Magnets in maxillofacial/ General orthodontics

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INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

MAGNETIC RETENTIONMAGNETIC RETENTION
IN MAXILLO FACIALIN MAXILLO FACIAL
PROSTHESESPROSTHESES

INTRODUCTIONINTRODUCTION

 The success of most extra oral prosthesesThe success of most extra oral prostheses
depends on retention.depends on retention.
 The problem of retention in maxillofacialThe problem of retention in maxillofacial
prosthesis is a great challenge posed to theprosthesis is a great challenge posed to the
prosthodontists.prosthodontists.
 When the prosthesis is designed, fullWhen the prosthesis is designed, full
consideration must be given to the retentionconsideration must be given to the retention
of the prosthesis.of the prosthesis.

 A number of methods of retention areA number of methods of retention are
available.available.
These include :-These include :-
 Mechanical devicesMechanical devices
 Anatomic methods andAnatomic methods and
 Adhesives with or without the use of the otherAdhesives with or without the use of the other
methods.methods.
 The mechanical retention methods includesThe mechanical retention methods includes
the use of magnets amongst many otherthe use of magnets amongst many other
methods.methods.

 The use of magnets has been popular inThe use of magnets has been popular in
dentistry.dentistry.
 The reason of popularity is related to theirThe reason of popularity is related to their
small size and strong attractive forces.small size and strong attractive forces.
 Magnets have generated great interest inMagnets have generated great interest in
dentistry, and their application are numerous.dentistry, and their application are numerous.
 They are being used as retentive aids forThey are being used as retentive aids for
over dentures, removable partial denturesover dentures, removable partial dentures
and implants.and implants.

 Javid, in 1971 constructed an extensiveJavid, in 1971 constructed an extensive
prostheses for both extra-oral and intra-prostheses for both extra-oral and intra-
oral aspects connected with magnets.oral aspects connected with magnets.
 Federick, in 1976, rehabilitated a patientFederick, in 1976, rehabilitated a patient
with a large orofacial defect using a 2-with a large orofacial defect using a 2-
component obturator that was locked tocomponent obturator that was locked to
each other with help of magnets.each other with help of magnets.
In maxillofacial prosthodontics theyIn maxillofacial prosthodontics they
have been used for decades tohave been used for decades to
reconstruct large defects with the helpreconstruct large defects with the help
of multiple component prostheses.of multiple component prostheses.

HISTORYHISTORY

 Magnets were first introduced for applications inMagnets were first introduced for applications in
dentistry in 1953 in the field of orthodontics.dentistry in 1953 in the field of orthodontics.
 Conventional magnets were applied inConventional magnets were applied in
prosthodontics in the year 1960 as retentiveprosthodontics in the year 1960 as retentive
devices for over dentures, removable partialdevices for over dentures, removable partial
dentures and maxillofacial prostheses.dentures and maxillofacial prostheses.

 One of the earliest magnets was pairedOne of the earliest magnets was paired
AlnicoAlnico which is a permanent magnet alloy ofwhich is a permanent magnet alloy of
iron, cobalt ,nickel and aluminum. But theiron, cobalt ,nickel and aluminum. But the
main disadvantage of this system was themain disadvantage of this system was the
large size.large size.
 Coated and uncoated cobalt-platinum barCoated and uncoated cobalt-platinum bar
magnets(co-pt) were implanted in themagnets(co-pt) were implanted in the
mandible by Behr man and Toto to retain amandible by Behr man and Toto to retain a
denture.denture.

 In late 1960s another permanent magnet inIn late 1960s another permanent magnet in
which cobalt was alloyed with Samariumwhich cobalt was alloyed with Samarium
(Co(Co55sm) was introduced, it has twice thesm) was introduced, it has twice the
magnetic field strength of co-pt and themagnetic field strength of co-pt and the
strongest of Alnico alloys.strongest of Alnico alloys.
 These magnets could be produced in veryThese magnets could be produced in very
small dimensions and approximately one fifthsmall dimensions and approximately one fifth
of Co-pt magnets and still could provide sameof Co-pt magnets and still could provide same
force.force.

 Another alloy based on neodymium – iron –Another alloy based on neodymium – iron –
boron became available in 1980s for dentalboron became available in 1980s for dental
applications. Both Coapplications. Both Co55Sm and Nd-Fe-B areSm and Nd-Fe-B are
termed as rare earth magnets because they aretermed as rare earth magnets because they are
rare from the standpoint of extraction.rare from the standpoint of extraction.
 Another material Samarium iron nitride is beingAnother material Samarium iron nitride is being
developed for medical and dental appliances. Itdeveloped for medical and dental appliances. It
is highly resistant to demagnetization and hasis highly resistant to demagnetization and has
better resistance to temperature and corrosionbetter resistance to temperature and corrosion
than Nd-Fe-B. It is still under development.than Nd-Fe-B. It is still under development.

CLASSIFICATIONCLASSIFICATION

 Based on alloys usedBased on alloys used
• Those containing cobalt.Those containing cobalt.
E.g. Alnico, Alnico V, Co-Pt.E.g. Alnico, Alnico V, Co-Pt.
• Those not containing cobalt.Those not containing cobalt.
E.g. Nd-Fe-B, Samarium iron nitride.E.g. Nd-Fe-B, Samarium iron nitride.
 Based on ability to retain magneticBased on ability to retain magnetic
propertiesproperties
• Soft (Easy to magnetize or demagnetize – less permanent).Soft (Easy to magnetize or demagnetize – less permanent).
E.g. Pd-Co-Ni alloy, Pd-Co alloyE.g. Pd-Co-Ni alloy, Pd-Co alloy
• Hard (Retain magnetism permanently).Hard (Retain magnetism permanently).
E.g. Alnico alloy, Co-Pt.E.g. Alnico alloy, Co-Pt.

 Based on surface coatingBased on surface coating
• CoatedCoated
• UncoatedUncoated

Based on the type of magnetismBased on the type of magnetism
• RepulsionRepulsion
• AttractionAttraction
 Based on the type of magnetic fieldBased on the type of magnetic field
• Open fieldOpen field
• Closed fieldClosed field
 Rectangular closed – field sandwich designRectangular closed – field sandwich design
 Circular closed – field sandwich designCircular closed – field sandwich design

 Based on number of magnets in theBased on number of magnets in the
systemsystem
 SingleSingle
 PairedPaired
 Based on the arrangement of polesBased on the arrangement of poles
 Reversed polesReversed poles
 Non-reversed polesNon-reversed poles

MECHANISM OF MAGNETISMMECHANISM OF MAGNETISM
 Every atom in a material is a magnet becauseEvery atom in a material is a magnet because
electrons orbit it’s nucleus. While theseelectrons orbit it’s nucleus. While these
electrons move they produce a magnetic fieldelectrons move they produce a magnetic field
around the atom.around the atom.
 In some atoms such as Fe, Ni, and Co, thereIn some atoms such as Fe, Ni, and Co, there
are unpaired electrons that create a tinyare unpaired electrons that create a tiny
magnetic field.magnetic field.
 In a magnetic material, a large portion of theseIn a magnetic material, a large portion of these
atoms align in small regions called “domains”.atoms align in small regions called “domains”.

 On application of a magnetic field, these domainsOn application of a magnetic field, these domains
align to reach a saturation point, at this point thealign to reach a saturation point, at this point the
material is magnetized.material is magnetized.
 Some materials require small magnetic field to reachSome materials require small magnetic field to reach
the saturation point called “the saturation point called “softsoft” magnet, some” magnet, some
require larger magnetic field to be magnetized, suchrequire larger magnetic field to be magnetized, such
material becomes a “material becomes a “hardhard”” magnet.magnet.
 When the external magnetic field is removed, if theWhen the external magnetic field is removed, if the
material retains its magnetization then it is called amaterial retains its magnetization then it is called a
permanent magnetpermanent magnet..

MAGNETIC MATERIALSMAGNETIC MATERIALS
Over the last century, significant advances have madeOver the last century, significant advances have made
in the development of magnetic materials. Thesein the development of magnetic materials. These
advances have been quickly transferred into dentaladvances have been quickly transferred into dental
applications.applications.
 NeodymiumNeodymium –– iron boroniron boron––(Nd-Fe-B)(Nd-Fe-B)
 RE-alloy samarium cobalt.RE-alloy samarium cobalt.
 Alnico-alloysAlnico-alloys
 Samarium iron nitrideSamarium iron nitride

 The main magnetic material used isThe main magnetic material used is
the rare earth materialthe rare earth material NeodymiumNeodymium
– iron boron–(Nd-Fe-B)– iron boron–(Nd-Fe-B)
 It is the most powerful commerciallyIt is the most powerful commercially
available magnetic material.available magnetic material.
 This group of magnetic materialsThis group of magnetic materials
provides the highest availableprovides the highest available
magnetic energies of any material.magnetic energies of any material.
 NdFeB magnets allow small shapesNdFeB magnets allow small shapes
and sizes with high magnetic fields.and sizes with high magnetic fields.
 Coating is needed for NdFeBCoating is needed for NdFeB
Neodymium – iron boron

 Samarium Cobalt (SmCo) magnets: ofSamarium Cobalt (SmCo) magnets: of
the Rare Earth class, have been availablethe Rare Earth class, have been available
since the early 1970's.since the early 1970's.
 These magnets possess very highThese magnets possess very high
magnetic properties, excellent thermalmagnetic properties, excellent thermal
stability, and remarkable resistancestability, and remarkable resistance
against corrosion and oxidation.against corrosion and oxidation.
 These characteristics make SmCoThese characteristics make SmCo
magnets ideal for applications requiring amagnets ideal for applications requiring a
resistance to wide-ranging temperaturesresistance to wide-ranging temperatures
and environments.and environments.
Samarium cobalt

Alnico-alloysAlnico-alloys
 The Aluminum/Nickel/CobaltThe Aluminum/Nickel/Cobalt
combination is excellent for highcombination is excellent for high
temperature use, and is readilytemperature use, and is readily
available in rods or bars.available in rods or bars.
 The direction of magnetizationThe direction of magnetization
for Alnico is usually much longerfor Alnico is usually much longer
than the other dimensionsthan the other dimensions
(parallel to the length) for best(parallel to the length) for best
results.results.
 As cast material, it is gray toAs cast material, it is gray to
dark brown in color, but looksdark brown in color, but looks
metallic when ground.metallic when ground.

 Samarium iron nitride is a promising newSamarium iron nitride is a promising new
material for permanent magnet applicationsmaterial for permanent magnet applications
because of its high resistance tobecause of its high resistance to
demagnetization, high magnetization and betterdemagnetization, high magnetization and better
resistance than Nd-Fe-B to temperature andresistance than Nd-Fe-B to temperature and
corrosion.corrosion.
Samarium iron nitride

Design of Magnetic Attachments.Design of Magnetic Attachments.
Magnet systems may be either anMagnet systems may be either an
 Open fieldOpen field
 Closed field designsClosed field designs
 A cup typeA cup type
 A sandwich typeA sandwich type
 A modified split-pole typeA modified split-pole type
 A split pole with slant magnetizationA split pole with slant magnetization
 A cylinder typeA cylinder type

 An open field system consistsAn open field system consists
of a cylindrical magnet withof a cylindrical magnet with
open ends, it can be single oropen ends, it can be single or
paired.paired.
 For simple, cylindrical, openFor simple, cylindrical, open
field magnet encased in nonfield magnet encased in non
magnetic housing, magneticmagnetic housing, magnetic
field is experienced outside thefield is experienced outside the
magnetic specimen.magnetic specimen.
 Only one pole is used forOnly one pole is used for
attachment to the keeper.attachment to the keeper.

 In closed field system Consists ofIn closed field system Consists of
paired magnets and an attachable andpaired magnets and an attachable and
detachable keepers.detachable keepers.
 The magnet pairs are arranged withThe magnet pairs are arranged with
opposite poles adjacent and magnetopposite poles adjacent and magnet
faces abut magnetizable alloy keepers.faces abut magnetizable alloy keepers.
 In general, closed field magnets haveIn general, closed field magnets have
higher contact forces than open fieldhigher contact forces than open field
devices of an equivalent size.devices of an equivalent size.

 Attachment of closed-field magnets is moreAttachment of closed-field magnets is more
efficient because both the north and south polesefficient because both the north and south poles
can be used for attachment to the keeper andcan be used for attachment to the keeper and
the keepers can contain the magnetic flux.the keepers can contain the magnetic flux.
 The first closed field design was the split poleThe first closed field design was the split pole
design, which consisted of 2 magnets arrangeddesign, which consisted of 2 magnets arranged
with opposite poles adjacent to each other.with opposite poles adjacent to each other.

 A small magnetic field is attached to the top ofA small magnetic field is attached to the top of
the magnets.the magnets.
 Comparisons of the forces provided by pairedComparisons of the forces provided by paired
magnets, single magnets and soft magneticmagnets, single magnets and soft magnetic
material, and reversed and non-reversed polesmaterial, and reversed and non-reversed poles
have been performed.have been performed.
 Paired magnets provided a greater breakawayPaired magnets provided a greater breakaway
force than a single magnet with a soft magneticforce than a single magnet with a soft magnetic
keeper.keeper.

 A reversed split pole system was designed byA reversed split pole system was designed by
Gillings, provided a greater force than a nonGillings, provided a greater force than a non
reversed split pole design.reversed split pole design.
 Various designs exist that are based on circularVarious designs exist that are based on circular
and rectangular assemblies.and rectangular assemblies.
 A magnet sandwich design, has been shown toA magnet sandwich design, has been shown to
work well, the amount of retention depends onwork well, the amount of retention depends on
the thickness of the side plates and base.the thickness of the side plates and base.

 Finite element analysis has been used to the design ofFinite element analysis has been used to the design of
attachments to maximize that they provide.attachments to maximize that they provide.
 A closed –field design consisting of a magnet in a cupA closed –field design consisting of a magnet in a cup
which in turn is placed in an outer cup provides a higherwhich in turn is placed in an outer cup provides a higher
retention force than a simple open field system.retention force than a simple open field system.
 A circular closed field sandwich-type design provides aA circular closed field sandwich-type design provides a
greater amount of retention, if keeper materials aregreater amount of retention, if keeper materials are
made ellipsoidal, then retention will increase further.made ellipsoidal, then retention will increase further.

ADVANTAGESADVANTAGES
 Ease of placementEase of placement
 Automatic reseatingAutomatic reseating
 Constant retention with many cyclesConstant retention with many cycles
 Easy replacement if neededEasy replacement if needed
 Small size with strong attractive forces.Small size with strong attractive forces.
 Can be placed within the prosthesisCan be placed within the prosthesis
 Dissipate lateral functional forcesDissipate lateral functional forces
 Less need for parallel abutmentsLess need for parallel abutments
 Can be used for implant – supported prosthesis.Can be used for implant – supported prosthesis.
 Ease of cleaningEase of cleaning

DISADVANTAGESDISADVANTAGES
 Low corrosion resistanceLow corrosion resistance
 Cytotoxic effectsCytotoxic effects
 High costHigh cost
 Short track record.Short track record.

MAGNETIC RETENTIONMAGNETIC RETENTION
 Application of magnetic force in retention ofApplication of magnetic force in retention of
prostheses has been tried more than halfprostheses has been tried more than half
century.century.
 With the development of magnetic materialsWith the development of magnetic materials
and manufacturing technique, it has become aand manufacturing technique, it has become a
realization to use magnetic force to retain oralrealization to use magnetic force to retain oral
and maxillofacial prostheses in recent 20 years.and maxillofacial prostheses in recent 20 years.
 As a mature retentive technique, magneticAs a mature retentive technique, magnetic
attachment has been applied in variousattachment has been applied in various
prostheses more and more popularly now.prostheses more and more popularly now.

MAGNETIC RETENTION IN DIFFERENTMAGNETIC RETENTION IN DIFFERENT
MAXILLO FACIAL PROSTHESESMAXILLO FACIAL PROSTHESES
 EXTRA ORAL PROSTHESES-EXTRA ORAL PROSTHESES-
 Free standing magnetic retention for prosthesis withFree standing magnetic retention for prosthesis with
osseointegraded implants.osseointegraded implants.
 Magnetic retention in endosteal implants used forMagnetic retention in endosteal implants used for
facial prostheses.facial prostheses.
 Magnetic retention in midfacial prostheses withoutMagnetic retention in midfacial prostheses without
implants.implants.
 Magnetic retention in combined prostheses.Magnetic retention in combined prostheses.

 Intra oral prostheses-Intra oral prostheses-
 ObturatorsObturators

FREESTANDING MAGNETIC RETENTION FORFREESTANDING MAGNETIC RETENTION FOR
EXTRAORAL PROSTHESES WITHEXTRAORAL PROSTHESES WITH
OSSEOINTEGRATED IMPLANTSOSSEOINTEGRATED IMPLANTS
 The use of extra oral Osseo integrated implantsThe use of extra oral Osseo integrated implants
for prosthetic rehabilitation of facial defects isfor prosthetic rehabilitation of facial defects is
now widely accepted and practiced throughoutnow widely accepted and practiced throughout
world.world.
 Extra oral Osseo integrated implants are notExtra oral Osseo integrated implants are not
without problems, most common is hygiene ofwithout problems, most common is hygiene of
the implant abutment.the implant abutment.

 The most common method of retentionThe most common method of retention
used in conjunction with implants is theused in conjunction with implants is the
bar splint and clip assembly, itbar splint and clip assembly, it
provides good retention but theprovides good retention but the
presence of the bar may inhibitpresence of the bar may inhibit
abutment hygiene by preventingabutment hygiene by preventing
sufficient patient access to the area.sufficient patient access to the area.
 Other complication include the initialOther complication include the initial
difficulty in placing the prosthesis anddifficulty in placing the prosthesis and
fracture of the base if the clips are setfracture of the base if the clips are set
too tightly.too tightly.

 The use of magnets in conjunction with a barThe use of magnets in conjunction with a bar
splint or as a complete magneticsplint or as a complete magnetic
superstructure have been well documented,superstructure have been well documented,
however the problem of abutment hygienehowever the problem of abutment hygiene
may still be compromised by presence ofmay still be compromised by presence of
superstructure or bar.superstructure or bar.
 Newer generation magnets and associatedNewer generation magnets and associated
abutment magna-cup components haveabutment magna-cup components have
been successfully used is a variety ofbeen successfully used is a variety of
patients over the past 5 years.patients over the past 5 years.

 It is important to be selective in the use of freestandingIt is important to be selective in the use of freestanding
magnetic retention.magnetic retention.
 A common use of freestanding magnets has been in smallA common use of freestanding magnets has been in small
orbital defects that are subject to minimal soft tissueorbital defects that are subject to minimal soft tissue
movement.movement.
 The original Neo-mini magnet has a pull force ofThe original Neo-mini magnet has a pull force of
approximately 500 gm and when used for orbitalapproximately 500 gm and when used for orbital
prostheses, where there is no fear of lateral displacement,prostheses, where there is no fear of lateral displacement,
complete security of retention is assured.complete security of retention is assured.

RETENTION OF MAGNETS IN ENDOSTEALRETENTION OF MAGNETS IN ENDOSTEAL
IMPLANTS USED FOR FACIAL PROSTHESESIMPLANTS USED FOR FACIAL PROSTHESES
 Facial defects, whether the result of trauma orFacial defects, whether the result of trauma or
ablative surgery, are usually surgically treatedablative surgery, are usually surgically treated
whereby lost parts are replaced by soft tissue orwhereby lost parts are replaced by soft tissue or
bone grafts or both.bone grafts or both.
 Some cases where reconstruction is notSome cases where reconstruction is not
possible or contraindicated, the treatment ofpossible or contraindicated, the treatment of
choice is facial prostheses to restore lostchoice is facial prostheses to restore lost
structures.structures.

 At present, endosteal implants andAt present, endosteal implants and
implant-supported epitheses are the stateimplant-supported epitheses are the state
of art. Anchoring components may exist ofof art. Anchoring components may exist of
bar constructions or magnets.bar constructions or magnets.
 Magnets are often used as abutments forMagnets are often used as abutments for
nasal, auricular and orbital epitheses.nasal, auricular and orbital epitheses.


 End osseous Fixtures in the Calotte used for retaining
Wigs With magnetic attachments


Magnetic retention in midfacialMagnetic retention in midfacial
prostheses without implants.prostheses without implants.

MAGNETIC RETENTION IN AURICULAR PROSTHESES

MAGNETIC RETENTION INMAGNETIC RETENTION IN
COMBINED PROSTHESESCOMBINED PROSTHESES

 Intra-oral magnetic retentionIntra-oral magnetic retention
The hollow facial epithese was made with medical silicone material
and two pairs of magnetic attachments were also applied to connect
the epithese and the obturator.

CONCLUSIONCONCLUSION
 Magnets have been effectively used forMagnets have been effectively used for
the retention, maintenance andthe retention, maintenance and
stabilization of maxillo facial prosthesisstabilization of maxillo facial prosthesis
and they are effective for this purpose.and they are effective for this purpose.
Retention is like a castle held togetherRetention is like a castle held together
by proper Support and Stability. If anyby proper Support and Stability. If any
one fails the whole castle comesone fails the whole castle comes
crumbling down….crumbling down….

Thank you
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Magnets in maxillofacial/ General orthodontics

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