THEORIES OF TOOTH MOVEMENT

1. GOOD MORNING

2. THEORIES OF
ORTHODONTIC TOOTH
MOVEMENT
MEHDI MUSTAFA
JR1

3. CONTENTS
 OBJECTIVE
 INTRODUCTION
 HISTORY
 KINGSLEY AND WALKHOFF HYPOTHESIS
 WORKS OF SANDSTEDT(1904-05)
 OPPENHEIMS TRANSFORMATION HYPOTHESIS
 COMPARISON BETWEEN SANDSTEDT AND OPPENHEIM MODEL
 SCHWARZ (1932)
 PRESSURE TENSION HYPOYHESIS
 DRAWBACK OF PRESSURE TENSION HYPOTHESIS
 BONE BENDING /PIEZOELECTRIC THEORY
 DRAWBACKS OF BONE BENDING THEORY
 FLUID DYNAMIC THEORY
 SECOND MESSENGER CONCEPT IN ORTHODONTICS
 CONCLUSION

4. OBJECTIVE
TO HAVE AN OVERVIEW OF
SOME OF THE IMPORTANT
THEORIES OF ORTHODONTIC
TOOTH MOVEMENT

5. INTRODUCTION
 Orthodontic tooth movement is the result of a biological
response to interference in the physiological equilibirium of
the dentofacial complex by an externally applied
force(Profitt,2013)
 The biological foundations of force induced orthodontic tooth
movement along with some of the concepts related to it has
been investigated extensively since the onset of 20th century

6. HISTORY
The old pressure hypothesis of Schwalbe Flourens ,
which postulated that pressure moves teeth preceded
the concept that alveolar bone resorption takes place
on one side of the dental root while deposition takes
place on the opposite side

7. KINGSLEY (1881)
Based on his vast clinical
experience,Kingsley stated that
 Slow Orthodontic Tooth Movement is
associated with favourable tissue
remodeling changes(resorption and
deposition of alveolar bone),while
 Quick movements displace entire bony
lamellae along with the teeth.
The functional and structural integrity is
retained.He attributed these features to
elasticity,compressibility and flexibility of bone
tissue

8. WALKHOFF’S HYPOTHESIS(1890)
 Walkhoff stated that “Movement of a tooth consists in
creation of different tensions in the bony tissue ,its
consolidation in the compensation of these tensions .
 Walkhoff’s hypothesis was larglely based on the
elasticity ,flexibility and compressibility of bone.
 He also stated that alveolar bone,after all the
remodeling changes,maintains its thickness,due to
transformation or apposition of bone during the
consolidating period.

9. SANDSTEDT (1904-05)
 Histological examination of paradental tissues during
orthodontic tooth movement was reported for the first time by
Sandstedt who tipped teeth uncontrollably in dogs,and later
studied their tissues by light microscopy
In Sandstedt’s experimental model
 a labial arch was bent to engage the six maxillary incisors of a dog and
inserted into horizontal tubes attached to bands on the canines..

10. Distal to the tubes was a screw mechanism ,which when tightened moved
incisors lingually and canines mesially

11. Results of Sandstedt’s experimental
model
TENSION SIDE PRESSURE SIDE
LIGHT FORCE BONE DEPOSITED ON
ALVEOLAR WALL
ALVEOLAR BONE
RESORBED
HEAVY FORCE BONE DEPOSITED ON
ALVEOLAR WALL
HYALINIZATION

12. PRESSURE SIDE – Resorptive bone
surface with numerous osteoclasts in
Howship’s lacunae
TENSION SIDE-New bony
trabeculae oriented along the
principal fibres of the ligament
HISTOLOGICAL PICTURE

13. OPPENHEIM’S TRANSFORMATION
HYPOTHESIS
 Oppenheim (1911 , 1930 ) published the results of
experimental work carried out on the primary teeth of
monkeys.
 He found that where a tooth had been tipped labially, the
original bone disappeared completely from the labial surface
and was replaced by new bone.
 According to him,this takes place by resorption of the bone
present and deposition of new bone tissue; both processes
occured simultaneously.

14. COMPARISON BETWEEN
SANDSTEDT AND OPPENHEIM’S
MODEL
Sandstedt:
In the regions of pressure in the PDL,the
old alveolar bone is resorbed and in the
regions of tension ,new alveolar bone is
added
Oppenheim:
On the side of the pull, bone is resorbed
and new bone is added by resorption of the
bone present and deposition of new bone
tissue; both processes occur
simultaneously

15. Schwarz (1932)
 Schwarz (1932) attempted to explain the difference between
the findings of Sandstedt and Oppenheim by the fact that
Oppenheim had euthanized his experimental animals several
days after the appliance had been last activated
 Moreover Oppenheim ignored the acute phase reactions and
focused only on the stage of regeneration after the force had
been exhausted.

16.  Following Schwarz publication Oppenheim worked
further(1944) on tissue reactions in mature monkeys to light
and heavy forces
LIGHT FORCES HEAVY FORCES
Osteoclasts mobilized at a fast pace
and attack bone by uniform lacunar
resorption
Resulted in undermining resorption

17. PRESSURE TENSION HYPOTHESIS
The studies of tooth movement through histological
analysis by Carl Sandstedt,Oppenheim and Schwarz led
them to hypothesise that tooth moves within the
periodontal space by generating a “pressure side” and a
tension side”

18. Diagram illustrating pressure-tension hypothesis. Application of orthodontic force
results in pressure on certain areas of the periodontal ligament while tension on the
others.Bone under pressure shows resorption while on the tension side,deposition
takes place

19.  On the pressure side
 PDL displays
disorganization and
diminution of fibre
production
 There is vascular
constriction
 Decrease in cell
replication
 On the tension side
 Stimulation produced by
stretching of PDL fibre
bundles results in an
increase in cell replication
 This eventually leads to an
increased fibre production

20.  Schwarz detailed the concept further ,by correlating the tissue
response to the magnitude of the force applied with the capillary
blood pressure
 According to him forces that are delivered as a part of orthodontic
treatment should not exceed the capillary blood pressure (20-
25gm/cm2)
 If this pressure is exceeded compression could cause necrosis
through “suffocation of the strangulated periodontium”
 Application of even greater force levels will result areas of
undermining resorption or hyalinization in adjacent marrow
spaces

21. DRAWBACK OF PRESSURE
TENSION HYPOTHESIS
 According to Baumrind,the
periodontal ligament is a
continuous hydrostatic system
and not a solid one
 Only part of the periodontium
where differential pressures as
mentioned in the pressure tension
hypothesis can be developed ,is
solid i.e bone,tooth, and discrete
solid fractures of PDL

22. BONE BENDING /PIEZOELECTRIC
THEORY
 Farrar(1876) first suggested that bone bending maybe a possible
mechanism for bringing about tooth movement
 Baumrind proposed a hypothesis in 1969,known as bone bending
theory
 Baumrind (1969) also observed that the crown of the first molar
was displaced, on average, 10 times more than the average
reduction in PDL width on the pressure side,suggesting that bone
deforms more readily than the PDL

23.  According to this hypothesis orthodontic forces routinely
produce
 alveolar bone deflection accompanied by resultant changes in
the PDL
 bending of the bone,tooth,as well as of solid structures of PDL
 Bone was found to be more elastic than the other two
tissues,which bend far more readily in response to force
application

24.  Zengo et al measured the electric potential in mechanically
stressed alveolar bone and demonstrated that
 concave side of the orthodontically treated bone is
electronegative and favours osteoblastic activity
 The convex side is electropositive and showed elevated
osteoclastic activity

25. HYPOTHETICAL MODEL OF THE ROLE OF STRESS INDUCED BIO ELECTRIC
POTENTIALS IN REGULATING ALVEOLAR BONE REMODELLING
ELECTRONEGATIVE/CONCAVE
BONE SURFACE
Characterized by osteoblastc activity
ELECTROPOSITIVE/CONVEX
BONE SURFACE
Characterized by osteoclastic
activity

26. The findings led to the suggestion that bioelectric
potentials(piezo-electricity and streaming
potentials) propagated by bone bending incident to
orthodontic force application might be functioning
as pivotal cellular first messengers

27. Piezoelectric potentials
 According to this concept when a crystal structure is
deformed,electrons migrate from one location to another
resulting in an electric charge
 The mineral content of bone in hydroxyapatite crystalline form
as well as collagen matrix,have piezoelectric properties
 Also,the mucopolysaccharides of ground substance can
generate piezo-electricity when deformed

28.  Two features of piezoelectricity are
Quick decay rate:When a force is applied,piezoelectricity is
generated,which immediately goes to zero level ,even if the force
is applied.This property is called quick decay rate.
Reverse piezoelectricity: When the force is removed ,the
crystals after returning to its original positions produce flow of
electrons in the opposite direction .This is reverse piezoelectricity

29.  Though piezo-elelectrical model enjoyed support initially
,there were problems from a biological point of view
 Piezoelectricity doesnot require the presence of living
cell;dead bone displays the same activity
 Wether the electrical phenomenon is sufficiently discriminatory
to be able to regulate the metabolic activity of cell types as
diverse as osteoblasts and osteoclasts is doubtful

30. DRAWBACKS OF BONE BENDING
THEORY
 The main drawback is that this theory was based on stress
generated signals which are produced by vibratory type of tooth
movement, but for optimum tooth movement light continuous
forces are applied
 A simple relationship between stress generated potentials and
cellular activation seemed unlikely since higher potentials are
seen in dentin than in other dental tissues,yet remodeling of
dentin doesnot occur in response to stress

31. FLUID DYNAMIC THEORY
 Bien in 1966 found out that there are three distinct but
interacting fluid systems involved in providing response to
intrusive forces in PDL
 Vascular system enclosed within the blood and lymph vessels
 The system of periodontal membrane, comprised of cells and
periodontal fibres
 Interstitial fluid continuum that permeates the spaces between
the cells,fibres,blood vessels,tooth and bone

32.  During intrusive cycle ,exhaustion of extracellular fluids from
the PDL membrane into the vascular reservoir of the marrow
space occurs .This damping rate is dependent upon size and
number of perforations.
 As a momentary effect the fluid that is trapped between the
tooth and the socket tends to move to the boundaries of the
film at neck of the tooth and the apex while acting to cushion
the load and is referred to as “squeeze film effect”

33.  As the squeeze film becomes depleted
and the pressure continued ,the second
damping effect occurs after exhaustion
of the extracellular fluid and the
ordinarily slack fibres tighten.
 These fibres which criss-cross the blood
vessels tighten ,then compress and
constrict the blood vessel which run
between them,causing stenosis of the
blood vessel.
 This causes vessels to balloon creating
a back pressure.

34.  At the stenosis a drop of pressure
would occur in the vessel in accordance
with Bernoulli’s principle
 Bien suggested that there is an
alteration in the chemical environment
at the site of the vascular stenosis due
to decreased oxygen level in the
compressed areas as compared to the
tension side
 The formation of these aneurysms and
vascular stenosis causes blood gases
to escape into interstitial fluid thereby
creating a favourable local environment
for resorption

35. SECOND MESSENGER CONCEPT
IN ORTHODONTICS
 According to this concept,increase in the tissue or cellular
concentrations of second messengers are generally viewed as
evidence that an applied extracellular ‘first messenger’,such as
an orthodontic force,has stimulated target cells.

36.  Arachidonic acid metabolites i.e prostaglandins and
leukotriens play a key role in conversion of orthodontic
pressure stimuli into a cell mediated response
 However considering the different response of osteoblasts
and osteoclasts to the same chemical stimuli that leads to
deposition of bone on tension side and resorption on pressure
side it has been suggested that it is the messenger system
that modulates the behavior of cells
 The messenger system translates a wide array of external
stimuli(first messenger) into a narrow range of internal
signals(second messengers)

37. CELLULAR RESPONSE TO
MECHANICAL FORCE
APPLICATION

38. The second messenger hypothesis postulates that
target cells respond to external stimuli,chemical or
physical,by enzymatic transformation of certain
membrane bound and cytoplasmic molecules to
derivatives capable of promoting the phosphorylation of
cascades of intracellular enzymes

39. CONCLUSION
 After 100 years of attempts by Sandstedt, we have reasonably
good understanding of the sequence of events involved in
orthodontic tooth movement at the tissue and cellular levels on
both the tensile and compression sides of the periodontium
 Tooth movement is not confined to events within the periodontal
ligament. Orthodontic tooth movement involves two interrelated
processes:
 deflection or bending of the alveolar bone and
 remodelling of the periodontal tissues

40. REFERENCES
 Biological Mechanisms of Tooth Movement,2nd Edition; Vinod Krishnan,Ze’ev
Davidovitch
 The tissue, cellular, and molecular regulation of orthodontic tooth movement:
100 years after Carl Sandstedt:Murray C. Meikle,Department of Oral Sciences,
Faculty of Dentistry, University of Otago, Dunedin, New Zealand
 Baumrind S 1969 A reconsideration of the propriety of the “ pressure tension”
hypothesis. American Journal of Orthodontics 55 : 12 – 22
 Orthodontics:Diagnosis and Management of Malocclusion an Dentofacial
Deformities-Om Prakash Kharbanda
 Orthodontics:Current Principles and Techniques;Graber ,Vanarsdall,Vig,Huang
 Bien S M 1966 Hydrodynamic damping of tooth movement. Journal of Dental
Research 45 : 907 – 914

41. THANK YOU