Download - 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