Biomechanics of Space Closure

Orthodontics

1. Biomechanics of Space Closure
DEPARTMENT OF ORTHODONTICS AND
DENTOFACIAL ORTHOPAEDICS.
SEMINAR PRESENTATION
Presented by: Guided by:
Dr. Deeksha Bhanotia Dr. Mridula Trehan
M.D.S. Third year Professor & Head
Department of Orthodontics
and Dentofacial Orthopaedics

2. Biomechanics of Space Closure
Introduction.
Relevance of center of resistance.
Statistically determinate and indeterminate
system.
Orthodontic space closure.
Determinants of space closure.
Fundamental concepts and clinical method of
anchorage control.
Anchorage from a biomechanical perspective.

3. Biomechanics of Space Closure
Biomechanical strategies for differential space
closure.
Center of resistance of anterior teeth during
retraction.
Methods of canine retraction.
Controlled space closure with a pre adjusted
appliance.
Effects of overly rapid space closure.
Inhibitors to sliding mechanics.
Friction in sliding mechanics.
Segmented approach to space closure
T-loop
Opus loop

4. Biomechanics of Space Closure
Introduction
Everyobjectorfreebodyhasonepointonwhichitcanbeperfectly
balanced.Thispointisknownasthecenterofgravity
Inarestrainedbody,suchasatooth,apointanalogoustothecenterof
gravityisused;thisiscalledthecenterofresistance.
Bydefinition,aforcewithalineofactionpassingthroughthecenterof
resistanceproducestranslation.
Thecenterofresistanceofasingle-rootedtoothisonthelongaxisofthe
tooth,probablybetweenonethirdandonehalfoftherootlengthapicaltothe
alveolarcrest.
Foramultirootedtooth,thecenterofresistanceisprobablybetweenthe
roots,1or2mmapicaltothefurcation.

5. Biomechanics of Space Closure
Relevance of the center of resistance
First,thepositionofthecenterofresistancevarieswithrootlength
Thetoothmovementresultingfromaforcedeliveredatthebracketdepends
uponthedistanceofthelineofactionoftheforcefromthecenterof
resistance;
Identicalforcesappliedtoteethwithdifferentrootlengthscanhavedifferent
effects.
Asecondimportantpointisthatthecenterofresistancevarieswith
alveolarboneheight.
Themovementofteethinadultswithalveolarbonelosswillbedifferentthan
inadolescents.
Smith RJ, Burstone CJ.Mechanics of tooth movement.AJODO1984;85(4):294-307.

6. Biomechanics of Space Closure
TheM/Fratioistherelationshipbetweentheappliedforceandthecounterbalancing
couple
Thetypeofmovementisdictatedbythemomenttoforceratio(M/F)generatedby
theapplianceattheattachments.
Typically,M/Fratiosofapproximately7:1millimetersresultincontrolledtipping,
10:1millimetersresultintranslationalmovements,andvaluesof12:1millimeters
orgreateraccomplishrootmovement.
This has important implications.
It is the ratio between the applied couple and force that determines the type of
tooth movement, not the absolute magnitudes.
Smith RJ, Burstone CJ.Mechanics of tooth movement.AJODO1984;85(4):294-
307.

7. Biomechanics of Space Closure
Theseratiosarebasedontheassumptionsthat
therootlengthsare12millimeters,
thedistancefromthebracketslottothealveolarcrestisfivemillimeters,
thealveolarboneconditionisnormal,
theaxialinclinationoftheteethisnormal,
andthecenterofresistanceislocatedapicallyadistance.40timestheroot
lengthwhenmeasuredfromthealveolarcresttotheapex.
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using
the segmented arch technique. Angle Orthodontist1989;59(3):205-210.

8. Biomechanics of Space Closure
Force systems can be defined as statically determinatewhen the
moments and forces can be readily determined, measured and evaluated
.
Statically indeterminate systemsare too complex for precisely
determining all the forces and moments in the equilibrium.
Usually only the direction of the net moment and the appropriate net
force levels can be determined.
Determinate systems in orthodontics are those in which a couple is
created in one end of an attachment with only a force and not a couple at
the other end .e.g. a spring which is inserted to a tube or bracket at one
end and tied at the other end to only one point.
STATICALLY DETERMINATE AND INDETERMINATE
SYSTEMS
Proffit WR, Sarver DM.Contemporary Orthodontics elsevier.2013(5);530-555

9. Biomechanics of Space Closure
Orthodontic space closure
should be individually tailored
based on the diagnosis and
treatment plan.
The selection of any treatment
whether a particular technique,
stage spring or appliance
designs should be based on the
desired tooth movement.
Orthodontic space closure
Braun S, Marcotte M.Rationale of the segmented approach to orthodontic
treatment. A JODO 1995;108:31-8.

10. Biomechanics of Space Closure
A well-designed appliance should exhibit three general
characteristics:
(1) It should deliver a known, relatively constant moment-to-force
ratio over a long range of activation;
(2) the resultant motion of the active unit (teeth being moved)
occurs about a predictable center of rotation; and
(3) the force system at the reactive unit (anchor teeth) should be
known and controllable.
Braun S, Marcotte M.Rationale of the segmented approach to orthodontic
treatment. A JODO 1995;108:31-8.

11. Biomechanics of Space Closure
(1) Differential space closure..
(2) Minimum patient cooperation.
(3) Axial inclination control
(4) Control of rotations and arch width.
(5) Optimum biologic response.
(6) Operator convenience.
The six goals to be considered for
any universal method of space closure:
To achieve controlled extraction site closure, the appliance used must deliver
definable force systems regulated by the clinician and not produce closure in
some ambiguous, indeterminate way. Only when force systems are definable
are the dental movements predictable and treatment outcomes forecast able
with confidence.
Burstone CJ.The Segmented arch approach to space closure. AJODO 1982;82(5):361-378.

12. Biomechanics of Space Closure
Space closure should result in upright well aligned teeth with parallel
roots and parallel occlusal plane.
Therefore some degree of bodily or even root movement is required.
Idealized objective of space closure:
Burstone CJ.The Segmented arch approach to space closure. AJODO
1982;82(5):361-3

13. Biomechanics of Space Closure
Amount of crowding:
in cases of severe crowding, anchorage
control is very important to
maintain the extraction space for
relieving the anterior crowding
Anchorage
using the same mechanics for different
anchorage needs is very important.
Traditional anchorage methods like
lip bumpers, headgears,
transpalatal arches may be utilized
but non compliance methods for
anchorage control based on
biomechanics can also be used.
DETERMINANTS OF SPACE CLOSURE
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics. elsevier.2008(5);1-16
The main factors which determine the tooth movement during space closure are:

14. Biomechanics of Space Closure
Axialinclinationofcanines
thesameforce/andormomentappliedtoteethwithdifferentaxial
inclinationswillresultindifferenttypesoftoothmovement.
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

15. Biomechanics of Space Closure
Midlinediscrepanciesandleftrightsymmetry.
Midlinediscrepanciesshouldbecorrectedasearlyas
possibleintreatmentasitallowstheremainingspaceclosuretobe
completedsymmetrically.Usingasymmetricmechanicscancausein
unilateralanchorageloss,skewingofthedentalarches,orunilateral
verticalforces.
Verticaldimension
Controlofverticaldimensionisessentialinspaceclosure.
Undesiredverticalextrusiveforcesontheposteriorteethcanresult
inincreasedLAFH,increasedinterlabialgap,andexcessivegingival
display.ClassIIelasticsmaypotentatethisproblem.
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

16. Biomechanics of Space Closure
Itistheabilitytopreventtoothmovementofonegroupofteethwhile
movinganothergroupofteeth.
TheproblemofanchorageisrootedinNewton’sthirdlaw:
Foreveryactionthereisanequalandoppositereaction.
Severalanchoragecontrolmethodshavebeendevelopedoverthelast
century.
ThecontributionsofAngle,Begg,Case,Tweedandothershaveprovided
afoundationformodernorthodonticmechanotherapy.
Althougheachofthemadvocateddifferentmethodsandphilosophies,a
reviewoftheirworkshowsalotofsimilarities.
FUNDAMENTAL CONCEPTS AND CLINICAL METHODS
OF ANCHORAGE CONTROL
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod .2001;7:42-49.

17. Biomechanics of Space Closure
In1907,EHAngleadvocated5typesofanchoragecontrol.
Occipitalanchoragedependedontheuseofextraoralanchorage
Intermaxillaryanchorageincludedtheuseofelastics.
Theremainingthreeweredentalanchorage:
Simple,reciprocalandstationarymethodsfordentalanchorage.
CalvinSCasealsoadvocatedstationaryanchoragemethodsdespitehis
differenceswithAngle’sschoolofthought.
Healsodescribedtheuseofextraoralandintermaxillaryanchorageaswell
astheprerequisitethatresistancetotippingmovementswasrequisitefor
intraarchcontrol.
Caseadvocatedtheuseofsolderedfirmattachmentofanchorageteethtoone
anothertomaintaintheiruprightpositions.
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod .2001;7:42-49.

18. Biomechanics of Space Closure
20yearslaterCharlesTweedadvocatedsimilartechniques.Hismethod
ofanchoragepreparationagainstunwantedtippingandextrusiveside
effectswereaseriesoftipbackbendstoanchortheteethliketentstakes
toresistverticalandanteriorposteriordisplacementduringintermaxillary
traction.
AlthoughTweedsaidhismethodsofanchoragepreparationweremore
mechanicalthanbiological,thetipbackbendswereafurtherrefinement
ofAngle’sstationaryanchoragemethods.
Despitehisadherencetothedifferentialforcetheory,PRBegg
alsousedasimilartechniqueforanchoragecontrol.Histipbackbendto
maintaintheanteroposteriorpositionofteethtoeffectpreferential
movementofteethwasalsosupplementedbyinitiallytippingtheteethto
beretractedfollowedbyuprightingthem.
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod .2001;7:42-49.

19. Biomechanics of Space Closure
AANCHORAGE
Thiscategorydescribesthecriticalmaintenanceoftheposteriortooth
position.
75%ormoreoftheextractionspaceisneededforanteriorretraction.
GroupAarchestendtobeoftwotypes:
BANCHORAGE
Thiscategorydescribesrelativelysymmetricspaceclosurewith
equalmovementoftheanteriorandposteriorteethtoclosethespace.
Thisistheleastdifficultofthespaceclosures.
CANCHORAGE
Thiscategorydescribesnoncriticalanchorage,where75%ormore
ofthespaceclosureisachievedthroughmesialmovementoftheposterior
segment;thiscouldalsobedescribedascriticalanterioranchorage.
Anchorage can be classified as:
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod .2001;7:42-49.

20. Biomechanics of Space Closure
Dividing the extraction space into quarters aids in visualizing the anchorage
classification
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

21. Biomechanics of Space Closure
Thebasictechniquesforanchoragecontrolbasicallyrelyonthreefundamental
similarities:
extraoralforcesontheanchorageunit
intermaxillaryelastics
Tippingtoothmovementwhilesimultaneouslydiscouragingtipping
ofanchorageteeth.
Patientcomplianceismandatoryforthefirsttwotechniques.
Withoutcooperationcontroloftoothmovementislostandtheresultsmaybe
compromised.
Thewayatoothmovesisdependentonthenatureoftheforcesystemsthatact
onit.Thisincludestheactualforceandmomentsatthebracket,theforce
distributionaroundtheperiodontalligament,.
Theforcedistributionisafunctionofthecentreofrotation.
ANCHORAGE FROMABIOMECHANICAL PERSPECTIVE:
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

22. Biomechanics of Space Closure
CONTROLLED TIPPING:
Istoothmovementwiththecenterofrotationattheroot
apex.Theresultantforcesaredistributedatthemarginal
portionoftheperiodontalligament
TheM/Fratioisapprox.7/1
TRANSLATION orbodilymovementmaintainstheaxial
inclinationofthetoothandthecentreofrotationisat
infinity.TheresultantforceonthePDLisequally
distributedalongthepressuresideofthealveolar
structures.
TheM/Fratioisapprox.10/1
ROOTMOVEMENT ordisplacementofthetoothapex
whilethecrownremainsstationaryoccurswithaM/F
ratioofapprox.12/1hereforcestendtobeconcentrated
ontheapicalthirdoftheroot.
Withinthesebasicsliethefundamental
principlesofanchoragecontrol.
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

23. Biomechanics of Space Closure
WhathappenswhenahighM/Fratioisappliedtotheanchorteeth?
Anappliedforcecausesuncontrolledtippingwhiletheapplied
momentcounteractsthetippingeffectoftheforce.Thisapplied
momentactsintheoppositedirectionandmovestherootstothe
extractionsiteandifthemagnitudefurtherincreases,tipsthecrown
distally
AlowM/Fratioproducestippingwiththecrownmoment
noticeablygreater
Howcantheseforcesbeproducedclinically?
IfM/Fratioofposteriors>M/Fratiooftheanteriorstheremustbe
eitherunequalforcesorunequalmoments
Unequalforcescanbeproducedbyheadgear,Jhookheadgear,and
intermaxillaryelastics.Unfortunatelythisiscooperationdependant
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

24. Biomechanics of Space Closure
TheidealforsystemforagroupAspaceclosurewouldhaveonlyaforce
systemresultinginanteriortranslationandnoforcesactingonthe
posteriorteeththerebymaintainingperfectanchoragecontrol.
Thisispossibleonlywithextraoralanchorageoriftheoppositearchisused
asanchorage.
Twoapproaches:
differentialforces
differentialmomenttoforceratios
groupArequirestheposteriorsegmenttohavehigherM/Fratios(whenthe
forceisreducedM/Fisincreased)andtheanteriorsegmenttohavea
decreaseinM/Fratios.
BIOMECHANICAL STRATEGIES FOR
DIFFERENTIAL SPACE CLOSURE:
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

25. Biomechanics of Space Closure
Center of resistance of anterior teeth during retraction
The location of the center of resistance of various consolidated units of the
maxillary anterior dentition was studied using a dry human skull when
subject to retrusive forces.
The units studied consisted of
(a)two central incisors,
(b)four incisors, and
(c)six anterior teeth.
The laser reflection techniqueand the holographic interferometric
techniquewere employed to measure the displacement of the dentition
to the applied forces.

26. Biomechanics of Space Closure
1.For an anterior segment comprising two central incisors,
the center of resistance was located on a projection line parallel to the
midsagittal plane on a point situated at the distal half of the
canines.
2. For an anterior segment that included the four incisors, the center of
resistance was situated on a projection line perpendicular to the
occlusal plane between the canines and first premolars.
3. For a rigid anterior segment that included the six anterior teeth, the
center of resistance was situated on a projection line perpendicular
to the occlusal plane distal to the first premolar.
Results:
Bulcke MMV, Burstone CJ,Sachdeva RL,Dermaut LR.Location of the centres
of resistance for anterior teeth during retraction using laser reflection
technique.AJODO;1987;91:375-84.

27. Biomechanics of Space Closure
4. The centers of resistance of the anterior segments incorporating
two or four anterior teeth were within ±2 mm of each other.
However, inclusion of the canines in the anterior segment resulted in
the center of resistance moving distally by approximately one
premolar width (7 mm). This effect may have been the result of the
resistance of bony structures at the level of the canines and some
bending of the maxillary complex as was observed on the
holograms.
5. No appreciable shift in the location of the centers of resistance of
the various segments studied was detected as varying magnitudes of
retractive force were applied.
Bulcke MMV, Burstone CJ,Sachdeva RL,Dermaut LR.Location of the centres
of resistance for anterior teeth during retraction using laser reflection
technique.AJODO;1987;91:375-84.

28. Biomechanics of Space Closure
METHODSOFCANINERETRACTION:
Friction
Frictionless(PGspring,BurstoneTloop,Ricketts)
METHODSOFENMASSERETRACTION:
OFFOURINCISORS
Friction
Frictionless
PGretractionspring,
Utilityarch,OmegaLooparchwire
Extraoral
Headgears
OFSIXANTERIORS
Closinglooparchwire
BurstoneTloopcontinuousarchwire
Opusloop
INTRUSIONANDRERACTIONOFFOURINCISORS
Burstone’sthreepieceintrusionarch
Ricketsretractionandintrusionutilityarch
SIMULTANEOUS INTRUSIONANDRETRACTIONOFSIXANTERIORS
K-sirarch

29. Biomechanics of Space Closure
Themostsignificantdistinctionbetweenthemechanicsof
standardedgewiseandpreadjustedapplianceswasobserved
duringspaceclosure.
Withstandardedgewiseappliances,rectangulararchwiresdidnot
effectivelyslidethroughtheposteriorbracketslotsbecauseofthe
1st-,2nd-,and3rd-orderbends.
Theorthodontistnormallyusedaclosinglooparch,whichwas
activatedintheofficebyopeningtheclosingloopandmovingthe
archwirethroughtheposteriorbracketslots
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

30. Biomechanics of Space Closure
Thelevelbracketslotalignmentofthenewappliancesallowed
archwires,forthefirsttime,tomovemoreeffectivelythroughthe
posteriorslotswhenthepatientwasnotintheoffice.
Asaresult,manyorthodontistsdiscontinueduseofclosingloopsand
beganusingvariousformsofslidingmechanics—forexample,placing
hooksintheanteriorsectionsofstraightarchwiresandtyingelasticsor
springstothemfrommolarbrackets
Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment
mechanics.Mosby 2001(1)

31. Biomechanics of Space Closure
Closing loop arches had several
disadvantages:
1. Extra wire-bending time
2. Poor sliding mechanics
3. Tendency to run out of space for activation
(after two or three activations, the omega loop
contacted the molar bracket and the archwire
had to be adjusted or remade)
4. High initial force levels
They also had advantages:
1. Precise control of the amount of loop
activation (often as little as 1mm), limiting
the amount of initial tipping
2. Adequate rebound time for uprighting
between appointments (with minimal
activations, loops closed quickly with little
tipping)
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

32. Biomechanics of Space Closure
Sliding mechanics had these advantages:
1.Minimalwire-bendingtime
2.Moreefficientslidingofarchwiresthroughposteriorbracketslots
3.Sufficientspaceforactivations
But sliding mechanics at first also had disadvantages:
1.Noestablishedguidelinesonamountsofforcetobeusedduring
spaceclosure
2.Tendencyforinitialoveractivationofelasticandspringforces,
causinginitialtippingandinadequatereboundtimeforuprighting
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

33. Biomechanics of Space Closure
To maximize the advantages and minimize the disadvantages of
sliding mechanics
• force levels are reduced during space closure.
• Insteadofspringsoroveractivatedelastics(which
canproduce500gofforce),singleelasticmodulesareattached
toanteriorarchwirehookswithligaturewiresextended
forwardfromthemolars
These "elastic tiebacks", when activated 2-3mm, generate
about 100-150g of force.
If the arches have been properly leveled, such light force allows
for effective space closure; there is little tipping with
subsequent binding of the archwires, and leveling is maintained
.
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

34. Biomechanics of Space Closure
019" ×.025" archwires with .022" slots provide optimum
rigidity, but adequate freedom for the wires to slide through the
slots.
Round wires and smaller rectangular wires provided less
precise control of torque, curve of Spee, and overbite.
Hooks of .024 " stainless steel or .028 " brass are soldered to
the upper and lower archwires
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

35. Biomechanics of Space Closure
Space closure typically occurs
more easily in high-angle patterns
with weak musculature than in
low-angle patterns with stronger
musculature. The rate of closure
can be increased, particularly in
high-angle cases, by slightly
raising the force level or using
thinner archwires. However, more
rapid space closure can lead to
loss of control of torque, rotation,
and tip.
Effects of Overly Rapid Space Closure

36. Biomechanics of Space Closure
Loss of torque controlresults in upper
incisors being too upright at the end of
space closure with spaces distal to the
canines and a consequent unaesthetic
appearance. The lost torque is difficult
to regain. Also, rapid mesial movement
of the upper molars can allow the
palatal cusps to hang down, resulting in
functional interferences, and rapid
movement of the lower molars causes
"rolling in"

37. Biomechanics of Space Closure
Reducedrotationcontrolcanbe
seenmainlyintheteethadjacentto
extractionsites,whichalsotendto
rollinifspacesareclosedtoo
rapidly
Reducedtipcontrolproduces
unwantedmovementofcanines,
premolars,andmolars,alongwitha
tendencyforlateralopenbite.In
high-anglecases,wherelower
molarstipmostfreely,theelevated
distalcuspscreatethepossibilityof
amolarfulcrumeffect

38. Biomechanics of Space Closure
Insomeinstances,excessive
soft-tissue hyperplasia
occursattheextractionsites
,thisisnotonlyunhygienic,
butitcanpreventfullspace
closureorallowspacesto
reopenaftertreatment.Local
gingivalsurgerymaybe
necessaryinsuchcases.

39. Biomechanics of Space Closure
Properalignmentofbracketslotsisessentialtoeliminate
frictionalresistancetoslidingmechanics.Thecommon
procedureistouse.018"or.020"roundwireforatleastone
monthbeforeplacing.019"´.025"rectangularwires.Leveling
andaligningcontinuesforatleastamonthafterinsertionofthe
rectangularwires,andthatspaceclosurecannotproceedduring
thatperiod.
Inhibitors to Sliding Mechanics
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

40. Biomechanics of Space Closure
Thereforetherectangularwiresaretiedpassivelyforat
leastthefirstmonth,untillevelingandaligningiscomplete
andthearchwiresarepassivelyengagedinallbracketsand
tubes
Conventionalelastictiebacksarethanplaced,Insomecases,
thisphasetakesthreemonths.
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

41. Biomechanics of Space Closure
First-order or rotational
resistance
atthemesiobuccaland
distolingualaspectsoftheposterior
bracketslotsisproducedby
rotationalforcesonthebuccal
aspectsoftheposteriorteeth.
Themosteffectivewayto
counteractthisresistanceisto
applyintermittentlingualelastic
forces—
onemonthfromcuspidtofirst
molar,thenextmonthfromcuspid
tosecondmolar.
There are three primary sources of friction during space closure
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

42. Biomechanics of Space Closure
Second-order or tipping resistance
at the mesio-occlusal and distogingival
aspects of the posterior bracket slots is
caused by
excessive and overactivated
tieback forces, which lead to
•tipping of the posterior teeth,
•inadequate rebound time to
upright these teeth,
•and a resultant binding of the system.
The importance of light forces (50-
150g) and minimal activation length (to
provide time for uprighting) cannot be
overemphasized.
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

43. Biomechanics of Space Closure
Third-order or torsional resistance
occursatanyofthefourareasofthe
bracketslotwheretheedgesofthe
archwiremakecontact.
Liketippingresistance,thisisproduced
mainlyby
excessiveandoveractivated
tiebackforces,whichcausetheupper
posteriorlingualcuspstodropdown
andthelowerposteriorteethtorollin
lingually
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

44. Biomechanics of Space Closure
1.Inadequateleveling,resultinginarchwirebinding
2.Posteriortorquesuchthattorquingandslidingcannotoccur
simultaneously
3.Blockageofthedistalendofthemainarchwirebyaligaturewire
4.Damagedorcrushedbracketsthatbindthemainarchwire
5.Softtissueresistancefrombuild-upinextractionsites
6.Corticalplateresistancefromanarrowingofthealveolarbonein
extractionsites
7.Excessiveforce,causingtippingandbinding
8.Interferencesfromteethortheopposingarch
9.Insufficientforce
Constant attention is required to prevent any of the
following inhibiting factors:
-Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

45. Biomechanics of Space Closure
Frictionisafunctionoftherelativeroughnessoftwosurfacesincontact.Itis
theforcethatresiststhemovementofonesurfacepastanotherandactsina
directionoppositethedirectionofmotion.
VARIABLES AFFECTING FRICTIONAL RESISTANCE DURING
TOOTH MOVEMENT
PHYSICAL
ARCHWIRE
LIGATION
BRACKET
ORTHODONTIC APPLIANCE
BIOLOGICAL
SALIVA
PLAQUE
ACQUIRED PELLICLE
CORROSSION
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

46. Biomechanics of Space Closure
PHYSICAL
ARCHWIRE
crossectionalsize/shape
material
surfacetexture
stiffness
LIGATION
ligaturewires
elastomerics
selfligatingbrackets
BRACKET
material
manufacturingprocess
slotwidthanddepth
first/second/thirdorderbends
ORTHODONTICAPPLIANCE
interbracketdistance
levelofbracketslotsbetweenadjacentteeth
forcesappliedforretraction
BIOLOGICAL
Saliva
Plaque
Acquiredpellicle
Corrosion
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

47. Biomechanics of Space Closure
The segmental arch technique as
developed by Burstone utilizes
T loop space closure springs for
anterior retraction, symmetric
closure or posterior protraction.
The segmental T loop as
described by Burstone is one of
the most versatile space closure
devices available.
One of the main principles of the segmental arch technique is considering
the anterior segment and posterior segment as one large tooth
respectively. The right and left buccal units are connected by a
transpalatal arch forming one big posterior unit.
The basic configuration of the TMA loops consists of a .017X.025” TMA
wire.
Burstone CJ.The Segmented arch approach to space closure. AJODO 1982;82(5):361-378.

48. Biomechanics of Space Closure
TheadvantagesoftheT-loopdesignoveraverticalloop
isthattheT-loopproducesahigherM/Fratio,alowerload-deflection
rate,anddeliversamoreconstantforceandM/Fratio
Ofteninadultpatients,wherenogrowthisanticipated,extraction
therapyisperformed.Thesituationisoftencomplicatedthroughloss
ofbone.Inordertomaintainanassumedstressmagnitudeand
distributionundertheconditionofreducedbonysupportarea,force
magnitudemustbereducedandtheM/Fratiomustbeincreased.
Thenecessityofproducingalowerloaddeflectionrateinsuchcases
suggeststheuseofawirewithlowerstiffness
SEGMENTED ARCH TECHNIQUE FOR SPACE CLOSURE IN ADULTS:
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using the segmented
arch technique. Angle Orthodontist1989;59(3):205-210.

49. Biomechanics of Space Closure
The rate of decay of the force applied by a spring is called
the load-deflection rate, and it averages 33 Gm. per
millimeter in the Burstone’s T loop.
The low load-deflection rate is important in this spring,
since it enables the orthodontist to deliver optimal
magnitudes of force.
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using
the segmented arch technique. Angle Orthodontist1989;59(3):205-210.

50. Biomechanics of Space Closure
.
The attachment on the posterior tooth (segment) is a 0.018 by 0.025 inch
auxiliary tube on the first molar, and the one on the anterior tooth (segment) is
an auxiliary vertical tube on the canine bracket
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using the
segmented arch technique. Angle Orthodontist1989;59(3):205-210.

51. Biomechanics of Space Closure
Differential moments are obtained by the principle of off center V bends
which results in unequal moments. the closer the V bend is to the tooth
the higher the moment. the segmented T loops approximated a V bend.
Clinically the spring needs to be positioned at least 1-2mm closer to one
side than another to obtain a moment differential.
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using the
segmented arch technique. Angle Orthodontist1989;59(3):205-210.

52. Biomechanics of Space Closure
Thisdemonstratesanothermethod
thatmaybeusedforcontrollingtheforces
andmomentsproducedbysegmented
0.017´0.025-inchTMAT-loopspringsor
closingloopsingeneral.
Previously,theapproachdescribedfor
achievingdifferentialalpha/betamoments
withsegmentedT-loopsusedasymmetric
angulationsofthepreactivationbends.
However,withthismethodthe
momentdifferentialdoesnotremain
constantwithspringactivation,i.e.,the
momentdifferentialisdependentonboth
springactivationandthedifferencesinthe
preactivationangulations.
OFF CENTERED T LOOPS
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod
.2001;7:42-49.

53. Biomechanics of Space Closure
TheTloopispositionedclosertothe
posteriorsegment
(1-2mmoffcentering)issufficient.
activationof4mmisnecessary.
Thisreducesthehorizontalforces
withoutalteringthemoment
differential.
Theforcesystemactingontheanterior
segmentfavorstipping.Themoment
differenceremainsasthespacecloses
andthespringdeactivates.
Thespringmustbereactivatedwhen2
orlessmmofactivationremains.
MAXIMUM POSTERIOR ANCHORAGE:
(Group A anchorage)
Kulberg AJ, Priebe DN.Space Closure and
anchorage control.Semin Orthod
.2001;7:42-49.

54. Biomechanics of Space Closure
CONTROL OF THE SIDE EFFECTS OF SPACE CLOSURE:
Careful monitoring is essential during space closure.
A frequently overlooked side effect of space closure is the first order side
effects.
The mesially directed buccally located force of the molar may lead to the
erroneous supposition that there is anchorage loss.
Distalization is not necessary . A mesially out directed force is all that is
needed to regain the original molar position.
A transpalatal arch provides an excellent mean to prevent this or actively
corrects it.
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod
.2001;7:42-49.

55. Biomechanics of Space Closure
CORRECTION OF THE SIDE EFFECTS
Tipping of the anterior and posterior teeth into the extraction space
Increase the alpha and beta moments
Flaring of the anterior teeth
Reduce the alpha moment or increase the distal activation
Mesial in rotation of the buccal segments
Mesial out rotation of the palatal arch, archwire or lingual arch
Excessive lingual tipping of the anterior teeth
Increase the alpha moment
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod
.2001;7:42-49.

56. Biomechanics of Space Closure
The OPUS loop was designed to deliver an inherent M/F ratio
sufficient for enmasse space closure via translation of teeth of
average dimensions with no bone loss.
Because its inherent M/F ratio is high enough no preactivation
bends is needed before insertion
The neutral position is the passive position of the spring as it sits
before insertion.
Simple cinch back activations can take care of the tooth movement
thresholds to meet anchorage objectives.
Siatkowski RE.Continuous arch wire closing loop design, optimization and
verification . AJODO 1997;112:487-95.

57. Biomechanics of Space Closure
Theapicalhorizontallegis10mmlong,
Theascendinglegsatanangleof70degreestotheplaneofthebrackets
Theapicalhelixisonthelegascendingfromtheanteriorteeth,(that
ascentmustbeginwithin1.5mmposteriortothemostdistalbracketofthe
anteriorteethbeingretracted)
Thespacingbetweentheascendinglegsespeciallytheapicalloopslegs
mustbe1mmorless
Allthesedimensionsarecriticaltotheperformanceoftheloop.
Clinicallycomfortbendsarenotnecessary.

58. Biomechanics of Space Closure
Theadvantageofhavingtheopusloopformedin17X25TMAisthatit
providesarelativelylongrangeofactivation;
unfortunatelyitisdifficulttobendthewirewithsufficientincisortorque
toreducethewireplay.
Itisdifficulttocontourtheloopforcomfortononesidewithoutaltering
theothersidealsoandalargestockofwiresisnecessaryforpreformed
wires.
Thiscanbeovercomebyhaving:
AnanteriorwireofNitialloywithtwoseparate17X25TMAposterior
segments,whichareattachedbyaForestadentcrosstube
Thisbialloyhasthefollowingadvantages:
Infrequentactivations
Easeofcomfortbending
Incisoraxialinclinationcontrol
Siatkowski RE.Continuous arch wire closing loop design, optimization and
verification . AJODO 1997;112:487-95.

59. Biomechanics of Space Closure
Siatkowski
RE.Continuous
arch wire closing
loop design,
optimization and
verification .
AJODO
1997;112:487-95.

60. Biomechanics of Space Closure
Althoughlesssothanwithotherclosingloopdesigns,Opusloopsdo
havethepotentialtosteepenthecantofocclusalplaneinthemaxillary
archandflattenitinthemandibulararch.
Althoughsteepeningocclusalplanecanbeusefulforovertreatmentof
ClassIIIrelationships(andflatteningocclusalplaneforClassII
relationships),thatpotentialshouldbemonitoredforpossible
intervention.
Suchinterventioncouldbereducingmaximumactivationforcelevelsor
usinganoccipitalheadgearwithshortandhighouterbowstogeneratea
momenttendingtoflattenmaxillaryocclusalplane.
Forthemostsevereanchoragerequiredtoachievetreatmentgoals,
secondmolars,ifavailable,couldbeincludedwiththeposteriorsand/ora
Combiheadgearused.
Forlesssevereormoderateanchorage,thecaninescouldbeincorporated
withtheanteriors
DISADVANTAGES OF THE OPUS LOOP
Siatkowski RE.Continuous arch wire closing loop design, optimization and
verification . AJODO 1997;112:487-95.

61. Biomechanics of Space Closure
Theclosinglooparchwiregeneratesthemomentsrequiredandsomeofthe
protractionforce.
Mostoftheprotractionforceisgeneratedbythelargeanteriormomentandby
theintermaxillaryelasticstoarigidrectangulararchwireintheopposingarch.
IntermaxillaryNiticlosedcoilspringscapableofdelivering150gmforcecanbe
substitutedfortheelastics.Thepotentialexistsforchangingocclusalplaneinthe
opposingarch.Shouldsuchcantchangesbegintobeobserved,the
intermaxillaryforcecanbereduced.
The configuration for posterior protraction
Siatkowski RE.Continuous arch wire closing loop design, optimization and
verification . AJODO 1997;112:487-95.

62. Biomechanics of Space Closure
In group C anchorage cases, class III elastics with a force of
150gms/side from the opposite arch which has a rigid rectangular
stainless steel archwire can be used.
Another alternative is to use TP 256 torquing auxiliary which when
overlaid over the closing loop provides an additional protraction force
to the posteriors.
It has the following advantages:
The clinician is free to continue treatment in the lower arch
Undesired vertical forces from the elastics are not a problem
Posterior arch width increases are not a problem when using a
TMA wire
Siatkowski RE.Continuous arch wire closing loop design, optimization and
verification . AJODO 1997;112:487-95.

63. Biomechanics of Space Closure
Theclinicaldisciplineoforthodonticspaceclosurerequirescomplete
understandingofitscomplexities
Justasanorthodontistisprovidedwithinnumerablealternativesof
appliancesystems,itisimperativetobeawareitthemeritsaswellas
thelimitationsofthetechniquesinvolved
Mechanicalaswellasbiologicfactorsmustbeconsideredinselecting
theappliancebestsuitedforthepatient
Conclusion

64. Biomechanics of Space Closure
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65. Biomechanics of Space Closure
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66. Biomechanics of Space Closure
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