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Introduction
More than
a decade has passed since magnetic attachments for dentures were
manufactured and marketed for the first time in Japan. The magnetic
attachments have become increasingly compact, from a rectangular
parallelepiped shape of 4.2 mm ´
3.2 mm
´
2.5 mm, to a disk shape of 3.6 mm in diameter and 1.2 mm in height.
The magnet material has changed from Sm2Co17
to NdFeB and their clinical use has
expanded. Although several reports1-3) discuss the service lives of
magnetic attachments, these are experimental predictions and do not
deal with the loss of magnetic force in actual clinical cases.
Therefore,
the authors studied problems reported by two patients with magnetic
attachments and one patient with a magnetic implant. The patients
with magnetic attachments visited our annex hospital after more than
five years of attachment and complained of a loss of magnetic force.
In the case of the magnetic implant, examination revealed
considerable damage to the keeper and magnetic assembly. In the
present report, we observed the adsorption and keeper surfaces of
the magnet structures under a microscope and studied the loss of
magnetic force and abrasion in these areas.
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Cases
Patient
1 Male
aged 63
1999 |
Using a Magfit
EX600 with right maxillary first premolar,
left maxillary incisors and left maxillary first premolar as supporting teeth, an
complete over-denture was inserted. When a metal-base denture was
fabricated six months later, a magnetic attachment was implanted for
the denture. At annual recall, no abnormality was detected. |
2004 |
The patient visited the hospital, complaining of a low retention of
the denture, and upon examination the attachment was revealed to be
damaged. |
Patient
2 Female
aged 79
1994 |
Using a Magfit 600
with right maxillary second premolar, left maxillary first premolar, and
left maxillary second molar as abutment teeth, a complete over-denture was
inserted. |
2000 |
Because of periodontal disease, left
maxillary second molar was extracted. |
2001 |
Because the magnetic attachment had detached from left maxillary
first premolar and was lost, a
new Magfit EX600
was inserted. |
2002 |
A new denture was fabricated and a magnetic attachment was moved to
this denture. |
2003 |
Coping had come off from right maxillary
second
premolar because of caries and was reattached. |
2004 |
The patient visited the hospital, complaining of low retention, and
examination revealed that coping had detached from right maxillary second
premolar
and the
magnetic attachment at left maxillary second premolar was damaged.
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Patient
3 Male
aged 53
2000 |
A right and left maxillary canines implant operation was performed
and a second operation was performed six months later. |
2001 |
Together insertion of a maxillary denture, a dome-type Magfit
IP
was attached. |
2004 |
Wrench insertion to check the magnetic keeper could not detect any
looseness, however, the magnetic attachment was replaced due to
changes noticed on the keeper surface.
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Table
1 Outline of cases
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Method
The magnetic forces of
the magnetic attachments obtained from the patients were measured on
a Dental Magnet Tester
(DMT-TW, Aichi MI). The surfaces of the magnet keepers
and implant keepers were observed under a Digital Microscope
(VHX-200, Keyence).
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Results and
Discussion
For Patient
1, all of the three Magfit
EX attachments no longer had any magnetic
force. Under a microscope, all the magnets were found to be damaged
at the micro-laser welded sections and the magnet
cases were found to be deformed. Metallic
corrosion, scratches, and abrasions were also apparent. A magnet
case used for an anterior tooth was partially chipped. Damage to the
magnet cases might have caused the magnets to corrode and thereby
lose their magnetic force. Deformation of the magnet cases and
damage to the welded sections seemed attributable to the occlusal
force concentrated on the magnet cases. These experimental
observations indicate the necessity of stress endurance testing.
For Patient
2, the magnetic force of the
Magfit 600 attached 10 years ago was 600 gf, similar to the
initial value. Microscopic observation did not show any significant
deformation. Although slight corrosion and abrasion were observed,
the magnetic force was retained. However, the Magfit
EX600, which had replaced a previous
attachment five years before, no longer had any magnetic force. AS
with Patient 1,
the attachment of Patient 2 showed deformation, destruction of the
welded sections, and chipping over the entire keeper surface of the
magnet case.
For Patient
3, the two Magfit
IP attachments showed a magnetic force of
600 g, unchanged from the original. Under a microscope, both the
keeper and magnet structure were found to be unevenly abraded. Since
Magfit IP is a dome-shaped magnetic attachment, slight movements of
the denture seem to have caused the magnet abrasion.
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Conclusion
Judging
from the results of microscope examinations of magnetic attachments
used over a long period, it is necessary to recall the users of
magnetic attachments
periodically and to examine the attachments carefully with regard to
the balance of factors including the base teeth, the mucous membrane
and the occlusion. If the magnet structure and keeper surfaces are
observed and considerable changes are detected, replacing the magnet
structure or keeper will greatly affect the long-term prognosis of
the denture.
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References
1) Shuiau
Y.Y.:Magnetic attachment reserch in asian region.Clinical application of magnetic attachment -abstracts
of international symposium-:29-36,2000.
2) Mizutani Y.,Ogura
R., Kakumoto Y.et al.: A single
case of corroded magnetic attachments
to implants. J Jpn Soc Oral Implant 12:584-590,2000.
3) Endo K., Suzuki
M. and Ohno H.;Corrpsion Characteristics of ferric austenitic steels
for dental magnetic attachment. Dent Mater J 19:34-49,2000.
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