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Tweed Mechanics



Graduated from an Angle coursegiven by George Hahn in 1928

Tweed diagnosed & treated casesunder Angle‟s guidance

He held to Angle‟s firm convictionthat one must never extract -for 3 yrs.

High frequency of relapse – discouraging

Important observation-

1) facial balance & post

treatment success related toupright mandibular incisors

2) to get lower incisorsupright, one must prepareanchorage & extract teeth

Dr. Tweed



His technique can be summarized as an anchorage technique.

While most operators were concentrating on how best to moveteeth, 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 thecart.

Angle gave orthodontics the edgewise bracket, but Tweed gavethe 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 boneesp. 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 preorthodontic guidance program using & popularizing serialextraction of primary & permanent teeth



Over the years several modifications have taken place in theappliance, 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-Lcrown inclinations, axial root inclinations & incisor crown-root torque



Tweed’s philosophy

Based on the following :-

a) Practically all malocclusions are characterized by a forwardadjustment of teeth in relation to their basal bones --- thisis due to deficiency between the basal bone & toothmaterial

b) The establishment & maintenance of a stable anchorageshould be the initial concern of the operator & is afundamental factor in successful orthodontic treatment

c) Teeth like inanimate objects, best resist the force ofdisplacement when tipped to the angulation that offers themost advantageous mechanics against the pull ofdislodging forces, they are best stabilized when they overliethe basal bone



d)Teeth are most readily moved when their property & powerof mechanical resistance has been primarily reduced

e) All forces emanating from an orthodontic appliance must besynchronized if they are to be most effective in the massstabilization or the mass movement of teeth

f) Nature being an expert mechanic herself, offers biologiccompensations & adjustments when teeth are placed inposition 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 incisorteeth are in mild lingual axial inclination & overlying asubstantial bony foundation

“ placing the incisors on the ridge”



Every malocclusion exemplifies a denture that is stabilized bybalanced muscular forces & this muscular balance must bepreserved in treatment if stability in the end result is to beaccomplished

( Strang & Thompson )



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



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 incisorangle

Tweed’s Diagnostic facial triangle



Angle FMA IMPA FMIA

Visual 25 90 65

cephalometric 24.57 86.93 68.20Range 15 – 36 76 – 99 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 incisormandibular angle IMPA would have to be decreased by 1°



Cephalogram or Headplate Correction

Based on the requirements of diagnostic facial triangle

Consists of constructing the triangle on a tracing of the patientslateral ceph and measuring the 3 angles.

According to the FMA measured the required IMPA and FMIAare then constructed on the tracing, involving relocating the axialinclinations of the mandibbular incisors.

This new hypothetical position is considered and the change inarch length is calculated, which is the cephalogram correction

This is added to the arch length discrepancy measured on thecast to give us the total discrepancy.



Tweed summarized his philosophy on which his appliancetherapy is based:-

i) Normal occlusion is best maintained with the mandibularincisors in their normal axial inclination when related to theF-H plane approx. 65°(FMIA)

ii) The ultimate in balance & harmony of facial esthetics isachieved only when the mandibular incisors are positionedover the basal bone

iii) The normal relationship of the mandibular incisors totheir basal bone is the most reliable guide in diagnosis &treatment of cl. I ,cl. II & bimaxillary protrusion cases andalso 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 movementof mandibular denture when cl.II intermaxillary force isapplied

On histological basis Brodie (1937) believes that the strongestanchorage is provided by stable fixation of teeth – to allow aslittle movement as possible

Tweed – anchor teeth best resist the dislodging forces whentheir vertical axes are parallel to the direction which offersthe most advantageous mechanical resistance against the pullof dislodging forces



Strongest anchorage is provided by tipping back the crowns ofthe 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 intermaxillaryelastics causes

-elevation of terminal molars & depression of mandibularincisors

-canting of occlusal plane,

-increase in FMA,

-point B drops downward & backward,

-entire mandibular denture is tipped & displaced forward intoprotrusion



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 pointB 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 atgum 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



orthodontic arch is the form which moulds the dental arch with every bend reflected inthe position of the teeth

Angle “if an archwire is placed

in brackets with uniform slotdepths,it must take the formof the outline of the buccal &labial surfaces of the teeth”

Ideal arch form



Unique alignment of upper lateral incisor – thinner labio-lingually & short crown length

Contact points lie on an ellipsoid curve

There is a straight line from canine to mesio buccal cusp of firstmolar, 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 & ofthe muscle behavior of the patient rather than based upon widths of teeth themselves



Movements necessary to bring the teeth into the line ofocclusion 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 positionof the teeth if expansionary forces are used

Three orders of tooth movement



Second order bends

-represent a vertical change

-also called tip/angulation

-used to tip posterior teethmesially or distally-may be

tip back or tip forwardbends



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 pressureby the archwire

Lingual torquecombined withlabial spring action



Labial torquecombined with labial spring

Labial torquecombined with lingual spring



Incorporation of torque



Other tooth movements

Opening spacesClosing 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

D bl i l i l ili f



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 treatmentobjectives



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 .026in. with mild second orderbends

Uprighting of canines - horizontal loops soldered mesial to



Uprighting of canines horizontal loops soldered mesial to

second premolars and a staple attached to anterior end ofloop

-ligature tied from here to distal staple on canineCanine bracket is not engaged in the wire



Anchorage preparation

1) placing mandibular incisors upright

2) changing axial inclinations of the maxillary incisors, to makethem less resistant to distal movement

3) changing the axial inclinations of buccal teeth to a more distalaxial inclination



.021 X .027 stabilization wire with mild second orderbends in upper arch

.019 X .026 in working wire inlower arch with tip backbends & sliding jigs to bearpressure on 2nd premolar

bracket

cl. III elastics are worn

Once anchorage preparation inlower arch done – reverse the

mechanics

cl. II elastics are worn

Distal enmasse movement of maxillary



Canine retraction

U/L .019 X .026 archwires with second order bends & opencoil springs compressed mesial to canines are inserted

Cl. III elastics aid in distal movement of mandibular canineHeadgear applied to upper arch aids in upper canine retraction

Distal enmasse movement of maxillary

buccal segments



Incisor retraction

Using .019 X .026 archwire with closed Bull loop distal tocanine – activated 1mm every 3 wks.

Mandibular incisors are retracted to an FMIA of 65° in cl.Icases & 70° in cl.II cases



Maxillary incisor retraction completed with heavier .021 X .027in. wire, reduced posterior to lateral incisors & passed free

of canineStrong 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 entireposterior segment

Correction of cl II relationship



Correction of cl. II relationshipNow, mand. arch - .021 X .027 in.

max.arch -.019 X .026 in. with accentuated tip

back bendsMand. arch tied back to receive cl. II elastics while maxillary

archwire is not tied backIntermaxillary hooks soldered mesial to maxillary caninesClass II elastics worn till normal cusp relation is achieved



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

Completion procedure



Vertical elastics are used forseating cusps if bite is open

In case of a deepening of bite abiteplate is used along withbox elastics to increase the

vertical opening to thedesired level.

Biteplate is retained for 3-4months to allow for osseous

develpoment.



cl. II div.1 – non-extraction treatment

Preparation of anchorage in the lower arch

Preparation of anchorage in the upper arch

Distal enmasse movement of maxillary arch

Detailed positioning of teeth

A h P i



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 bendscl. 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 backbends

Intermediate pull headgear mesial to canine is used to augmentthe anchorage - min. 14 hrs./day

Distal pull by headgear – twice as much as mesial pull on thearch by cl. III elastics

During day – light cl. III

During night – heavy cl. III

Distal tip back bends increased slightly every 2-3 wks.

b h



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 reducedby 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



Upper arch wire -.021 X .027 in. reduced distal to lateralincisors

Mild lingual crown torque if incisors are proclinedIntermaxillary 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 normalrelation of teeth attained

Mild palatal root torque in anteriorsContinue till incisors in edge – edge relation & posteriors in

good occlusion

y

arch



Proper seating of cusps is obtained by fitting correlated U & Lideal arches carrying vertical spurs for vertical elasticsbetween them

Detailed positioning of teeth

Bimaxillary dentoalveolar protrusion



Two types of cases:-

1)Axial inclinations of all the teeth in the arch inclinedabnormally forward (both in cl.I & cl. II cases ), dentalarches are more or less well aligned

2) Axial inclinations of teeth in buccal segments fairly upright,

irregular & crowdedSteps in treatment :- 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

Bimaxillary dentoalveolar protrusion



Objective:-

1)To correct abnormal buccolingual inclination of all posteriorteeth in both arches

2)Constrict the mandibular arch which is too broad3)Expand the maxillary arch which is too narrow

4)Move maxillary arch forward enmasse, using

mandibular arch as stationary anchorage

Treatment of cl.III malocclusion

S i



Steps in treatment -

Initial .016 in. round wires After 2 wks. ,.021X .027 in. U/L ideal archesBrass wire hooks mesial to canineMandibular archwire is bent considerably narrower than the

ideal & torque is placed in the buccal segment

Step forward 2nd

order bends placed in maxillary posteriorsegment (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 mandibulararch.

edgewise mechanism

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