The document discusses the treatment philosophy of Tweed-Merrifield Edgewise appliance which includes 5 concepts: 1) sequential appliance placement, 2) sequential tooth movement, 3) sequential mandibular anchorage preparation, 4) directional force including control of vertical dimension, and 5) proper timing of treatment. It provides details on each concept such as only moving a few teeth at a time and maintaining anchorage.

1. There are five concepts composing the treatment philosophy:
•Sequential appliance placement
•Sequential tooth movement
•Sequential mandibular anchorage preparation
•Directional force including the control of the vertical
dimension to enhance mandibular response
•Proper timing of treatment.
Based on Tweed’s diagnostic philosophy
Merrifield has developed the force systems.
Treatment with the Tweed-Merrifield Edgewise Appliance.
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2. Sequential appliance placement:
•In the first premolar extraction case the;
•1st
molars are left unbanded, the 2nd
molars and 2nd
premolars are banded.
•The central incisors, lateral incisors, canines are bonded.
In cases of malaligned are not bonded initially.
After these teeth respond to the forces the 1st
molars are
banded; maxillary first molars are banded after one
appointment, mandibular first molars banded after second
appointment.
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3. Advantages:
•Longer interbracket distance in the posterior segment of
archwire, this ensures rapid second molar movement
•Wires of larger dimensions that are less subject to occlusal
or bracket engagement distortion can be used.
•Allows much greater efficiency in action of archwire.
•Less traumatic to the patient.
•Easier and less time consuming for the Orthodontist.
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4. Sequential tooth movement:
•Unlike the method of en masse tooth movement used by
Tweed; tooth movement is sequential
•Teeth are moved rapidly and with precision because they
are moved individually.
Sequential mandibular anchorage preparation:
Tweed method;
•Used the en masse anchorage by giving all compensation bends
in the archwire at the same time.
•This force system caused the mandibular incisors to flare
labially and intrude.
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5. Steps:
•Second molars are tipped to its desired anchorage prepared
position. After space is closed a compensating bend is placed
mesial to maintain its tip
•First molars are tipped to an anchorage prepared
position.Similar compensation bend is placed mesially to
maintain its tip.
•Second premolar is tipped distally to its anchorage prepared
position
Merrifield:
•Utilized sequential mandibular anchorage preparation.
•Only two teeth were tipped at a time.
•Accomplished by using ten teeth as anchorage unit to tip two
teeth at a time. This is referred as “Merrifield 10-2 system”.
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6. Directional force including the control of the vertical dimension
to enhance mandibular response:
•During the course of
treatment it is crucial to
maintain control over
mandibular anterior and
posterior teeth and the
maxillary anteriors.
•The resultant vector of all
orthodontic forces should
be counterclockwise so that
the opportunity for a
favorable skeletal change is
enhanced
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7. Such a force system
requires that the
mandibular incisors be
upright over basal bone so
the maxillary incisors can
be moved distally and
superiorly.
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8. For the counterclockwise force
system to be a reality,vertical
control is critical. To control
the vertical dimension, one
must control the mandibular
plane, the occlusal plane, and
the palatal plane
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9. If Point B drops down and
back, the face becomes
lengthened, the mandibular
incisor is tipped forward off
basal bone, and the maxillary
incisor drops down and back
instead of being moved up
and back
Sequelae of downward and backward force system:
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10. Timing
Timing of treatment is an integral part of the treatment
philosophy.
Treatment should be initiated when predetermined objectives
can be most readily accomplished.
Interceptive treatment in the mixed dentition,
Selected extractions in the mixed dentition, or
Waiting for second molar eruption before initiating active
treatment.
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