition resembling a hydraulic
mechanism & shock absorber .mechanism & shock absorber .
When force is removed, the fluid is replenished by When force is removed, the fluid is replenished by
diffusion from capillary walls & recirculation of diffusion from capillary walls & recirculation of
interstitial fluids. interstitial fluids.
Squeeze film effect by Squeeze film effect by BienBien . .
 When orthodontic force applied,the compression When orthodontic force applied,the compression
of ligament results.Blood vessels of PDL gets of ligament results.Blood vessels of PDL gets
trapped between the principle fibres & this results trapped between the principle fibres & this results
in stenosis. in stenosis.
Vessels above the stenosis then balloons resulting Vessels above the stenosis then balloons resulting
in formation of an aneurysm in formation of an aneurysm

41. Stenosis Stenosis ++ Aneurysm Aneurysm  blood gases to blood gases to
escape into interstitial fluids, creating escape into interstitial fluids, creating
favourable local environment for favourable local environment for
resorption. resorption.

42. Bone bending & piezoelectric theory:Bone bending & piezoelectric theory:
Farrar in 1876, first noted deformation or bending Farrar in 1876, first noted deformation or bending
of interseptal alveolar bones. of interseptal alveolar bones.
suggest that bone bending may be a possible suggest that bone bending may be a possible
mechanism for bringing about tooth movement. mechanism for bringing about tooth movement.
Piezo-electricity is a phenomenon observed in Piezo-electricity is a phenomenon observed in
many crystalline materials in which deformation many crystalline materials in which deformation
of the crystal structure produces a flow of electric of the crystal structure produces a flow of electric
current as a result displacement of electrons from current as a result displacement of electrons from
one part of the crystal lattice to the other.A small one part of the crystal lattice to the other.A small
electric current is generated & bone is electric current is generated & bone is
mechanically deformed. mechanically deformed.

43. The possible source of electric current are :-The possible source of electric current are :-
• Collagen.Collagen.
•Hydroxyapetite.Hydroxyapetite.
•Collagen hydroxyapetite interface.Collagen hydroxyapetite interface.
•Mucopolysaccharide.Mucopolysaccharide.

44. As long as the force is maintained ,The As long as the force is maintained ,The
crystal structure is stable & no further crystal structure is stable & no further
electric effect is observed. electric effect is observed.
When the force is released the crystals When the force is released the crystals
return to their original shape & reverse return to their original shape & reverse
flow of electrons is observed. flow of electrons is observed.
This rhythmic activity produces a This rhythmic activity produces a
constant interplay of electric signals .constant interplay of electric signals .

45. Piezoelectric signals have two Piezoelectric signals have two
unusual characteristics.unusual characteristics.
Quick decay rate: Quick decay rate:
When the force is released electrons flow in the When the force is released electrons flow in the
opposite direction.opposite direction.
On application of a force on a toothOn application of a force on a tooth , ,
Areas of concavity Areas of concavity  negative charges negative charges  bone bone
deposition.deposition.
 Areas of convexity Areas of convexity  + +
veve
charges and charges and  bone bone
resorption. resorption.

46. Bone deposition:Bone deposition:
On the On the tension side.tension side.
 Increase in number of osteoblasts .Increase in number of osteoblasts .
Osteoblasts are ovoid cells with basophilic Osteoblasts are ovoid cells with basophilic
cytoplasm and a oval nucleus. cytoplasm and a oval nucleus.
Osteoblast increase in number by proliferation Osteoblast increase in number by proliferation
of their precursor cells. of their precursor cells.
The PDL fibers readapt to new position of the The PDL fibers readapt to new position of the
tooth by proliferation of intermediate zone.tooth by proliferation of intermediate zone.

48. Bone resorption:Bone resorption:
By By OSTEOCLASTSOSTEOCLASTS
Multi-nucleated giant cells and may have 12 or Multi-nucleated giant cells and may have 12 or
more nuclei. more nuclei.
They are irregularly and or club shaped with They are irregularly and or club shaped with
branching processes .branching processes .
They lie in bay like depressions called They lie in bay like depressions called
Howship’s lacunae. Howship’s lacunae.
The part of osteoclast in contact with resorbing The part of osteoclast in contact with resorbing
bone has a ruffled border. bone has a ruffled border.

49. Osteoclasts derived from:-Osteoclasts derived from:-
Activation of previously present Activation of previously present
inactive cells.inactive cells.
Migration from adjacent bones.Migration from adjacent bones.
Formation of new osteoclasts from Formation of new osteoclasts from
local macrophages of PDL.local macrophages of PDL.
Influx of monocytes from blood vessels.Influx of monocytes from blood vessels.

50. During bone resorption three processes During bone resorption three processes
occur:occur:
3.3.Decalcification.Decalcification.
4.4.Degradation of matrix.Degradation of matrix.
5.5.Transport of soluble products to the Transport of soluble products to the
extracellular fluid or blood vascular extracellular fluid or blood vascular
system system

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