dynamics of tooth movement
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Suzan sahana
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ContentsMAJOR TYPES OF TOOTH MOVEMENT
1. PhysiologicPattern of tooth movement
Periodontal & bone response to normal function
2. Pathologic toothMigration3. Orthodontic
Periodontal & bone response to orthodontic forces
Theories of tooth movementPhases of tooth movement
Deleterious effects of orthodontic force
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MECHANICS OF TOOTH MOVEMENT
Principles of biomechanics
Types of forces
Effects of force magnitude, duration, distribution and
force decayGENERAL PRINCIPLES OF TOOTH MOVEMENT
AnchorageinOrthodontics
Age factor in tooth movement
CONCLUSION
REFERENCES
Contents
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Physiologic tooth movement
These are naturally occurring tooth movements.Tooth eruption
Changes in tooth position during function/mastiction
Migration or drift of teeth:Stein & Weinmann (1965) -- molars migrate in a mesial direction
Bjork in 1925 described migration of erupting teeth in
radiographic studies. They demonstrated that the socket moves as
the tooth moves. Although movement is in a single direction
remodeling occurs all throughout.
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Physiologic tooth movemen
Eruption : Part of the total pattern ofphysiologic tooth movement.
Consists of the following:
Preeruptive tooth movement
Eruptive tooth movement
Posteruptive tooth movement
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Pattern of tooth movement
Preeruptive tooth movement:
Histology: whether it involves
drifting or growth of the tooth
germ, demands remodelling of
the bony wall of the crypt that
is achieved by selective deposn
& removal of bone byosteoblastic & osteoclastic
activity.
Physiologic tooth movem
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Permanent molars
Physiologic tooth moveme
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Eruptive tooth
movement:Tooth moves from its
position within the
jaw to its functionalposition in occlusion.
Principal direction of
movement axial/occlusal
Physiologic tooth moveme
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FORCES of Tooth EruptionRoot FormationBone Remodeling and DentalFolliclePeriodontal Ligament
M h i f ti t th
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Root elongation theory
suggests that teeth erupt as aresult of root pushing against
an immovable base
(disproved byMarks & Cahill
by their work on rootless
teeth which erupted by
compensatory bone growth)
Mechanisms of eruptive tooth movem
M h i f ti t th
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Periodontal ligament theory
suggests the impetus fortooth eruption was derived
from the developing
periodontal ligament.
Moxham & Berkovitzshowed
that root transection failed
to prevent the tooth
erupting. This stronglyimplicates the PDL effect.
Mechanisms of eruptive tooth movem
Mechanisms of eruptive tooth movem
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Bone remodelingApposition & resorption of
bone
Evidence: when devping tooth
is removed without disturbing
dental follicle eruptive
pathway forms within bone
Mechanisms of eruptive tooth movem
Mechanisms of eruptive tooth move
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dentalfollicleControl resorption and formation of
bone around tooth germ: Cahill & Mark
1974,1980,1983,1987
no dental follicle, no eruption
PDL , alveolar bone and cementumare derivative of Dental Follicle
Mechanisms of eruptive tooth move
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Molecular biology of Bone RemodelingTooth movement- balance b/w tissue destructio
& formn
Influx of monocytes at the onset of eruption
appearance of osteoclasts
signaling molecules
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MultifactorialConclusion of FORCES of Tooth Eruption
(However, Dental Follicle Activity & Bone
Remodeling have the Highest Potential)
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Post eruptive tooth movement
Made by the tooth after it has reached itsfunctional position in occlusal plane
3 categories:
i. Movements to accommodate growing jaws
ii. Those to compensate continued occlusal wear
iii. Those to accommodate interproximal wear
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Post eruptive tooth moveme
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Compensation for occlusal wear:
Axial movement that a tooth makes to
compensate for occlusal wear.
Deposition of cementum at the tooth apex.
Post eruptive tooth moveme
Post eruptive tooth movemen
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Accommodation for interproximal wear:
Compensated by mesial drift
Forces causing mesial drift:
Anterior component of occlusal force
Contraction of transseptal ligament
Soft tissue pressures
Post eruptive tooth movemen
Mesial
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Anterior component of occlusal force
Anterior force- result of mesial inclination of most
teeth & summation of intercuspal planes.
Billiard ball analogy
Mesial
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Contraction of transseptal ligament
Fibres of PDL draw
neighboring teeth closetogether & maintain them in
contact
Supporting evidence:Relapse of orthodontically
moved teeth is reduced if a
gingivectomy removing
transeptal ligament is
perfomed
Mesial drift is achieved by a contracti
mechanism associated with transeptafibres & enhanced by occlusal forces
S f iMesial
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Soft tissue pressures
Pressures generated by
cheeks & tongue may push
teeth mesially.
When such pressures
eliminated by constructing
acrylic dome over teeth
mesial drift occurs.
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Normal forces that affect tooth position &
stabilization:Natural forces generated by muscles
Tooth size & general shape of arches
Primary & residual eruption forces of each tooth
Combined mesial vector of force
Inclination of cusps & occlusal tables
Natural forces generated by muscles
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Natural forces generated by muscles
Muscles of the lips, cheeks,
tongue & mastication forms
functional matrix of soft
tissue
Forming an envelope of forces surroundinthe developing bones of the jaw & face
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Tooth size & general shape of arches
Harmony b/w tooth size& arch length
teeth size--- crowding
teeth size--- spacing
Tooth shape Peg laterals spacing &
migration of teeth
Primary & residual eruption forces of each
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Primary & residual eruption forces of eachtooth
Serves to keep teeth in
normal alignment &
allows wear & abrasion
to occur
In some cases, may result
in supraeruption.
Class II
C bi d i l t f f
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Combined mesial vector of force
The pronounced tendency toward mesial drifting of teeth i
both the arches
Some rules it seems to follow (Moyers)
1. Mesial vector of force is not strongly present until after
the first perm. Molars erupt.2. Mesial vector is present only if all teeth in arch are in
contact mesial to I perm. Molar.
3. If interproximal contact of teeth is lost, the vector onlyacts mesially through the area of II bicuspid. In the area o
I bicuspid & cuspid, the vector may act distally
When II primary molar is lost prematurely
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When II primary molar is lost prematurely
Impetus for distal drift :force from active contraction of transeptal fibers in the gingipressures from lips & cheeks
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Inclination of cusps & occlusal tables
Deeper the occlusal
table, the more likely
teeth will remain in the
same locked position.
Ectopic eruption
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Ectopic eruption
abnormal eruption of a
permanent tooth, which is
both out of position and
causing abnormal root
resorption of a primary tooth
May be due to genetic or
environmental causes.
Most common positional
aberration: Upper I perm molar
Lower lateral incisor
Deviation of dental midline in the direction of least
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Deviation of dental midline in the direction of leastresistance
Arrow Rule
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Ugly duckling stage
Periodontal and bone response to normal
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pfunction ( mastication)
PDL space filled with
fluid that is derived from
vascular systemFluid filled chamber
acts as shock absorber
Physiologic response to heavy pressure against ah
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y g p y p gtooth
TIME
(seconds)
EVENTS
< 1 PDL fluid is incompressible, alveolar bonebends, piezoelectric signal generated
1-2 PDL fluid expressed, tooth moves within
PDL space.3-5 PDL fluid squeezed out, tissues compressed
Immediate pain if pressure is heavy
During masticatory function-- teeth & periodontal
structures subjected to Intermittent heavy forces
Pathologic tooth migration
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Pathologic tooth migration
Refers to tooth displacement that results from the
balance among the factors that maintain
physiologic tooth position is disturbed by
periodontal disease.
Pathogenesis:
health & normal height of periodontium
forces exerted on teeth
Changes in the forces exerted on teeth:Pathologic tooth migra
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Changes in the forces exerted on teeth: Unreplaced missing teeth
Failure to replace I molars:
2nd & 3rd molars tilt
premolars move distally, mn incisors tilt
lingually
ant. Overbite increasedmx incsors pushed labially & laterally
Other causes
TFO
Pressure from tongue
Pressure from granulation tissue of
periodontal pockets
O h d i h
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Orthodontic tooth movement
Orthodontics is based on theprinciple that if prolonged
force is applied to a tooth,
tooth movement will occur.
The force creates pressure
that causes the bone around
the tooth to remodel
Periodontal and bone response to
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porthodontic force
Heavy force lead to
Rapidly developing
pain
Necrosis of cellular
elements within PDL
Undermining
resorption of alveolarbone.
Lighter forces arecompatible with:
Survival of cells within
the PDL Remodelling of tooth
socket by frontalresorption.
Theories of tooth movement
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f
Pressure tension theoryBlood flow theory
The piezoelectric theory
Pressure tension theory(Schwarz 1932)
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(Schwarz 1932)
Acc. To schwarz, when a
tooth is subjected to an
orthodontic force, it results
in areas of pressure andtension
Areas of pressure bone
resorption
Areas of tension bone
deposition
Fluid dynamic theory
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y y
Blood flow theory by Bien (1966).
PDL space is a fluid system acc. to this theory. An
alteration in blood flow within PDL space causes tooth
to shift position, compressing the ligament in some
areas while stretching it in others.
Blood flow where PDL is compressed
where PDL is under tension
Alt ti i bl d fl t h i h i lFluid dynamic theo
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Alterations in blood flow create changes in chemicalenvironment.
Oxygen levels fall in compressed area but
increase on tension side
Blood vessels of PDL get trapped b/w principal fibers
Anuerysms & vascular stenosis
Favourable local environment for resorption
Bone bending & piezoelectric theory of tooth
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g p y fmovement
Faraar (1876) noted deformation or bending ofinterseptal alveolar walls.
Electric signals are produced when the alveolar bone
bends or flexes.
Piezoelectricity is a phenomenon of a crystalline
material which when deformed produces a a flow of
electric current due to the displacement of electrons
from one crystal lattice to another.
S
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Sources
Hydroxyapatite
CollagenCollagen-hydroxyapatite
interface
Mucopolysaccaride fraction
of ground substance Properties
Quick decay
Equivalent and opposite in
direction
Phases of Tooth movement (Burstone)
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Initial phase
Very rapid tooth movement
Short distanceBending of bone
Lag phase
Little / no tooth movement
Hyalinization
Post lag phaseRapid tooth movement
Direct resorption seen over large areas of bone
Biochemical reaction to orthodontic tooth movement
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Biomechanics
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Mechanics: branch of engineering science thatdescribes the effect of force on a body.
Every body continues in its state of rest or ofuniform motion in a straight line, unless it is
compelled to change that state by forces
impressed on it (Sir Isaac Newton) & teeth areno exception.
Fundamental mechanical concepts
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Fundamental mechanical concepts
Center of resistance:
Equivalent balance point
for restraint bodies.Defined as that point on tooth
when a single force is passed
through it, would bring
about its translation alongthe line of action of the force.
In free space
Fundamental mechanical conc
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Force actions applied to
bodies
A vector having bothmagnitude & direction
Units: newton or gram
mm/sec2
Common means of producing
orthodontic forces:
deflection of wiresactivation of springs
elastics
Force systems
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Force systems
Biological effect = magnitude+
frequency+
Direction
+constancy+
range of activation+
functional modification
Effects of force magnitude
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When light force is applied
Blood flow through PDL
Within few hrs change in chemical environment produces a diffpattern of cellular activity
Levels of cyclic AMP appears after 4 hrs
This correlates well with the human response to removableappliances
If a removable appliance worn less than 4-6 hrs per day, noOrthodontic effects produced
Above this duration threshold, movement does occur
When forces applied are withinEffects of force magnitu
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physiological limits
Monocytes within PDL area are
stimulated to form osteoclasts.
First appear within 36-72 hrs
Osetoclasts attack adjacent lamina
dura removing bone--frontal
resorption
Tooth movement begins
Effects of force magnituIf forces are great enough
T t l l i f bl d l
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Total occlusion of blood vessels
Sterile necrosis ensues
Avascular areahyalinized
After several days, cellular elements
from other areas of PDL invadenecrotic area
Ie osteoclasts diff from adjacent bone
marrow & attack on the undersideof bone adjacent to necrotic PDL
area---- undermining resorption
Wh h li i ti & d i i ti
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When hyalinization & undermining resorption
occur ---inevitable delay in tooth movement
Delay in stimulating differentiation of cells within the
marrow spaces
A considerable thickness of bone must be removed
from underside before tooth movement begins
Effects of force distribution
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Force duration
Sustenance of force required for the
action of the second messenger
In humans effective tooth
movement requires 4-8 hours range
Fixed appliance more effective than
removable
PDL response is determined by force per unit
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area or pressure.
5 basic types of tooth movement:
Tipping
Bodily Movement
Intrusion
Extrusion
Rotation
Tipping
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Simplest form
Single force is applied against the crown of
a tooth.
Tipping can be of 2 types:
Controlled tipping: when a tooth tips about
a COR at its apex
Uncontrolled tipping: movement of tooth
that occurs about a CORot apical to COR.
Ex: spring extending from a removable
appliance
Ideal force 25 to 50 gms
Bodily movement/ translation
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if the line of action of an applied
force passes through the COR of a
tooth, all the points on the tooth will
move an equal distance in the same
direction
forces are applied simultaneously to
the crown of tooth
Force: 100 to 150 gms
Intrusion
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A translational type of
tooth movement parallelto the long axis of the
tooth in an apical
direction
Force: 15 to 20 gms
Extrusion
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A translational type of toothmovement parallel to the
long axis of the tooth in an
occlusal direction
Produce only areas of
tension
Force: 50 to 100 gms
Rotation
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Labial or lingualmovements of a tooth
around its long axis
Force: 50 to 100 gms
Force decay
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After the tooth has moved even a short distance,
the force delivered by some mechanisms may
drop all the way to zero.
Orthodontic force duration classified by rate of
decay
Continuous
Interrupted
Intermittent
Continuous force maintained at same
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appreciable fraction of the original from
one patient visit to the next. Interrupted force levels decline steadily
to zero b/w activations.
Ex: fixed appliances
Intermittent force levels decline
abruptly to zero when the orthodontic
appliance is removed by the patient.Ex: removable plates, headgear & elastics
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Activating an appliance too frequently shortcircuits the repair process.
Orthodontic appliance not to be reactivated
more frequently than 4 weeks interval
Anchorage
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g
Definition: nature & degree of resistance todisplacement offered by an anatomic unit for
the purpose of effecting tooth movement.
(Graber)
Sources of anchorage
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Intraoral sources:
Teeth
Alveolar bone
Basal jaw bone
MusculatureExtraoral sources:
Cranium
Back of the neckFacial bones
Classification of anchorage (Moyers)
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Acc. to manner of force application:
Simple anchorage
Stationary anchorage
Reciprocal anchorage
Acc to jaws involved:
Intramaxillary
Intermaxillary
Acc to site of anchorage:1. Intraoral
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2. Extraoral
cervicaloccipetal
cranial
facial3. Muscular
Acc to number of anchorage units:
single/primarycompound
multi le or reinforced
Simple anchorage
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Planned resistance to a
tipping force that would
change the axial inclination
of tooth/teeth serving as
anchorage unit
Ex: Palatally placed premolar
is pushed bucally with the
rest of the teeth in the dental
arch as anchor units.
Stationary Anchorage
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Planned resistance to a bodily movement thatwould change the position of an anchorage unit
with no tipping involved
Reciprocal anchorage Planned resistance of 2
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Planned resistance of 2
dental units to movements
secured such that equal &
opposite forces tends to
move each unit towards a
more normal occlusionEx: Traction forces set up to
close
ant. Diastema
Cross bite elastics
Dental arch ex ansion
Muscular anchorage
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Perioral musculatureemployed as resistance
units
Ex: Use of lip bumper todistalize molars
Reinforced or multiple anchorage
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More than one type of
resistance unit is utilized
Refers to augmentation
of anchorage by various
means
Ex: Upper anterior inclined
plane
Transpalatal arch
Deleterious effects of orthodontic forces
Eff t th l t i t i fl t
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Effects on the pulp: transient inflammatory response
discomfort for few days
moving endo treated teeth-- feasible
Root structure: only at apex
minimal & clinically insignificant
Height of alveolar bone: gingival inflammation
never exceeds 1mm
Pain & mobility: heavy pressure immediate pain
appropriate forces- several hrs later
mobility corrects itself
Tooth movement & age
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Vitality of tissue:effectively carried out inyoung patients
vascularity & cellularityof periodontalmembrane & bone
Role of growth
Tooth movement & a
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Role of apical foramen
Density of bone
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2. Oral Histology, Development, Structure And Function
5th Edition Tenkate. A. R.
3. Orbans Oral Histology and Embryology
11th ed. Bhaskar .S.N
3. .Color atlas of oral histology and embryology.Berkovitz
4. Contemporary orthodontics. 3rd edition Profitt.
5. Orthodontics. The art & science. S.I. Bhalajhi
6. Biomechanics in clinical orthodontics. Ravindra nandawww.dentist ro.or to find mo
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