abstracts2-1-e

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Improvements of the Cup Yoke Magnetic Attachment by Use of a Thinner Shield Ring

Osamu Okuno, Yuhkyo Takada, Kazuo Nakamura^*, Hiroshi Mizutani^*, Minoru Ai^*, Yohsuke Kinouchi^**, Hirohide Yamada^*** and Hiroya Suzuki^****

Department of Dental Materials Science, School of Dentistry, Tohoku University
^*The First Department of Prosthodontics, Faculty of Dentistry, Tokyo Medical and Dental University
^**Department of Electronic Engineering, Faculty of Engineering, The University of Tokushima
^***Magnetic and Electronic Materials Research Laboratory, Hitachi Metals, Ltd.
^****Hitachi Metals Technox, Ltd.

The purpose of this study was to improve the cup yoke magnetic attachment by reducing the width of the shield ring. The optimum dimension was derived through finite element method and experimentation. The performance of the improved magnetic attachment was also investigated. The results may be summarized as follows :

(1) The optimum width of the shield ring was 0.25mm. On average, the break away force of the 0.25mm shield ring attachment was 449 gf using a ø4.4mm keeper and 482 gf using a ø4.0mm keeper. Cutting of the cup yoke bottom corner also increased the break away force.

(2) The shift between the keeper and the magnet structure had a small effect on break away force.

(3) Trimming of the keeper side did not affect the break away force.

(4) The maximum magnetic leakage on the side of the attachment was about 3 mT by FEM calculation.

Keywords : magnetic attachment, finite element method, retention, cup yoke

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Experimental Observations of an Effect of Dental Magnetic Attachments on a Cardiac Pacemaker

Hidetoshi Miyata, Yoshinobu Tanaka, Tomohiko Ishigami, Yasuo Kishimoto, Hironobu Kiba, Kazuo Arai^* and Yoshinobu Honkura^*

The First Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University
^*Technical Research Section Electronics Development, Aichi Steel Works, Ltd.

Cardiac Pacemakers are being used by more than ten thousand Japanese who have experienced cardiac trouble such as sick sinus syndrome or atrioventricular block. These pacemakers are commonly considered by medical equipment which is influenced considerably by outside magnetic fields. The purpose of this paper is to investigate the influence of dental magnetic attachments on the function of cardiac pacemakers. A couple of cardiac pacemakers were studied with electric magnets and actual dental magnetic attachments. The results showed that certain types of cardiac pacemakers are definitely affected by magnetism. However, the minimum level was confirmed to about 60mT. Although magnetic flux leakage was measured on several commercially available magnetic attachments, the maximum flux distributed on the surface of each attachment was only between 2.0~55.0mT. As the above experiment results show, cardiac pacemakers are not affected by dental magnetic attachments

Keywords : cardiac pacemaker, magnetic attachment, leakage magnetic flux, magnet rate

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A Study of Small Sized Magnetic Attachments for Mandibular Incisors

Hiroshi Mizutani, Kazuo Nakamura, Minoru Ai, Shin Ishikawa and Osamu Okuno^*

First Department of Prosthodontics, Faculty of Dentistry
^*Department of Dental Materials Science, School of Dentistry, Tokyo University

For mandibular incisors, dental magnetic attachments are required to be smaller size than usual. The purpose of this study is to develop new smaller magnetic attachments and to investigate the possibility of the clinical use of these attachments. The results were as follows ;

1, A ø2.8×2.1mm cup yoke type magnetic attachment was developed for the mandibular incisors.

2, The attachment sealed ring of 0.2mm width produced higher attractive force than that of 0.1mm width.

3, The Nd-Fe-B magnet with a cup yoke of SUS 430 stainless steel achieved the highest attractive force of 260gf, which showed us the possibility of clinical use.

Keywords : magnetic attachment for mandibular incisor, attractive force, Nd-Fe-B magnet

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Basic Studies on the Application of Neural Networks for Measurement of Jaw Movements Using a Magnetic Sensor System

Masatake Akutagawa and Yohsuke Kinouchi

Department of Electrical and Electronic Engineering, Faculty of Engineering, The University of Tokushima

The purpose of this study is to examine the applicability of neural networks for measuring jaw movement using a magnetic sensor system. Estimation of magnet position and direction from sensor outputs is an inverse problem. Two types of neural networks were applied here to solve this problem. It has been found from computer simulation that the networks give reliable data and, therefore, they can be used for measuring jaw movement. Resultant accuracy for position measuring has been about 2% on average which is not high enough for practical use. Increasing the accuracy is a problem that will be addressed in the future by optimizing the network with respect to network structure and learning method.

Keywords : jaw movement, magnetic measurement, neural network, inverse problem

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Effects of Homogeneous Magnetic Fields on Potassium (Rubidium) Ion Transport of HeLa Cells at Different Temperatures

Toshitaka Ikehara, Hisao Yamaguchi, Keiko Hosokawa, Akira Takahashi, Yohsuke Kinouchi^* and Hiroshi Miyamoto^**

Department of Physiology, School of Medicine, The University of Tokushima
^*Department of Electrical and Electronic Engineering, Faculty of Engineering, The University of Tokushima
^**General Education, Tokushima Bunri University

We studied the effects of homogeneous magnetic fields on the membrane K⁺ transport of HeLa cells by Rb⁺ influx determination. To keep the temperature of the cultures constant, a specially designed incubator was used. Both ouabain-sensitive and -insensitive Rb⁺ uptakes of the cells were not significantly affected when exposed to homogeneous magnetic fields of 0.5, l, 1.5 and 1.6T. At various temperatures from 15 to 45°C, exposure of the cells to a magnetic field of 1. 5T showed no significant influences on the ouabain-sensitive and -insensitive Rb⁺ influxes. Evidence of phase transition of the cell membrane was not detected either. With respect to the Arrhenius plot of the data from Rb⁺ influxes and the activation energies calculated from the slopes of the lines, statistic regression lines were not influenced by magnetic fields of 1.5T.

Key word : HeLa cells, homogeneous magnetic field, membrane K⁺ transport, culture temperature, Arrhenius plot

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A New Removable Magnetic Keeper for Clear Magnetic Resonance Imaging

Shuji Ohkawa^*, Hideaki Tajima^*, Yasumasa Akagawa^***, Hiroya Sakurai^*** and Hirohide Yamada^****

^*Department of Removable Prosthodontics, Hiroshima University, School of Dentistry
^**Dental Technicians School, Hiroshima University, School of Dentistry
^***Matsuyama Red Cross Hospital
^****Magnetic and Electronic Materials Research Laboratory, Hitachi Metals, Ltd.

A new removable magnetic keeper, called a "screw keeper", was designed in order to cope with the potential hazards encountered during magnetic resonance imaging (MRI). This screw keeper consists of the following unique characteristics.

l. The screw keeper can be easily installed and removed from the root cap by use of a conventional screwdriver.

2. The installation and removal procedures produce little wear on the screw keepers and the root caps.

3. The screw keeper can be applied to roots with smaller diameter than that of the keeper.

Keywords : magnetic attachment, MRI, removable keeper, root cap

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The Practical Side of the Clinical Application of MRI in our Department

Eturou Kajimura, Tadasi Sado and Isao Furuta

Department of Oral and Maxillofacial Surgery, Faculty of Medicine, Toyama Medical and Pharmaceutical University

MRI has become more and more useful for the diagnosis and surgical treatment of head and neck tumors. MRI has many potential advantages over CT because of its finer soft tissue detail and its capability of identifying fluid containing structures and abnormal soft tissue lesions without the use of contrast material. By obtaining direct sugittal and coronal images, one can determine the total extent of head and neck tumor in a plane that is better for us and radiation oncologist, who are trying to plan the most suitable treatment.

We wish to report on the clinical applications of MRI which we have dealt with, together with some bibliographical comments.

Keywords : diagnostic imaging, MRI, malignant tumors of head and neck

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