Magnets in orthodontics /certified fixed orthodontic courses by Indian dental academy

MAGNETS IN ORTHODONTICS

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INDIAN DENTAL ACADEMY
Leader in continuing dental education


CONTENTS
 HISTROY
 TYPES OF MAGNETIC MATERIALS
 PROPERTIES OF MAGNETS
 MAGNETS IN DENTISTRY

Diastema closure
Magnetic edge wise brackets
Distalisation of molars
Intrusion of teeth
Extrusion of teeth
Functional magnetic system
Magnetic Twin Blocks

HISTROY
 Why magnet ,is named as such ?
 Magnet is a material which has the ability to attract iron and

and to lie in a North-South direction when freely suspended.

 The first historical use of lodestones was the development of

the compass around the 8th century AD by the Chinese. The first recorded use was documented by Zheng He of the Yunnan
province.

It is now commonly believed that the Earth's magnetic fieldis produced by fluid dynamos in the Earth's mantle.

Magnetic fields are produced when current moves around a
coiled wire. The idea is that fluid motions play the role of a
rotating current inside the Earth.


 In 1820 Hans Christian Oersted, demonstrated that when-

ever current flows there will be an associated magnetic field in
the surrounding space, or more generally that the movement of
any charged particle will produce a magnetic field.
Microscopic origin of magnetism:Every electron on account of its spin,is a small magnet .In most
materials the countless electrons have randomly oriented spins
leaving no magnetic effect on average.


 However, in a bar magnet many of the electron spins,

are aligned in the same direction so they act co-operatively creating a net magnetic field.
 Magnetic field:

It is defined as that which can exert a magnetic force and
can produce magnetic induction in the matter placed in
it.


Types of Magnetic materials
1.Weak magnetic materials
a)Diamagnetic materials
b)paramagnetic materials
2.Strong magnetic materials
-Ferromagnetic materials


 Diamagnetic materials:

When placed in an external magnetic field, a weak
resultant magnetic moment is induced in a direction
opposite to the external field.
eg:- bismuth, lead, copper, silicon, water, glass.


 Paramagnetic materials:

When they are placed in external magnetic field , a
weak resultant magnetic moment is induced in the
Same direction.If the external field is withdrawn the
material gets demagnetized, this behaviour is called
Paramanetism.
eg:- Aluminium, platinum, maganese, chromium,
calcium, oxygen, nitrogen.

Ferromagnetism:
When they are placed in an external magnetic field,
a magnetic moment is induced in same direction.
 If the external field is removed, the material

remains magnetised permanently to some extent
this nature of matter is known as Ferromagnetism.
eg:- iron, cobalt, nickel ,alloys like alnico(AL,Ni,Co).

MAGNETIC PROPERTIES
 1.High Force -to –Volume Ratio:

Rare earth magnets,which belongs to Lan- thanide
elements such as SmCo2, Sm2Co17 alloys are 20 times
stronger than previous strongest permanent magnet,
AlNiCo5.
A new magnetic alloy, neodymium-iron- boran(Nd2Fe14B)
is 3 times stronger than Sm -Co magnets.


Samarium –cobalt Magnet:-

This magnet was introduced by Becker in 1970 but the
Original compound SmCo5 was discovered in the mid
1960s by karl strnart.

 It is available in two forms, SmCo5 and Sm2Co17


Neodynium-iron-boran Magnet:This is the most recently(1985)developed alloy.
Types: Neo 1i) Most suitable since it is cheaper and
has sufficient corrosion resistance.
Neo 3i)It can withstand demagnetization but
poor resistance to corrosion.
Neo 5i)It is the newest sophisticated magnet.
It has superior energy production and resistance to demagnetization.

2.Maximal force at short distances:Conventional forces (eg.,coil,spring,elastics,screws)react
according to Hooke’s law, F Ed.
Magnetic force reacts according to coulombs law.


Coulombs Law:It states that the force of attraction or repulsion between
two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to
the square of the distance between them and acts along
the line joining the poles.
F
m1 m2
d

2

F = K m1 m2
d

2

3)Three- Dimentional Centripetal Orientation of
Attractive Magnetic Force:This implies that if two magnets are displaced from
each other in more than one plane, they attract to
a full overlap.


4)No Interruption of Magnetic Force Lines by
Intermittent Media:Another unique feature of magnetic forces is that
any media interposed between two magnets cannot
bar the passage of magnetic force lines.


5)No Friction in Attractive force configuration: Clinician should remember that guiding elements
introduce friction in the appliance.


6)No Energy Loss: New generation of rare earth magnets can maintain energy capacity for years without any loss.
 The high energy product(B×H) losts only as long

as the magnets are protected against corrosion and
temperature does not exceed curie temperature.


ADVANTAGES OF MAGNETIC FORCE
1)Constant force i.e., no force decay over time,

2)Better directional force,
3)Better force and working range control,
4)Rapid tooth movement thus less treatment duration,
5)Minimum appliance adjustment and
6) Less chair side time.

DISADVANTAGES OF MAGNETIC FORCE
1)Corrosion of the magnets,
2)Bulkiness of the magnets,

3)Thermal sensitivity of magnets and
4)Difficult to design appropriate size of magnets as they
are very hard and brittle.


MAGNETS IN DENTISTRY
 According to Behrman and Egan in (1953), initially
Magnets were used to aid in retention of dental proProstheses when used as jaw implants.
 The use of magnets for orthodontic tooth movement was first described by Blechman and smiley in

1978.


DIASTEMA CLOSURE
 Muller (1984) suggested midline diastema closure

with small SmCo magnets.
 He recommended magnet size of 5mm 3mm 1mm
 For better control of tooth movement, a mesial bevel is

given for both magnets.
 Magnets should be fixed to the labial surface of central

incisors by indirect bonding.

MAGNETIC EDGE WISE BRACKET
 Introduced by Kawata et al(1987)
Bracket design:
• SmCo magnet of 6mm 2mm 1mm and 3mm
2mm 1mm.
• Standard edge wise design with 0.018” 0.025”
slot.
• Chromium coating over the magnet.
• Soldering of magnet to bracket with nickel.
• Soldering a mesh onto the magnet.

DISTALIZATION OF MOLARS
 If the upper molars could be moved posteriorly,
this would correct a Class II molar relationship and
provide space into which the other maxillary teeth

could be retracted.
 Distal movement of upper molars is difficult when

second molars are present.

 Force to move the molars back can be derived from
nickel-titanium springs, magnets, or other spring
arrangements.


INTRUSION OF TEETH
Long Face (Skeletal Open Bite) Class II:
 In an older patient with excess facial height, both
prevention of further eruption and intrusion of
posterior teeth is needed.
 It is better to use more force. some clinicians have
advocated the use of magnets in upper and lower

splints oriented so that the magnets repel each
other as the splints come together.

EXTRUSION OF TEETH
 Impacted or Unerupted Teeth:-

Initiation of movement of an uneruted tooth,using
magnetic force.
 The technique involves bonding a small magnet to
an unerupted maxillary canine, and using magnetic attraction to a larger magnet contained with in

a palate-covering removable appliance.

 success depends entirely on the patient's cooperation

in wearing the removable appliance with the intraoral
magnet.


FUNCTIONAL MAGNETIC SYSTEM
 Vardimon et al(1989)suggest that the magnetic

Force offer a solution to counterbalance the issue
of incompetent neuromuscular adaptation.
Construction and classification
It consists of upper and lower removable plates that
each contain a magnetic unit. Both are arranged in
a attractive pole orientation.


UPPER MAGNETIC UNIT
 Comprises a stainless-steel magnetic housing with
a single prong attached to it.
 The magnetic housing incorporates two cylindric-

rare earth magnets(SmCo5).
 If expansion of maxillary arch is required, an expa-

sion screw is linked to the maxillary housing and
prong.

 An extension arm with a bend of 130 degrees connects the expansion screw with the magnetic unit.
 The prong is inclined at 70 degrees to magnetic

interface or occlusion plane.
 The prong also has a small bend of 45 degrees at its

occlusal end to enable a smooth initiation of
guidence.

LOWER MAGNETIC UNIT
 It consists of a magnetic housing that encompasses
two cylindric rare earth magnets.
 The lower magnetic housing has a posterior inclin-

ed wall that forms an oblique plane.
 Guidence of the mandible into the cpcp is provided

by slicing of the Mandibular oblique plane along
the maxillary prong on mouth closure.

ANCHORING UNITS
1)Adams,2)triangle and 3)elastic clasps.
If elastic clasp is being designed for canine tooth,
two hooks are soldered on the vertical extension of
the U-shaped loop of the labial bow.
A two unit elastic chain is then stretched between
the hooks.The anchor tooth is affixed with abonded
button or Begg bracket.

CLASSIFICATION
 Forms of upper magnetic units:

1)Magnetic units with no screws,
2)Magnetic units with expansion screws and
3)Magnetic units with expansion and protraction screws
 Lower magnetic units:

1)With expansion screws and
2)Without expansion screws.


 Almost all class II malocclusions can be treated clinic-

ally by one of the following four types of FMS:
Type I:- An upper magnetic unit with an expansion
screw combined with a lower magnetic unit
with no expansion screw.
Indications:-In class II cases with minute overjet and
hormonised arches or slightly narrwed
upper arch.

Type II:-Upper and Lower magnetic units with
expansion screws.

Indications: class II with moderate to severe
overjet and transversal deficiency
of both arches.


 TypeIII:-An upper magnetic unit with expansion screw

and protraction screw combined with a lower
magnetic unit no expansion screw.
 Indications:-class II with severe overjet in which one

step mandibular advancement will not be tolerated by
neuromuscular system.There is a tranversal deficiency
of both arches.


Type IV:-An upper magnetic unit with expansion and
protraction screws combined with a lower
magnetic unit with expansion screw.

Indications:-class II with extremely severe overjet and
transversal deficiency of both arches .A progressive
mandibular advancement is required.
Type III and Type IV also used in class II division 2
malocclusions.

DESIGN CONSIDERATIONS
1) Bite registraton is usually taken at an almost edge-toedge incisal relationship.
2) The working models are then mounted in a fixator in
accordence with the bite registration.
3) The lower magnetic unit is plased close to the lingual
aspect of the lower incisors.

4) When the upper and lower magnetic units match, the
Prong in aligned with the mid saggital line.

5)U- shaped loops of the labial bow are wide enough
that the vertical legs of the loops do not contact the
bonded attachments.
6)The patient is instructed to hook the elastic clasp on
The bonded attachments using an expansion screw-key.
If a type III or IV is applied to correct class II, =division 1
malocclusion, acrylic(b∕w anterior wall of upper magnetc housing and palatal aspect of the upper incisors) is
removed from its contact with the magnet each time the
Protraction screw is activated.

MAGNETIC TWIN BLOCKS
This technique involves addition of magnets to occlusal
inclined planes.
The purpose of the magnets is to encourage increased
occlusal contact on the bite blocks to maximise the
favourable functional forces applied to correct malocclusion.
As the patient adapts to the presence of inclined planes
and the muscles establish a new postural position of
equilibrium.

 In this technique attracting or repelling magnets may be

used.
Attracting magnets:-the attracting magnetic force pulls the
appliance together and encourages the patient to occlude
actively and consistently in forward position.
Care must be taken to limit attractive force magnitude.
Clark has used two materials-samarium cobalt and neodynium
boran-to test the clinical response to magnetic twin blocks.

Situations where rare earth magnets were used by Clark are:
1)Class II division 1 malocclusion with large overjet.
2)Mild residual class II, buccal segment relationship.

3)Mild class II, division 1 malocclusion.
4)Adults with severe class II, division 2 malocclusion and persistent headaches associated with occlusal interference.
5)Marked skeletal class III malocclusion.

Correction of facial asymmetry:Indication for the use of magnets in this condition is to counter
act asymmetric muscle action.

 To correct unilateral Mandibular displacement, attracting

magnets are used in the occlusal inclined planes on the woring side.
 On inactive side there may be an upper bite block.


Repelling magnets:Repelling magnets are intended to apply additional stimulus
to forward posture as the patient closes into occlusion.
Whether attracting or repelling magnets are used, reactivation
of the blocks by addition of acrylic to inclined planes deactivtes the magnets.
Response to Magnetic Twin Blocks:-

Attracting magnets are indicated in cases in which the patient
does not or cannot make the muscular effort to posture consistently to correctedwww.indiandentalacademy.com
occlusion.

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Magnets in orthodontics /certified fixed orthodontic courses by Indian dental academy

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