magnets and dentistry

1. MAGNETS IN
PROSTHODONTICS

2. MAGNETS AROUND US

3. “
BASICS ABOUT MAGNETS

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.

8. “
INTRODUCTION

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

10. “
MAGNETIC MATERIALS HISTORY AND ITS
EVOLUTION

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.

13. “
CLASSIFICATION

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

26. “IMPLANTATION OF MAGNETS IN THE JAW
TO
AID DENTURE RETENTION

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

28. 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

37. “
Magnet-Retained Implant-Supported
Overdentures

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

43. “
EXTRAORAL PROSTHESIS

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.)

47. ◍Brass abutment replica analogs
with assembled Magna-cap
components
J Prosthet Dent. 1987:55;334-40.

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

51. Magnet retained intraoral-extra oral
combination prosthesis
J Adv Prosthodont. 2012 Nov; 4(4): 235–238.

52. Two piece magnet retained orbital
prosthesis
Dental, Oral and Craniofacial Research

53. Implant-retained skull prosthesis to cover
a large defect of the hairy skull
J Prosthet Dent 2016;

54. Orofacial rehabilitation with zygomatic
implants: CAD-CAM bar
and magnets

55. Implant-supported and magnet-retained oral-nasal
combination prosthesis in a patient with a total rhinectomy
and partial maxillectomy due to cancer

56. J Prosthet Dent 2016

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

61. “
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