This document by Dr. Mohammed Alruby discusses various methods of transmitting orthodontic forces through removable, fixed, and functional appliances. It details the mechanics of springs, arch wires, and elastics, including their design, application, and adjustments, emphasizing the importance of force characteristics and patient comfort. Types of springs and their uses in orthodontics are outlined, along with guidance on force application for effective tooth movement.

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Dr. Mohammed Alruby
Methods of transmitting orthodontic force
Prepared by
Dr. Mohammed Alruby

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Dr. Mohammed Alruby
Methods of transmitting orthodontic forces
Differ according to the type of appliance: as removable, fixed, or functional appliances
I- Removable appliances:
A- Springs:
The springs incorporated into removable appliances, usually has one end fixed to the appliance
and other free end is used to apply force upon the teeth.
The force exerted by spring is:
- Directly proportional to the deflection as doubling activation double the force applied,
convexly as the tooth moves there is decrease in force applied but this within the elastic
limit of the wire
- Directly proportional to the diameter of wire as, the activation of about 3mm in 0.6 give
double force than the activation of 3mm in 0.5
- Inversely proportional to the length of spring. For a given activation doubling the length
will decrease the force to 1/8 of its original value
For designing the spring, attention should be given to the following:
a- Wire dimension:
= The flexibility of the spring depends on the diameter and length of the wire
= Doubling the diameter for a given deflection increase the force 16 times
= When doubling the length decrease the force to 1/8
= The length of the wire should be increase as possible if you wish to obtain light force because
you cannot decrease the diameter below 0.5mm because the spring will be weak and will be
distorted
= The effective length of the spring can be increase by incorporating coils but the coil should be
at least 3mm in diameter
= Protected palatal springs usually made of 0.5mm but unprotected labial bow and springs should
be made of 0.7mm wire
b- The force applied:
For single rooted teeth, it should between 25 and 40gm, the low value for lateral incisors and the
high value for canines
c- Deflection:
In most cases activation of 3mm is satisfactory.
With larger activation: the patient is liable to insert the spring incorrectly
With smaller activation: the force will drop off rapidly as the tooth moves and reactivation becomes
necessary at shorter interval.
The expected rate of tooth movement with deflection of 3mm at monthly interval is 1:2mm / month
0.7 spring should not activate more than 1mm every month if heavy force to be avoided
Types of springs:
1- Palatal springs:
a- Single cantilever spring: finger spring
This spring may be used to move the teeth labially or in the line of the arch mesiodistally, it usually
constructed of 0.5 hard stst wire.
Some operators use 0.6 and activate it only by 1.5mm / month. A coil with diameter less than 3mm
is incorporated close to the emergence of the baseplate
Increase the length of spring increase flexibility
The spring may be guarded by a room of acrylic to prevent its distortion but this depend upon the
reference of operator

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Dr. Mohammed Alruby
** adjustment of the spring:
The palatal spring should be checked by mirror to ensure correct tooth contact close to the gingival
margin
The spring may be activated 1 to 2mm at the initial insertion but should increase to 3mm in
subsequent visits.
The spring should be not bent at the point where it emerges from the baseplate because working
at this point may cause fracture of spring.
The correct site of activation is the free arm as close as possible from the coil
b- Double cantilever spring: Z and T spring
= Double cantilever spring is used when the space for finger is limited so that double spring is
made incorporating coils or bends to increase the effective length of wire
= T spring may be used when premolars, sometime canines are to be moved bucally, since insertion
of appliance with single finger spring may be very difficult by the patient
c- Coffin spring:
Made of heavy wire 1.25mm and used for palatal expansion, it is preferable than screw when
differential expansion of molars or premolars is required but it is less stable and require much
adjustment than screw, so that the expansion screw is used unless differential expansion is required
2- Buccal spring:
The buccal spring may be used to moves canines lingually as well as distally. Buccal springs are
often not popular because it is uncomfortable by the patient and is difficult to be adjusted
In addition, they unstable in vertical direction and tend to slide over the slop of canine
It is usually constructed of 0.7mm wire so that it is less flexible and can exert heavy force
Adjustment:
The spring should be activated only by 1mm; it should construct to contact the tooth correctly.
Distal activation is carried by opening the coil slightly and palatal activation is carried be bending
the free limb as it emerges from the coil palatally.
B- Screws:
Introduced by Hayanes and Jakson 1962, there is a great varieties of screws are available which
provides a large intermittent force which decrease as tooth moves
Screws is opened by patient 0.2mm at weekly interval (this about quarter turn 1mm / month)
Screws can be used for many tooth movements but most commonly used in expansion, they also
may be used for distalization of molars.
Screws are available as one pin screw or two pin screw according to direction of expansion
Advantages:
1- More stable
2- Easy adjust by the patient
3- May be used for many types of tooth movement
4- Allows rapid palatal expansion can be also used in splitting the palatal suture
5- Can be used as retainer after active treatment
Disadvantages:
1- More bulky
2- Expensive
3- Cannot provide differential palatal expansion
4- May turn back under load
5- If left outside the patient mouth for considerable periods, the patient cannot reinsert it with
subsequent delay

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Dr. Mohammed Alruby
II- Fixed appliances
The force of fixed appliance is delivered from one or more of the following;
Elastics, Arch wires, coil spring, auxiliary spring, arch wire loops as: vertical, horizontal, helical,
open, closed, torqueing,
1- Elastics:
= Introduced by Clavin and Angle to apply forces upon the teeth, this force depends on:
- Type and size of elastics
- The site of application: inter-max or intra-max
- The distribution of force
- Root length, direction, and diameter
- Character of alveolar bone
- Age, health, and cooperation of patient
- The distance to which is stretched
- Duration of application
= Elastics are available in several forms for orthodontic use, most orthodontic rubber elastics are
made of latex, also it may be made of natural rubber
= Rubber bands, elastics loops or rings available in different sizes 2/16, 4/16, 5/16, 6/16, each of
these sizes are available in 3 forms, light pull, heavy, extra heavy, or light, medium, heavy pull
= It was found that gm pulls elastic band 7mm in diameter when stretched 20mm, 30mm, 40mm
produce force of 168, 243, 350 gm respectively.
= Note that the force delivered by elastic band decrease about 20% in the mouth as a result of
absorption of water from saliva
= The remaining force after one day is about 50% of its original forces so we can use safety an
elastic band exerting double force than that required because after one day using, it will exert just
the required force, the remains constant for about one week, so that replacement of elastic band is
recommended after week
= The force dispensed by elastic bands depend on the cross section and diameter of the lumen,
elastics should not wear a full time, some investigator recommended the daily replacement of
elastics.
N: B: when stretching the intra-maxillary elastics, the gm pulls while stretching the inter-maxillary
elastics decrease the gm pull due to the force is analyzed into two components, vertical and
horizontal component, as Class I, II, III elastics
= Another forms of elastics products are:
- Elastics threads; used for closing space and correction of rotation
- Elastic chain: used for closing spaces along the arch wire
- Elastic separator: used for separation of the teeth
- Elastic bracket ligation: used for ligating the arch wire into the bracket (small elastic
ring)
Uses of elastics;
1- intra-maxillary force application as canine retraction
2- inter-maxillary force application as Class II, III
3- vertical force for correction of open bite
4- cross elastics for correction of cross bite
5- used in combination of extra-oral forces

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Dr. Mohammed Alruby
2- arch wires:
active arch wire is designed in such a way that when the teeth are ligated to them, they are
distorted from their passive form and thus exerting force upon the teeth as they move to their
original form.
The force exerted by the arch wire upon the teeth depend on:
a- diameter: the force is directly proportional to diameter of wire thus, light wire producing
light force and heavy wires ------ heavy force when diameter is doubled the force increase
16 times
b- length: inter-bracket distance: the force decrease as inter-bracket distance increase
c- load deflection: the distance to which the wire is deformed within the elastic limit
d- bracket arch wire relationship: is very important consideration particularly if full
engagement of arch wire within the bracket is to be maintained
active arch wire must be sufficiently flexible to produce significant movement without
applying an excessive force or because permanently deformed
treatment should be started by round light wire, 0.012, 0.014, 0.016 because they are more
flexible and provide light force and high load deflection.
Influence of arch diameter:
= the force exerted by wire is directly proportional to cross section (diameter of wire), so that wire
exerting light forces than heavy wires
= when diameter of wire is doubled the force will increase 16 times for a given deflection, thus the
diameter of wire has a major influence upon its elastic proportion.
= The smaller the diameter, the greater the flexibility because the wire can be deflected, relatively
larger distances within its elastic limit without permanent deformation and without applying an
excessive force upon the teeth
= The plane arches of smaller diameter as that used in twin arch technique may be used for initial
alignment when there is considerable crowding
= The larger diameter wire used when rigidity is required to prevent anchorage loss amd in
finishing the case
= Multistrand wire (ortho-flex) are manufactured by braiding 3 fine high tensile stst wires
together, it was more flexible than single strand wire of the same over all diameter
Advantage of Multistrand wires:
1- higher flexibility which enable it to be fully engaged the bracket at the initial stage of
treatment
2- exert lighter force
3- permanent deformation under desirable forces is minimized.
Disadvantages:
Lack of rigidity --- loss of anchorage and inability to reduce over bite
Influence of wire length between adjacent bracket
Inter-bracket distance
As the length of inter-bracket span increase the wire become more flexible and the force become
more lighter
Flexibility of wire is directly proportional to effective length, and the force is inversely proportional
to the inter-bracket distance
The inter-bracket distance can be increase by:

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Dr. Mohammed Alruby
1- using of small single bracket: the using of twin and Begg bracket provides increase inter-
bracket distance and thus lighter force while edge-wise bracket is wide so inter-bracket
distance decrease, so the less flexibility and the heavier force
2- incorporating loops into the wire to increase the inter-bracket span
3- coil springs:
Maynard 1843 used coil spring for closing extraction space, Robison used it for retraction of
maxillary incisors, Thomas 1854 used it for correction of maxillary protrusion, the force exerted
by coil spring depends on:
1- diameter of wire; the force increase as diameter increase
2- diameter of lumen: the force decrease as the diameter of lumen increase
3- the size of the wire on which the spring around: as the size of the base arch increase the
friction will be greater and thus the spring force decrease
4- the spacing between the coil of spring in open coil spring, the force increase as the spaces
increase while in closed coil spring the force increase as the space decrease
5- the amount of activation
coil springs are made of stst or chrome-cobalt alloys, springs can be described by:
1- the diameter of wire must commonly used for manufacture of spring range between 0.006
to 0.009 inch
2- the diameter of lumen ranges between 0.020 to 0.036 inch
3- the spaces between the coils if wide ---- open coil, smaller coils ---- closed coil spring
the spring should be stretched to fit a wire of smaller diameter than that of its lumen to avoid
friction which may cause marked decrease in force.
Uses of coil springs:
a- pull coil, closed spring:
used for space closure, canine retraction, incisors retraction
stop coil and tie back bends is necessary to prevent mesial movement of molars or slippage of the
arch from buccal tubes
b- push (coil open spring:
used for space opening for malposed teeth or prosthetic restoration, as well as for canine retraction
by placing the spring between right and left canines or between canine and lateral incisors
it also used in distalization of molars in conjunction with inter-maxillary elastics and extra-oral
force
the spring should be activated nor more than one 1/3 (larger or smaller) of the space, coil spring
is also used in closing median diastema, it is vital component in twin-wire appliance
4- auxiliary springs:
the auxiliary springs can be used in conjunction with the base arch to produce tooth movements
auxiliary springs usually made of 0.014 inch round wire
auxiliary springs are the vital component of Begg technique it used to produce torque in the 3rd
stage of treatment
a- auxiliary spring to produce rotation:
establish two point of contact and thus produce rotation of the tooth around it long axis
b- uprighting springs:
used to achieve uprighting and paralleling of roots at the extraction space
c- the anterior root torque spring:
used to achieve anterior root torque after incisors retraction, it is locked with the basal arch and
their vertical loops exert a lingual force upon incisors near the center of resistance more gingivally

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Dr. Mohammed Alruby
while the crown of incisors are prevented from labial movement by tying back the base arch into
the molar tube
5- the arch wire loops:
incorporating loops into the arch help to increase the effective length of the wire (inter-bracket
span) which has the following advantages:
a- increase the flexibility of wire which ensure high load deflection and full engagement in the
bracket without applying excessive force and without becoming permanently deformed
b- Decrease the applied force, the force become lighter, so that the tooth movement is uniform
without damaged of periodontium
c- Decrease the anchorage demands on posterior segment hence the vertical loops utilize a
reciprocal anchorage in correction of crowding in anterior segment
d- Vertical loops can move the teeth buccolingually as well as mesiodistally by opening the
lops thus increase intercanine distance during alignment.
It is used also for correction of rotation
Disadvantage of loops:
1- May be uncomfortable by the patient
2- May cause injury to soft tissue
3- Less hygienic, the patient cannot clean them properly
4- Difficulties in fabrication of multilooped wire
Types of loops:
1- Vertical loops: for levelling:
Used for buccolingual, mesiodistal tooth movement as well as for correction of rotation
The length of loop varies according to the maxillary or mandibular arch and the presence of local
condition
In practice it is about 5 –6mm not more, it should not be imping on soft tissues
2- Horizontal loops:
Help to increase the inter-bracket distance and its main application in correction of vertical
malposition (super occlusion or Infraocclusion) and it is helpful in correction of rotation
3- Opening loops:
When activated by compressing their legs it will open the space
4- Closing loops:
When activated by pulling its legs it will close the spaces