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Effects of the Dental
Magnetic Keeper on MRI
-positional distinction-
Minoru Yoshida, Kazutoshi Furukawa, Tsutomu Takashima,
Yoshiharu Horii, Kanji Ishibashi, Shiori Itou* and Kimio Sakamaki*
Department of Fixed Prosthodontics, School of Dentistry,
Iwate Medical University
*Department of Dental Radiology,
School of Dentistry, Iwate Medical University
The purpose of this paper was to ascertain the degree of MRI
degradation due to the number and positioning of dental magnetic
keepers. The MAGFIT 600 KEEPER and HICOREX KEEPER MK40 were placed
within the head and brain stem regions and observed. The results were
as follows; l. MRI degradation was enlarged with an increase in the
number of keepers, and was dependent upon the distance from the
keeper. 2. The extent of MRI degradation was limited chiefly around
the tongue and hard palate regions. Although parts of the soft palate
and ethmoid regions also appeared to be affected, the brain stem was
not. 3. The extent and bulk of the MRI degradation was not affected
by the type of dental magnetic keepers. 4. MRI degradation within the
T2 weighted image appeared to be affected more than T1.
Keywords : dental magnetic keeper, MRI, degradation, brain
stem
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Soft Magnetic Stainless Steel
Powder filled Composites
Susumu Hirano, Tadashi Hirasawa
Department of Dental Engineering, Tsurumi University
School of Dental Medicine
Three experimental composites using two paste types were fabricated.
Two monomer formulations were used; bisMPEPP as a catalyst monomer,
and bis-MPEPP or bisGMA/TEGDMA as a base monomer. 17Cr-2Mo stainless
steel powder ( under 500 mesh) was used as filler. These composites
had a good shelf life. The composites containing 80-85 wt% filler
were easy to handle. These composites set about 3-4 min after the
start of mixing and showed about 5 kg/mm2 in flexural strength and 80-l40 gf in
attractive force to a commercially available magnet for denture
attachments. The values for the magnetic attractive force was 1/3-1/4
smaller than the keeper attached to the magnet.
Keywords : composite resin, soft magnetic stainless steel
powder, magnet, magnetic attractive force
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Corrosion Behavior of Stainless
Steels and Dental Precious Alloys Used for Dental Magnetic
Attachments
Yukyo Takada, Osamu Okuno
Department of Dental Materials Science, School of
Dentistry, Tohoku University
This paper discusses corrosion behavior of stainless steels and
dental precious alloys used for dental magnetic attachments. After
the stainless steels and dental precious alloys were immersed in
0.9%NaCl solutions at 37°C for 7 days, each eluate was analyzed
by ICP emission spectrochemical analysis. In the tests, Fe ions were
detected in the eluates of the stainless steels. The Elutions from
SUS304, SUS316L, SUS444 and SUS447J1 were l.06, 0.89, 0.97 and
0.32µ g/cm2, respectively.
According to their anodic polarization, a pitting corrosion potential
of SUS304 was 0.21 (V vs NHE) and it was the lowest potential among
all of them. The potentials of SUS316L and SUS444 were 0.3l and 0.52
(V vs NHE), respectively. SUS447J1 showed the highest potential with
about 1.27 (V vs NHE). These results suggested that SUS447J‚P showed
better corrosion resistance than the other stainless steels, and that
SUS444 seemed to show resistance as well as SUS316L.
In the same elution tests for dental precious alloys, a
12%Au-Ag-Pd alloy (CASTWELL MC) released Ag and Cu ions of 2.37 and
3.82 µ g/cm2‚ respectively.
Type IV gold alloy (FGA-2) released only Cu ion of about 2.97 µ
g/cm2.
Key Words : magnetic attachment, corrosion, elution test,
anodic polarization, natural electrode potential
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Influences of the Side Slot Form
of Magnetic Attachments on the Combining Force to Resin and the
Attractive Force
Shin Ishikawa, Hiroshi Mizutani, Minoru Ai, Takuya
Takahashi, Toshiaki Yoshino, Kazuo Nakamura
The First Department of Prosthodontics, Faculty of
Dentistry, Tokyo Medical and Dental University
The purpose of this study is to investigate the relationship between
side slot form of the magnetic attachment and the combining force to
resin. In addition, the attractive force of the magnetic attachment
with slot was analyzed by finite element method.
The results were as follows:
l. After the magnetic attachments covered with resin were immersed
in 37°C hot water for thirty-five days, the combining force to
the attachment without slot was 35.3N, while the combining force with
slot was 3~5 times as much as that without slot.
2. When the slot which had 0.4~0.8mm width and 0.1~0.4mm depth and
0.4~0.8mm below the top of the magnetic assembly was added to the
side of the magnetic attachment, the attractive force was 4.22~4.40N.
It seemed that the slot hardly influenced the attractive forces.
Keywords : magnetic attachment, side slot, attractive force,
combining force to resin, finite element method
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Methods of removal for a
Commercial Dental Magnetic Keeper
Shin-ichi Masumi, Mayumi Ozamoto, Hirofumi Kido, Masahiro
Arita, Masao Morikawa
Department of Removable Prosthodontics, Kyushu Dental
College
The aim of this study was to develop a method for removal for a
commercial dental magnetic keeper. Three types of removal methods are
discussed.
l. A revolving keeper, which is easy to fix and remove by
revolving the retention knob of the keeper.
2. A sliding keeper, which is easy to fix and remove by sliding a
tapered keeper.
3. A keeper with a screw, which is easy to fix and remove by using
a screw in the center hole of the keeper.
These three methods were easy to make and very useful as a
countermeasure for MRI. We also obtained good results from the
clinical application of a revolving keeper.
Keywords : dental magnetic attachment, MRI, removable keeper,
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Clinical Evaluation of the HICOREX
MD® Dental Magnetic Attachment
Masahiro Arita, Shin-ichi Masumi, Mayumi Ozamoto, Masao
Morikawa
Department of Removable Prosthodontics, Kyushu Dental
College
This recall study was a clinical evaluation of 46 patients treated
with the HICOREX MD® dental magnetic attachment
retained denture. 48 removable prostheses ( 23 in the maxillae and 25
in the mandible jaw ) were constructed by 18 practitioners. There was
a mean wearing time of 13 months ( ranging from 3 to 20 ). Patients
were generally satisfied. The absolute success rate of prosthesis was
89.5%. The number of abutment teeth used in applying the attachment
was 72. Of the 72 abutment teeth, an increase of tooth mobility was
seen in only 2 and periodontal disease was also seen in 2. In no
case, was there any indication for tooth extraction or for removal of
this attachment. A questionnaire about the clinical usefulness of
this attachment was answered by 14 practitioners. Although they
considered this attachment more useful than any other stud
attachments in clinical application, they requested that this
attachment be smaller in size and have higher attractive force.
Keywords : dental magnetic attachment, clinical evaluation
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A Statistical Study of the
Clinical Applications of the MAGFIT 600® Dental Magnetic
Attachment
Hirofumi Kido, Shin-ich Masumi, Masahiro Arita, Katsuaki
Takeya, Ryuji Chigusa, Masao Morikawa
The First Department of Prosthetic Dentistry, Kyushu
Dental College
The purpose of this study was to evaluate the prognosis of removable
prostheses using the MAGFIT 600. 42 removable prostheses, which have
been setting since April, 1992 were examined. One examination was
done when the prostheses were set and another was done after three
months. The first examination included a number of dental magnetic
attachments in each denture ; the types of prosthesis and the
gingival conditions; and the mobility and the pocket depth of
abutment teeth. The same items, their usefulness and a comprehensive
judgment of the prostheses were included in a second examination.
Furthermore, A survey about dental magnetic attachments was conducted
among dentists. The results were as follows; l. Because many dental
magnetic attachments were used in the posterior region of upper jaw,
the necessity of a removable keeper for measures against MRI was
suggested. 2. Dental magnetic attachments were most often applied to
over dentures. 3. Patients were satisfied with dentures with dental
magnetic attachments in regards to aesthetics and function. 4. Since
the gingival condition of some abutment teeth became worse after
setting of the dentures, the importance of abutment teeth cleaning
was suggested. 5. Many dentists answered that they could use dental
magnetic attachments positively. 6. Many dentists hoped for stronger
attractive force and smaller sized magnets, for further improvements
in dental magnetic attachments.
Keywords : dental magnetic attachment, MAGFIT 600, prognosis
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A Magnetically Retained Removable
Bridge And its Long Term Clinical Observation
Hideki Sasaki and Yohsuke Kinouchi*
Sasaki Dental Clinic
*Department of Electrical and
Electronic Engineering, The University of Tokushima
Magnetic force was used for retaining a telescope type of removable
was cast with a Pd-Co-Ni dental casting ferromagnetic alloy. The
magnetic attractive f bridge. The bridge was cast with a Pd-Co-Ni
dental casing ferromagnetic alloy. The magnetic attractive force was
generated between the outer crown of the bridge and the rare earth
magnet embedded in the abutment tooth which was covered by an inner
crown made of Au-Ag-Pd alloy. A male patient wore this type of
removable bridge for 6+6 in which the teeth 65| 3-6
were used as an abut met and porcelain was fused for 3+3. The
magnetic retention was not great at 420gf due to open magnetic paths.
However, the patient was very satisfied with this bridge.
The oral state of the patient and the bridge were observed for as
long a term as l4 years. Examining the long term usefulness of the
magnetic retention of a bridge was an important feature of this
paper. As a result, the bridge was able to be used for this term,
though magnetic force decreased gradually due to the corrosion of the
magnets. There was no loosening of the abutment teeth. Therefore,
this method was found to be very useful for the retention of a
removable bridge.
Keywords : removable bridge, dental casting ferromagnetic
alloy, long term observation
Copyright (c) The Japanese Society of Magnetic Applications in
Dentistry. All rights reserved.
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