Edgewise technique 2 /certified fixed orthodontic courses by Indian dental academy

Tweed Mechanics

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INDIAN DENTAL ACADEMY
Leader in continuing dental education


Graduated from an Angle course
given by George Hahn in 1928
Tweed diagnosed & treated cases
under Angle’s guidance
He held to Angle’s firm conviction
that one must never extract for 3 yrs.
High frequency of relapse –
discouraging
Important observation1) facial balance & post
treatment success related to
upright mandibular incisors
2) to get lower incisors
upright, one must prepare
anchorage & extract teeth

Dr. Tweed

His technique can be summarized as an anchorage technique.
While most operators were concentrating on how best to move
teeth, he focused himself on how not to move teeth.
To a great extent “cart has been placed before the horse”,
Dr.Tweed placed the horse where it belongs, in front of the
cart.
Angle gave orthodontics the edgewise bracket, but Tweed gave
the specialty the appliance


Among his other contributions:a) Emphasized the four objectives of orthodontic treatment
with emphasis & concern for facial esthetics
b) Developed the concept of uprighting teeth over basal bone
esp. lower incisors
c) Made the extraction of teeth for treatment acceptable
d) Enhanced the clinical application of cephalometrics


e) Developed the diagnostic facial triangle to make cephalometrics a
diagnostic tool & a guide in treatment & evaluation of results
f) He developed the concepts of orderly treatment procedures &
introduced anchorage preparation as a major step in treatment
g) He developed a fundamentally sound & consistent pre
orthodontic guidance program using & popularizing serial
extraction of primary & permanent teeth


Over the years several modifications have taken place in the
appliance, however the concepts remain the same.
Basic concepts which are cornerstones of modern edgewise orthodontics:1)Ability to obtain tooth movement in all 3 planes of space with
a single archwire
2)The philosophy of treating to an ideal arch or to Angle’s
concept of ‘Line of Occlusion’
The line with which, in form and position according to type,the teeth must
be in harmony if in normal occlusion
3)The use of rectangular or square edgewise arches which if
properly employed can control arch width, arch form, B-L
crown inclinations, axial root inclinations & incisor crownroot torque


Tweed’s philosophy
Based on the following :a)

Practically all malocclusions are characterized by a forward
adjustment of teeth in relation to their basal bones --- this
is due to deficiency between the basal bone & tooth
material

b)

The establishment & maintenance of a stable anchorage
should be the initial concern of the operator & is a
fundamental factor in successful orthodontic treatment

c)

Teeth like inanimate objects, best resist the force of
displacement when tipped to the angulation that offers the
most advantageous mechanics against the pull of
dislodging forces, they are best stabilized when they overlie
the basal bone

d)Teeth are most readily moved when their property & power
of mechanical resistance has been primarily reduced
e) All forces emanating from an orthodontic appliance must be
synchronized if they are to be most effective in the mass
stabilization or the mass movement of teeth
f) Nature being an expert mechanic herself, offers biologic
compensations & adjustments when teeth are placed in
position of mechanical advantage for force resistance
g) The dental units will best resist forward displacement when
the buccal teeth are in mild distal axial position & the incisor
teeth are in mild lingual axial inclination & overlying a
substantial bony foundation
“placing the incisors on the ridge”

Every malocclusion exemplifies a denture that is stabilized by
balanced muscular forces & this muscular balance must be
preserved in treatment if stability in the end result is to be
accomplished
( Strang & Thompson )


Facial types
Tweed divided the facial types into following types:TYPE A :-Maxilla & mandible show forward &
downward growth
-ANB angle remains the same -Prognosis is good
-Treatment not indicated during mixed
dentition if ANB angle does not exceed 4.5
TYPE A Subdivision:-ANB angle greater than 4.5


TYBE B :- Maxilla & mandible grow downward & forward with
maxilla growing more rapidly than mandible
- When ANB angle is 4.5 or less prognosis is favorable
- Extraoral appliances should be used immediately after
extraction
TYBE B Subdivision :-ANB is large & found to be increasing
-Undesirable growth trend, treatment long & difficult


TYPE C :- -Maxilla & mandible grow downward &
forward with mandible growing more than
maxilla
-ANB decreasing
-Growth is favourable & treatment is
facilitated by growth
TYPE C Subdivision :-mandible grows more than maxilla but only to a
little extent


Tweed’s Diagnostic facial triangle
Basis for diagnosis & treatment planning
Consists of the following :1) FMA –the Frankfort mandibular plane angle
2) IMPA –the incisor mandibular plane angle
3) FMIA – the Frankfort mandibular incisor
angle

Angle FMA
Visual
25
cephalometric 24.57
Range
15 – 36

IMPA
90
86.93
76 – 99

FMIA
65
68.20
56 – 80

For successful treatment triangle should be attainable
Aim should be to obtain:FMIA of 70° – 75° ( when FMA = 20 )
FMIA of 65°
( when FMA = 30)
When FMA is less than 20° FMIA should be more than 70°
& IMPA should not exceed 94°
He showed that in well balanced faces – IMPA was 90°±5°
For every degree that FMA was in excess of 25° .the incisor
mandibular angle IMPA would have to be decreased by 1°

Cephalogram or Headplate Correction
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Based on the requirements of diagnostic facial triangle
Consists of constructing the triangle on a tracing of the patients
lateral ceph and measuring the 3 angles.
According to the FMA measured the required IMPA and FMIA
are then constructed on the tracing, involving relocating the axial
inclinations of the mandibbular incisors.
This new hypothetical position is considered and the change in
arch length is calculated, which is the cephalogram correction
This is added to the arch length discrepancy measured on the
cast to give us the total discrepancy.


Tweed summarized his philosophy on which his appliance
therapy is based:i) Normal occlusion is best maintained with the mandibular
incisors in their normal axial inclination when related to the
F-H plane approx. 65°(FMIA)
ii) The ultimate in balance & harmony of facial esthetics is
achieved only when the mandibular incisors are positioned
over the basal bone
iii) The normal relationship of the mandibular incisors to
their basal bone is the most reliable guide in diagnosis &
treatment of cl. I ,cl. II & bimaxillary protrusion cases and
also in attainment of balance & harmony of facial profile &
permanence of tooth position

Treatment objectives :-

Facial balance & harmony
Stability of the post treatment dentition
Healthy oral tissues
Efficient mastication


Anchorage preparation
Stable anchorage – important to prevent forward movement
of mandibular denture when cl.II intermaxillary force is
applied
On histological basis Brodie (1937) believes that the strongest
anchorage is provided by stable fixation of teeth – to allow as
little movement as possible
Tweed – anchor teeth best resist the dislodging forces when
their vertical axes are parallel to the direction which offers
the most advantageous mechanical resistance against the pull
of dislodging forces

Strongest anchorage is provided by tipping back the crowns of
the teeth so that they will have a disto-axial inclination that
will resist a forward pull therefore, first & most important
step in treatment - Anchorage preparation
If anchorage preparation is not done the action of intermaxillary
elastics causes
-elevation of terminal molars & depression of mandibular
incisors
-canting of occlusal plane,
-increase in FMA,
-point B drops downward & backward,
-entire mandibular denture is tipped & displaced forward into
protrusion

Classification of anchorage preparation
First degree -minimal anchorage preparation,
-applicable to all malocclusion with ANB =0
to 4 ,
-total discrepancy does not exceed 10 mm,
-terminal molars must be uprighted & or
maintained in an upright position to
prevent their being elongated when cl. II
intermaxillary force is used .


Second degree -for malocclusions with ANB more than
0° to 4°
-facial esthetics requires to move point
B anteriorly & point A posteriorly i,e
cl. II cases
-usually accompanied by type A, type A
subdiv.,type B & type B subdiv.
-degree of distal tipping of mandibular
molars more severe than first degree
anch.prep. –they should be tipped so
that their distal marginal ridges are at
gum level


Third degree -severe discrepancy cases –14-20mm or
more
-ANB does not exceed 5°
-generally cl.I bimaxillary cases
-sliding jigs are necessary
-2nd ,1st molars & 2nd premolar must be
tipped to such an extent that the distal
marginal ridges are below the gum level
also called total anchorage preparation


Ideal arch form
orthodontic arch is the form
which moulds the dental arch
with every bend reflected in
the position of the teeth
Angle “if an archwire is placed
in brackets with uniform slot
depths,it must take the form
of the outline of the buccal &
labial surfaces of the teeth”


Unique alignment of upper lateral incisor –thinner labiolingually & short crown length
Contact points lie on an ellipsoid curve
There is a straight line from canine to mesio buccal cusp of first
molar, but beyond that it curves inward progressively

Bonwill-Hawley diagram is widely used to decide arch form
General pattern – decided by studying the original models & of
the muscle behavior of the patient rather than based upon
widths of teeth themselves


Three orders of tooth movement
Movements necessary to bring the teeth into the line of
occlusion are of three kinds –first, second and third order
First order bends-horizontal change relative to the line of occlusion
-also called in -out bends
-do not alter the horizontal plane of the wire
-the action & reaction of these bends affect expansion or
contraction
-used to move individual teeth
-the interaction of bends can affect the third order position
of the teeth if expansionary forces are used

Second order bends
-represent a vertical change
-also called tip/angulation
-used to tip posterior teeth
mesially or distallymay be
tip back or tip forward
bends


Third order bends
-torsional change (with the line of occlusion serving as axis)
-also called torque or inclination movement
-used to obtain axial changes in the bucco-lingual or
labio-lingual root & crown axis on one or more teeth
-involves twisting of the wire


Labial and Lingual torque in Wires


Lingual torque

Labial torque


Lingual torque
with lingual spring pressure
by the archwire

Lingual torque
combined with
labial spring action


Labial torque
combined with labial spring

Labial torque
combined with lingual spring


Incorporation of torque


Other tooth movements
Opening spaces
Closing spaces


Effect on teeth mesial and distal to loop


Activation with ligature traction
Distalization of molar + space opening for 2nd premolar


Opening spaces in anterior region


Vertical spring loop used to tip a molar distally
and upright


Vertical spring loop used for root paralleling


Double vertical spring loop auxiliary for mass
movement of incisors


General plan of treatment
Treatment divided into 3 phases:a)Anchorage preparation
b)Distal enmasse movement of maxillary buccal segments
c)Establishing correct denture form & completing treatment
objectives


Cl. II Div I - Extraction treatment
Leveling of arches
-.018 in. wire with molar stops/tie
back spurs at the molar tube
-distal tip back bends in posteriors
- cl. III elastics & headgear
- Working arches U/L .019 X .026
in. with mild second order
bends


Uprighting of canines - horizontal loops soldered mesial to
second premolars and a staple attached to anterior end of
loop
-ligature tied from here to distal staple on canine
Canine bracket is not engaged in the wire


Anchorage preparation
1) placing mandibular incisors upright
2) changing axial inclinations of the maxillary incisors, to make
them less resistant to distal movement
3) changing the axial inclinations of buccal teeth to a more distal
axial inclination


.021 X .027 stabilization wire
with mild second order
bends in upper arch
.019 X .026 in working wire in
lower arch with tip back
bends & sliding jigs to bear
pressure on 2nd premolar
bracket
cl. III elastics are worn
Once anchorage preparation in
lower arch done – reverse the
mechanics
cl. II elastics are worn


Distal enmasse movement of maxillary
buccal segments
Canine retraction
U/L .019 X .026 archwires with second order bends & open
coil springs compressed mesial to canines are inserted
Cl. III elastics aid in distal movement of mandibular canine
Headgear applied to upper arch aids in upper canine retraction


Incisor retraction
Using .019 X .026 archwire with closed Bull loop distal to
canine – activated 1mm every 3 wks.
Mandibular incisors are retracted to an FMIA of 65° in cl.I
cases & 70° in cl.II cases


Maxillary incisor retraction completed with heavier .021 X .027
in. wire, reduced posterior to lateral incisors & passed free
of canine
Strong lingual root torque in upper wire for bodily retraction


to facilitate retraction, stops are soldered 3mm mesial to 2nd
premolar brackets
Coil springs compressed against the stops and tied to the entire
posterior segment


Correction of cl. II relationship
Now, mand. arch - .021 X .027 in.
max.arch -.019 X .026 in. with accentuated tip
back bends
Mand. arch tied back to receive cl. II elastics while maxillary
archwire is not tied back
Intermaxillary hooks soldered mesial to maxillary canines
Class II elastics worn till normal cusp relation is achieved


Completion procedure
Final space closure & detailed tooth positioning -.019 X .026 in.
max. & mand. ideal arches, coil springs compressed mesial
to 2nd molar tubes until space closure is completed


Vertical elastics are used for
seating cusps if bite is open
In case of a deepening of bite a
biteplate is used along with
box elastics to increase the
vertical opening to the
desired level.
Biteplate is retained for 3-4
months to allow for osseous
develpoment.


cl. II div.1 –non-extraction treatment
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Preparation of anchorage in the lower arch
Preparation of anchorage in the upper arch
Distal enmasse movement of maxillary arch
Detailed positioning of teeth


Anchorage Preparation
Anchorage preparation in mandibular arch
Initial leveling & alignment - .016 or .018 round wires
Working arch wire .019 X .026 in. with coordinated tip back bends
cl. III intermaxillary hooks soldered mesial to canine
Loop stops are made mesial to molar tubes but the archwire not
tied to molar anchor teeth


Upper arch is stabilized -.021 X .027 in.wire with mild tip back
bends
Intermediate pull headgear mesial to canine is used to augment
the anchorage - min. 14 hrs./day
Distal pull by headgear – twice as much as mesial pull on the
arch by cl. III elastics
During day – light cl. III
During night – heavy cl. III
Distal tip back bends increased slightly every 2-3 wks.


Stabilization arch -.021 X .027 in. wire with same degree of
tip back bends as in working archwire
Passive in mandibular incisor region
Total time required – aprrox. 4 mons.

Anchorage preparation in upper arch
Excessive inclination of the proclined upper incisors is reduced
by using .018 in. round wire
Important – this provides unfavorable stationary anchorage &
resist distal / lingual movement of the teeth
Heavy stabilization wire with mild second order bends is placed


Enmasse distal movement of maxillary
arch
Upper arch wire -.021 X .027 in. reduced distal to lateral
incisors
Mild lingual crown torque if incisors are proclined
Intermaxillary hooks on archwire – patient put on cl. II elastics
Watch out for mandibular anchorage – any signs of mobility,
increase the tip back bends
After 3 wks. – tip back bends in the maxillary arch are
increased, stronger elastic force is applied until normal
relation of teeth attained
Mild palatal root torque in anteriors
Continue till incisors in edge – edge relation & posteriors in
good occlusion

Detailed positioning of teeth
Proper seating of cusps is obtained by fitting correlated U & L
ideal arches carrying vertical spurs for vertical elastics
between them


Bimaxillary dentoalveolar protrusion
Two types of cases:1)Axial inclinations of all the teeth in the arch inclined
abnormally forward (both in cl.I & cl. II cases ), dental
arches are more or less well aligned
2) Axial inclinations of teeth in buccal segments fairly upright,
irregular & crowded

Steps in treatment :
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Anchorage preparation in lower arch
Anchorage preparation in upper arch
Extraction of four premolars
Multiple loops .016 in. archwire U/L used for alignment
Space closure done using looped archwire

Treatment of cl.III malocclusion
Objective:1)To correct abnormal buccolingual inclination of all posterior
teeth in both arches
2)Constrict the mandibular arch which is too broad
3)Expand the maxillary arch which is too narrow
4)Move maxillary arch forward enmasse, using
mandibular arch as stationary anchorage


Steps in treatment Initial .016 in. round wires
After 2 wks. ,.021X .027 in. U/L ideal arches
Brass wire hooks mesial to canine
Mandibular archwire is bent considerably narrower than the
ideal & torque is placed in the buccal segment
Step forward 2nd order bends placed in maxillary posterior
segment (direct opp. of tip back bends)
Intermaxillary elastics from lingual of maxillary molar to hook
mesial to mandibular canine
When cross bite is corrected –archwires are reshaped to the
ideal
Treatment continued until the maxillary teeth have moved
forward enmasse into occlusion with teeth in mandibular
arch.

Leader in continuing dental education


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