Tweed merrifield edgewise. /certified fixed orthodontic courses by Indian dental academy

THE
TWEED - MERRIFIELD
EDGEWISE APPLIANCE
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Seminar by Dr. Siddhartha Dhar
Under the guidance of

Prof. Ashima Valiathan
BDS, DDS, MS (USA)
Head of Dept and Director of PG
Studies ,
Dept of Orthodontics and Dentofacial
Orthopaedics,
Manipal College of Dental Sciences,
Manipal.

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Introduction
Basic Concepts
Diagnostic Aspects
Treatment with the Tweed –
Merrifield Edgewise Appliance.
Conclusion


Introduction
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For over 50 years the
Tweed philosophy played
a dominant role in
American orthodontics.
Dr Tweed is considered
by many to be the
greatest clinical
orthodontist of his time,
and his reputation,
technique and skill as a
teacher attracted
thousands of students to
study at the Tweed
Foundation, Tucson,
Arizona.

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Although it produces, outstanding results
in terms of improving the occlusion and
facial profile, the classic Tweed technique
is demanding for both the orthodontist and
for the patient.
It requires a high degree of technical skill,
lengthy sequence of archwires, excellent
patient co-operation, and a relatively
modest patient load to maintain control
and achieve its results.

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In 1960, Tweed
selected one of his
most outstanding
students, Levern
Merrifield from Ponca
City, Oklahoma, to
continue his work on
the Edgewise appliance
and be the co-director
of his course with him.
At the time of Tweed’s
death, in 1970, he
became course
director.

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From 1965 onwards, Merrifield and
members of his study group began
to develop a series of modifications
that taken collectively, constitute the
course currently taught at Tucson,
Arizona.
This is known as the TweedMerrifield Edgewise Appliance.

Basic Concepts
These include:
1. The fundamental concept of the dimensions of
the dentition.
2. Dimensions of the lower face.
3. Total space analysis
4. Guidelines for space management
5. Directional control during treatment
6. Sequential tooth movement
7. Sequential mandibular anchorage preparation.
8. The organization of treatment into four orderly
steps.

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Merrifield’s innovations in diagnosis
and experience in the use of the
Edgewise appliance have improved
on Tweed’s contributions and
concepts to give the modern
orthodontist a more accurate,
reliable, precise efficient, and
practical protocol of diagnosis and
treatment.

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Adherence to this protocol allows the
clinician to achieve the following:
Define objectives for the face,
dentition and skeletal pattern.
Properly diagnose the malocclusion
Use the Edgewise appliance to reach
the predetermined objectives
efficiently.

Dimensions of the Dentition.
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There are three dimensions of the
denture, length, width, and height.
These dimensions allow the teeth to be
moved in six directions, mesially, distally,
laterally, lingually, intrusively, and
extrusively.
All these movements, which are easily
accomplished with orthodontic appliances,
are limited and restricted by the physical
environment of bone, muscle, and soft
tissue that exerts influence on the teeth
and the jaws.

Arch length- The anterior limit
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Anterior expansion of the denture is
characterized by a protrusion of the lips, a
lack of balance and harmony of the lower
face, and a lack of health of the bone and
investing tissue.
Unless the musculature is very weak, the
muscular environment will reassert itself
and cause a collapse or crowding of the
teeth, a deepening of the bite, an increase
in overjet, and finally a deterioration of
the investing tissues.

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Charles Tweed concluded that mandibular
incisor position must be maintained or that
these teeth must be contracted lingually
so that they are positioned over basal
bone and in harmony with the muscles of
this region.
Otherwise, either facial esthetics or
denture stability or both would be in
jeopardy.


The use of
Tweed's
diagnostic facial
triangle is a very
simple and
accurate means
of determining
the dimensions of
the denture in
the mandibular
incisor area.

Arch length-The posterior limit
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The orthodontist, while considering
the anterior end of the denture, must
put an equal amount of thought and
consideration into the posterior end.
The bony environment of the
mandibular molars effectively
prohibits significant posterior
expansion of the mandibular molar
teeth.

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Because the maxilla does not have heavy
bone support at the tuberosity, it seems to
invite one to attempt to use orthodontic
forces to move maxillary molars distally
into "normal Class I" inclined plane
relationships.
However, strong muscular pressure being
exerted by the buccinator, the masseter,
the temporalis, and the internal pterygoid
muscles, limits posterior expansion.
Class II malocclusions, if treated to Class I
inclined plane relationships by any
combination of distal driving forces, when
space does not exist, show certain
characteristic symptoms.

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The maxillary second molars will, if
banded, be driven distally off the
tuberosity. If unbanded, these second
molars will be driven both distally and
buccally.
The third molars will, in most cases, be
deeply impacted because there is
generally not enough tuberosity growth to
accommodate these teeth in the arch.
This illustration brings home the point that
to create a posterior discrepancy in an
attempt to correct an anterior discrepancy
is not sound reasoning.

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It is important to note that
uprighting mesially inclined maxillary
or mandibular molars that are in a
forward position as a result of habits
or the premature loss of deciduous
teeth is not a form of posterior
expansion.
It is a proper treatment objective if
the original malocclusion arch length,
both anteriorly and posteriorly, is
respected.

Arch width
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Robert Strang did a great deal of work on denture
stability and lateral expansion.
He stated, "The mandibular cuspid width, as
measured across the arch from one canine to the
other, is an accurate index of the muscular balance
of the individual and dictates the limit of denture
expansion in this area.“
He further stated, "With very minor exception, the
original mandibular malocclusion width must also
be respected in the premolar and molar areas."
The recent studies reported in the literature by
Little, et al. seem to confirm Strang's hypothesis
that mandibular canine width is inviolate.

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According to Merrifield, (AJODO 1994)
orthodontists must accept the original
tooth position as the extreme width of the
buccal segments in patients with normal
muscular balance.
He also suggested that the environment
will tolerate some contraction in the buccal
segments and that further contraction will
occur after the cessation of treatment.

Vertical dimension
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Tooth movements that can be involved are
intrusion and extrusion.
The muscles of mastication limit this
dimension of tooth movement.
Vertical expansion of either the maxillary
or mandibular posterior teeth causes
many undesirable reactions.
Included among these could be (1)
mandibular rotation, (2) freeway space
impingement, (3) maxillary reorientation
to cranial base, and (4) an unstable
orthodontic treatment result.

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Extrusive forces that cause vertical expansion
create a downward descent of the anterior part of
the lower face. One millimeter of vertical expansion
in the maxillary molar area results in a 1.3 mm
descent in the maxillary incisor area.
This reaction is not complimentary to facial balance
and certainly does not enhance a facial pattern that
needs horizontal development.
Vertical control should be monitored with lateral
head films during the course of treatment.
The relative relationship of the palatal plane, the
occlusal plane and the mandibular plane when
superimposed on head film tracings could be the
best guide to control of vertical expansion.
These three planes should remain parallel or flatten
slightly posteriorly as treatment progresses.

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Vertical expansion, like lateral expansion,
seems to occur with posterior expansion.
If maxillary molars are moved distally into
Class I relationships when there is no
space for this movement, there is a
wedging open in the posterior part of the
mouth.
This wedging effect encourages a drop of
anterior nasal spine and pogonion. These
reactions result in the convex face which
has been described as the "orthodontic
look."

Diagnostic aspects

1.
2.
3.
4.

According to Merrifield and coworkers, any valid identification and
classification of orthodontic and
orthognathic disharmony should be
based on four major areas:
Facial
Cranial
Dental
Environmental

I. Facial disharmonies- Factors in differential
diagnosis

1. Positions of the teeth
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Facial balance is affected by marked protrusion
and/or crowding of the teeth.
Lip protrusion is a reflection of the amount of
maxillary incisor protrusion.
Merrifield and others have shown that the upper
and lower lips are very responsive to maxillary
incisor tooth movements.
The lower lip follows the upper anterior tooth
retraction very closely, and the upper lip
recontours with retraction and some thickening.

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Merrifield (AJO 1966) concluded that 4 mm of
upper incisor retraction is accompanied by 3 mm
of upper lip retraction and 1 mm of upper lip
thickening.
Proper directional tooth repositioning can also
enhance the chin-lip relationship.
The chin-lip relationship can be defined in relation
to the nose, nasal-labial contour, smile line and
vertical proportions of the face.
Lower facial contour is a direct responsibility of
the orthodontist.

2. Frankfort Mandibular Plane Angle (FMA):
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This is a crucial skeletal value in
differential diagnosis.
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Dental compensation for a high FMA
requires additional upright positioning of
the mandibular incisors.
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Conversely, dental compensation for a
low FMA requires less mandibular incisor
upright positioning

3. Soft tissue
measurements:
a. Total chin thickness
(mm)
b. Upper lip thickness
(mm)
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Total chin thickness
should equal upper lip
thickness. If it is less
than upper lip
thickness, the anterior
teeth must be
positioned further
upright to facilitate a
more balanced profile.

4. Profile line:
 The profile line and its relationship to
facial structures and FH plane can be
used to give an idea of lip
procumbency.
 The ideal relationship of profile line is
tangent to the chin and the vermilion
border of both lips, and bisecting the
nose.

5. Z angle:
 This is the angle
made by the profile
line with the FH
Plane.
 It has a normal range
of 70-80 degrees.
 It is an adjunct to the
FMIA and is more
indicative of the soft
tissue profile than
FMIA.
 It quantifies the
combined
abnormalities in the
values of FMA, FMIA
and soft tissue
thickness, and gives
immediate guidance
relative to anterior
tooth positioning.

6. FMIA
 Tweed believed this angle was
significant in establishing balance
and harmony of the face.
 He established a standard of 68˚ for
individuals with FMA of 22-28˚.
 The standard should be 65˚if FMA is
30˚or more, and the FMIA will
increase if the FMA is lower.

II. Cranial DisharmonyDifferential Diagnosis
1. FMA:
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The FMA defines the direction of
lower facial growth in both the
horizontal and vertical dimensions.
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An FMA greater than the normal
range indicates excessive vertical
growth, and an FMA less than the
normal range indicates deficient
vertical growth.

2. IMPA
 Defines the axial inclination of the
mandibular incisor in relation to the
mandibular plane.
 Guide to use in maintaining or positioning
teeth in relation to the basal bone.
 The standard of 88˚indicates an upright
position and with normal FMA, reflects
optimal balance and harmony of the lower
facial profile.


3. SNA:
 Indicates the relative horizontal
position of the maxilla to cranial
base. The range at termination of
growth ranges from 80-84 degrees.


4. SNB:
 Expresses the horizontal relationship of
mandible to cranial base. Range of 7882˚indicates a normal horizontal
mandibular position.
 Values below 74˚or greater than
84˚indicate a large maxillomandibular
discrepancy, and could require
orthognathic surgery, in addition to
orthodontics.

5.ANB:
 The normal range is 1-5˚. With
higher ANB angles, Class II
relationships become proportionately
more difficult to handle.
 An ANB angle greater than 10˚or
less than -3˚indicates a need for
surgery as an adjunct.

6. AO-BO:
 Indicates horizontal relation of mandible to
maxilla.
 More sensitive to malrelations than the
ANB angle because it is measured at the
occlusal plane.
 Treatment becomes more difficult when
AO-BO is greater than the normal range of
0-4mm.
 It changes in direct proportion to the
occlusal plane angle.


7. Occlusal Plane:
 The occlusal plane value expresses the
relation of the occlusal plane to the FH
plane.
 A range of 8-12˚is normal with variations
of about 2˚between males and females.
 In most orthodontic corrections, the
original value should be maintained or
decreased.
 An increase in occlusal plane angle
indicates a loss of control during
treatment.

8. Posterior facial height:
 Linear measurement in mms from
articulare to the mandibular plane tangent
to the posterior border of the ramus.
 An increase in ramus height is essential
for downward and forward mandibular
response.
 Relationship of posterior facial height to
anterior facial height determines the FMA
and lower facial proportion.

9. Anterior facial height:
 Linear measurement in mms of the
vertical distance between the palatal plane
and menton.
 In Class II correction it is essential to limit
increase in AFH.
 Accomplished by controlling mandibular
and maxillary molar extrusion and using
anterior high pull force on the maxilla.

10.Facial Height Index:
 Andre Horn studied the relationship
of AFH to PFH, and found that
normal PFH is 69% of the AFH.
(FHI= 0.69).
 Normal range is 0.65-0.75.
 Index values approaching 0.60 and
0.80 indicate divergent and
convergent patterns respectively.

11. Facial Height Change Ratio:
 A ratio of two times as much increase in PFH as
AFH increase during treatment is ideal for
correction of Class II div 1 and dento-alveolar
protrusion malocclusions.
 However, the actual volume of change is more
important than simply the ratio.
 Merrifeld and Gebeck ( AJODO 1995) evaluated
successfully and unsuccessfully treated Class II
malocclusions, and found that successful cases
were associated with greater increase in PFH,
while the opposite was true of unsuccessful
cases.

Gramling’s Probability Index.
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Over a period of 15 years, till his untimely
death in 1993, Jim Gramling of Jonesboro,
Arkansas was director of the Tweed
Foundation.
During this period he studied large
samples of successfully and unsuccessfully
treated Class II cases.
Based on the evidence gathered he
formulated a Probability Index (published
in J Charles Tweed Foundation 1989 and
posthumously in AJODO 1995)

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The elements of the Probability Index
are five key cephalometric angles.
When properly integrated, they
appear to be reliable in predicting
the prognosis of a given orthodontic
treatment.


The following conditions might be
necessary for Class II treatment success:
1.
2.
3.
4.
5.

FMA should be 20 -30˚.
ANB should be 6˚or less.
FMIA should be greater than 60˚.
Occlusal plane should be 7˚ or less.
SNB should be 80˚or more.


The Cranial Facial Analysis.
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The Cranial Facial Analysis has been
developed from Gramling's work, from
Merrifield and Gebeck's work, and from
Andre Horn's ratio studies.
The Z angle has been substituted for the
FMIA because it is a better indicator of
facial form.
Horn's Facial Height Index was added to
further define horizontal and vertical
relationships of the craniofacial complex.

Dental Disharmony
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Along with a consideration of the face and
skeletal pattern, the orthodontist must
also consider the dentition.
Total space analysis as described by
Merrifield is divided into three parts
anterior, midarch and posterior.
This is done for simplicity in identifying the
area of space deficit or surplus, as well as
accuracy in differential diagnosis.

Anterior Space Analysis
1.Measurement in mms of the space
available in mandibular arch, from canine
to canine, as well as measurement of the
mesiodistal dimension of each of these
anterior teeth. Difference is referred to as
surplus or deficit.
2.The Tweed diagnostic triangle is also used
to analyze this area. The cephalometric
discrepancy i.e. the amount of space
required to position the mandibular
incisors for facial balance is added.

3.Soft tissue thickness is also
considered. Total chin thickness
should equal upper lip thickness. If it
is less than upper lip thickness,
anterior teeth need further
uprighting, for a more balanced
profile.


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The anterior discrepancy = Anterior
tooth surplus/ deficit +
cephalometric discrepancy + Soft
tissue imbalance.
Each of these three values has a
difficulty factor so that a difficulty
value can be calculated.


Midarch Space Analysis
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Midarch area includes the mandibular first
molars, and first and second premolars.
Analysis of this area reveal mesially inclined first
molars, rotations, spaces, deep curve of Spee,
crossbites, missing teeth, habit abnormalities,
blocked out teeth, occlusal disharmonies.
This area being in center of arch, allows easiest
method of space management for malocclusion
correction.
In addition to the arch length discrepancy and
curve of Spee, the occlusal disharmony is to be
measured.

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Occlusal disharmony (Class II or Class III) is
measured by articulating the casts and using the
maxillary 1st premolar cusp as reference.
Measurement is made mesially or distally from
maxillary first premolar buccal cusp to the
embrasure between mandibular first and second
premolars.
Average of both sides measurement is taken to
get the occlusal disharmony.
The difficulty factor is “2”, so the measurement is
doubled when added to the midarch difficulty.


Posterior Space Analysis
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The required space in the posterior space
analysis is the mesiodistal width of the
2nd molars and 3rd molars in the
mandibular arch.
Space available is the measurement in
mm from distal border of 1st molar to the
anterior border of ramus along occlusal
plane.
An estimate of posterior arch length
increase based on age and gender is
added to this value.

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The literature reveals an increase of 1.5 mm each
side per year after full eruption of 1st molars, till
age of 14 years for girls and 16 years for boys.
It is important not to create a posterior
discrepancy while adjusting the other areas.
On the other hand posterior space surplus should
be used to alleviate midarch and anterior
discrepancies.
Posterior space analysis value has a low difficulty
factor of 0.5 because a deficit can easily be
resolved by extraction of third molars.


Differential Analysis System.
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The Cranial Facial Analysis and the
Dentition Space Analysis together
make up the Differential Analysis
System.
Sum of Cranial Facial Difficulty and
Dentition Space Difficulty gives the
Total Difficulty.


The Tweed Merrifield Edgewise
Appliance.
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The approach used at the Tweed
Foundation employs a “straight bracket”
appliance.
It consists of posterior bands and anterior
mesh pads with single, double width 0.022
brackets on the six anterior teeth;
intermediate single width brackets on the
premolar bands; twin brackets on the first
molars; and heavy edgewise 0.022 tubes
with mesial hooks on the second molars.
Lingual hooks and cleats are also provided
on molars and premolars respectively.

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Each of the brackets and tubes is placed at
right angles to the long axis of the tooth.
No tip, torque, variations in thickness are
present in the bracket.
According to Merrifield “ this prescription,
in my opinion is the only one that provides
sufficient versatility to provide for
individualized tooth positioning.”


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The commonly used archwire sizes are
017 x 022, 018 x 025, 019 x 025, 020 x
025, 0215 x 028.
These wire dimensions give a great deal of
versatility with the 022 x 028 bracket slot.
Knowledge of first, second and third order
bends and their interactions is crucial.
The commonly used auxiliaries include
elastics, directionally oriented headgear
( High pull J hook, straight pull J hook.)

Treatment with the Tweed
Merrifield Edgewise Appliance.
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Using Tweed’s treatment concepts as
a foundation, Merrifield developed
force systems that simplify the use
of the Edgewise appliance.
The twelve sets of arch wires used
by Tweed have been reduced to four
or five sets of wires.

Essentially five concepts compose
the treatment philosophy.
1. Sequential appliance placement
2. Sequential tooth movement
3.Sequential Mandibular Anchorage
Preparation
4. Directional Force
5. Treatment Timing.
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1.Sequential Appliance Placement
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In a 1st premolar extraction patient, second
molars and 2nd premolars are banded.
Initially 1st molars are left unbanded. Incisors and
canines are bonded, any malaligned anteriors are
not ligated to the archwire.
Less traumatic to patient, easier for orthodontist.
After the engaged teeth respond to forces of
archwire and auxiliaries, the maxillary and then
mandibular 1st molars are banded.


2.Sequential tooth movement
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Tooth movement is sequential.
It is rapid and precise because they
are moved individually or in small
units.


3. Sequential mandibular
anchorage preparation.
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Unlike Tweed who prepared mandibular
anchorage using Class III elastics and
place all the compensation bends in the
archwire at one time.
Merrifield’s technique allows mandibular
anchorage to be prepared quickly and
easily, tipping only two teeth at a time,
using headgear rather than Class III
elastics for support.
Known as Merrifield “10-2” system.

4. Directional Force
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Defined as controlled forces that place the
teeth in the most harmonious relationship
with their environment.
The resultant vector of all forces should be
in an upward and forward direction to
enhance the possibility of favorable
skeletal change, especially in dentoalveolar protrusion, Class II correction.
To achieve this, vertical control is crucial.

5. Timing of treatment
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Should be initiated at a time when
treatment objectives can be most
readily accomplished.
This may mean interceptive
treatment in the mixed dentition,
selected extractions in mixed
dentition, or waiting for second
molar eruption before starting active
treatment.

Steps of treatment
1.
2.
3.
4.

Denture
Denture
Denture
Denture

preparation
correction
completion
recovery


1. Denture preparation
Objectives:
 Leveling
 Individual tooth movement and
rotation correction
 Retraction of maxillary and
mandibular canines.
 Preparation of terminal molars for
stress resistance.
(Takes approximately 6 months.)

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Teeth of the original malocclusion are
sequentially banded and bonded.
018 x 025 resilient mandibular archwire
and 017 x 022 resilient maxillary archwire
are inserted.
The stop loops are flush with the second
molar tubes in each arch.
Mandibular 2nd molars receive effective
tip of 15 degrees from the archwire and
maxillary 2nd molars receive 5 degrees
distal tip.
Offset placed mesial to 2nd premolar is in
each archwire, to prevent outward
expansion of canines

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High pull J hook headgear used to retract both
maxillary and mandibular canines.
After first month of treatment, maxillary first
molars are banded and after second month,
mandibular first molars.
After each month, terminal molar tip in
mandibular archwire is increased to maintain
effective tip of 15 degrees.
As canines retract and arches are leveled, lateral
incisors are ligated, and power chain force to aid
canine retraction can be used.
Note: During each visit, archwires are removed,
carefully coordinated, 1st, 2nd and 3rd order bends
checked, and religated.

At end of denture preparation stage
of treatment:
1.
Dentition should be fully banded
and leveled.
2.
Canines should be retracted.
3.
All rotations should be corrected
4.
Mandibular terminal molars tipped
distally into an anchorage prepared
position.

2. Denture correction
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Spaces are closed with maxillary and mandibular
closing loop archwires.
Mandibular archwire: 019 x 025 working archwire
with 6.5 mm vertical loops distal to the lateral
incisor brackets.
Maxillary archwire: 020 x 025 archwire with 7
mm vertical loops distal to lateral incisor
brackets.
Stop loops in both arches are immediately distal
to brackets of 1st molars.
Stop loop in mandibular archwire incorporates a
compensation to maintain the 15 degree terminal
molar tip.



At end of space closure the curve of
occlusion in maxillary arch should be
maintained and mandibular arch
completely level with a 15 degree
distal tip in the second molar.


The dentition is now ready for mandibular
anchorage preparation.

Sequential mandibular anchorage
preparation
 Archwire produces an active force on only two
teeth while remaining passive to the other teeth
in the arch, which act as anchoring units.
 Referred to as 10-2 anchorage system
 Anchorage preparation is supported by high pull
headgear worn on anterior vertical spurs,
soldered distal to mandibular central incisors.

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At end of mandibular space closure, the lower 2nd
molars are tipped to 15 degrees distal angulation.
First molar anchorage is initiated with an 019 x
025 archwire with loop stops bent flush against
second molars, and 10 degree distal tip placed
just mesial to loop stop.
Compensating bend is given to maintain second
molar tip.
After 1 month, the 1st molars should show 5 -8
degrees distal inclination of 1st molars.
Third and final step involves placement of 5
degree distal tip 1 mm mesial to 2nd premolar
brackets.
Compensating bend is given mesial to first molar,
so that arch wire is passive to 1st and 2nd molars

At end of anchorage preparation, a readout
will show distal axial inclinations as
follows:
 2nd molars: 15 degrees.
 1st molars: 5-8 degrees.
 Second premolars: 0-3 degrees.
This brings to an end, the denture correction
step for Class I malocclusion.

The Class II force system
1.For patients with end-on or full-cusp
Class II dental relationship of buccal
segments a new force system is
required to complete denture
correction.
 Final decision for Class II correction
is made on basis of ANB relationship,
maxillary posterior space analysis
and patient co-operation.

Guidelines for use:




The Class II force system achieves
best results when ANB is 5 degrees
or less, patient is co-operative, and
maxillary 3rd molars are missing.
If present and approaching eruption,
they should be removed to facilitate
distalization of maxillary teeth.


2.If a co-operative patient has a mild
Class II dental relationship, normal
vertical skeletal pattern, ANB of 5-8
degrees, and normally erupting
maxillary 3rd molars, extraction of 2nd
molars is most advantageous for
distalizing maxillary arch.


3.If ANB is greater than 10, maxillary 3rd
molars are present and patient cooperation is questionable, either first
molars should be removed after space
closure, or surgery should be considered.
 Note: The Class II force system needs
excellent compliance from patient, else
maxillary anterior teeth will be pushed
forward off basal bone.

Class II force system- the
procedure.






At end of Sequential mandibular
anchorage preparation, mandibular 0215 x
028 stabilizing archwire with ideal 1st, 2nd ,
3rd order bends is fabricated, with the stop
loop 0.5 mm short of molar tubes.
Gingival spurs soldered distal to
mandibular lateral incisors.
Wire seated and terminal molar cinched to
loop stop.










Maxillary archwire (020 x 025)with closed helical
bulbous loops bent flush against 2nd molar tubes is
fabricated.
Ideal 1st, 2nd order bends and 7 degrees of
progressive lingual crown torque in molar
segment.
Gingival spur immediately distal to 2nd premolar.
Gingival high pull headgear hooks soldered distal
to central incisors.
Class II lay on hooks with gingival extension for
anterior vertical elastics are soldered distal to
lateral incisors.









Closed helical bulbous loops are opened 1mm
each side and wire ligated in place.
Eight ounce Class II elastics from hooks on 2nd
mandibular molar tubes to Class II hooks on
maxillary wire.
Anterior vertical elastics, as well as maxillary
high pull headgear are worn.
The helical loops are activated 1mm monthly till
second molars have Class I molar relationship.






Then, first molar is
distalized using a
coil spring wound
and compressed
mesial to it, as well
as E chain from
second molar.
Class II elastics,
anterior vertical
elastics and high
pull headgear (14
hours per day) are
continued.
After 1st molars have been distalized into
overcorrected Class I relationship, second
premolars followed by canines are moved
distally







After overcorrection
of maxillary posterior
segment, an 020 x
025 maxillary
archwire with 7mm
closing loops distal to
lateral incisors is
fabricated.
Wire is activated 1
mm per visit
Light Class II elastics,
anterior vertical
elastics and high pull
headgear are used .

3.Denture completion








Ideal 1st 2nd 3rd order bends are
placed in finishing mandibular
and maxillary 0215 x 028
resilient archwires.
The mandibular archwire
duplicates the previous wire
used.
The maxillary archwire has
artistic bends and hooks for
highpull headgear, anterior
vertical elastics and Class II
elastics.
This stage can be regarded as
a mini treatment of the
malocclusion.


At the end of this stage the following
objectives should be achieved:
1.
2.
3.
4.

5.

6.

7.

Alignment of incisors.
Occlusion over treated to Class I relation.
Anterior teeth edge to edge.
Maxillary canines and 2nd premolars locked
tightly into Class I dental relation.
Mesiobuccal cusp of upper 1st molar occluding in
mesiobuccal groove of lower 1st molar.
Distal cusps of 1st molars as well as 2nd molars
out of occlusion.
All spaces from 2nd premolar forward closed
tightly.

4. Denture recovery.






Orthodontist should not strive for ideal
final result at the end of treatment.
This ideal result will occur after all
treatment mechanics are discontinued and
uninhibited functional and environmental
influences in the post treatment period
stabilize and finalize the position of the
total dentition.
This recovery phase occurs when all
appliances are removed and retainers are
placed.





Orthodontists not familiar with the
concept of overtreatment express
concern about the posterior
disclusion achieved at completion
of treatment.
Often referred to as Tweed
occlusion, but properly identified
as transitional occlusion.

Transitional occlusion




The concept of transitional occlusion
followed by a period of recovery is
based on the belief that an
individual’s own oral environment
will determine the ultimate position
of the dentition and overtreatment
allows greatest opportunity for
maximal stability and functional
efficiency.

Stable occlusion achieved


Conclusion:






Since Angle through Tweed and to date with
Levern Merrifield, the Edgewise appliance has
endured the test of time.
Although the Tweed Merrifield appliance is the
direct descendant of Angle’s original appliance in
1928, it is used with a totally different philosophy
of treatment.
The introduction of concepts of differential
diagnosis, directional force and sequential wire
manipulation have made it the most precise and
efficient instrument for the correction of major
malocclusions, that exists in the world today.


1.

2.

3.

References:
Gebeck TR, Merrifield LL. Orthodontic diagnosis
and treatment analysis: concepts and values,
Part I, Am J Orthod Dentofac Orthop 1995; 107:
434-443.
Gebeck TR, Merrifield LL. Orthodontic diagnosis
and treatment analysis: concepts and values,
Part II, Am J Orthod Dentofac Orthop 1995;
107: 541-7.
Gramling JF. The probability index. Am J Orthod
Dentofac Orthop 1995; 107: 165-71.


4.Horn A. Facial height index. Am J Orthod Dentofac Orthop
1992; 102: 180-183.
5.Merrifield LL, Klontz HA, Vaden JL. Differential diagnostic
analysis system. Am J Orthod Dentofac Orthop 1994;
106: 641-648.
6. Merrifield LL. The dimensions of the denture: Back to
basics. Am J Orthod Dentofac Orthop 1994; 106: 535-41.
7.Merrifield LL, Directional forces. Am J Orthod 1970; 57:
435-464.
8.Merrifield LL. The sequential directional force edgewise
technique. In Johnston L, editor: New vistas in
orthodontics, Philadelphia, 1985, Lea and Febiger.


9. Vaden JL, Dale JG, Klontz HA. The Tweed
Merrifield Edgewise appliance:
Philosophy, Diagnosis and Treatment. In
Graber , Vanarsdall, Vig, editors:
Orthodontics-Current principles and
techniques, 4th edn, St. Louis, 2005,
Mosby.Pgs: 675-715.


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