Tweed merrifield philosophy

Contents:
 Introduction
 Historical perspective
 Tweed’s philosophy
 Levern Merrifield
 Tweed-Merrifield philosophy
 Tweed-Merrifield Edgewise Appliance
 Steps of treatment
 Conclusion
 References
www.indiandentalacademy.com

Introduction
The Tweed – Merrifield edgewise appliance is the
direct descendent of the appliance invented in 1928
by Edward H. Angle, but it is used with a totally
different philosophy of treatment.

Historical perspective

Dr. Edward H. Angle
•Simplicity
•Stability
•Efficiency
•Delicacy
•Inconspicuousness

The Edgewise Appliance
 To overcome the deficiencies of his previous
appliances, Angle changed the form of the bracket
 Placed the slot in the centre and placing it in a
horizontal plane

Edgewise appliance

 Edgewise bracket when formed consisted of a
rectangular box with 3 walls within the bracket.
 0.022 x0.028”

 Unique feature  rectangular wire in rectangular
slot  twisting / torquing forces could be imparted to
control the axial inclination of teeth
 Possible to move teeth in all 3 planes of space with a
single arch wire.

Dr. Charles H. tweed

Charles H. Tweed
 Graduated from an improved Angle course (George Hahn) in
1928 at the age of 33yrs.
 Helped Dr. Angle in publishing an article in the Dental
Cosmos
 Dr. Angle urged his dear student to : Dedicate his life to the
development of the edgewise appliance
To make every effort to establish orthodontics as an
specialty within the dental profession.
 Dr. Tweed instigated the passing of first orthodontic
specialty law in the U.S.. In 1929 first law limiting the
practice of orthodontics to specialists was passed
 Dr. Tweed-first certified specialist in orthodontics in the U.S.

•Aug 11, 1930, Angle died at age of 75yr.
•Tweed held to Angle’s conviction, but this lasted for only
4yrs.In 1932 published article in Angle orthodontist
“reports of cases treated with Edgewise Arch mechanism.”
•Upright mandibular incisors frequently were related to
post treatment facial balance and successful treatment.
•To position mandibular incisors upright ,he concluded one
must prepare anchorage and extract teeth.

• He selected failed cases and treated them with
premolar extractions.
• 1936- paper on extraction of teeth for orthodontic
malocclusion correction.
• Was called a traitor ,faced criticism.
• In 1940 he produced case reports of the retreated
cases.

 “just put your plaster on the table”- let the
treatment speak for itself.
 Dr. Robert Strang- supporter
 1947- Charles H. Tweed Foundation for Orthodontic
Research

Tweed’s contributions:
•Emphasized four objectives of orthodontic treatment.
1.the best balance and harmony of facial lines
2.Stability of dentures after treatment
3.Healthy mouth tissues
4.An efficient chewing mechanism
•Concept of uprighting teeth over basal bone.
•Extraction of teeth acceptable.
•Enhanced clinical application of cephalometrics.

Diagnostic facial triangle
•Diagnostic facial triangle.
•Anchorage system as a major step in treatment.
• Serial extraction

1.Type A growth trends :
• middle and lower face
growing forward and
downward in unision with no
change in the ANB angle.
• growth is approximately
equal in both vertical and
horizontal dimensions.
• Type A subdiv growth
trend.
• Prognosis good

Type B growth trend :
• middle face growing
forward more rapidly than
the lower, ANB increases in
size with growth.
• ANB <4 deg prognosis is
fair.
• ANB 7-12 deg prognosis
poor.

Type C growth trend:
• lower face growing forward and downward more rapidly
than the middle face, with a decrease in the size of the
ANB.

2)That the establishment and maintenance of stable
anchorage is the fundamental factor in successful
orthodontic treatment and should be the initial
concern of the operator.
 Outstanding feature of Dr.Tweed’s philosophy

Anchorage preparation
•It was believed at that time that-“An undisturbed tooth
affords the best resistance to movement.”
•Tweed-It is impossible to band a tooth that’s in tight
contact with a neighbor and have it undisturbed.
•Reatin –when teeth are tipped distally as during Anchor
preparation, osteoid tissue is laid down adjacent to
mesial surface of the tooth being moved distally.

 In the use of intermaxillary force, it was Dr.Tweed’s
contention that the teeth in the anchorage denture
must be placed in distal axial inclination if they are to
be expected to resist forward and occlusal strain of
elastics.

Anchorage preparation
1. First degree anchorage preparation:
 Minimal anchorage preparation required.
applicable in : malocclusions with ANB 0-4deg ,facial
esthetics are good, total discrepancy does not exceed
10mm.
 Mandibular anchor molars uprighted /maintained
in their upright positions to prevent being elongated
by Class II elastics.
 The direction of pull of the elastics in function, will
not exceed 90 deg when related to the long axis of the
terminal molars.

2. Second degree anchorage preparation:
 necessary for malocclusions in which ANB > 4.5 deg
 facial esthetics demand that point B moved
anteriorly and point A posteriorly.
 Class II cases, accompanied by type A, type A
subdivision, type B growth trends.
 Distal marginal ridge of terminal molar at gum
level.

3.Third degree anchorage preparation :
• total anchorage preparation necessary in severe
malocclusions where total discrepancy 14- 20mm ,ANB
doesn’t exceed 5 deg.
• Class I cases with exceedingly irregular teeth.
• all three posterior teeth tipped distally

Levern Merrifield

LEVERN MERRIFIELD
1953 : took TWEED course
1960 : selected by
Dr.Tweed to be codirector
and continue his work on
edgewise appliance.
1970 : Director  study of
orthodontic dentistry &
development of
edgewise appliance
Dr. Levern Merrified

A.Diagnostic concepts:
Introduced diagnostic analyses which allow clinicians
to determine whether and when extractions are
necessary, if indicated which teeth to be extracted.
1. Fundamental concept of dimensions of the dentition
2. Dimensions of the lower face
3. Total space analysis
4. Guidelines for space management decisions
a. facilitate maximal orthodontic correction
b. Define areas of skeletal, facial, and dental
disharmony

B. Treatment concepts:
1. Sequential appliance placement
2. Sequential tooth movement
3. Sequential mandibular anchorage preparation
4. Directional force
5. Proper timing of treatment

Dimensions of the dentition
 Premise 1: anterior limit exists
 Premise 2: posterior limit exists
 Premise 3: lateral limit exists
 Premise 4: vertical limit exists

Anterior limit
 Mandibular incisors positioned over basal bone.
 Tweed’s diagnostic facial triangle

Posterior limit
 Muscular pressure: buccinator, masseter, temporalis,
medial pterygoid- limit for posterior expansion
 “to create a posterior discrepancy in an attempt to
correct an anterior discrepancy is not sound
reasoning”
- Dimensions of the denture
L. Levern Merrifield. AJODO 1994;106:535-42

Lateral limit
 “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.”
 “ with very minor exception, the original mandibular
malocclusion width must also be respected in the
premolar and molar areas”
- Robert Strang

Vertical limit
 Muscles of mastication limit this dimension.
 Functional balance allows a normal freeway space
and efficient functioning of the temporomandibular
joint

Facial disharmony
3 factors affect facial balance:
 Position of teeth: protruded teeth
 Skeletal pattern
 Soft tissue thickness : total chin thickness and upper lip
thickness must be equal

Upper lip thickness and total chin thickness
If the total chin
thickness is lesser than
upper lip thickness, the
anterior teeth must be
positioned upright
further to facilitate a
more balanced facial
profile because lip retraction
follows tooth retraction

Some measurements to judge facial balance
1. Profile line
2. Facial balance on frontal view- vermilion border of the
lower lip should bisect the distance between the
bottom of the chin and the ala of the nose.
3. Z angle
4. FMIA

Profile line in a balanced face
When facial balance is
present, the ideal
relationship of profile line is
to be tangent to the chin
and the vermillion border of
both the lips and should lie
in the anterior 1/3rd of the
nose.

Profile line drawn on a protrusive face

FMIA : Tweed believed this angle was significant in
establishing balance and harmony of the lower
face. Related to FMA.
• FMA 22-28 deg, FMIA 68deg
• FMA 30 deg or more ; FMIA 65deg.
• dental compensation for a high FMA requires
additional uprighting of flared mandibular
incisors..visa versa.
Z – angle : indicative of soft tissue profile and more
responsive to maxillary incisor retraction than
FMIA

Z angle and FMIA
Z- angle :
70-80 deg range
75 -78 deg ideal
Maxillary incisor
retraction of 4mm
allows 4mm of lower lip
retraction and 3mm of
upper lip response

Cranial disharmony
Skeletal analysis factors
• FMA
• IMPA
• SNA
• SNB
• ANB

• Ao-Bo
• Occlusal plane angle- 8-
12 deg
• PFH
• AFH- 65mm
• facial height index -
0.65-0.75
• facial height change
ratio
Merrifield and Gebeck
reported a 2:1 increase
in PFH compared to
AFH in successfully
treated class II patients.

Craniofacial analysis
• Jim Gramling’s probability index:
observed that in successfully treated Class II patients
FMA was controlled , FMIA increased, IMPA reduced ,
Z-angle increased , SNB remained same, AO-BO
reduced.
• Probability index suggests that the following pre
treatment conditions might be necessary for Class II
treatment success :
FMA should be 22-28 deg .
ANB should be 6 deg or less .
FMIA should be greater than 60 deg .
Occlusal plane should be 7 deg or less .
SNB should be 80 deg or more .

Dental disharmony
3. Total space analysis: 3 parts:
a. Anterior space analysis:
 anterior tooth arch surplus/deficit : difference
between space available in mandibular arch from canine
to canine and sum of mesiodistal dimension of six
anterior teeth.
 anterior discrepency: surplus/deficit + cephalometric
discrepancy (the amount of space required to upright
the mandibular incisors for optimum facial balance)

Mid arch discrepancy :
mid arch tooth discrepancy = diff b/t available midarch
space and mesio distal width of 1st
premolar, 2nd premolar,1st molar, space required to level
curve of spee.
+
occlusal disharmony : measure distance b/t maxillary
premolar buccal cusp to embrasure b/t mandibular 1st
and 2nd premolar.

c. Posterior space analysis:
Posterior tooth arch discrepancy:
space available = distal of mandibular first
molar to anterior border of ramus along occlusal
plane.
required space = sum of mesio-distal width of 2nd
molar and 3rd molars.
Most easily recognizable sign of posterior space
deficit is late 2nd molar eruption.

Differential Diagnostic Analysis System
 Craniofacial analysis + total dentition analysis
 Craniofacial difficulty + total dentition space analysis
difficulty is called total difficulty
 Mild : 0-60
 Moderate : 60-120
 Severe: >120

Merrifield’s treatment philosophy
1. Sequential appliance placement
2. Sequential tooth movement
3. Sequential mandibular anchorage preparation
4. Directional force
5. Proper timing of treatment

Sequential appliance placement
Advantages:
• Less traumatic
• Easier
• Less time consuming
• Allows greater
efficiency in arch wire
action (longer inter
bracket span in
posterior
segment)

Sequential tooth movement
Advantage : Rapid and precise tooth
movement because they are moved
individually/in small unitswww.indiandentalacademy.com

Sequential mandibular anchorage preparation:
 developed by MERRIFIELD- “10 – 2” system.
 Tweed : En masse anchor preparation ; all
compensation bends placed at one time in the
archwire and Class III elastics used for support ----
result :
Labially flared and intruded
mandibular incisors

Merrifield technique –
 `10 – 2’ Force systems(10 ten teeth used as
 Anchor units to tip 2 teeth)
 High pull head gear for support rather than Class-III
elastics
 Tooth movement is controlled, sequential and
precise.

Directional force :
 Hallmark of modern Tweed-Merrifield
edgewise treatment.
 Controlled forces which place teeth in the most
harmonious relationship with their environment

Resultant force vector
of all forces should be
upward and forward
(counterclockwise),
giving opportunity for
favourable skeletal
change, especially in
dentoalveolar
protrusion Class II
malocclusion correction
Upward and forward force
system

Mandibular incisors
upright over basal
bone needed so that
the maxillary incisors
can be moved distally
and superiorly

If point B is allowed
to move down,
mandibular incisors
are tipped off the
basal bone and
maxillary incisor
drops down and back
instead of being
moved up and back.
This leads to a patient
with lengthened face,
a gummy smile,
incompetent lips and
a more recessive
chin.
Downward and backward
force system

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

Tweed- Merrifield Edgewise
appliance

Brackets and Tubes

Arch wires
 0.017 x0.022”
 0.018 x0.025”
 0.019 x0.025”
 0.020 x 0.025”
 0.0215 x0.028”
 Different wire dimensions allow greater versatility
and allow sequential application of forces at different
stages.

First-, second-; and third- order bends
 First-order bends:
 Expansion or contraction

 Second-order bends

Third-order bends
Mandibular arch
 Objective is to place some degree of lingual crown
torque on all mandibular teeth.
 Ideal 3rd order bends in mandibular segment:
 Incisor : -7deg
 Canines : -12 deg
 2nd premolars and molars : -20 deg

Maxillary arch
 Anterior segment needs no torque (0 deg) or slight
lingual root torque.
 Posterior segment needs lingual crown torque:
 Canines and 1st premolar : -7 deg
 Second premolars : -12 deg

Auxiliaries used:
 Elastics
 Directionally oriented headgear:
high pull J-hook headgear
straight pull J- hook headgear

STEPS OF TREATMENT
with Tweed – Merrifield Technique

STEPS OF TREATMENT
CLASSIC TWEED MERRIFIELD
EDGEWISE DIRECTIONAL FORCE
TREATMENT can be organized into four force systems :
1) Denture preparation
2) Denture correction
3) Denture completion
4) Denture recovery

1.DENTURE PREPARATION
(approx 6 months)
OBJECTIVES:
a) Leveling
b) Individual tooth movement and rotation correction
c) Retraction of both maxillary and mandibular
canines
d) Preparation of terminal molars for stress resistance

Denture preparation
 Initial archwires
0.017 x 0.022
maxillary arch wire
 0.018 x0.025
mandibular arch wire
 J-hook head gear for
canine retraction.

 Maxillary molars
Banded after 1st month
of treatment
 Arches getting leveled
off
 Power chain force to aid
Canine retraction.

End of Denture preparation
 Terminal molar
anchorage:
 The mandibular terminal
molar should be tipped
to anchorage prepared
position at the end of
denture preparation.

 Full dentition bracketed and leveled
 Canines retracted , all rotations corrected

2.Denture Correction –
OBJECTIVES:
1. Complete space closure in both the arches
2. Class I intercuspation of canines and premolars
3. Sequential anchorage preparation

 Mandibular wire:
0.019 x0.025 with 6.5mm
vertical loop distal to
lateral incisor bracket.
 Maxillary archwire:
0.020 x0.025 with 7mm
vertical loop.
 Loop stops immediately
distal to brackets of first
molars
 Loop stop in mandiblar
arch wire incorporates a
compensation to
maintain 15deg terminal
molar tip

 Closing loop application:
maxillary and
mandibular closing loops
are used to close spaces
mesial to the distalized
canines
 Vertical support in
maxillary arch through J
hook Headgear (hook b/t
central and lateral)
 Vertical support for
mandibular anterior
teeth through anterior
vertical elasticswww.indiandentalacademy.com

After space closure is
complete, mandibular
arch is leveled, curve
of occlusion in
maxillary arch
maintained and the
terminal molars
remain tipped to an
anchorage prepared
position.

Sequential Mandibular Anchorage Preparation
 Sequential tooth movement concept -
Arch wire exerts active force on only 2 teeth, while
remaining passive to other teeth in the arch.
Remaining teeth act as stabilizing anchor units as 2
teeth are tipped. “10-2” anchorage system

1. Tipping the 2nd
molar to a 15° distal
inclination
Readout

2. 1st molar anchorage
preparation
• 10° distal tip
• Compensating bend
mesial to loop stop
• 10-2-6

 3. 5° distal tip 1mm
mesial to 2nd premolar
brackets

Class II Force Systems
 A different system of forces may be used in patients
with end-on or full cusp Class II dental relationship.
 A final diagnostic decision made and treatment
planned based on – the ANB relationship, maxillary
posterior space analysis and patient co-
operation…using the following guidelines:

1. If the maxillary 3rd molar is missing or if ANB<= 5deg
and patient is cooperative… best prognosis. If 3rd molar
erupting, it is best to remove it to facilitate distal
movement of maxillary teeth.
2. If patient is cooperative, has a mild Class II dental
relation, normal vertical skeletal pattern, ANB 5-8deg
and normally erupting 3rd molars…then advantageous
to extract 2nd molars.
3. If ANB >10deg, poor patient cooperation, 3rd molars
present…after maxillary and mandibular first premolar
extraction space closure, either first molar extraction or
surgical correction considered.( poor prognosis)www.indiandentalacademy.com

Orthodontic Correction of Class II dental
relationships
• Mandibular anchorage preparation with 0.0215x0.028”
stabilizing archwire
• Maxillary arch wire with 0.020x 0.025” arch wire

Maxillary second molar distalization: helical bulbous loop
placed against maxillary second molar

Helical bulbous loop pushes the maxillary molar distally

Coil spring trapped mesial to the first molar

Maxillary first molar distalization

Maxillary second premolar and maxillary canine distalization

Maxillary anterior space closure. 0.020x0.025” maxillary loop
arch wire is used to close the maxillary anterior space

3. Denture Completion
Maxillary and mandibular stabilizing wires, along with
proper elastics and head gear force, are used to complete
orthodontic treatment.

At end of denture completion following characteristics
should be readily observed:
• Incisors must be aligned.
• Occlusion overcorrected
• Anterior teeth edge-edge relation
• Maxillary canines and 2nd premolars locked tightly into
Class I relation.
• Mesiobuccal cusp of maxillary 1st molar must occlude in
mesiobuzccal groove of mandibular first molar.
• Distal cusp of first molar and second molars must be
slightly out of occlusion.
• All spaces must be closed tightly from 2nd premolars
forward.

4. Denture recovery
 Forces involved are those of surrounding
environment, primarily muscles and periodontium.
 Concept of overcorrection:
if mechanical corrective procedures barely
achieve normal relationships of teeth, relapse is
inevitable.

 Transitional occlusion: disclusion of second molars

Final occlusion is characterized by the teeth settling into
their most efficient, healthy and stable positions-
functional occlusion

Conclusion

 It is designed to achieve individualized tooth
movements and precision to each patient, to achieve
functional occlusion and optimal esthetics, to shorten
treatment duration through use of sophisticated
force systems.
 The edgewise appliance has stood the test of time
and will be used by many more generations of
orthodontics.

References:
 Orthodontics-Current principles and techniques-
Graber and Vansardall; 3rd and 4th edition
 The tweed philosophy: the Tweed years: James J.
Cross; Seminars in Orthodontics;1996:2;231-267
 The Tweed-Merrifield Philosophy: James L. Vaden;
Seminars in Orthodontics;1996:2;237-240
 Differential Diagnosis- L. Levern Merrifield; Seminars
in Orthodontics;1996:2;241-253
 Tweed-Merrifield Sequential Directional Force
Treatment;1996:2;254-268

 Merrifield L.L. The dimensions of the denture: Back to
basics. AJODO 1994;106:535-542
 Clinical Orthodontics- Charles H. Tweed, Vol. 1

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Tweed merrifield philosophy

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