basic principles of orthodontic

8/18/2019 Basic Principles of Orthodontic

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BASIC PRINCIPLES OF

ORTHODONTIC TREATMENT


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• The teeth and their supporting tissues show life-long ability to reposit themselves and adapt tofunctional demands.

• It is ilustrated by the fenomenon of physiologicalmigration. It is well known that the teeth of the

side segments tend to migrate in a mesialdirection. There is also a tendency for contineder!tion if a balance is not established with theantagonistic tooth, or if the balance is lost.

• By these means , eruptiom and migration,throughout life the teeth will seek to esta"lis# t#e"est !ossi"le relations#i! "et$een t#e %a$s.


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These continuous physiological processes areaffected by the gro$t# of the craniofacial skeletonand are sensitive to any type of !resre ( pressure

from muscles, soft tissues, oclusal and functionalfactors or direct eternal forces !.

The great potential for dentoalveolar modification is

due to"&. an e'traordinar( a"ilit( o) t#e !eriodontalmem"rane to remodel itsel) and

*. an ada!ta"ilit( o) s!!orting al+eolarstrctres in res!onse to mo+ement o) t#eteet#

#hat is more, the basal parts of the $aws showadaptive reactions to stimuli directed at growth

%ones.


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&rthodontic treatment may involve "

&. t#e control of forces physiologicaly acting uponthe teeth and associated structures or

2. producing and use external forces. The goal for orthodontic treatment may be limited to

preventing or eliminating unwanted impulses ( i.e.dysplastic muscle function ! by restraining such

forces from acting on the teeth or ad$acentsupporting structures. 'uch a change in theeuilibrium of forces may lead to considerablepositional changes if continued over prolonged periodof time.

) tooth can be guided into position during eruption bybeing sub$ected to occasional contact with aninclined plane or a lightly activated element, whilemore etensive tooth movement may be obtained by

sub$ecting the teeth, and eventualy also the alveolrprocess, to direct eternal forces.


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*uring the physiological tooth migration as theorthodontic therapeutic movement the

characteristic tissue changes take place.The bone in direction which tooth is moving is

resorbed while on the bone wall which the tooth is

moving away from an bone apposition occurs.

)mong the fundamental problems that reuire

elucidation are following"

• ,#( is t#e al+eolar "one resor"ed dring toot#mo+ement $#ilst t#e cementm remains intact-

• ,#at !rotects t#e root sr)ace-


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• It is known that trno+er rate o) t#e "one tisse is

#ig#. The bone system acts as a mineral reservoir

for the whole organism and there is permanentcirculation of minerals between the bone system

and inside environment of organism. T#e "one

tisse s#o$s #ig# a"ilit( to remodel itsel)

)ollo$ing t#e )nctional !ressre on it.

• &n the other hand t#e cementm is )ll(

matrated tisse "ilt ! as a !ermanentde!ositor( o) mineral salts. But slow apposition

continues on the cementum surface throughout life.


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This fact is of great

importance for the

resorptive mechanism.T#e nminerali/ed

!recementm la(er

#as "een considered

to "e a resor!tion0resistant coating

la(er. It !rotects t#e

root sr)ace and

!ermit !#(siologicaltoot# migration and

ort#odontic toot#

mo+ement


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• The periodontal ligament, the conective tissue whichattaches the teeth to the alveolar bone, has alsoability to remodel itself. +owever, the turnover rate is

not uniform throughout the ligament. The cells aremore active on the bone side than near thecementum, so that ma%or remodelling ta1e !lacenear t#e al+eolar "one.


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P#(siological toot# migration

*uring the physiological migration the resorbing cells, calledosteoclasts, are seen in the scattered lacunae associated

with the resorptive surface. Resor!ti+e sr)ace is t#e

al+eolar "one $all to$ards $#ic# t#e toot# is mo+ing.


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nlike the osteoclastic resorption of bone to

provide the space for tooth movements, the

corresponding remodeling !rocesses o) t#e

)i"ros attac#ement is not clearl(nderstood. There is a meshwork of collagen

fibres of small diameter present, which eplaines

this rapid reorganisation process.


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The al+eolar "one $all $#ic# t#e toot# is mo+ing a$a()rom is c#aracteri/ed "( osteo"lasts de!ositing non0minerali/ed osteoid whichlater minerali%es in the deeperlayer.


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• The older fibres of the periodontal membrane are

surrounded by newly deposited bone matri and

become embedded in bone. 'imultaneously, new

collagen fibrils are produced by the cells on thebone surface. The sites o) acti+e lengt#ening

and re"ilding o) t#e )i"ros a!!arats lie in

t#e middle o) t#e ligament and near t#e

al+eolar "one side. +ow this comes about isunknown.


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Ort#odontic toot#mo+ement

&rthodontic forces areusually more !o$er)l than normal functionalforces so res!onseelicited in t#e!eriodontal ligamentis more mar1ed ande'tensi+e, although itis the same inprinciples as than seenduring physiologicalmigration.


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Pressre side2 )pplication of a continuous

force on the crown of a tooth

will lead to a tooth movement

within the alveolous that is

marked initially by narro$ing

o) t#e !eriodontal

mem"rane, particularly in themarginal area. This

com!resion $ill im!ede t#e

+asclar circlation and cell

di))erentiation. )fter a fewhours a certain reduction in the

number of cells may be

observed, indicating

a temporary slowing down of

cell renewal.


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Pressre side2

)fter a few hours a certain redction in the numberof cells may be observed, indicating a temporaryslowing down of cell renewal.

)fter a certain period of time, when conditions arefavourable, the cells $ill increase in nm"er anddi))erentiate into osteoclasts and )i"ro"lasts.

The $idt# o) t#e mem"rane is increased "(direct osteoclastic remo+al o) "one andorientation of the fibres in the periodontalmembrane will change.


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Pressre side2


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Pressre side2

• *uring the critical stage ofthe initial application of

force, high compression in

some areas may cause

degradation of the cells andvascular structures. The

tissue reveals a glass-like

appearance in light

microscopy, which is

termed hyalinization. It

represents a sterile necrotic

area.


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In a hyalini%ed %one"• t#e cells cannot di))erentiate into osteoclasts and• no "one resor!tion can take place from the periodontal

membrane• toot# mo+ement $ill sto! until the hyalini%ed structures hasbeen removed and the area repopulated by cells.

The process displays three main stages "• degeneration

• elimination o) destro(ed tisse and• esta"lis#ment o) t#e ne$ toot# attac#ment

The hyalini%ation may be limited to parts of the membrane ormay etend from the root surface to the alveolar bone. imitedhyalini%ation is almost unavoidable in the initial period of toothmovement in clinical orthodontics. +owever, etendedhyalinisation areas may later cause root resorptions which maylead to permanent root shortening.

The ad$acent alveolar bone is removed by indirect resor!tion by cells which have differentiated into osteoclasts on the

surface of ad$acent marrow spaces.


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Pressre side2

#hen the application offorce is favourable, directresor!tion of the alveolarbone is likely to occur.arge number of ostoclastswill be seen along the bone

surface and toothmovement will be rapid. Thefibrous attachmentapparatus will to someetent be reorgani%ed by

the production of newperiodontal fibrils, Theseare attached to the rootsurface and to those part ofthe alveolar bone wallwhere direct resorption isnot occurring.


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Pressre side2


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Pressre side2


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Tension side

• The main feature is the

deposition of new bone onthe alveolar surface whichthe tooth is moving awayfrom. ell proliferation isusually seen after /0-10

hours in young humans.The original periodontalfibres become embedded inthe new layers of pre-bone,or osteoid, whichminerali%es in the deeper

parts. 2ew bone isdeposited until the width ofthe membrane has returnedto normal limits, and thefibrous system is

remodelled.


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Tension side


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Tension side


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Tension side


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Tension side


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Tension side


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In order to maintain thedimension of the supporting

bone tissue, concomitantlywith bone apposition on theperiodontal surface on thetension side, anaccompanying resorptionprocess occurs on the

spongiosa surface of thealveolar bone.

orrespondingly, during theresorption of the alveolarbone on a pressure side,

maintenance of the alveolarlamina thickness is ensuredby apposition on thespongiosa surface.


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These processes are

mediated by the cells of

endosteum, which cover allthe internal bone surfaces,

marrow spaces, +aversion

canals and dental alveoli.

3tensive remodelling,a reaction which tends to

restore the thickness of

supporting bone, takes

place in periosteum, in

deeper cell-rich layers.


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)s regards control of tissue reactions many

mechanisms have been considered responsible

for the differentiation of cells incident upon theapplication of an orthodontic force.

&rthodontic tooth movement shows local traits ofa damage3re!air !rocess with inflammation-like

reactions"

• #ig# +asclar acti+it(

• man( lecoc(tes and macro!#ages

• in+ol+ement o) t#e ner+os and immne

s(stems


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The forces in orthodontics should be veryprecisely controled not to damage periodontalligament tissue, pulp of the teeth or cementum

of the roots. )s a response to high presure and very rapid

tooth movement may occur"• t#e de+itali/ation o) teet# or

• root resor!tion 'ince we wish our terapeutic movements to stay

within physiological limits, knowledge oforthodontic forces needed in terms of magnitude

and duration is very important.The critical uestion regarding orthodontic tooth

movement is whether direct resor!tion $it#ot#(alini/ation areas take place on the alveolarsurface


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It has been observed that a ligt# )orce actingo+er a certain distance mo+es a toot# more

ra!idl( t#an a !o$er)l one, because there isno need to eliminate necrotic hyaline tissue.

#hat is considered a light or powerful force

depends on"• t(!e and anatom( o) t#e toot# to "e mo+ed

• arc#itectre o) t#e !eriodontal ligament andt#e s!!orting "one

• t(!e o) t#e toot# mo+ement and

• mode o) )orce a!!lication


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• The size, form, number and characteristic ofthe roots will influence the mechanical resistance

to an eternal force. Thus cuspids or molarsreuire stronger force to move than incisors orpremolars.

• )s regards the architecture of the periodontalligament and alveolar bone, it is closely relatedto age. The number of cementoblasts, fibroblastsand osteoblasts is much higher in young patientsthan in adults, indicating higher activity.

The necessary increase in cell numbers during theinitial phase of the application of force in adultsoccurs more slowly and is more critical than inyoung individuals, and the deposition of the

osteoid is similarly slower and less etensive.


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In addition the type of bonethrough which the tooth isdisplaced must be consideredin the treatment plan. The

alveolar process consists of "• the dense oter cortical

"one !lates and• s!ongios or cancellos

"one between them

The movement of the tooth ismore di))iclt and slo$er int#e cortical dense "one t#anin s!ongios "one.

In general the bone is moredense in side segments thananteriorly, and in the mandiblethan in mailla.


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,#en a toot# is mo+ed

into t#e reorgani/ingal+eols o) a ne$l(

e'tracted toot#

remodeling is +er(

ra!id, due to the many

differentiating cellspresent and to the limited

amount of bone to be

resorbed.

*espite these facts,individual variations in

alveolar bone architecture

are considerable


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• The magnitude of the force needed depend also on

type of the tooth movement wanted. ( i.e. intrusion

or etrusion reuires very light forces while bodilymovement of a tooth reuires stronger force!.

• The mode of application and the mechanical

arrangement of the recipient tooth units are also of

importance. ) local force intended to move an

individual tooth should be only a small fraction of

a force which is applied against full dental arch,where all teeth are united into a block.


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• The magnitude of a force depends also on its

duration.

#e distinguish"

&. continos )orces

*. continos "t interr!ted a)ter a limited !eriod

( forces working over a short distance, typicaly

eemplified by a tooth ligated to a labial arch wire!4. intermittent )orces, mainly induced by removable

plates

5. intermittent )orms o) a )nctional t(!e, inducedby functional appliances, transmitting muscular

activity into impulses directed at the teeth and

alveolar processes


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The strong continuous force is unwanted because

it may lead to considerable in$ury.


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Interupted continuous forces create favourable conditions for

further tissue changes.

'ince the force decreases rapidly, despite inicial hyalinisation,


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In case of intermittent application , freuent discontinuation

provokes increased vascular circulation and cell proliferation


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basic principles of orthodontic

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