Biomechanics and Types of Movement 9b670d85

7/26/2019 Biomechanics and Types of Movement 9b670d85

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In the name of

GOD


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Biomechanic and types of toothmovement

Presented by:

Dr Somayeh Heidari

Orthodontist


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Reference:

Contemporary Orthodontics

Chapter 8

William R. Prot Henry W. !ields Da"id #.Sar"er. $%&'. #osby


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De(nition of terms


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orce

a loadapplied to an ob)e*t that +ill tend to mo"eit to a di,erent positio

! - m.a

its nits are /e+tons or 0ram. #illimeters1 Se*onds$

is sally measred in +ei0ht nits of Grams oron*es

a for*e is a "e*tor

2ine of 3*tion

Ori0in 1

Point of appli*ation

Sense 1 Dire*tion


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Resultant


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Center of resistance

a point at +hi*h resistan*e to mo"ement *an be *on*entrated

for an ob)e*t in freespa*e is the same as the *enter of mass

for a partially restrained ob)e*t determined by the natre of

the e4ternal *onstraints


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5he *enter of resistan*e for a tooth is at the appro4imate midpoint of

the embedded portion of the root: abot half+ay bet+een the root

ape4 and al"eolar bone *rest.


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2o*ation of the *enter of resistan*e depends on the al"eolar

bone hei0ht root len0th morpholo0yand nmber of roots.


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oment

a for*e6!7 a*tin0 at a distan*efrom the *enter of resistan*e 6d7

m - ! d 60m9mm7

moment of a for*e reslts in some rotational mo"ement

it tends to rotate the ob)e*t arond the *enter of resistan*e

it is pre*isely the sitation +hen a for*e is applied to the *ro+nof a toot


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F

Distance (d)M = F d

Moment of Force


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Clini*al e4amples of moments of the for*es


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Couple

t+o parallel for*es eal in ma0nitdeand opposite in

dire*tion that separated by a distan*e

the reslt is a pre moment

+ill prod*e pre rotation arond the *enter of

resistan*e

*ople - ma0nitde of for*e6s7 distan*e bet+een

for*es


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F

F

d

M

M

! "

! "

# mm

$!! "%mm

Couple force = F d


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Center of rotation

the point arond +hi*h rotation a*tally o**rs +hen an ob)e*t

is mo"ed

If a for*eand a *opleare applied to an ob)e*t the *enter of

rotation *an be *ontrolled


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&ypes of tooth movement


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optimm orthodonti* for*e +ill stimlate *elllar a*ti"ity

+ithot *ompletely o**ldin0 blood"essels in the PD2.

the PD2 response is determined not by for*e ma0nitde alone

bt by for*e per nit area or pressre.

the distribtion of for*e +ithin the PD2 di,ers +ith di,erent

types of tooth mo"ement


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'ressure = Force rea


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&ippin"

the *ro+nand the rootmo"e in oppositedire*tions

0reatermo"ement of the *ro+nthan the root

the *enter of rotation is api*alto the *enter of resistan*e

based on the lo*ationof the *enter of rotation is *lassi(ed into

n*ontrolledand *ontrolledtippin0


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*ncontrolled &ippin"

the simplestform of orthodonti* mo"ement

prod*ed +hen a sin0le for*e is applied a0ainst the *ro+n

the tooth +ill rotatedrin0 mo"ement

the PD2 is *ompressed near the ape4 6same side as the for*e7

and at the al"eolar *rest6opposite side from the for*e7


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ma4immpressre is at the al"eolar *rest and the root ape4

pro0ressi"ely less pressre is *reated as the *enter of resistan*e is approa*he

only one9halfthe PD2 area is loaded

hi0h pressre in the t+o areas is *on*entrated

for*e mst be ;ept itelo+:

ot e4*eed appro4imately


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Controlled &ippin"

the *enter of rotation is at the root ape4

by appli*ation a for*e to mo"e the *ro+n and a moment to *ontrol the ape4

*on*entrationof stresses at the al"eolar *rest

minimalstress at the root ape4

#1! ratio - >:&


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&ranslation

also ;no+n as ?bodilymo"ement@

the root ape4and *ro+nmo"e in the same dire*tion and the same distan*e

PD2 area is loaded niformly

t+i*eas m*h for*e is reired for translation

as for tippin0


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a horiAontal for*eapplied at the *enter of resistan*e +ill

reslt in translation

t+o for*es are applied simltaneosly 6a *opleand a for*e

are reired7

the *enter of rotation is at in(nity

#1!ratio - &%:&


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Rotation

pre rotation reires a *ople

no net for*e a*ts at the *enter of resistan*e

in theory rotational for*e *an be more lar0er than other mo"ements

in fa*t rotational mo"ement +ithot tippin0 is essentially impossible

appropriate for*es for rotation are similar

to those for tippin0


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+,trusion

ideally+old prod*e no area of *ompression in the PD2 only

tension

pra*ti*allythe tooth tippedat all +hile bein0 e4trded

e"en if *ompressed areas a"oided hea"y for*es in pre tension

+old be ndesirable nless for e4tra*tion

abot the same ma0nitde of for*e as those for tippin0


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ntrusion

s**essfl intrsion *an be a**omplished only if "ery li0ht for*es are applied

the for*e *on*entration is in a small area at the root ape4

the tooth probably +ill tipsome+hat as it is intrded


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Root movement

;eepin0 the *ro+n stationary and applyin0 a momentand for*eto

mo"e the root

the *enter of rotation is at the in*isal ed0e

root mo"ement reires a lar0e moment

*on*entration of stress is in the ape4area

#1!- at or abo"e &$:&


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Optimum forces for orthodontic tooth

movement

Force. ("m) &ype of movement

'%9&$% 5ranslation


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+/ects of force duration and force decay


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animale4periments after abot E hors*y*li* n*leotide

le"els in*reased

*lini*ale4periments threshold for tooth mo"ement is in

the E98 hors ran0e

lon0erfor*e maintenan*e in*reasin0ly e,e*ti"e tooth

mo"ement

(4ed applian*es are more e,e*ti"e nless the remo"able applian*e

sed almost all the time


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Dration of for*e has another aspe*t related to ho+ for*e

ma0nitde *han0esas the tooth responds by mo"in0.

!rom this perspe*ti"e orthodonti* for*e dration is

*lassi(ed by the rate of de*ay as: ContinosF for*e

Interrpted F for*e

Intermittent 9 for*e


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Continuous force


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-nterrupted force


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-ntermittent force


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theoreti*ally li0ht *ontinos for*es prod*e the mst e*ient

tooth mo"ement.

the hea"ierfor*es are physiolo0i*ally a**eptable only if:

for*e le"els de*line so that there is a period of repairandre0eneration beforethe ne4t a*ti"ation

or

the for*e de*reases at least to the point that no se*ond and

third ronds of nderminin0 resorption o**r


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4periments has sho+n that orthodonti* applian*es shold not

be rea*ti"atedmore freently than at ' +ee; inter"als.

3 E to B +ee; appointment *y*le is more typi*al in *lini*al

pra*ti*e.

nderminin0 resorption reires > to &E days : eal orlon0er

period is need for PD2 re0eneration and repair before for*e is

applied a0ain.


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0s for your attention

Biomechanics and Types of Movement 9b670d85

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