efficiency of pendulum applaincefor molar distalization related to second & third molar erupting stage. ajodo 2004

Efficiency Of A Pendulum Appliance For
Molar
Distalization Related To Second And Third
Molar
Eruption Stage
WWW.INDIANDENTALACADEMY.COM

Correction of a Class II malocclusion without extractions
requires maxillary molar distalization by means of intraoral
or extraoral forces

Although headgears have proven useful
in the correction of skeletal problems, as well as in
providing anchorage for extraction cases, they depend
heavily on patient cooperation

Various fixed intraoral appliances for molar distalization
have been introduced, in avoiding undesirable
biomechanical
side effects.

In the 1970s, Bernstein described the ACCO (acrylic
resin cervico-occipital) appliance, a cross between the
removable plate-type appliance with pendulum springs
and cervical or occipital headgear

In the 1980s, the Wilson appliance
(Rocky Mountain Orthodontics, Denver, Colo) was introduced
in which the molars are distalized via compression springs,
thus requiring the patient to wear Class II elastics to prevent
the loss of anchorage.

The active elements of the pendulum appliance are pendulum springs
inserted palatally into the molar bands.

The Pendulum appliance appliance, first described in 1992
by Hilgers, was later modified by him and others, including
Snodgrass
Byloff et al,
Favero,
Grummons, Scuzzo et al, and
Kinzinger etal.

Ideal Intraoral Molar-distalization Appliance
Should Meet The Following Criteria
• Minimal need for patient compliance.
• Acceptable esthetics and comfort.
• Minimal loss of anterior anchorage (as evidenced
by axial proclination of the incisors).
• Bodily movement of molars to avoid undesirable
side effects, lengthening of treatment, and
unstable results .
Minimal chairtime for placement and reactivations

According to studies by Byloff et al,Bussick and
McNamara,Ghosh and Nanda, and Joseph and Butchart,
the position of the second molar when distalizing the first
molar with a pendulum appliance is of little if any
importance .
The aim of the present study was to assess this
hypothesis

A modified pendulum appliance for bilateral molar
distalization was fixed in the maxillae of 36 patients (25
girls, 11 boys; mean age, 12 years 5 months).
The dentition in the anchoring complex was identical (with
the appliance fixed to the 4 premolars), the patients were
divided into 3 groups, according to the stage of second and
third molar eruption

Group 1(PG:1): Bilateral distalization of first molars; second
molars on both sides not yet erupted.
Group 2(PG:2): Bilateral, simultaneous distalization
of first and second molars with third molar at budding stage.
Group 3(PG:3): Simultaneous distalization of first
and second molars on both sides, with germectomy of third
molars.

In PG 1 (18 patients), eruption of the second molars had either notyet
taken place or was not complete.
In PG 2 (15 patients), the second molars had already developed to the
occlusal plane with the third molars at the budding stage.
In PG 3 (3 patients), third-molar germectomy had been completed, and
eruption of the first and secondmolars was complete.

The pendulum appliance is pendulum K, used in this study is
a modification of the standard pendulum appliance
according to Hilgers. The appliance includes a distal screw
dividing the Nance button into 2 sections.

The anterior section provides anchorage, and the posterior
section accommodates
the pendulum springs

These pendulum springs are not only activated for distalization (as an approximate
guideline 180-200 centinewtons [cN]). Additionally applied is a built-in
straightening activation and toe-in bending.
The appliance is activated intraorally by the therapist at the checkup appointments
by adjusting the distal screw; there is no need for the pendulum springs to be
disengaged from the lingual sheaths

Molar movement in the horizontal plane was monitored
by taking alginate impressions and making dental casts both
at the outset of therapy (T1) and after removal of the
pendulum appliance (T2).

. The measurements were to identify in each
patient group any increase or decrease in transverse
arch width in the region of the first and second molars
as well as the magnitude and mode of molar rotation
achieved by the therapy

Methods to determine the change in transverse dimension in the
1st
and 2nd
molar region and the and
the mangitude and the direction of molar rotations

Measurements were taken of the distance from the lowest
point in the central fossa to the mesiobuccal a distobuccal cusp tips of the
first and second molars for change in tranverse dimension .
The angles between the straight line transversing the mesiobuccal and
distobuccal cusp tips and the raphe-median line weretaken for checking molar
rotation

Changes in the sagittal plane were determined

SNA, angle between anterior cranium floor and alveolar point
SN/ANS-PNS, angle between anterior cranium floor and palatal plane
Facial axis angle, angle between nasion-basion line and facial axis
Facial plane angle, angle between facial plane and Frankfort horizontal
Mandibular plane angle, angle between mandibular plane and Frankfort horizontal
Lower facial height angle, angle between anterior nasal spine, Xi-point and PM-point
i-CEJ/PTV, distance from maxillary incisor to pterygoid vertical
m1-CEJ/PTV, distance from first maxillary molar to pterygoid vertical

● m2-CEJ/PTV, distance from second maxillary molar to pterygoid vertical
● m1-CEJ/ANS-PNS, distance from first maxillary molar to palatal plane
● i/ANS-PNS, angle between maxillary incisor andpalatal plane
● i/SN, angle between maxillary incisor and anterior cranium floor
● m1/ANS-PNS, angle between first maxillary molar and palatal plane
● m2/ANS-PNS, angle between second maxillary molar and palatal plane
● m1/SN, angle between first maxillary molar and anterior cranium floor
● m2/SN, angle between second maxillary molar and
anterior cranium floor

To check for any vertical changes, the angles between the
anterior cranium floor and the alveolar point (SNA), between
the anterior cranium floor and the palatal plane (SN/ANSPNS),
and the angles of the facial axis, facial plane, mandibular plane,
and lower facial height, were measured.

In the sagittal plane, relative mesial incisor movement, loss
of anchorage, and relative distal movement of the first and
second molars to the vertical of the pterygoid were
measured
(i-CEJ/PTV, m1-CEJ/PTV, m2-CEJ/PTV).

The degrees of labial incisor and distal molar tipping
were determined by measuring the angles between
the longitudinal tooth axis and the palatal plane and
the anterior cranium floor, respectively.

In the vertical plane, any intrusion or extrusion of the first
molars in relation to the palatal plane was checked (m1-
SZG/ANS-PNS). The baseline for these measurements was the
cementoenamel junction on the longitudinal tooth axis.

In the horizontal plane, dental cast measurements for the 18
patients in PG 2 and PG 3 (in whom the distalization effect of
the pendulum spring on the first molars extended to the
already erupted second molars) showed not only mesiobuccal
rotation of both maxillary molars but also vestibular drift of
the unbanded second molars

In the 3 patients of PG 3, in whom germectomy of the
wisdom teeth had already been completed, the increase in
transverse arch width was average.
The possible factor behind the phenomenon of vestibular drift
( clearly not depending on the third molars) might be the morpholog
of the molars and the contact point regions, the relative position of
the molars to each other, or the anatomically fixed position of the
spongiosa groove.
A third molar bud seemed to place no restriction on the degree of
vestibular drift.

In the sagittal plane, cephalometric analysis for
identifying any changes showed that, in the
distalization direction, a tooth bud acts on the mesial
neighboring tooth in the same way as a fulcrum

In sagittal plane, tooth bud in direction of distalization acts like fulcrum on its
mesial neighbor. Degree of tipping of first molars was much greater in patients
whose second molars were still at budding stage

Degree of tipping of fully erupted second molars was still greater when
third molar was located in direction of movement. In contrast, distalization
of first molars was almost completely bodily.

After third molar germectomy, almost completely bodily distalization of
both molars is possible, even when second molars are left unbanded.

Biomechanical analysis
(approximation)
When the lingual sheath of the molar band is acted
on by a force FP (due to pendulum spring activation), a
torque MP, resulting from the product of the force FP
and the vertical distance to the center of resistance of
the molar, simultaneously arises.

Horizontal plane
In the horizontal plane, a distobuccal torque, MP, results from the force of the
pendulum spring FP acting on the lingual sheath of the molar band at the first
molar (thus palatal to the center of resistance of that tooth). The magnitude of
this torque, although present, is extremely small and can be ignored for clinical
purposes. The direction of the force FP
depends directly on the path of the circular arc
described by the pendulum spring.

The closed loop is positioned at the center of rotation of the pendulum
spring distal from the center of resistance and
With the activation of the distal screw taking place at the zenith of the arc
impact the distally directed line of force and the force-torque ratio in the
lingual sheath

Up to the zenith of the circular arc, the force FP due to the pendulum spring can be
broken down into 2 vectors, 1 acting distally, the other vestibularly. The resulting line
of force acts in the distovestibular direction
This direction of in the region of the lingual sheath, has the same direction and
impact as would result from toe-in bending.
This is in the mesiobuccally directed torque Mti on the first Molar), which acts in
opposition to the distobuccal torque MP..

An additional toe-in-bend applied directly to the pendulum spring
amplifies the corresponding torque in a therapeutically desirable way.
The net effect is that the first molar is subjected to the desired expansion
and distalization, together with mesiobuccal rotation. Deviation in the
orovestibular direction is avoided

Because of the rhomboid shape of the molar crown, the mean mesial
rotation of the first molars (as determined by the study) and the
approximal surface running diagonally from mesiobuccal to distopalatal
net movement of the second molar is both distal and buccal.

Sagittal plane
In the sagittal plane, a distinction must be made between the
force systems involved in the 3 different stages of the dentition:
For the second molar at the budding stage.
When eruption of the second molar is complete and a third molar
bud is located distal to.
Second molar when the eruption of the first and second molars is
complete and no third molar bud is present (missing, germectomy).

The force FP applied to the first molars with
thependulum spring acts coronal to the center of
resistance, a resulting torque MP acts simultaneously
on the molars.
In the zone of contact between the first and second
molars, a second molar at the budding stage produces
a counterforce FK, in opposition to the distalization
force FP. At static equilibrium, both forces are of the
same magnitude
FP =FK.

The corresponding torque MK acts in parallel to
torque MP, and thus the 2 torques are summed. To
achieve maximum translatory first molar distalization
in this configuration, the sum of all torques needs to
have a magnitude of zero.
Ideally the torque MA arising from the straightening
activation should therefore be equal to the sum of
MP and MK
Straightening activation also produces an intrusion
force FA on the molars that acts in opposition to the
extrusion produced by the arc described by the
pendulum spring.

When eruption of the second molar is
complete and a third molar bud is present:
At static equilibrium, the magnitude of the
distalization force FP is equal to the sum of
the magnitudes of the opposing forces acting
at the points of contact:
FP = FK +FK

The line of force of the counterforce FK
produced by the second molar in the contact
point area runs approximately at the same
level as the line of force of the distalization
force FP. The resulting torque MK acts here in
opposition to the torque MP.

To achieve maximum physical distalization of the first
molars, the straightening activation on the first molar can
be correspondingly weaker compared with the not yet
completely erupted second molar. This is because, in terms
of direction, the resulting torque MA is the same as the
torque MK and, acting together with it, should nullify
torque MP
Summation M at the first molar + MP +MA _+0

The force conditions for the second molar are similar to
those applying in the first system to the first molar.
Torque MK’ is also directionally the same as torque
MP’. Because no straightening activation can be
applied to the second molar, there is no
therapeuticmeans of producing an opposing torque
Summation M at the second molar = MP’ _ MK’

In conditions where the second molar when the eruption of the first and second molars
is complete and no third molar bud is present (missing, germectomy)The only force
acting at the distal alveolar crest of the second molar is a biological resistance due to the
periodontium. Thus, in this instance, the torque MP’ does not become large ;
Summation M at the second molar = MP’.
Unlike in the second system, although second molar distalization is not bodily in this case
either, there is
comparatively little tipping.

CONCLUSIONS
For young patients, the best time to start therapy with a pendulum
appliance is before the eruption of the second molars
However, if distalization of the first and second molars is to be carried out
simultaneously (in which case the banded first molars are pushing the
second molars along during distalization), prior germectomy of the third
molar is strongly recommended. However, greater loss of anchorage and
vestibular drift of the second molar must be accepted

efficiency of pendulum applaincefor molar distalization related to second & third molar erupting stage. ajodo 2004

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