Biomechanics of molar distalization

BIOMECHANICS
OF
MOLAR DISTALIZATION
APPLIANCE
www.indiandentalacademy.com

CONTENTS
• INTRODUCTION
• INDICATIONS AND CONTRAINDICATIONS
• BIOMECHANICS
• TYPES OF APPLIANCES
-EXTRAORAL
-INTRA ORAL
• APPLIANCE SELECTION CRITERIA
• CONCLUSION
• REFERENCES

INTRODUCTION
Correction of class II malocclusion without
extractions requires maxillary molar
distalization by means intraoral or extra-
oral forces.

• William Kingsley (1892) described for the
first time headgear apparatus with which
class I molar relationship could be
achieved successfully.

• Oppenheim advocated that position of
mandibular teeth as being the most
correct for individual and use of occipital
anchorage for moving maxillary teeth
distally into correct relationship without
disturbing mandibular teeth.
• In 1944, he treated a case with extra-oral
anchorage for distalizing maxillary molar.

• Kloehn in 1947 started a long and
beneficial series of investigations and
clinical applications of cervical anchorage
to the maxillary dentition.

• The headgears over the years have
shown to be effective in maxillary molar
distalization with movements in all planes
of space. With the recent trend more
towards non extraction treatment, several
inter/intra arch devices have been
advocated to distalize molars in the upper
arch.

• Researchers have focused on the
simplicity and efficiency of these intra arch
devices, which improves the continuity
and constancy of forces. Oral hygiene is
easier to maintain and the need for patient
compliance is eliminated.

• Molar distalization is a technique that has
added a new column in the practice of
every orthodontist to produce consistent,
predictable and high quality results. The
goals of practicing with efficiency and
profitability are positively affected.

• Since space is easier to gain in the
maxillary arch than in the mandible
because of increased trabecular structure
of supporting bone and increased
anchorage afforded by palatal vault, the
distalization of maxillary molar becomes of
significant value for the treatment of cases
with mild to moderate arch discrepancy
and class II molar relationship associated
with a normal mandible.

INDICATIONS
• Profile - should be acceptable with minimal
facial change or straight profile

• Functional – Normal TMJ

• Skeletal - Class I skeletal pattern
- Normal, short lower face height
- Skeletal closed bite

Dental
• class II / End-on molar relationship

• Deep overbite
• Maxillary first molar mesially inclined
• Maxillary cuspids labially displaced

• Loss of arch length due to premature
loss of second deciduous molar
• Mild to moderate arch perimeter
discrepancy

UPPER MOLAR POSITION
• This is a linear measurement between the
distal surface of the maxillary first
permanent molar and the pterygoid
vertical line (PTV).
• It is an indication of the forward position of
the upper molar and illustrates to the
clinician whether or not sufficient space is
present for the second and third molars.

• This measurement indicates or
contraindicates molar distalization.
• An interesting aspect of this measurement
is that its mean value is the patient's age
in years plus 3mm until growth is
complete. Therefore the mean
• measurement for nine - year old child is
l2mm.

TIMING
• A favorable time to move molars distally
appears to be in mixed dentition, before
the eruption of the second molars, and an
efficient force system to move molars
distally is a continuously acting force.

CONTRAINDICATIONS
• Profile:- Retrognathic profile

• Functional:-abnormal temporomandibular
Joint

• Skeletal:- Class II skeletal
- Skeletal open bite
- Excess lower face height

• Dental:-Class I or III molar relation.
- Dental open bite/shallow bite

BIOMECHANICS
MD

MD

BP BP

P B

B
P
MD

TYPES OF APPLIANCES
• EXTRAORAL
• INTRA ORAL

EXTRA ORAL
• Bilateral molar distalization
a) Cervical pull head gear.
b) Combi pull head gear.
• Unilateral molar distalization with unilateral face
bows
a) power-arm face bow
b) soldered offset face bow
c) swivel-offset face bow
d) spring-attachment face bow.

INTRA ORAL
• INTER ARCH
• INTRA ARCH

INTER ARCH
 Atkinson buccal bar
 Tandem yoke
 3d biometric distalizing arch
 Modified herbst appliance for distalization of
molars
 Jasper jumper
 Sliding jig
Crickett appliance

INTRA ARCH
Sagittal appliance
Magnets
Modified lingual and Nance holding
arches
Jones jig
NiTi coil springs

 Pendulum appliance
 Super elastic NiTi wires
 Molar distalizing bow
 Space regainers
 K-Loop
 Fixed piston appliance
 Distal jet

C-Space Regainer
 Palatal orthodontic implants
 First class appliance
 Fixed palatal expander
 Lokar molar distalisation
 Transpalatal arch

Acrylic cervical occipital appliance
Rremovable molar distalization splint
Compressed springs
Mini distalization appliance
IBMD

SPACE REGAINERS
 Sling Shot Appliance
 Modified Kings Appliance
 Removable or fixed lingual arch with
spring
 Clasp ring

MOLAR DISTALIZATION IN
LOWER ARCH :
• Lip bumper
• Modified lingual appliance
• Distal jet for lower molar
• Franzulum appliance

EXTAORAL FORCES

LOW-PULL HEADGEAR

MEDIUM-PULL HEADGEAR

HIGH-PULL HEADGEAR

ASYMMETRIC HEADGEAR

EXTRA ORAL
• Bilateral molar distalization
a) Cervical pull head gear.
b) Combi pull head gear.

Cervical pull head gear.

Cervical Anchorage
with low-pull Headgear
Anti-clockwise
Rotation
Clockwise
Rotation
Translation

COMBI PULL HEAD GEAR

combi-pull Headgear
Anti-clockwise
Rotation
Clockwise
Rotation
Translation

Unilateral molar distalization with
unilateral face bows
power-arm face bow

soldered offset face bow

swivel-offset face bow
Swivel union

spring-attachment face bow

INTRA ORAL

STANDARD PENDULUM
APPLIANCE
• In 1992, Hilgers
• made of 0.032 TMA wire,
• Springs deliver approximately 230 gms of
force per side.
• Springs have adjustment loop that can be
manipulated to increase molar expansion,
rotation and distal root tip.

MODIFIED PENDULUM
APPLIANCE
• M- pendulum
• Inverted loop
• Activation - 40-450
• Springs deliver approximately 125 gms of
force per side.
• Springs have adjustment loop

K -LOOP
• By Kalra in 1995
• The appliance consists of a K-loop to
provide the forces and moments and
Nance button to resist anchorage

K-loop made of .017”x.025”TMA
wire with each loop 8mm long
and 1.5mm wide

Legs of appliance bent down
200

Wire marked at mesial of
molar tube distal of premolar
bracket

Bend placed 1 mm distal to distal1 mm distal to distal
mark and 1 mm mesial to mesialmark and 1 mm mesial to mesial
mark.mark. Stop should be well defined
and about 1.5mm long

K-loop in place with 2mm
activation

Moments and forces
produced by K-loop

Reactivation sequence
Open loop 1mm at (1); Open loop
1mm at (2); Open at (3) to regain the
200
bent of mesial and distal legs

COMPRESSED SPRINGS
• Gianelly and co-workers.
• Springs made from compressed stainless
steel or NiTi.

• NiTi coil is activated to about 10 mm o
produce 100 gm.
• First premolars are anchored by Nance
holding arch.
• Coil springs can also be compressed by
placing a sliding Gurin lock.

REPELLING MAGNETIC
APPLIANCE
• First and second premolar are banded
and an impression is made. A palatal
stabilizing plate is fabricated and
cemented in place. First molars are also
banded.

• An assembly containing repelling magnets
is placed into the molar tubes on maxillary
first molar and magnets are placed in a
repelling portion facing by ligating a sliding
yoke to an eyelet as premolar.

• Activation every two or four weeks.
• Not gained wide acceptance because the
magnets tend to be expensive and bulky.

SLIDING JIG
• Auxillary sectional arch wires used to tip or
move one or a group of teeth in buccal
segments distally without disturbing
anteriors.
• Have bent in eyelets on each side.
• To avoid friction or binding they should be
made of 0.022 inch round wire and can
also be made of rectangular wire.

• Location of intermaxillary hook on the jig,
soldered or bent-in, is on the occlusal area
of anterior eyelet of jig.
• To move maxillary molar distally, eyelet on
distal end of jig must but against molar
tube, mesial eyelet is located between
cuspid and first premolar bracket at least 2
mm anterior to premolar bracket.

BIMETRIC DISTALIZING ARCH
• Developed by Wilson and Wilson.
• components

• Distalizing force on the molars is produced
by compression of push coil spring
anchored by pull of class II elastics. The
force of the elastics counteracts the forces
of the push coil springs so that the anterior
segment of the Wilson arch approximates
the incisor brackets before ligation to the
anterior teeth

• Posterior ends of Omega loop should
contact the face bow tubes on maxillary
first molar, and anterior section of arch
should approximate brackets on maxillary
anterior teeth. 5 mm section of 0.010 x
0.045” open wound coil is placed over end
of William’s arch bilaterally.

• Advocated sequential use of elastics with
decreasing force values i.e. 5/16” 6-oz in
first week, similar size 4-oz in second and
and similar size 2-oz in third and
subsequent weeks of treatment.

• Appliance is activated by placing loop
forming pliers into Omega loop, forcing
posterior leg distally. Elastic sequence
begins again when reactivated.
• Lower arch should have a stiffer
rectangular arch wire or lingual arc.

HERBST APPLIANCE
• Emil Herbst in 1905.
• Original design consisted of placement of
bands on maxillary first premolar and
molar and mandibular first premolar, which
were connected with lingual bar to support
anterior teeth.

• The arches are connected with a
telescopic adjustable piston mechanism to
produce a protrusive force on mandible.

• Class II correction is by equal amounts of
dental and skeletal changes.
• Dental changes include distalization of
maxillary molar and mesial movement of
mandibular molar and incisors.

• Skeletal changes include inhibition of
maxillary antero-posterior growth and to
produce an increase in mandibular length
and lower face height.

MOLAR DISTALIZATION IN LOWER
ARCH

LIP BUMPER
• used for molar anchorage, prevention of
poor lip habits and creation of increased
space for mandibular arch.
• Made of 0.045” stainless steel that spans
the facial structures of mandibular arch
without contacting teeth and inserted into
molar tubes.

• Anteriorly wire is covered by plastic tubing
or acrylic shield to hold lip away from
incisors.
• Force from mentalis muscle is transmitted
to molar, enabling them to move to an
upright and distal position

APPLIANCE SELECTION
CRITERIA
• Regardless of approach, one should
ponder several issues before considering
any of these appliances for use
Side effects
Case types
Arch length
Treatment timing
Co-operation

Side Effects
• Did incisors flare?
• If mandible is used as an anchor unit, did
anything occur in that arch?

• Side effects are a fact of life, especially in
orthodontics.
• There are some side effects that would be
favorable in certain cases, while the same
effects may be detrimental in others.

• The key to correct appliance selection is to
know, and be able to predict these effects.
• For this a sound and thorough knowledge
of biomechanics is essential.

Case types
• Consider an individual case at hand and his/her
needs.
• If mandibular dentition can be slightly
mesialized, if this in the case then Herbst or
BDA may be appliance of choice.
• If not pendulum and other intra-arch appliances
can be used.
• If you may not afford flaring of incisors then
headgear would be treatment of choice.

Arch length
How much distalization is required.
TPA has limited application of 2-3 mm, if
in need of greater amount of correction
then Herbst and headgear are of choice
followed by pendulum, Wilson BDA etc.

Treatment timing
Perhaps best time to initiate distalization is
late mixed dentition and it may be too late
after eruption of second molar.
Some synergistic effect as dentition
transits from primary to permanent as
canines and premolars follow molars as
they moved distally. Thus appliances that
requires some anterior anchorage like
pendulum may dilute these results.

Co-operation
• Invariably appliances that require least
co-operation come with side effects that
have to be considered.

CONCLUSION
• There are many advantages and
disadvantages of both the intra-oral and
extra-oral methods.
• It should be remembered that patient
selection for a particular method of
distalization is of utmost importance and
should not be overlooked .

• Right appliance should be selected for the
right patient and one should not select the
patient for the appliance rather the
appliance should be for the patient

Biomechanics of molar distalization

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