Development of appliance Development of controlled root movement Pin and Tube appliance Ribbon arch appliance Edgewise appliance Baker anchorage Labio-lingual appliance Open tube attachment The universal appliance Johnston – Twin wire attachment appliance Extraction in conjunction with orthodontic therapy Light wire technique – Begg appliance Rickets bio- progressive technique Straight wire appliance – Andrews appliance Tweed philosophy

1. 1
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
Orthodontic appliance
and
Treatment philosophy
Prepared by:
Dr. Mohammed Alruby

2. 2
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
Development of appliance
Development of controlled root movement
Pin and Tube appliance
Ribbon arch appliance
Edgewise appliance
Baker anchorage
Labio-lingual appliance
Open tube attachment
The universal appliance
Johnston – Twin wire attachment appliance
Extraction in conjunction with orthodontic therapy
Light wire technique – Begg appliance
Rickets bio- progressive technique
Straight wire appliance – Andrews appliance
Tweed philosophy

3. 3
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
The development of appliance
The 1st
description of tooth movement, dated a few years BC, most of early appliance were
of the removable type
The early fixed appliance can be traced back to a French Man P. Fauchared who, made a buccal
metal arch to which the teeth were ligated by fibrous ligation. This appliance was described in
1726 and it enable alignment of the teeth by means of expansion of dental arches
= Schange invented a band in 1841 that were fitted to the teeth by means of clamps which were
adjustable to accommodate the different sized teeth, bands were made from precious metal, copper
and brass
= in 1871 Megill first used dental cement
== The extra-oral force was first described by Kisngsley in 1866, and inter-maxillary traction
(Baker anchorage) was used late in the nineteenth century. By that time, the need for greater
control over the tooth development led to the development of the attachment which were soldered
to the lingual aspect of the bands enabling the misplaced tooth to be ligated to the buccal arch
wire
==The early attachment was a single spur which act to prevent slippage of ligature wire from
upon the tooth and allows some rotational control
= brass ligature was used and progressively tightened as the tooth moves. At this stage of
development, there was no attempts to correct the malocclusion by placing the teeth in a stable
soft tissue environment
= Angle stated that: {if the teeth were moved into their correct occlusal relationship, stability
would be assured}.
Angle’s early appliance had a buccal tubes soldered to the molar bands and a buccal expansion
arch wire which was activated by screws to which the malposed teeth were tied, tooth movement
took place by tipping
Development of controlled root movement
Farrar, Kingsley, Angle, Case and others soon found most of the treated cases by tipping
movement underwent relapse. They soon realized that, for any effective tooth movement, some
means must be advised to control the individual teeth, this led to the development of attachment
that were soldered on modified crown or bands – the early attachment were in the form of spurs,
spurs were soon modified to form hooks and hooks become the early form of modern bracket
The Pin and Tubes appliance
Angle was well aware of the value of bodily movement of the teeth so, one of the most effective
early appliance was developed by Angle in 1912 is the Pin and tube appliance which was the 1st
appliance capable of root movement. This appliance consists of:
1- Bands to which vertical tubes were soldered, the tubes are parallel to the long axis of the
teeth
2- The arch wire to which vertical Pins were soldered to fit the vertical tubes on the bands of
individual teeth

4. 4
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
This appliance was very difficult to use, requiring a high degree of technical skills to fabricate the
arch wire, however in the hands of few men it was very successful appliance that showed greater
control over the tooth movement
The Ribbon arch appliance
= The Ribbon arch appliance was described by Angle in 1916. This appliance consists of modified
hooks or machined brackets soldered to the bands of individual teeth to which a flat rectangular
arch wire was fitted with its wide dimension toward the labial surface of the teeth (lies vertically)
= This is being the first use of rectangular arch wire which provide a greater control over the tooth
movement and produce an accurate repositioning of the roots
= The philosophy of treatment was changed a little with the development of more efficient
attachment but expansion was still the major therapeutic goal in most cases
The Edgewise mechanism
About 10 years later to 1926 Angle described the Edgewise mechanism to provide a better control
over the individual teeth
This attachment consists of:
1- Bands soldered and fitted to most of the teeth
2- Brackets: machined brackets with their longer dimension horizontally soldered to the bands
3- Rectangular arch wire made to fit the bracket with its narrow dimension toward the labial
surface of the teeth and its wide dimension lies horizontally, hence the term Edgewise was
applied
The arch wire was tied in place by ligature wire and eyelets were soldered on to the bands to aids
in correction of rotations
Treatment was still based on non-extraction philosophy or expansion
Baker Anchorage
Many authors noticed that a large percentage of patients had a relatively straight tooth, at the
same time the upper and lower teeth were not properly related to each other with the presence of
large over jet or reversed over jet (Class II and Class III)
In such cases the expansion of the arch would not produce a desired correction so Baker anchorage
was developed which utilized correction of class II and class III by using inter-maxillary rubber
bands
Labio-lingual appliance
= in the middle of 1920, the lingual appliance was developed by Mershon. This appliance consisted
of a relatively rigid mandibular and maxillary lingual arch attached to the molar bands, these
arches carried a spring that produce tooth movement by tipping, similar to the action of modern
removable appliance
= The mandibular arch was used also to produce a tooth movement in the maxillary arch by means
of inter-maxillary elastics using the principle of baker anchorage, but proclination of lower
incisors was frequently occurs (during use of class II elastics)
= As with philosophy of expansion, there was a little concern over the movement of lower incisors
into an abnormal position with this type of therapy. The primary consideration was to achieve
normal occlusion regardless the environmental and functional forces

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Orthodontic appliance and philosophy
Dr. Mohammed Alruby
= The subsequent experience had shown that Mershon lingual arch is better used as a space
maintainer or for part time inter-maxillary elastic traction
= Combination of labial and lingual arches were refined by Oliver, he introduced the fixed guide
plane to be used in conjunction with inter-maxillary elastics, the fixed guide plane is constructed
on the maxillary lingual arch and has the following functions:
1- Guide the mandible to close in proper position and eliminate functional retrusion
2- Activate the growth at condyles like activators
3- Reduce the excessive overbite in class II
4- Inhibit the abnormal tongue thrust habit
Open tube attachment
Also in the middle of 1920, the open tube attachment was developed by John Mcloy
This appliance consisted of round arch wire which fit within a horizontal tubes soldered on the
labial surface of the bands cemented on the teeth
The arch wire contains a soldered spur which produce root movement
This technique is also based on no-extraction philosophy of arch expansion regardless the
functional forces so that neither this technique nor Edgewise mechanism was capable of producing
satisfactory results to overcome relapse
The Universal Appliance
Universal appliance which is a combination of Edgewise and Ribbon arch attachment was
developed by Spancer Atkinson to provide a greater fine control over the individual teeth, the
appliance consists of:
1- The attachments: machined double slot brackets which have lower Edgewise slot and upper
Ribbon arch slot
2- The arch wire: round and rectangular arch wire may be used, three combinations are
possible:
a- Two round arch fit the lower slot and tied with ligature
b- Rectangular Edgewise arch fit the lower slot
c- Rectangular Edgewise arch fit the lower slot and Ribbon arch fit the upper slot
This technique is also based on – non-extraction philosophy.
Johnston – Twin wire attachment appliance
The force generated by the early Edgewise mechanism was very high so that, Twin wire appliance
was introduced by Josef Johnson in 1930 which designed to produce lighter forces
The original appliance was consisting of:
1- Two round light buccal arches used in combination to produce alignment and rotation
correction of upper incisors
2- The maxillary arch wires were filled into the upper four incisors bracket and molars tubes
3- Class II traction can be used on the lower lingual arch
An advantage of this appliance is the ability to correct the incisor displacement with minimum of
bands
The twin arches are constructed of two 0.25mm diameter hard stst wires inserted into ends tubes
of 0,90mm outside diameter. The ach is rigid in buccal segment and flexible in the labial segment
Special brackets were advised in the original technique but it can also use with Edgewise brackets

6. 6
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
If there is considerable rotation or teeth displacement, partial engagement of the arch is indicated
at the start of treatment. Also it is possible to engage wire to the twin arch into the brackets of
severely displaced tooth to reduce the force applied
In cases of over rotation, it may be necessary to use spurs or wings soldered to the bands or to use
a rotating spring, which forced under the wire and tied to the bracket with ligature wire.
The Twin arch wire can be also used for over jet correction using inter-maxillary elastics on the
lower lingual arch or intra-maxillary elastics hooked into hooks at the medial aspect of the end
tube
The twin arch usually suffers from permanent deformation rapidly and often replacement before
satisfactory alignment is achieved
Another disadvantage of Twin arch wire is the less control of anchorage in extraction cases, 4
incisors against two molars
Extraction in conjunction with orthodontic therapy
= as we mentioned before that, Angle’s philosophy of non-extraction or expansion therapy was not
capable to produce satisfactory results and followed by relapse in the majority of cases, So that,
an alternative philosophy utilizing the extraction of the teeth for correction of crowding and dental
arch mal-relationship was developed to overcome the problem of over expansion and its
undesirable sequelae
Tweed was the 1st
to use Edgewise technique in conjunction with extraction and his treatment
method forms the basis of many todays Edgewise techniques
Tweed said that, (when the cannot brought into normal alignment and proper occlusion without
procumbancy of incisors, then extraction is indicated to reduce the dental arch)
= of course this philosophy met a great antagonism from Angle’s followers in their defense, it must
be said that, (extraction have produced orthognathic malocclusion, deep bite, collapsed lower
anterior segment, pockets, spacing and tissue damaged when done by faulty decision.
Light wire technique
The use of light forces in fixed appliances techniques of which Johnson Twin wire appliance
is an early example has continued, in this way, the light wire appliance was developed by Begg in
1926. The Begg bracket are modifications of the early Angle’s Ribbon arch brackets
Begg technique is based on the idea of differential force control, since some types of tooth
movements evoke more tissue resistance than another and some movements occurs faster than
others, so Begg was selectively chosen the movements required and relating the reciprocal action
properly
The Begg system is an extraction based philosophy which utilized intra-oral anchorage and use of
an auxiliary spring for certain tooth movements
Differential light force:

7. 7
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
The new light wire differential forces philosophy has been introduced by many authors such as:
Holmes, Kissling, Begg, Steiner, and others to overcome:
= the limitation of Twin wire appliance
= the frictional component in classic Edgewise appliance
= the production of orthognathic malocclusion in labio-lingual appliances.
The new trend in the Edgewise technique is to use a lighter round arch wires in the initial tooth
movement keeping the thicker rectangular wires for the later stage of treatment to overcome the
lack of torque control in the light wire technique
Begg Technique
The Begg technique was developed by Dr P R Begg in 1926 and is widely used. Dr Begg was the
1st
who introduced the idea of differential force control, since some teeth evoke more tissue
resistance than others and some movements occurs faster than others, Begg selectively chosen the
movements required for each tooth and magnitude of force required to achieve this movement and
relating the reciprocal reactions properly
Disadvantages of this technique:
1- Low mechanical efficiency which make the control of mesio – distal axial inclination is more
difficult during the 3rd
phase of treatment
2- Root torqueing is difficult to obtain by this technique
3- Difficulty in coordination the maxillary and mandibular arch form, an elastomeric
positioner is usually employed to obtain the desired root movement
4- Difficulties in obtaining bilateral symmetry
5- Difficulties in stabilizing the teeth in the final artistic position
6- The vertical loops may cause injuries of labial and gingival tissues
7- Difficulties in cleaning the appliance and in maintaining good oral hygiene
Principles of Begg technique:
Begg technique is based on 3 fundamental concepts:
1- Employment of light, continuous physical forces (differential force concepts):
Vertical loops occasionally with helical are made in the light wire to permit the following:
a- Full engagement of the arch within the brackets without applying an excessive force
b- The wire become more resilience thus the force becomes lighter with longer duration
c- This allows a reciprocal anchorage in the anterior region and minimize the load over the
anchor unit, thus the stability of molars can be maintained during treatment and no needs
for extra-oral anchorage, this make suit extraction case.
d- Rapid controlled tooth movement without causing discomfort of the patient, loosening of
the teeth or damaged of periodontium
The use of small vertical brackets increases the inter-bracket distance which make the appliance
more resilient
2- The Begg technique utilize two tooth movements:
a- The first is allowing the teeth to tip freely, this can be achieved by insertion of light round
wire so that it is fit into the bracket loosely
b- The 2nd
movement is uprighting of the teeth by using auxiliary springs, thus the Begg
technique involve 1st
, tipping of crowns then followed by tipping of the root

8. 8
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
3- The third concept:
There is continuous mesial and vertical physiologic migration of the teeth throughout the life
Begg used this fact in movement of the teeth in favorable direction assisted by growth
Combination of Edgewise and light wire techniques
Other combination has been developed which combine certain aspect of the Edgewise and Begg
methods
Attempts have been made to unite the precision and greater torque control of Edgewise mechanism
with the light continuous forces and rapid tooth movement of Begg technique in a single technique
 Tweed introduced the use of light wires in the initial stage of edgewise treatment, while the
rectangular heavy arch is placed later in treatment and during finishing the case.
 The light wire appliance described by Jabark, the bracket used is basically of Edgewise
type, however large part of treatment is carried out by using light round wires incorporating
carefully designed vertical loops and horizontal helical
 In the combination technique described by Fogel and Mcgill, a Siamese Edgewise brackets
with vertical slots are used, in the initial stage of treatment, the light wire placed in the
vertical slot of the bracket which permit single point of contact and less friction like Begg
brackets, while in the later stage of treatment the rectangular wire is inserted into the
Edgewise slot for finishing the case
Fogell and Mcgill described 3 stages of treatment:
a- Gentle tipping of the teeth; using single round wire
b- Uprighting and general alignment of the teeth: using Multistrand round light wire
(orthoflex)
c- Detailed axial positioning of the teeth: using Edgewise rectangular arch wire
Rickets Bioprogressive technique
This technique described by Ricketts does not demand bonding of all teeth in the arch at the
beginning of treatment
Banding is carried out progressively throughout treatment and removable appliance may be used
in the early stage (as expansion screw and correction of cross bite)
The technique is a combination of light wire and Edgewise mechanisms
Arch wire flexibility is increased by incorporation of loops and helical performed arch wire can
be used for easily fabrications
Pretorqued brackets are used with this technique, this achieved torque without the needs for
bending the wire

9. 9
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
Straight wire appliance
Andrew’s technique
Most of orthodontic techniques can achieved a successful esthetic results in the majority of cases,
but would you capable to obtain the same successful results in two similar cases
Andrews provided us with the solution, through his straight wire appliance which was developed
to achieved the same beautiful results in all case. Time after time in a more predictable and efficient
manner
Andrews philosophy is based upon the possibility of transferring the 6 keys of ideal occlusion which
are normally present in the nature untreated case into treated cases
To achieve this objective, Andrews used a careful designed brackets with pre-angulated base which
are capable to producing torque in the three planes, so that, there is no needs to placing any
torqueing bends in the wire, hence the name straight wire technique
In this manner, the orthodontist goes ahead to treat only the malocclusion and not consuming his
time in treating his appliance
With the use of this appliance, the teeth can move automatically into ideal occlusion
Bracket design and six keys of occlusion:
1- Key 1: molar relationship:
- The distal surface of the distal marginal ridge of upper 6 contacts and occlude with the
mesial surface of mesial marginal ridge of lower 7
- The mesio-buccal cusp of upper 6 occlude within the buccal groove of lower 6
- The mesio-lingual cusp of upper 6 occludes within the central fossa of lower 6
The straight wire appliance has been carefully designed to move the molars into normal
relationship that will achieve a solid points of contact
2- Key 2: crown angulation: the mesio-distal tip:
In normally occluded teeth, the gingival portion of the long axis of each crown is distal to the
occlusal portion of that axis
The degree of mesio-distal tip varies according to each tooth
Each straight wire bracket has a predictable degree of mesio-distal tip which suit each individual
tooth, so that, each tooth will achieve the proper mesio-distal angle
3- Key 3: crown inclination: labio-lingual torque:
It is the angle between a line perpendicular to the occlusal plane and a line tangent to the middle
of the labial or buccal clinical crown
a- The anterior crown: in maxillary incisors, the occlusal portion of the crown is labial to the
gingival portion. In all other anterior crowns, the occlusal portion of the crown is lingual
to the gingival portion
b- Upper posterior crowns: the buccal the degree of lingual inclination is more pronounced
in the molars than cuspids and bicuspids

10. 10
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
c- Lower posterior crowns: the occlusal portion of crowns is buccal to the gingival portion.
The degree of inclination is progressively increase from cuspids to molars
The inter-incisal angle was found in Andrews non treated best norm 174 degree
Straight wire bracket has been designed with a specific torque which made at the bracket
base help each tooth to achieve proper bucco-lingual inclination relative to the arch. All
inclination is based on the crown long axis, not the tooth long axis
The torque made in the base of the bracket has a great advantage than the torque made in the
bracket slot which is:
The center of slot and center of the base lies on the same plane which is very important in bracket
positioning at the proper height, while when the torque is placed in bracket slot like pre-torqued
edgewise bracket used by Ricketts in bioprogressive technique, the center of slot not coincident
with the center of bracket which may be misleading during the bracket placement
4- Key 4: rotation:
The teeth should be free from undesirable rotation
Rotated molars and bicuspids will occupy space molars and bicuspids will occupy space more than
the normal while incisors if rotated will occupy a space less than normal
Straight wire appliance is carefully designed to rapidly correct the rotation
5- Key 5: tight contact:
In the absence of tooth size discrepancies, the contact point should be tight. With correct bracket
placement at the center of clinical crown’s long axis at the beginning of treatment, the straight
wire appliance can be achieved a tight contact without crowding
6- Key 6: the curve of spee:
It is an imaginary curve passing through condyles and measured from the most prominent cusp of
the lower 2nd
molar to the incisal tip of most prominent lower incisors
The flat curve is most respective to normal occlusion, the curve of spee should not deeper than
1.5mm
Advantages of straight wire mechanism:
1- Can adapt well to varieties of technique and mechanisms as the operator can use the
straight wire appliance without the need to learn a new procedure
2- Reliable results and reduced chair time
3- The bracket is carefully contoured to fit each tooth in a specific single point so that enable
the operator to place brackets more easily
4- The pre-torqued and pre-angulated bracket base eliminate the needs for placing torque
bends in wire which is time consuming and may complicate treatment if done improperly
5- The appliance is more esthetically pleasant
6- The teeth are automatically guided into ideal occlusion
7- Precise control in finishing the case and more stable results
8- Precise control of molar and premolar torque
9- Bilateral symmetry of bucco-lingual and mesio-distal inclination which is difficult to be
obtained by wire bending
10-The appliance is simple, easily cleaned and more hygienic
11-Less discomfort in practiced by the patient

11. 11
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
12-Place the teeth in functional excellent positions so that:
more stable results are obtained,
decreased occlusal wear
less periodontal problems
less TMJ pain dysfunction or problems
Disadvantages of straight wire mechanisms:
1- The wider bracket ------ the smaller inter-bracket distance, so that, the force is more heavy
2- Difficulties in obtaining rapid correction of crowding because the angular relation of the
bracket to the malposed teeth
3- Difficulties in obtaining rapid correction of overbite
4- Addition anchorage is necessary
5- Extra-oral force often required
Appliance selection
A company straight wire appliance
Developed by Lawrence Andrews to move the teeth into positions oriented to the six keys of
occlusion as he found in his untreated best sample
Straight wire bracket:
= Are precisely contoured in both horizontal and vertical direction and designed to seat at the
midpoint of vertical long axis of each crown in a specific single point, so that, the bracket can seat
themselves in the proper position making bracket placement simpler, faster and more easy
= Most other bracket bases are not contoured to fit a specific area on the crown, so that, the
bracket placement may be difficulties and create a source of error. And if you attempt to contour
the bracket by a plier the bracket will be distorted
= The bracket base is torqued so that, the center of the slot on the same plane with the center of
the base, this allows bracket placement at proper height
= the torque incorporated into the base is predicted for each tooth, so that, the 3rd
order bends are
not necessary thus the teeth will move automatically into ideal occlusion which balanced well with
muscle function, thus more efficient and stable results are obtained
= Other pre-torqued brackets have a slot which is not coordinated with the base, thus when the
bracket bases are lined-up horizontally, their slot will lie at different heights making the 2nd
order
bends are necessary which would complicate treatment, increase the variables and increase chair
time
= The in and out measurement of each tooth is incorporated to the bracket base so that, the 1st
order bends the wire are not necessary
= Mesio-distal crown angulation is incorporated into the bracket base in a predictable manner so
that, artistic and Gable bends are not necessary incorporated into the wire
= Straight wire appliance provides a varieties of bracket such as twins, single wing bracket
(comfort) and active (self-ligating bracket) so that can adapt to any technique

12. 12
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
Roth set up appliance:
Roth modified the Andrews appliance for the purpose of moving the teeth into over corrected
position prior to the removal of the appliance and thus when the appliance removed, the slight
relapse movement will allow the teeth to occupy the ideal occlusal position found in non-treated
best sample studied by Andrews
Roth philosophy is based on two assumptions:
1- With the appliance in place, it is being impossible to position the teeth into occlusion shown
in non-orthodontic normal because of the bracket interference
2- After the appliance removal: the teeth is most cases may shift slightly from their corrected
position
For these reasons Roth modified the Andrews appliance to permit the teeth to occupies a slightly
over corrected position in the 3 planes of space, so that, when the appliance is removed, the over
correction will compensate for the slight relapse movement and thus the teeth will moves to the
ideal occlusion shown in non-orthodontic norm
Size of bracket used with Roth set up:
0.018, and 0.022 slot can be used but 0.022 is preferable for the following:
1- any size of wire up to 0.022 can be used so it will allow wire size selection, while 0.018 slot is
very restrictive in wire size selection
2-permit the use of many techniques
3-heavy rectangular wire can be used for finishing the case
4-permit the use of stabilizing arch in orthognathic surgery
5-more torque control in the buccal segment
Types of bracket used with Roth set up:
= single wing bracket with anti-rotational arms as, Steiner wings or long anti-rotational arms are
used. The use of single wing bracket will increase inter-bracket distance which is more
advantageous in the term of force delivered to the teeth, but this point is not important in straight
wire technique since this technique utilize highly flexible nickel titanium wires
= Roth has incorporated into his appliance a number of hooks for various types of elastics
configuration, also he used a double and triple tubes for the use of auxiliary wires and extra-oral
face bow
= Roth set up has its own specific requirements for bracket placement which varies slightly from
the position advocated by Andrews
= the major difference between Roth and Andrews philosophies lies in the manner of tooth
movement (Andrews moves the teeth bodily – translation without any tipping movement but Roth
allows slight tipping of the teeth)
= according to Roth opinion:
1- No appliance being effective in translating the teeth
2- Some tipping movement is necessary during the treatment course for seek of efficiency and
rapidity. After that a rectangular wire can be used to gradually move the teeth to their
desired final position

13. 13
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
Tweed method
Tweed philosophy
This method is based on Tweed contention that the majority of malocclusion are
characterized by a deficiency between the size of the teeth and basal bone which manifest itself in
an abnormally forward relationship of the teeth to the bodies of respective jaws
Tweed observed that, for achievement of harmony in occlusal and facial pattern, the mandibular
incisors should be suited in a correct position over the basal bone of the mandible, therefore,
orthodontic treatment should be directed first to correct procumbancy of incisors, then followed
by elimination of other dental abnormalities
When this procumbancy cannot be corrected due to excessive tooth materials and basal arch
deficiency, then extraction is indicated
The stable anchorage:
It is of fundamental importance in prevention of forward mandibular teeth movement during the
use of inter-maxillary elastics and during retraction of mandibular incisors
According to Tweed, the preparation of anchorage is the 1st
and important step in treatment of
malocclusion
Tweed 1st
prepare the anchorage in the mandibular arch, then moves the mandibular teeth to
correct axial inclination, after treatment in the mandibular arch is completed, the mandibular arch
then can be used successfully as an anchorage for the movement of maxillary teeth
Anchorage preparation:
Tipping of the teeth distally in the mandibular buccal segment using class III inter-maxillary
elastics, at the same time extra-oral forces with headgear is used on the maxillary arch to anchor
that arch against class III elastics
The last mandibular molars should not tie to the arch wire to prevent their roots from moving
mesially while tipping their crown distally
Thus the axial inclination of mandibular teeth is prepared from canine to 2nd
molars to create toe-
hold, to overcome the tendency for mesial shifting when class II elastics are used.
Also 2nd
order bends can be incorporated into the wire (tip back)
Principle of Tweed philosophy:
1- Normal occlusion is best maintained when the axial of mandibular incisors to FHP (FMIA)
is approximately 65 degree
2- The occlusal balance and facial harmony is achieved when mandibular incisors are placed
in correct position over the basal bone

14. 14
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
3- The normal relationship of mandibular incisors to their basal bone is most reliable guide
in diagnosis and treatment planning of class I and class II bimaxillary protrusion
Objectives of treatment:
1- Facial balance and harmony
2- Stability of post treatment results
3- Healthy oral tissues
4- Efficient functions
Facial types:
Using the lateral cephalogram, Tweed classified the facial skeleton into the following types:
1- Type A:
The maxilla and mandible on serial examination shows a forward and downward growth, the ANB
angle remains unchanged
The prognosis is good and treatment during mixed dentition is not indicated of ANB does not
exceeds 4.5 degree
Subdivision:
The ANB is greater than 4.5 degree, the headgear is used on maxillary arch after extrcation of the
1st
premolars, greater amount of tooth movement is required
2- Type B:
The maxilla and mandible on serial examination grows forward and downward but maxilla
growing forward more rapidly than mandible
The growth is undesirable, since the B point will not advance in relation to A point during treatment
When ANB is 4.5 degree or less, the prognosis is good
Headgear should be wear immediately after removal of 1st
premolars to restrict or redirect
maxillary growth
Subdivision:
The ANB angle is larg and increase during observation period
Prognosis may be poor, treatment may be long and difficult
Extraction is required as a rule
3- Type C:
The maxilla and mandible grows downward and forward but the mandible grows forward more
than the maxilla, the ANB angle decreased
Treatment is not indicated until eruption of canines
Subdivision:
The mandible grows more than maxilla but slightly downward
Tweed diagnostic triangle:
Tweed introduced his triangle as a basis for diagnosis –treatment planning and prognosis
It consists of:
Frankfort horizontal plane
Mandibular plane
Lower incisors axis
And contain 3 angles:

15. 15
Orthodontic appliance and philosophy
Dr. Mohammed Alruby
1- Frankfort mandibular plan angle FMA ------- 25 degree
2- Mandibular incisor plane angle ------- 90 degree
3- Frankfort mandibular incisors angle FMIA --- 65 degree
=== retraction of incisors ----- increase FMA
=== protraction of incisors ---- decrease FMIA
The use of class II elastics will displace the mandibular incisors forward about 5 degree during
treatment
Tweed advised never to exceed an IMP angle than 92 degree regardless the FMA angle when
treating in mixed dentition
FMA formula:
According to Tweed, the FMA angle average is 16 degree with a mean value 25 degree
If FMA between 16 and 25, less extraction is required than when exceeds 30 degree
When FMA is 30 degree, the mandibular incisors must be tipped to 35 degree to maintain FMIA
65 degree
The ANB angle is reduced by the following methods:
1- Distal movement of A point
2- Mesial movement of B point
3- Combination
Tweed provides the following instruction:
1- The aim is to obtain FMIA of 70 to 75 when FMA is 20 degree
2- FMIA 65 when FMA is 30
3- When FMA below 20, the aim should not to exceed with IMP than 92 degree, the FMIA
should be upward of 70 degree
Tweed showed that, in well balanced face, the IMP angle should be 90-+5 degree
He conceived a theory that, - for every degree that FMA in excess than 25 degree, -- the IMP would
to be decreased by 1 degree to preserve FMIA at normal value, as:
When FMA is 26 -------- the IMP should be 89
When FMA is 27 --------- the IMP should be 88
When FMA is 28 --------- the IMP should be 87
In this manner the FMIA is maintained at 65 degree