4. DEFINITIONS
Magnet-A magnet (from Greek "Magnesian stone")
is a material or object that produces a magnetic
field
Magnetic field- It is magnetic flux density ,also
called magnetic field, usually denoted as vector
field.
The overall strength of a magnet is measured by
its magnetic moment or, alternatively, the
total magnetic flux it produces
5. Magnets – how do they work
N S
Just what is
happening inside
the magnet to make
it magnetic?
We need to look closely at what is
happening to the particles (electrons)
inside the magnet.
In an unmagnetized
material, the tiny
electrons, or atomic
magnets point in random
directions.
When the material becomes magnetized,
more and more of the tiny atomic magnets
line up with each other. They act as one BIG
magnet.
6. Magnetic fields
It’s the space in which magnetic pole
experiences a force.
The force between two isolated magnetic poles
is directly proportional to product of their pole
strengths and inversely proportional to the
square of the distance between them(Coulomb’s
Inverse Square Law)
Field lines run from the north pole
(N) to the south pole (S). The
magnetic field is strongest where
the field lines are closer together.
7. Magnetic and Non-magnetic
Magnetic material – can be magnetized, and is attracted to magnets.
Strongly magnetic materials contain iron, nickel or cobalt (eg. Steel is
mainly iron).
Ferromagnets
Hard magnetic
materials, eg. Steel,
alloys (Alcomax,
Magnadur). Difficult to
magnetise, but do not
lose their magnetism.
Used for permanent
magnets.
Soft magnetic materials,
eg. Iron, Mumetal.
Relatively easy to
magnetise, but
magnetism is
temporary. Used in
electromagnets and
transformers.
Non-magnetic
materials. Metals
(brass, copper, zinc,
tin and aluminium);
non-metals.
9. Magnets have generated great interest within dentistry, and their
applications are numerous.
The 2 main areas of their use are orthodontics and removable
prosthodontics
The reason for their popularity is related to their small size and strong
attractive forces
And the challenge in maxillofacial prosthesis poses greatest challenge
to prosthodontics
Melissa Alessandra Riley J Prosthet Dent 2003;89:446-9
11. Magnet was first introduced in field of orthodontics.
Conventional dentures were first used in prosthodontics
for removal appliances and maxillofacial prosthesis
Before the development of rare earth magnets, Alnicos—
alloys based on aluminum, cobalt, and nickel-were the main
materials in use, but main disadvantage was large size.
The main magnetic material used is the rare earth material
neodymium iron boron (Nd-Fe-B) which is the most
powerful commercially available magnet material.
14. Based on alloy used
1)Co containing
2)Those not Co containing
Based on retaining of magnetic properties
1)Soft-easy to magnetize or demagnetize ie less permanent.
Pd-Co-Ni, Pd-Co
2)Hard-able to retain magnetic properties and be made into
permanent magnets (Alnico,Co-Pt)
15. OTHER CLASSIFICATIONS
Based on surface coating
Based on type of magnetism
Based on type of magnetic field
Based on number of magnets in system
Based on arrangement of poles
16. Neodymium – Iron-Boron
Most commonly used
Most powerful magnet that is commercially available
This group provides the highest possible magnetic
energies of any material
Small sizes and shapes available so better for
prosthetic concern
But coating is required
17. Samarium Cobalt Alloy
This are rare earth metal available since 1970
This magnets have high magnetic properties,
excellent thermal stability, and remarkable
resistance against corrosion and oxidation.
18. Alnico alloys
The Al-Ni-Co combination is excellent for high
temperature use and is readily available in
rods, bars and buttons.
The direction of magnetisation is usually much
longer than the other dimension for best
results
But corrodes easily
19. Design of Magnetic attachment
Magnetic system may be either
an
Open field
Closed field design
Cup type
Sandwich type
Modified split-pole type
Split pole with slant
magnetisation
Cylinder type
20. Open-field systems
First reported use of magnets for the retention
of overdentures took place in the 1960 with the
rehabilitation of a patient with a cleft lip and
palate.
Consists of a cylindrical magnet with open
ends, can be single or paired
Only one pole is used for the attachment to the
keeper
21. Closed-field systems
These attempt to reduce the magnetic field effects in the
oral cavity.
The magnetic attachments incorporate soft magnetic
materials (such as ferritic or martensitic stainless steel
or a Pd-Co-Ni alloy) that connect the 2 poles of a magnet
so the external field is shunted through the path of less
resistance, reducing external fields
Although these systems generally provide a higher
retentive force than a similarly sized open-field system,
the retention reduces rapidly with increasing
separation.
22. Closed-field systems
Attachment of closed-field magnets is more efficient because both the
north and south poles can be used for attachment to the keeper and
the keepers can contain the magnetic flux.
Paired magnets provided a greater breakaway force than a single
magnet with a soft magnet keeper.
23. ADVANTAGES OF MAGNET
Ease of placement
Automatic reseating
Constant retention with many cycles
Easy replacement if needed
Small size with strong attractive force
Can be easily placed within the prosthesis
Dissipate lateral functional forces
Less need for parallel abutment
Can be used for implant supported prosthesis
Ease of cleaning
24. DISADVANTAGES OF MAGNET
Low corrosion resistance
Cytotoxic effect
High cost
Short track record
Heat unstability
Cannot be repaired only replaced
Requires encapsulation with inert alloy
25. USAGE IN PROSTHODONTICS
1)IMPLANTATION OF MAGNETS IN THE JAW TO
AID DENTURE RETENTION
2)COMPLETE AND PARTIAL OVERDENTURES
3)IMPLANT RETAINED OVERDENTURES
4)MAXILLOFACIAL PROSTHESIS
27. Behrman implanted Teflon*-
coated cobalt-platinum(CoPt)
bar magnets in the mandible to
retain mandibular complete
dentures which contained
similar but opposite polarity
magnets
He claimed that his method was
completely safe, with no
adverse physiologic effects,
excellent gross and microscopic
tissue findings, favorable bone
response, enhanced denture
retention, and encouraging
reaction in 450 patients.
J. Pros. Den. Sept.-Oct., 1960
29. Reaction of Bone and Mucosa to Implanted
Magnets
The implantation of a platinum-cobalt alloy magnet is
well tolerated by cortical bone and the overlying
mucoperiosteum.
A dense fibrous capsule forms around the magnet,
separating it from the bone.
The addition of masticatory forces to the fixed splint
caused additional tension on the wires, causing
resorption of the bone. The resulting mobility of the
splint no doubt was a source of chronic irritation to the
mucosa.
J. D. Res. November-December 1962
30. Magnetic retention for overdentures.
The magnetic retention unit
consists of a denture retention
element and a detachable
“keeper”element.
The denture-retention element has
paired, cylindrical, cobalt-samarium
magnets, axially magnetized and
arranged with their opposite poles
adjacent
. J Prosthet Dent 1983:49; 607-18.
31. The flat magnet faces are covered on
one end by an attached stainless steel
keeper and on the other end by thin
stainless steel plates
The detachable keeper element is a
stainless steel disk that is fixed to a
decoronated, root-filled tooth
J Can Dent Assoc 2010;76:a52
32. CLINICAL PROCEDURES
Tooth selection and preparation
Magnetic retention has a very low potential for
trauma to the supporting root.
Maximum lateral forces are considerably less
because the retention element is also free to slide or
rotate on the keeper element in function.
2,3,or4units,widely spaced and bilateral, provide
optimum support and retention.
Almost any teeth can be used for magnetic
retention, but vital canines and premolars are
preferred Int Dent J. 1984 Sep;34(3):184-97
33. Keeper types
1)The cement-in keeper.
Fitted in one appointment
Not suitable for small roots because of the
danger of lateral root perforation
A magnetic retention element is used as a
handle to hold cement-in keeper element for
trial-fitting and cementation.
J Prosthet Dent 1983:49; 607-18.
34. The screw-on keeper.
Fitted in one appointment
Unsuitable where available denture space
is limited as the keeper face is 1.2 mm
higher than the gingival margin.
Screw-on keeper usually covers the whole
of the root face
It is a preformed, chamfered, oval disk 6
mm long, 4 mm wide, and 1.2 mm thick and
has two countersunk, cone-shaped holes.
TMS pins are used
J Prosthet Dent 1983:49; 607-18.
35. The cast root cap and dowel keeper
Cover the root face completely and is the system of
choice in subjects with a high caries susceptibility.
2 appointments are necessary, and the finished
preparation will be at least 1.2 mm higher than the
gingival margin.
Magnetizable casting alloys must be used.
Pd-Co-Ni and stainless steel
J Prosthet Dent 1983:49; 607-18.
36. POST INSERTION
The patient must be motivated to carry
out consistent and effective oral
hygiene
In addition, once a week the patient
should apply a small amount of 10%
stannous fluoride paste or gel to the
retention elements and then wear the
denture to improve caries resistance
38. Various types of attachment systems are
currently available to restore implant-
supported over-denture.
CRITERIA FOR SELECTING ATTACHMENTS
Available bone
Patients prosthetic expectation
Patients economical status
Clinical expertise of specialist
Availability of skilled technician
J Dent Implant 2014;4:176-81.
39. With development of rare-earth metals and closed field
magnetism The current resurgence of interest in this type of
attachment appears justified because, unlike mechanical
attachments, magnets have potential for unlimited durability
and might therefore be superior to mechanical ball or bar
attachments for the retention of removable prostheses on
implants
In addition, a new generation of laser-welded containers has
improved protection from salivary corrosion.
Can be used in moderately nonparallel abutments
They are more resilient and allow for free movement of the
prosthesis.
40. a) Magnet (on top) with
keeper (abutment and
screw)
and b) assembled
magnet-keeper unit.
J Can Dent Assoc 2010;76:a52
41. Magnetic attachments used to retain dentures are typically
shorter than mechanical attachments, which is particularly useful
for patients with restricted interocclusal space and challenging
esthetic demands
Magnetic attachments can also accommodate a moderate
divergence of alignment between 2 or more abutments, since they
do not depend on a particular path of insertion
J Can Dent Assoc 2010;76:a52
42. Magnetic attachment system may be useful for elderly patients or
disabled patients, who may have difficulty inserting and removing
the dental removable prostheses.
Richard Leesungbok ,Presented at the 24th Annual Scientific Meeting of
the European Association of Osseointegration, Stockholm, Sweden
44. MAGNETS AND MAXILLOFACIAL IMPLANT
Osseointegration has revolutionized the
treatment of congenital, surgical, or traumatic
soft tissue and bone defects. It has improved
restoration in terms of stability and retention.
The most common method of retention used in
conjunction with implants is the bar splint and
clip assembly.
Newer generation magnets and associated
abutment Magna-cap components (provide pull
force per magnet in excess of 900 gm)
45. Freestanding magnetic retention for extraoral prosthesis
with osseointegrated implants
Magna-cap components in place Prosthesis in situ.
(J PROSTHET DENT 1995;73:162-5.)
46. A, Acrylic base; B, magnet; C, Magna-
cap component;
D, implant fixture; E, model.
(J PROSTHET DENT 1995;73:162-5.)
49. Magnet-retained auricular prosthesis with an
implant-supported composite bar
Two magnets
incorporated into fitting
surface of ear prosthesis
Implant abutments in place. Composite bar secured
with gold screws.
Ear prosthesis anchored
over composite bar.
(J Prosthet Dent 2003;89:446-9.)
50. Prosthetic rehabilitation after orbital
exenteration with maxillary defect
Indian J Ophthalmol [serial online] 2014 [cited 2017 Apr 5];62:629-32
57. Gun shot defect and its maxillofacial
rehabilitation using implants studed with
magnet
J Prosthet Dent. 1971:25;334-40.
58. FUTURE IMPROVEMENTS
1. The lifetime of dental magnetic attachments depends on
several factors, but the main problem is the inadequate
protection of the encapsulation materials once they are
breached, rapid corrosion of the internal magnet occurs
2. Encapsulating materials such as stainless steel are
effective but susceptible to wear
3. The development of samarium-iron-nitride may offer
better resistance to corrosion, and its introduction into
prosthodontics will be viewed with much enthusiasm.
J Prosthet Dent. 2001; 86(1):137-42.
59. CONCLUSION
Dentistry is an ever changing science. As new research and
clinical experience broaden our knowledge, changes in
treatment are required.
The intra oral magnets are shaping the course of esthetic
and retention for both complete and removable partial
denture.
The clinical procedures for the fabrication do not require
any special skill and the option offered by the various
manufacturers gives the dentist a wide variety of choice.
60. REFERENCES
Winkler, S.: The effectiveness of embedded magnets on complete dentures during speech
and mastication: A cineradiographic study. Dent Dig 73:118, 1967.
Behrman, S. J.: The implantation of magnets in the jaw to aid denture retention. J PROSTHET
DENT 10:807, 1960.
Toto, P. D., Choukas, N. C., and Sanders, D. D.: Reaction ofbone and mucosa to implanted
magnets. J Dent Res 41:1438, 1962.
Riley MA, Williams AJ, Speight JD, Walmsley AD, Harris IR. Investigations into the failure of
dental magnets. Int J Prosthodont 1999;12:249-54.
Over dentures with magnetic attachments. Dental clinics of North America. 1990; 34(4):683-
709.
Magnetic retention for over dentures. Part II. J Prosthet Dent 1983:49; 607-18.
J Prosthet Dent 2003;89:446-9.
J Prosthet Dent. 1987:55;334-40
J Prosthet Dent. 1971:25;223-34.
J Prosthet Dent 2016
Indian J Ophthalmol [serial online] 2014 [cited 2017 Apr 5];62:629-32
These include iron, nickel, cobalt, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone.
If a magnet is hit with a hammer, if heated to high temperature, It demagnetises
Mrthods of retention available 1) mechanical 2)anatomic 3) ADHESIVE
For a permanent magnet, it is the maximum energy product, (BH)max, that gives an indication of its power
Alnico, co-pt 2)Nd-Fe-B ,SAMARIUM
Magnetically soft materials require only small fields to reach saturation, whereas magnetically hard materials require large fields to reach saturation
COATED UNCOATED/ REPULSION ATTRACTION/ OPEN FIELD CLOSED/SINGLE PAIRED/ REVERSED POLE NONREVERSED POLE
Attachment of closed-field magnets is more efficient because both the north and south poles can be used for attachment to the keeper
retention element and the keeper element separate when the denture-dislodging force exceeds approximately 250 gm.
For these reasons magnetic retention can be used on roots that would have a poor prognosis with conventional precision attachments.
Immediately on completion of the root treatment or at a later appointment, the tooth is decoronated and theroot face flattened to a level that reduces to a minimumthe exposed cementum surfaces
Because the holes are cone shaped, the pins can be screwed into the dentin at an angle if the root face is not axial to the long axis of the root
Pd-Co-Ni and stainless steel
Stability and retention were increased in relation to increasing the height of abutments. Self- adjustable type magnetic attachment had higher retention than flat type magnetic attachment
inhibit abutment hygiene initial difficulty in placing the prosthesis and fracture of the base if the clips are set too tightly.
A 70-year-old man was evaluated for prosthetic rehabilitation of the right pinna after surgery for eradication of a tumor. using skin adhesive.
Osseointegrated implant treatment was offered, and subsequently four 3 mm implants were placed in the mastoid bone
60 year old female
Common use of free standing magnet implant is small defect with minimal soft tissue movement or rebound
20-year-old man with right hemifacial microstomia, the use of a bar provides an increased area for placement of larger magnets/keepers, and the use of an increased number of magnets/keeper
Patient underwent orbital exenteration and maxillectomy of the right side because of squamous cell carcinoma eroding the right orbital floor, posterior wall of maxilla, infratemporal fossa, right hard palate, medial wall of maxilla, right nasal cavity and right ethmoidal air sinuses
Magnetic button of wallet
surgical defect subsequent to radical surgery involving subtotal maxillectomy of left side performed six months before The palatal defect was in continuation with the orbital defect Speech intelligibility and deglutition were severely affected since the patient's tongue could not make effective functional contacts due to lack of anatomic boundaries during speech and deglutition. Firstly the extra oral prosthesis was fabricated
Anecdotally, patients who require restoration of orofacial defects by using both obturators and nasal prostheses
using zygomatic implant-supported nasal and oral prostheses.