Space closure 1 /certified fixed orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


CONTENTS
o Types of tooth movements

o Space discrepancies
o Anchorage Classification
o Differential force systems

o Friction mechanics
o Frictionless mechanics
o Space closure in Begg


Types of tooth movements
o Uncontrolled tipping: M/F =0:1 - 5:1


o Controlled tipping: M/F=7:1


o Translation (bodily movement): M/F-10:1


o Root movement- M/F ratio at or above 12:1

o Rotation -


Space discrepancies
o Up to 4mm- without extraction (except for third

molars)
o 5-9mm- without extraction/ extraction
o 10mm or more- bicuspid extraction


Anchorage
To Anchor- to hold/ resist the movement of
an object.
“Give me a place to stand and I will move the earth.”Archimedes? Gaileo

„Every action has an equal and opposite reaction.‟
In orthodontics: amount of movement of posterior

teeth to close the extraction space in order to
achieve selected treatment goals.

Anchorage Classification
o Group A: >75% space needed for anterior
retraction. „Critical anchorage‟
o Group B: Equal movement of posterior and
anterior teeth.
o Group C: >75% space closure achieved through
mesial movement of posterior teeth.

Determinants of Space Closure
o Amount of crowding

o Anchorage
o Axial inclination of canines and incisors
o Midline discrepancies and symmetry

o Vertical dimension


Axial inclination of canines and incisors


Biomechanics of space closure
Centered “V” bend

o Creates equal and opposite couples at the
brackets.
o The associated equilibrium forces at each bracket-

equal and opposite – cancel each other out.


Off-center bend

Long segment- direction of tooth movement
Short segment- larger moment

Equilibrium situations


Differential force systems
Clockwise

Counterclockwise

Non existent

Net moment= Counterclockwise


Anchor unit

Non-anchor unit



Unequal moments in the same direction increase
the effectiveness of the anchorage

Unequal moments in opposite direction still favor the anchorage,
if the molar moment is large

Off- center bend
o Long segment- direction of force
short segment- opposite direction
o Short segment- larger moment.
Long segment- smaller moment
o Tooth closest to the bend- anchor side

opposite – non anchor side
o Anchor side- bodily movement
non-anchor side- tipping
o Away from the centre- differential torque increases
o More critical the anchorage- more distal the bend from the
centre

Components of force system
o Alpha moment: acting on anterior teeth
o Beta moment: acting on posterior teeth

o Horizontal forces: mesiodistal
o Vertical forces: intrusive-extrusive


β

>

α

β

β=α


<

α

Cuspid retraction


I bicuspid retraction &
Molar protraction


o Friction mechanics/ Sliding mechanics

Moments- continuous archwire
Forces -auxiliaries
o Frictionless mechanics


o Orthodontic forces- not exceed capillary BP- Schwartz
o Optimal force- minimum value of force that results in
maximum rate of tooth movement- Smith
o Rate of tooth movement increases with increase in force up to
a point- no in crease in tooth movement-Quinn and Yashikawa

o Friction- force dissipated, remainder transferred to supporting
structures


o Friction- function of relative roughness of 2

surfaces
o Frictional force- 2 components
1. Frictional component- parallel to direction of

motion & opposes motion
2. Perpendicular to one or both contacting surfaces
o Friction=Coefficient of friction x normal force


o Coefficient of static friction- force necessary to

initiate movement
o Coefficient of kinetic friction- force necessary to
perpetuate motion


Friction mechanics/ Sliding mechanics


o Friction mechanics: force needed for 2 purposes

*to overcome frictional resistance
*to create bone remodeling


Frictional effect on anchorage

 Independent of area of contact
 Plastic deformation- junctions begin to shear
 Interlocking of roughness
 Harder materials plow into surface of softer ones

Total frictional resistance=sum of
1. Force necessary to shear all junctions
2. Resistance caused by interlocking of roughness
3. Plowing component of the total friction force


Frictional effect on anchorage
o “stick-slip” phenomenon- tooth movement slowed


Dr. SAFEENA


o ANCHORAGE: “Resistance to unwanted tooth

movement.”- Proffit


Anchorage Classification


Off- center bend
o Long segment- direction of force
short segment- opposite direction
o Short segment- larger moment.
Long segment- smaller moment
o Tooth closest to the bend- anchor

Side opposite – non anchor
o Anchor side- bodily movement
non-anchor side- tipping
o Away from the centre- differential torque increases
o More critical the anchorage- more distal the bend from the
centre

Space Closure
o Segmental mechanics

o Sliding mechanics/Friction mechanics
- Movement of bracket along archwire
- Sliding of archwire through brackets and tubes


Magnitude of friction

Excess force- unnecessary movement of anchor teeth


Factors affecting frictional resistance
A. Physical

B. Biological

1. Archwire

1. Saliva

2. Bracket

2. Plaque

3. Ligation

3. Acquired pellicle

4. Others

4. Corrosion


1.

Archwire
o

Material- β-Ti >NiTi>Co-Cr>SS

o

Cross-section- rectangular >round

o

Surface texture

Roughness- NiTi>β-Ti >Co-Cr>SS
o

Wire stiffness:
stiffness = binding = friction
Vertical dimension α stiffness

o

Effect of second order deflection- increase in angulation

Complete leveling of arch prior to sliding mechanics

2. Bracket-Material


SS- most popular



Ceramic brackets- rough surface, low fracture
toughnessCombination- greater loss of anchorage



Zirconia- esthetic
Surface hardening treatment= increase fracture
toughness

Co-eff. of friction- similar to ceramic brackets



Plastic brackets – Ligature- deform- squeeze slot

Ceramic reinforced with/without metal slot inserts.


Friction free brackets- special coating

o Manufacturing process

 Conventional Cast bracket- cutting procedures
produce bulky brackets, rough surface
 Sintered bracket- compact fusion of individual

particles under heat, premoulded in smooth
streamlined manner.
Frictional resistance 40-45% less


o Width of bracket- length of moment arm

o Wider bracket- smaller contact angle
o Inter bracket distance


Controversial

o Frank & Nikolai- wider bracket =greater friction
-frequent binding
o Narrow bracket=binding severe in nature

o Kapila et al. wider bracket= elastomeric stretched
more=greater force on wire


3. Ligation

o Ligature wire
o Elastomerics- adversely affected by oral
environment, stress relaxation

o Method of ligation


Effect of ligature technique- Edward et al.
 Elastomeric module
 Elastomeric module in fig-of-8 pattern
 SS ligature
 Teflon coated ligatures

Elastomeric module in fig-of-8 pattern- highest friction
value
Teflon coated ligatures- lowest mean static friction
Self ligating brackets- only 12-23% of friction that of SS
bracket.
Kusy- composite ligature

o Saliva- excellent lubricant/ adhesive behavior

SS- adhesive, co-eff. of friction
β-Ti - co-eff. of friction-50% of that in dry state
Vary force levels in

• h/o xerostomia
• Radiation therapy
• Anticholinergics


Methods of force application
o Elastics- synthetic rubber polymers

Force degeneration depends on
- Salivary enzymes
- Mastication

- Oral hygiene
- Temperature
- Increase ph of saliva= increase force decay rate


o Elastics-

Advantages:
 Easy to use
 Less time consuming
 Hygienic
Disadvantages:
 Rapid force decay rate
 Patient compliance

Tiebacks

o Passive tiebacks
o Active tiebacks
 Type one (distal module)

 Type two (mesial module)
Reactivation: 4-6 wks. Trampoline effect


o Coil springs- introduced in 1931

 Stainless steel- 0.010”, coil diameter 0.040”
 Cobalt- chromium
 NiTi


Coil springs
Factors affecting force levels

o Alloy
o Wire size
o Lumen size

o Pitch angle of the coil
o Length of the spring
o Amount of activation


Coil springs
o NiTi coil springs- 150gms force

o Expansion – according to manufacturer‟s
instructions (1 ½ times their original length)
o Smaller wire size, larger lumen=low

LDR, consistent force for longer periods
o Force variation- SS > Co-Cr > NiTi


Elastics vs Coil springs
Elastics

Coil springs

oEasy to use

o More consistent space

oEconomical

closure

oWork well in most

o Rapid space closure

clinical situations

o Force decay occurs to a

oRapid force decay rate

oAffected by oral
environment

lesser extent
o Minimally affected by

temperature and other
environmental factors

oPatient compliance

Tie backs vs NiTi coilsprings
o 1991- Samuels, Rudge and Mair- rate of space closure

o NiTi closed coil springs- significantly greater,
- more consistent


Recommendations for sliding mechanics
o Bracket- SS material
o Wire- SS material
18 slot- 16 x 22 or 0.016”
22 slot- 19 x 25 or 0.018”
o Mechanics- complete leveling and aligning prior
to retraction and establishing torque control
o Force application- light, continuous, constant
force


Techniques
o Separate canine and incisor retraction
Edgewise
 Alexander- Vari-simplex discipline
 Viazis

o En-masse anterior retraction
 MBT
Begg
 Conventional Begg
 Modified Begg
 Refined Begg

Vari-Simplex Discilpine
o R. G. Wick Alexander

o Vari- variety of brackets
o Simplex- Archwire fabrication simplified
o Maxillary cuspids retracted prior to anteriors

- More control over molar anchorage
- Cuspid into class one relation early in treatment


- Power chain + 0.016” round wire

- Heavy forces- 250-300gms- cuspids rotate & tip
lingually
- Power chain changed every 4 wks

- 4-6 months
- Loop mechanics for anterior retraction


o 0.018 x 0.025” closing loop- anterior retraction


Bio-Efficient Therapy- Anthony D. Viazis
o Triangular (Viazis) bracket- friction 10 times lower

o Bioforce wires- 11% reduction in friction
o 2 parts
1. Alignment, leveling and space closure.

2. Finishing.


20 x 20 wire in 0.022” slot

Superelastic wires and coilsprings


o Space closure


MBT
o 1970s- preadjusted bracket system + traditional

edgewise force levels (500-600gms)
o Unwanted tip, rotation & torque changes
o Built in tip, rotation & torque –extraction series


MBT
o 1990- controlled space closure

o Sliding mechanics with light forces
o Archwires – 0.019 x 0.025- good overbite control
o Active tiebacks-


o NiTi coil springs- 150gms force

o Expansion – according to manufacturer‟s
instructions (1 ½ times their original length)


MBT
o Alternative mechanics for space resistant to closure
o Tiebacks with 2 modules
o Hycon device- a centimeter segment of 21 x 25 wire
–soldered 7mm screw device
o Placed in double or tripe tube of molar
o Screw with large head- ligature tie
o Activation- twice a week one full turn
o Space closure- 1mm/month

MBT
Space closure in maximum anchorage cases

o Second molar included in set up
o Palatal bar, lingual arches
o Headgear


Experimental evaluation of frictional resistance in

the posterior segment using different wires and
posterior attachments- Dr. Ashwini Joshi
o Frictional resistance during en masse retraction in
I premolar extraction condition in an edgewise
setup
o Rectangular steel wires in 3 sizes and six
configurations of arch form were tested

o Results –
1. 19 x 25 arch wire in general showed least value of

friction
2. Frictional force –seen to reduce with increase in
wire dimension

3. Frictional force values increased with increase in
number of attachments through which wire was
engaged

4. 19 x 25 wire without curvature recommended for
en masse anterior retraction in case of young or
periodontally www.indiandentalacademy.com
comprised patients

5. For deep bite cases 18 x 25 arch wire with a curvature
could provide reduced frictional values and better
retraction
6. Wire sliding through-multiple attachments on either
side – 19 x 25 –ideal for retraction

7. Adult patients and patients with high bone density –
resistance to tooth movement is high – 18 x 25
smoother retraction
8. 17 x 25 –no significant advantage for en masse
anterior retraction over 18 x 25 & 19 x 25 as regards
frictional force.

Thank you
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Space closure 1 /certified fixed orthodontic courses by Indian dental academy

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