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1 The application of Root Keeper system for handicapped patients

Yuh-Yuan Shiau

Professor and Director, Graduate Institute of Oral Biology, College of Medicine, National Taiwan University, Taipei, TAIWAN.

The application of Root Keeper System for handicapped patients For physically disable patients whose hands are not as skillful, insertion and withdrawal of a removable denture with clasps is more difficult than without clasps. Magnetic attachments provide sufficient retention of the denture through the magnetic attraction force between the magnet in the denture and the keeper on the abutment root. The retention of the denture remains high if not higher while withdrawal of it can easily be done just by pushing the denture sideward. The newly developed Root Keeper System provided magnetic retention force with a more convenient way, i.e., to insert the keeper with composite resin core material. The abutment root preparation, fitting the keeper in the root, and cementation and formation of the root cap with the keeper can be done in one visit. Impression of the root canal and casting of the waxed keeper pattern become unnecessary. Therefore the whole procedure can be performed in patient's home without laboratory work hence is more suitable for the handicapped patients. The present study reported cases of such application and discussed the merits and short comings of the Root Keeper System.

Poster 1

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2 A Simplified Approach to the Characterisation and Design of Magnetic Attachments

M.A. Riley^a, J.D.Speight^a, A.D.Walmsley^b, A.J. Williams^a and I.R.Harris^a

^a School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
^b School of Dentistry, St Chad’s Queensway, Birmingham, B4 6NN, UK.

A preliminary report was presented at the International Association of Dental Research conference (IADR ’99) in Vancouver, Canada. March 1999. Journal of Dental Research 1999;78:470 (Abstr. 2916).

Magnets have found wide use in the retention of dental prostheses and orthodontics. There have been several studies of the force (F) ?distance (x) relationship of these devices though none have been successful in modelling short gaps (less than 0.1mm) or contact forces. The present work describes how a simple analytical expression can be used to describe the observed force-distance relationship. The same expression serves as a design aid for characterising contact forces and force-distance at small separations. Force-distance measurements have been made on encapsulated and unencapsulated NdFeB magnets. These results, together with corresponding recently published data on dental magnets, have been analysed using the following techniques:
1) Force varying as 1/x2, where x is the distance of separation (Point magnet approximation).
2) Force varying as 1/x2, 1/x3 or 1/x4 (Linear or Cylindrical magnet approximation).
3) 1/square root of F versus x (derived from energy considerations in separating magnets).
4) Finite Element modelling of encapsulated magnets.

At separation distances of less than 0.1mm, methods 1) and 2) seriously over estimate the force-distance relationship. For separations over 0.1mm, all the analysed results show force-distance variation falling between 1/x2 and 1/x4, hence are predictable using method 2). For separations of less than 0.1mm, methods 3) and 4) provide a close fit for observed results and allow values of the contact force to be derived. Method 4) may be carried out using one of the available software packages for finite element analysis of magnet configurations. The expression of method 3) is, however, particularly useful in that it is simple to apply, fits all of the observed data and being approximately linear, allows straightforward derivation of contact forces and forces at specific separations. It may also be used as a method of measuring the thickness of magnetic coatings.

Poster 2

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3 Application of cast iron-platinum magnetic attachment to sectional collapsed complete dentures for an edentulous patient with microstomia: A clinical report

Ikuya Watanabe, DDS, PhD^a, Yasuhiro Tanaka, BS, MS^b, Chikahiro Ohkubo, DMD, PhD^c, Amp W Miller, DDS^d

^a Assistant Professor, Department of Biomaterials Science, Texas A&M University System, Baylor College of Dentistry, Dallas, Texas, USA.
^b Research Associate, Department of Dental Materials Science, Nagasaki University, School of Dentistry, Nagasaki JAPAN.
^c Instructor, Department of Removable Prosthodontics, Tsurumi University, School of Dental Medicine, Yokohama, JAPAN.
^d Professor, Department of Restorative Sciences, Texas A&M University System, Baylor College of Dentistry, Dallas, Texas, USA.

This clinical report described cast iron-platinum magnetic attachment system applied to sectional collapsed complete dentures for an edentulous patient with microstomia. With the use of the lingual and palatal midline hinges and Fe-Pt magnetic attachment, the sectional collapsed complete dentures could be successfully and easily installed and delivers adequate function in the patient's mouth.

Poster 3

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4 Fundamental Studies on Discoloration of Magnetic Stainless Steel -The influence of contact with different kind of metal-

T. Hikosaka^a, N. Mizutani^a, K. Hoshiai^a, Y. Tanaka^a, T. Satou^a, S. Okazaki^a, N. Muraji^a, H. Hirai^a and S. Tsuruta^b

aThe First Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University, Nagoya, JAPAN.
^bDepartment of Dental Materials Science, School of Dentistry, Aichi-Gakuin University, Nagoya, JAPAN.

Magnetic attachments have been tried, not only on the retainers of partial dentures, but also on overdenture and implants. The use of a magnetic attachment to the superstructure, may cause galvanic corrosion between the implant made by titanium alloy and the magnetic stainless steel (AUM20). In this study, we examined the discoloration of magnetism stainless steel (AUM20) in or out of contact ( gap 0.2mm ) with pure titanium (Ti), Ti-6Al-4V (Ti64) and Ti-29Nb-13Ta-4.6Zr (TNTZ) in 0.9%NaCl, 0.1MNaF, and 0.3MNaF solution after 3, 7, 14days respectively.
In each solution, the discoloration increased when out of contact in comparison with the ones in contact in the case of AUM20, Ti, Ti64 and TNTZ respectively. In the NaF solution, the discoloration of Ti, Ti64 and TNTZ greatly increased according to time, but, in AUM20, it was slight regardless of whether the metals were in contact or not. However, the discoloration of AUM20 was increased by combining Ti, Ti64 and TNTZ.

Poster 4

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5 Longitudinal Study on the Metal Plate Denture with Magnetic Attachments

M. Kawakita^a, K. Hoshiai^a,b, Y. Tanaka^a, N. Hasegawa ^a,b, N. Nozaki^a,b, T. Tadakoshi^a, W. Fujinami^a and A. Fuma ^a

^aThe First Department of Prosthodontics, School of Dentistry Aichi- Gakuin University, Nagoya, JAPAN.
^b Maguno Prosthetic Clinic, School of Dentistry, Aichi-Gakuin University, Nagoya, JAPAN.

The magnetic attachment was developed for the retainer of the partial denture and has become popular all over the country in a rather short time. But several clinicians desired a smaller design attachment with increased retentive force. The Magfit-EX developed and improved these clinical problems.
At present, about 10 years has passed since the magnetic attachment was applied clinically. The aim of this study is to investigate the long-term usefulness for prognosis of the magnetic attachment "Magfit" that can be used in the metal plate partial dentures. The evaluation was done "Magfit" in 756 plates at Aichi-Gakuin University Dental Clinic between 1993 and 2001. The metal plate dentures were introduced in 96 plates and was used in 225 abutment teeth.
The distribution of magnetic attachments of the whole teeth in maxilla and mandible were established as being the most commonly used to maxillary canine. The second is the mandibular canine, followed by the maxillary first premolar. In combined use situation with another type of retainer, the number of metal plate denture decreased as the number of attachments increased. The duty cycle for the remaining teeth tends to decrease, as their number increase.

Poster 5

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6 Intensity Comparison Test of Magnetic Extracoronal Attachment

T. Yamamoto, Y. Desaki, Y. Tanaka, N. Hashimoto, T. Ishida, Y. Nakamura, K. Tsuda, T. Miyata, D. Maeno and S. Miwa

The First Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University, Nagoya, JAPAN.

A magnetic attachment is an anchor for the pulpless tooth. It is fundamentally impossible to use a magnetic attachment for a vital tooth. The reason is that when the magnetic assembly is used on the crown there occurs a space shortage between the upper and lower occlusal surface. For this reason, the use of a magnetic attachment on a vital tooth corresponds to that of an extracoronal attachment.
We produced a standardized plastic pattern for the complex shapes of the extracoronal parts. The keeper tray is attached to the ready-made pattern to facilitate technical hand operation. The breaking strength of the pattern was then tested and two-dimensional finite element method was also used. The pattern was shown to be clinically usable without any problem.

Poster 6

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7 Effects of ELF magnetic fields on physiological functions in osteogenesis

Yoshiko Nakano^a, Keiko Hosokawa^b, Hisao Yamaguchi^b, Ki Ho Park^a, Toshitaka Ikehara^b, Mitsuo Kitamura^b, Yohsuke Kinouchi^a, Kazuo Yoshizaki^b, Hiroshi Miyamoto^c

^a Department of Electrical and Electronic Engineering, Faculty of Engineering, The University of Tokushima, Tokushima, JAPAN.
^b Department of Physiology, School of medicine, The University of Tokushima, Tokushima, JAPAN.
^cDepartment of Life, Environmental and Information, Faculty of Domestic Science, Tokushima Bunri University, Tokushima, JAPAN.

The objective of this study is to examine the physiological effects of exposure to ELF magnetic fields of intracellular signal transduction in cultured osteoblastic like cells(MC3T3-E1) at the growing and the differenciated state. Triiodothyronine(T3),a Regulator of Osteoblastic Differentiation. ELF exposure or T3 treatment showed similar positive effect on immunostaining with a osteocalcin antiserum,also the additive effects were apparently showed with higher persentage of positive cells when ELF exposure and T3 treatment was combined. Although PKC activity of growing cells was inhiited by ELF exposure,T3 treatments brought to little effect on PKC activity.Also,T3 had no effect for the inactivation of PKC induced by ELF exposure.
These results indicate that the mechanisms related to signal transduction involved with PKC from the growing stage to the differentiated stage in osteoblasts were altered by the magnetic fields of extremely low frequency.

Poster 7

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8 Role of Teeth Clenching in Head Posture and Body Sway

Shinsuke Tanaka, Yatomo Kibana, Tsutomu Ishijima, Yuichi Yokoyama, Hisashi Koshino, Toshihiro Hirai

Department of Removable Prosthodontics, Health Sciences University of Hokkaido School of Dentistry, Ishikari-Tobetsu, JAPAN.

In this study, the relationship among stomatognathic function, body equilibrium and head posture in teeth clenching was discussed. In 6 healthy, fully dentate males (mean age 29.8±2.0), body sway was recorded by the stabilometer (NEC medical systems, EB1101) and the head posture was also recorded simultaneously by the electromagnetic, six-degree-of-freedom tracking instrument (POLHMUS Co. Fastrak) outputting three-dimensional coordinates and orientation angles to each axis of coordinates. While standing on the stabilometer under the eyes closed condition, a force disturbing the body balance(8.82J) was applied. The body sway and the head posture were recorded at both the intercuspal position with the voluntary maximal clenching(VMC) and the mandibular rest position(RP) during the dynamic event and analyzed. From the analysis of head posture, the total locus length in RP was statistically greater than that in VMC (p<0.05). From the analysis of body sway, the total locus length, the locus length per second, and the area of sway (root mean square value) and the lateral body sway (maximum value) in RP were statistically greater than those in VMC (p<0.05). It is speculated that the teeth clenching play a role of stabilizing the head posture and the body sway against the force disturbing the body balance.

Poster 8

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9 Application of cast iron-platinum keeper to collapsed denture for a patient with constricted oral opening: A Case Report

Chikahiro OHKUBO^a, Yoshihiro MAEDA^b, Ikuya WATANABE ^c, Naoki BABA^c, Yasuhiro TANAKA^d, Toshio HOSOI^a

^a Dept. of Removable Prosthodontics, Tsurumi University School of Dental Medicine, Yokohama, JAPAN.
^bThe Dental Technician Training Institute, Tsurumi University School of Dental Medicine, Yokohama, JAPAN.
^cDept. of Biomaterials Science, Baylor College of Dentistry, Texas, USA.
^dDept. of Biomaterials Science, Nagasaki University Faculty of Dentistry, Nagasaki, JAPAN.

I. The ability to fabricate a denture for patients with constricted oral opening is problematic. Insertion of the denture into the mouth is especially difficult in the extraordinary limited oral opening. Thus, the collapsed removable partial denture with cast iron-platinum attachment was fabricated so that it can be inserted into mouth.

II. A 69-year-old partially edentulous woman with constricted oral opening by rheumatoid and craniotomy for subarachnoid hemorrhage.

III. Making definitive impression and registration of interocclusal relation bite were performed using sectional custom tray and sectional occlusion rim, respectively. Right side of denture base was composed upper and lower segments and they were collapsed with hinge. Since there is small space between maxillary natural teeth and mandibular ridge, the cast iron-platinum keeper and three commercial magnets (Hicorex-slim) were used for assemble of two segments. No problem has been observed both intra-oral and the denture for a service period of one year.

Poster 9

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10 A Study on Electro-Magnetic Interferences for Cardiac Pacemakers cause of Dental Electric Equipments

Takeo Suga, Ryohei IIDA, Koufuchi RYO, Shigeo HORIE, Kumiko MARUYA,Mitsuhiko MORITO

Dept. of Geriatric Dentistry, Tsurumi Univ. School of Dental Medicine, Yokohama, JAPAN.

no information

Poster 10

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11 The Effect of Occlusal Supracontact on the Tooth Deformation

Takayoshi Oshio, Motoharu Kori, Toyoko Satsuma, Shuji Shigemoto, Keisuke Nishigawa, Hisahiro Takeuchi, Masanori Nakano, Eiichi Bando

Department of Fixed Prosthodontics, School of Dentistry, The University of Tokushima, Tokushima, JAPAN.

The purpose of this research was to investigate the effect of Occlusal supracontact on the tooth deformation. Three adult male volunteers (age: 32, 30 and 29) were participated in this study. Tin foils were attached to the palatal cusp of subjects 1 & 2 and the buccal cusp of subjects 2 & 3 as experimental occlusal interference. A specially manufactured small transducer that could detect micro deformation was utilized to evaluate vertical tooth deformation during maximum clenching at the intercuspal position. This device was attached on the buccal surface of the tooth. Without occlusal interference, maximum amplitude of tooth deformation were 54 nm/mm (subject 1), 5 nm/mm (subject 2) and -20 nm/mm (subject 3). Maximum deformation with 100 オm tin foil interference were 82 nm/mm, 40 nm/mm, -54 nm/mm, -81 nm/mm respectively. Positive values represent extension of the buccal surface of the tooth and negative value represents shortening of that. Forceful clenching on the excessive occlusal contact caused large tooth deformation. These results indicated that excessive occlusal contacts might have harmful effects not only on periodontal tissue or stomatognathic system but also on tooth structure itself. They also suggested importance of proper occlusal adjustment of prosthesis in daily dental practice.

Poster 11

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12 Vibrational Assessment of the Stability of Root Keeper

Che-Tong Lin, Cheng-Chung Chang, Haw-Ming Huang, Yuh-Yuan Shiau and Sheng-Yang Lee

College of Oral Medicine, Taipei Medical University, , Taipei, TAIWAN.

Abs

Poster 12

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13 Effects of Intermittent magnetic fields on transient increase in intracellular Ca2+ concentration in pheochromocytoma cells
- For the application to frontier medical treatment.-

Ki Ho Park^a, Toshitaka Ikehara^b, Hitoshi Houchi^c, Hisao Yamaguchi^b, Yohsuke Kinouchi^a, Kazuo Yoshizaki^b, and Hiroshi Miyamoto^d

^a Department of Electrical and Electronic Engineering, Faculty of Engineering, The University of Tokushima, Tokushima, JAPAN.
^b Department of Physiology, School of Medicine, The University of Tokushima, Tokushima, JAPAN.
^c Department of Pharmacy, School of Medicine, The University of Tokushima, Tokushima, JAPAN.
^d Department of Life, Environment and Information, Faculty of Domestic Science, Tokushima Bunri University, Tokushima, JAPAN.

Studying on effects of magnetic fields for various cellular functions will lead to new applications to frontier medical treatment, e.g., regenerative medicine, biomaterial, biological repair, etc. In this study, we report the effects of intermittent magnetic fields on the responsiveness of pheochromocytoma cells (PC12 cells) by addition of several stimulants. Magnetic fields are produced by an electromagnet designed and set up by Hitachi Metal Indust. Co. This system produced intermittent magnetic fields varied between 0.07 to 1.5 T at an interval of 3 seconds. We tested the effects of the intermittent magnetic fields on increase in intracellular Ca2+ concentration ([Ca2+]i) of PC12 cells by addition of 30mM caffeine. The increase in [Ca2+]i was inhibited by 2 hours-exposure under balanced salt solution excluding Ca2+ (Ca2+-free BSS), but was unaffected under balanced salt solution (BSS). When the medium was changed to BSS with 1μM thapsigargin after the cells were incubated in Ca2+-free BSS for two minutes, the [Ca2+]i was increased strongly. But, the increase was not influenced by the exposure. Therefore these results suggest that the intermittent magnetic fields inhibit the Ca2+ release from intracellular Ca2+ stores of PC12 cells but not Ca2+ influx via cell membrane.

Poster 13

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14 Various Approaches and Possibilities of Magnetic Attachment to Implant Superstructure

Sung-Bok LEE^a, Boo-Byung CHOI^b

^aProfessor, Head of Division of Partial Removable Prosthodontics, Department of Prosthodontics, Kyung Hee University, Seoul, KOREA.
^b Professor, Head of Division of Fixed Prosthodontics, Department of Prosthodontics, Kyung Hee University, Seoul, KOREA.

This presentation is to show and evaluate the clinical application and laboratory work for the magnetic attachment to provide more effective function in various situations of implant-supported/assisted overdenture. The selection of a specific attachment depends on various factors: (1) the type of overdenture to be fabricated, (2) the relative importance of stability and retention, (3) the condition of the residual alveolar ridges, (4) the length and number of the implants used, (5) the esthetic requirements, (6) the dexterity of the patient in being able to insert and remove the prosthesis, (7) the psychological needs of the patient, (8) the position of the implants within the ridge, and (9) the controlled force to prevent the torque on the implants.

As for the magnetic attachments, in principle, the same indications may apply for both magnet and stud attachments. But, the advantages of the magnetic attachment are that the horizontal forces against the implant are practically eliminated, and that it allows some freedom in regard to the path of insertion although orientation between the implants is not parallel if they have a Bar-joint structure.

Two types of magnetic attachment for the implant-supported bar-joint structure(Magfit-EX600 and Magfit-EX400, Aiichi Steel Work, Japan) and three types of MagneDisc(MagneDisc, MagSoft, and MadneDisc Dome-top, Aiichi Steel Work, Japan) for the implant assisted overdentures were used, and I applied the magnetic attachments to implant-supported/assisted overdenture in 45 patients from 1997 as a member of IRPMD(International Research Project of Magnetic Dentistry, Hiranuma Project). There was no implant failure, and no decrease or change in attractive force of the magnetic attachments over 5 years.

The overall results suggest that the magnetic attachments combined with bar structure can provide a controlled attractive force, effective horizontal stability, and proper support for implant overdenture prostheses, and effectively avoid harmful stress to the implants in severely lowered alveolar ridge.

Poster 14

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15 A Proposed Classification Method For Complete Overdentures (Sakurai's Classification)

Naoki Tsukimura, Tomohiko Ishigami, Hiroshi Sakurai, Shigeru Ohno, Tetsuo Ohyama, Masaaki Ohwa, Hitoshi Toyoma

Nihon University School of Dentistry Department of Removable Partial Denture Prosthodontics, Tokyo, JAPAN.

It is best to visually and manually examine a patient when we want to know details regarding what is inside the oral cavity, and consider treatment options. However, it is frequently impossible for a doctor, other than the patient's regular doctor, to have access to this information. In the past, when an information exchange was necessary, Kennedy's and Eichner's classification methods were applied as a means to understand these type of cases. The usefulness of these classification methods is widely known. With the popularization of magnetic attachments in recent years, we have come to frequently use the method of making an overdenture using a rhizoplane attachment on the anchor tooth. Along with this change, we need to simplify overdenture classification to facilitate its use as a means of exchanging ppatient information. However, this proposed classification method has not yet been suggested. In this study, we focused on the supportive function of the coping installed under the denture base, and would like to propose an idea regarding the classification method of canine tooth-centered complete overdentures. The following is a report of this study.

Poster 15

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16 Dental Casting Fe-Pt magnetic alloy for Removable Prosthetic Appliance

T. Kanno^a, T. Nakayama^c, O. Okuno^b, K. Kimura^a

^a Division of Fixed Prosthodontics, Tohoku University Guraduate School of Dentistry, Sendai, JAPAN.
^b Division of Dental Biomaterials, Tohoku University Guraduate School of Dentistry, Sendai, JAPAN.
^c The Research Institute for Electric and Magnetic Materials, Sendai, JAPAN.

The ready-made magnetic attachments have been increasingly applied to dental clinical use. These attachments are made by rare earth permanent magnets and stainless steel yoke and cover. However there are some problems to use these ready-made magnetic attachments for removable prosthetic appliances, such as size, workability, etc. For solving these problems, a new system utilizing the castable magnets were designed. In this system, removable prosthetic appliances were made by dental casting technique using the castable magnetic alloys. The outer caps of the removable prosthetic appliance is the Fe-Pt magnet casting and inner caps is the magnetic stainless steel casting. Composition of the Fe-Pt magnet for the outer caps are Fe, 36-40mole%Pt, and very small amount of Nb and Si. Both of the Fe-Pt magnet and the stainless steel have the excellent magnetic properties and corrosion resistance. The aim of the present study was to evaluate the possibilities of clinical applications of Fe-Pt magnetic alloys for use in dental casting. In this study, optimum additional elements of these Fe-Pt-Nb-Si magnetic alloys for dental casting was investigated, and then their attractive force, mechanical property, and elusion were also investigated.

Poster 16

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17 Effects of ELF Magnetic Fields on Neuronal PC12 cellsTitle

R. Murato^*, K. H.Park^*, T. Ikehara^**, H. Houchi^***, Y. Kinouchi^*, K. Hosokawa^**, H. Yamaguchi^**, K. Yoshizaki^**, H. Miyamoto ^****

^* Department of Electorical and Electronic Engineering, Faculty of Engineering, The University of Tokushima, Tokushima, JAPAN.
^** Department of Physiology, The University of Tokushima, Tokushima, JAPAN.
^*** Department of Pharmacy,School of Medicine, The University of Tokushima, Tokushima, JAPAN.
^**** Department of Life, Environment and Information, Faculty of Domestic Science, Tokushima Bunri University, Tokushima, JAPAN.

Shignificant effects of exposure to magnetic fields produced by electronic devices on human body have been reported in recent years. We 　studied the effect of extremely low frequency (ELF) magnetic field on the differentiation of pheochromocytoma (PC12) cells in the presence of nerve growth factor (NGF) in this experiment. This ELF magnetic field produced by solenoid coils was sinusoidal (60Hz) and their rms values were from 1.25 to 3　mT. During exposure, the cells were cultured for 2-4 days in special incubator at 37℃. We evaluated the differentiation of the cell by measuring the length of neurite outgrowth. Exposure to the presence of NGF. When theconcentration of K+(30-40mM) in the medium was increased, it caused a further extention of neurite outgrowth. These results suggest that eddy current induced by ELF magnetic field affect the electric properties on PC12 cell membrane and stimulate the neurite outgrowth of PC12 cells in the presence of NGF.

Poster 17

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18 Photoelastic stress analysis for overdentures supported by roots and implants retained with Magsoft and Magnedisk magnetic attachment

Yimin Zhao, Shizhu Bai

College of Stomatology, Fourth Millitary Medical University. Shaanxi Province, The People's Republic of China.

Poster 18

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19 Development of titanium-posted keeper-removable magenic attachment

Lihong Lin, Yimin Zhao

College of Stomatology, Fourth Millitary Medical University. Shaanxi Province, The People's Republic of China.

Poster 19

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20 Corrosion Resistance of Magnetic Stainless Steel Keeper for Dental Magnetic Attachment

Osamu Okuno^a, Yukyo Takada^a, Masafumi Kikuchi^a and Kohei Kimura^b

^aDivision of Dental Biomaterials, Tohoku University Graduate School of Dentistry, Sendai, JAPAN.
^b Division of Fixed Prosthodontics, Tohoku University Graduate School of Dentistry, Sendai, JAPAN.

In dental magnetic attachment system, magnetic stainless steel keeper is used by fixing on precious metals root cap by cast bonding or cementing. SUS 444 or SUS 447J1 stainless steel are employed for magnetic stainless steel keeper. The purpose of the present paper was to discuss corrosion behavior of the magnetic stainless steel and possibility of the galvanic corrosion of the magnetic stainless steel coupling with casting precious alloys in oral environment. The corrosion resistance of the stainless steels was investigated through elution test, corrosion potential and potentiodynamic polarization curve in 0.9%NaCl at 37oC. The elusions of Fe ion from the magnetic stainless steels were equal to or lower than that of SUS 316L stainless steel for surgical implants. Comparing the anodic polarization curves of the magnetic stainless steels and the cathodic polarization curves of the dental casting precious alloys, the galvanic corrosion of the magnetic stainless steels was discussed.

Poster 20

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21 Characteristics of a split pole type of magnetic attachment

Masahiko Mukai^a, Yoshinori Tegawa^b,Yohsuke Kinouchi^a

^a Department of Electrical and Erectronic Engineering,The University of To kushima, Tokushima, JAPAN.
^b School of Health Sciences,The University of Tokushima, Tokushima, JAPAN

With spreading clinical uses of magnetic attachments placed on the m arket, a new magnetic attachment with different retention characteristic s has been required for more functional denture retention. Retention of a magnetic attachment is characterized by magnetic force at zero gap and at non-zero gap, typically 0.1 mm gap, where the gap means the separat ion between a magnetic assembly and a keeper. One of the clinical requir ement is to develop the magnetic attachment which holds relatively high magnetic force for the presence of a gap. This means that the attachment can provide higher stability and higher gapped-retention which are usef ul for effective retention of dentures.
For this requirement, new split-pole types of magnetic attachment ha ve been developed and analyzed theoretically as to magnetic retention ch aracteristics. As a result, it can supply large stability and gapped ret ention twice higher than that of usual attachments on the market. Thus, the magnetic attachment may extend the application scope of clinical use.

Poster 21

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Clinical Obsevations of Dental Magnetic Attachments

Hiroshi Mizutani^a

^a Graduate School, Tokyo Medical and Dental University Division of Oral Health Sciences Department of Masticatory Function Rehabilitation Section of Removable Prosthodontics, Tokyo, JAPAN.

More than 10 years have passed since dental magnetic attachments were applied to clinical use. As they utilize magnetic attractive force in place of friction, it is said that their retentive force is numerical and durable. However, it is not clear whether the problems of corrosion, wear and/or decreasing retentive force are occurred under the condition of oral cavity. 50 patients( 17 men and 33 women, ave.68.7 years) directly treated by the presenters were used in this study. The period after insertion of magnetic dentures extended from 0.5. to 6.5 years. The investigated items were (1) the corrosion, wear and retentive force of magnetic attachments and (2) the mobility, depth of pocket and alveolar bone height of abutment teeth. The results were as follows; 1)Regarding the magnetic attachments ① Cases with corrosion were not found ② In 3 teeth out of 75 abutment teeth color changes of the attachments were found. ③ On 5.5 year attachments, only slight scratches were found. 2)Regarding the abutment teeth ① Many cases with decreasing the depth of pockets and the tooth mobility were found during this period ② Cases with remarkable decreasing alveolar bone were not found.

Poster 22

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A Magnetic Measurement System for Jaw Movements Using Neural Networks and NLS Method

Xu Zhang^a, Masatake Akutagawa^b, Qinyu Zhang^c, Hirofumi Nagashino^c, and Yohsuke Kinouchi^c

^a Harbin Institute of Technology,Harbin, The People's Republic of China
^b School of Health Sciences, The University of Tokushima, Tokushima, JAPAN
^c Faculty of Engineering, The University of Tokushima, Tokusima, JAPAN.

Measurement using a small magnet are well-known method to measure the jaw movement. But the use of conventional methods are limited to the measurement of position of only one magnet because it is difficult to obtain precise solution using fast calculation. In the proposed system, the artificial neural network is used to realize a mapping from magnetic field to positions and orientations of the magnets. In addition, we make use of the Nonlinear least-square (NLS) method for precise measurement. Results of computer simulations indicated that the system has capability to measure the movement of one or two magnets in sufficient accuracy, and it can realize a real time measurement system for upper and lower jaw movement.

Poster 23

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Development of New Magnetic Attachments for Spreading Clinical Applications

Tegawa Yoshinori^a, Mukai Masahiko^b, Kinouchi Yohsuke^b

^a School of Health Sciences, The University of Tokushima, Tokushima, JAPAN.
^b Faculty of Engineering, The University of Tokushima, Tokushima, JAPAN.

Magnetic attachments are used extensively in the world as an effective retention device for dentures. Two types of magnetic attachment with different closed field paths, i.e., a cup type and a sandwich type, have been placed on the market by two makers in Japan, and are now applied for various clinical cases successfully. According to their spreading applications, various retention properties are required clinically to realize better functional prosthesis.
The retention properties of magnetic attachments are represented by the relation of magnetic force and a gap between a magnetic assembly and a keeper. The magnetic force at zero gap is used as normal retention, and the force with a gap, e.g., 0.1 mm, provides stability and gapped retention. These two forces should be combined effectively for better retention according to clinical cases.
To solve this clinical requirement, the authors have proposed various new types of magnetic attachment, i.e., two modified split-pole types and a cylinder type, which are analyzed and examined on their retention properties and clinical advantages, including the usual cup and sandwich types. As an example of results, a modified split-pole type gives higher stability and a cylinder type has smaller gapped retention with high zero gap retention.

Poster 24

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