dynamics of tooth movement

8/3/2019 Dynamics of Tooth Movement

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www.dentist ro.or to find mo
http://www.dentistpro.org/http://www.dentistpro.org/


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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
http://howmilktoothisreplaced.swf/


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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.




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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 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
http://uglyduckling.swf/


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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
http://www.unc.edu/depts/appl_sci/ortho/biologic/force.htmlhttp://www.unc.edu/depts/appl_sci/ortho/biologic/force.html


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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
http://toothmovement.swf/


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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
http://proclination.swf/


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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


Rotation


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Labial or lingualmovements of a tooth

around its long axis


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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1. Minor Tooth Movement In Children. Joseph M Sim

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
http://www.dentistpro.org/http://www.dentistpro.org/http://www.dentistpro.org/

dynamics of tooth movement

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