Magnets in orthodontics

Magnets in
Orthodontics
www.indiandentalacademy.com

Introduction
• Magnetic fields can be either Natural or
artificial.
• These fields were tested and proven to have
no adverse effects on humans.
• These test results have made possible the
use of magnets in the field of dentistry.

• The first use of magnets in Dentistry was by
Behran and Egan in the year 1953.
• They used it as implants for denture
retention.
• First use of magnets for tooth movement
was described by Blechman and Smiley by
experimenting on cats.
• Becker in 1970 introduced rare earth
magnets having properties superior to
previously used magnetic alloys.

Properties of magnets
• Magnetic field can be either Static or Time
varying.
• Static field produced by Direct current
• Time varying field by alternating current
• Static field characterized by flux lines
which start at the north pole and following a
smaller or wider curved path,return to the
magnet at the south pole.

Properties……..
• COULOMBS LAW:
States that the force
between two magnetic poles is proportional
to their magnitudes and inversely
proportional to the square of the distance
between them.
• CURIE POINT:
Pierre Currie observed magnets to loose
their properties if subjected to a specific
temperature which is called Curie point.www.indiandentalacademy.com

Properties……...
• High force to volume ratio:
• Introduction of rare
earth magnets has led to the use of smaller
magnets delevering a higher force than the
bulkier ones.
• An increase in the force to volume
ratio{miniaturizing effect}makes the use of
magnets in Dentistry a beneficial modality.

Properties……..
• Maximal force at short distances:
• Rare earth magnets give maximal
force at short distances in comparison to
elastics,which attain maximum force at
longer distances.
• Three Dimensional Centripetal orientation
of attractive magnetic forces gives the
operator a complete tooth control on precise
engagement. www.indiandentalacademy.com

Properties……….
• No interruption of magnetic force lines by
intermediate media.
• When using attractive forces frictional
forces are excluded.
• Rare earth magnets can maintain energy if
protected against corrosion, thermal and
other biologic pertuberances unlike other
force delivery systems that deteriorate over
a short time.

• A study by J.A Von Fraunhofer in 1992
found that magnets with a seperation of less
than 2mm obeyed coulombs law
• 0 -2mm seperation effective forces were
reduced
• Seperation beyond this created values
which are lesser than those required for
physiological tooth movement

Properties …...

• Types of Magnetic materials:
• In various dental
applications the following materials have
been used.
• 1. Platinum-cobalt
• 2. Aluminium-Nickel-Cobalt
• 3. Ferrite
• 4. Chromium-Cobalt-Iron
• 5. Samarium-Cobalt
• 6. Neodymium-iron-Boron.
•
•

• SAMARIUM -COBALT MAGNETS
• A powdered metallurgically
processed inter-metallic alloy of Cobalt and
rare earth metals when compared with other
rare earth magnets.
• Required force obtained from a small size
of the magnet making it ideal for
orthodontic use.
• Have high resistance to demagnetization
with time.
• High Curie point-680 centigrade
• They are Parylene coated to prevent leaking
of toxic substances.

• Biologic concept of Magnetic force and
Histologic changes.
• It was found that magnetic forces
inflicted a minimum of stress that induces
various bio-chemical changes in a patient
during orthodontic tooth movement.
• No subcutaneous changes as
inflammation or adverse reaction under the
magnets.
• Resorption of bone occurred under
magnets after 3-4 weeks.
• Reduced chances of necrosis of
bone as magnets make erythrocytes thinner.

• Lars Bondemark and Jure Kurol studied
changes in human pulp and gingival tissue
on exposure to magnetic field and found no
changes.
• Mac Donald 1993 reported an increased
proliferation and systemic activity in
fibroblasts on the use of static magnetic
fields.
• Astudy by Cerny and Sandler found no
bioharzardous effect with rare earth
magnets.

• A study by Lars Bondemark &Alf
Wennberg in 1994 showed
• Uncoated Samarium Cobalt magnets
showed severe toxicity
• Parylene coated Samarium magnets showed
mild toxicity
• Coated &uncoated Neodymium magnets
showed negligible toxicity
• Short term exposure to magnet fields did
not cause any cytotoxic effect on cells

• Magnetic Force systems in Orthodontics
• 1.Relocating impacted teeth
• 2.Expansion of arch
• 3.Distal/mesialization of molars
• 4.Intrusion of posterior teeth in open
• bite cases
• 5.Class 11 correction with functional
• appliances
• 6.Skeletal correction with functional
• appliances
• 7.Closure of diastemawww.indiandentalacademy.com

• 9. Uprighting and Derotation of teeth
• 10. Magnetic Brackets
• 11. Class 11 correction with Magnetic
• Twin block
• 12.Magnetic appliance for treatment of
• snoring patients with and without sleep
• apnoea
• 13. Extrusion of fractured teeth
• 14.Extraction and Non-extraction cases
• 15.Treatment of hemifacial microsomia

Magnetic Appliances

• Magnetic Appliance for an extraction case
• Attractive magnetic forces are used to
bring about orthodontic tooth movement
• Magnetic Appliance for a non-extraction
case
• Derived from magnets in attraction or
repulsive mode

Magnetic Activator Devise
• Magnetic functional appliance developed
by Darendilier in 1993 for correction of
mandibular deviations
• Active vertical correcter introduced by
Darendilier in in 1986 as a non surgical
alternative treatment for Skeletal open bite

Fixed Magnetic Appliance
• Introduced by Varun Kalra &Charles
Burstone in 1989
• Appliance has the magnets in repelling
mode embedded in the upper and lower
acrylic splints

Magnetic Twin Blocks
• Clark used magnets in his Twin Block
• Magnets were embeded in the inclined
surface of the twin block in attractive mode
• When used in the repelling mode it reduces
the need for reactivation
• Used in different ways for treating Class 11
and Class111 malocclusion

Magnetic Brackets
• Introduced by Kawata et al in 1987
• Samarium Cobalt magnets with an
edgewise bracket on one surface to receive
the archwire and a mesh on the inferior
surface for direct bonding
• Designed to deliver 250gms force
• Complex lab procedures&dimensions of the
brackets to obtain necessary force levels
were seen as maximum disadvantageswww.indiandentalacademy.com

Propellent Unilateral Magnetic
Appliance
• Introduced by Chafe 1995 for stimulating
an autogenous costochondral graft in
hemifacial microsomia
• Consists of Samarium - Cobalt magnets
embedded in upper & lower acrylic bite
blocks in the repelling mode

Magnetic Appliance For
treatment of Snoring Patients
• Introduced in 1998 by Mars Bernhold &
Bondemark
• Two intraoral occlusal splints each with
four parylene coated Neodynium magnets
are used
• Full tooth coverage is required to prevent
unwanted tooth movements

Deimpaction with Magnets
• Used by Vardimone et al in 1991
• He used a magnetic bracket bonded to an
impacted tooth & intraoral magnet linked to
a Hawley type retainer to guide the
erupting tooth
• Darendeliler in 1994 used a small bonded
magnet on an impacted Canine
• Sandler 1991used a similar method

Functional Orthopedic Magnetic
Appliance
• Developed by Vardimon in 1989 for
Class 11 & class 111 malocclusion
• FOMA 11 consists of upper magnet located
anterior to lower magnet in a non displaced
jaw relationship
• FOMA 111 consists of upper and lower
plates with magnets
• all magnets kept in an attractive mode

Autonomous Fixed Appliance
• Darendelier &Jobor in 1992 used this to
treat a Class 11 Bimaxillary protrusion
• Samarium Cobalt were bonded to individual
teeth at an appropriate level forming the
Autonomous Fixed Appliance

Magnets for closing Diastemas
• Muller in 1984 bonded rectangular
magnets delivering 117.5 gms of force of
attraction on each maxillary central incissor
to close a midline diastema

Expansion with magnets
• A study on Facicularis monkeys proved that
repelling magnets delivered ideal forces for
expansion compared to a jack screw
appliance
• Darendililer et al in 1993 used mid palatal
repelling magnets and showed both dental
and skeletal expansion in his report

Magnets For Molar Distalization
• Molar Distalization was reported by
Gianelly et al in 1998,Bondemark et al
1990,Takami et al 1991 and Steger et al
1975
• they used repelling magnets between upper
premolar and molar
• Bondemark et al 1994 compared push coils
versus magnets for molar distalization

Molar Distalization

Extrusion of fractured teth
• Bondemark &Kurol in 1997 used magnets
to extrude the fractured root
• Magnets used were in the attractive mode
with a minimum gap of 2mm
• after the desired extrusion the tooth can be
restored

Extrusion of crown-root
fractured teeth

• Advantages of magnetic appliances
• Eliminates patient co-operation
• Produces less pain and discomfort
• Continous force exerted
• Treatment time reduced
• Reduced periodontal disturbance
• No friction
• Less chair side time
• Better force
• Better directional control

• Disadvantages
• Tarnish &corrosion
• Cytotoxic effects
• Bulk of the magnets
• Taste - Bitter
• Costly

Recycling of Magnets
• Bondemark &Kurol conducted extensive
studies on recycling of rare earth magnets
• concluded that the biocompatability &force
stability is not effected
• Darendililer felt that magnets should not be
recycled for ethical reasons

• Summary & Conclusion
Magnets can be used to give
predictable forces in either attraction or
repelling mode & can be made small
enough to suit most dental applications.
The evidence currently available
from biological safety testing would suggest
that the risk of harmful biological effects
are negligible.The high cost can be
overcome by reusing it after sterilization &
recycling.

Thank you

Magnets in orthodontics

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