abstracts6-1-e

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Electromagnetic Mechanisms of Biomagnetic Effects

Yohsuke Kinouchi

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

It is important for understanding biological effects of electromagnetic fields to analyze basic mechanisms underlaid and to evaluate the threshold on the effects. These are discussed here from the viewpoint of electromagnetics. Static magnetic fields yield electromagnetic forces such as Coulomb force, torque, Maxwell stress and Lorentz force which may influence fiber orientation, blood flow in the aorta and so on in field strength over 1[T]. ELF time-varying magnetic fields induce currents which may affect directly nervous activities in the field more than 100[mT] and cell surface states in the range of 1 to 100[mT]. The weak fields in the range of 1 to 100[µT] may cause some effects based on resonance phenomena.

Keywords : electromagnetic field, biological effect, mechanism, electromagnetics

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Application of Electromagnetic and Magnetic Fields to Medicine

Osamu Okai

Department of Clinical Physiology, Kyorin University School of Health Sciences

Many issues of health hazards associated with weak, extremely low frequency-frequency electromagnetic fields (EMF) as produced by power lines and household appliance continues to be debated. Epidemiological studies investigating the link between EMF and increased risk of certain cancers has not clarified the issues. Thus, the researchers have looked to laboratory studies of EMF effects to determine whether there is biological plausibity for increased cancer risk. Unfortunately, those laboratory studies yielded same results.

However, our studies have been carried out on effects of high magnetic fields on animals and human. Human body has artcrial and venous vessels. High magnetic fields produces blood flow-induced electromotive force, which can be measured by surface electrodes without injuring body. Main medical treatments are as follows. Using low altrmative magnetic fields have been used to promote the healing of ununited fractures and skin lesions. Furthermore, low-frequency, low-energy pulsing electromagnetic fields have the effect on the healing of skin ulcers. In forty-four patients success was significantly higher than control group. In another study on patients with neck pain, symptoms resolved spontaneously or quite quickly in response to the low frequency electromagnetic therapy. After three-week therapy there are significant improvements in observed patients with pain.

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Advances in Permanent Magnetic Materials over the Last Decade

Motofumi Homma

Department of Materials Science, Graduate School of Engineering, Tohoku University

The discovery of Nd₂Fe₁₄B based magnets provided a large impetus for an accelerated pace of research and development in permanent magnet materials. The energy products (BH) max is recorded over 400kJ/m³ in Nd₂Fe₁₄B based sintered magnets. In this article, advances in permanent magnet materials over the last decade are outlined.

Keywords : Nd₂Fe₁₄B sintered permanent magnet, bonded magnet, HDDR process, composite nanocrystalline magnet, FePt thin film magnet

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Studies for a Magnetic Measurement System for Mandibular Movement Using Neural Networks

Masatake Akutagawa and Yohsuke Kinouchi^*

School of Medical Science, The University of Tokushima
^*Faculty of Engineering, The University of Tokushima

This paper describes a measurement system for the position and orientation of mandible using a permanent magnet, magnetic sensors and a artificial neural network technique. The problem in estimating the magnet position and direction is an inverse problem, Typical methods such as iterative calculations or calibration matching involve intensive calculations. Our Technique makes use of the neural network's ability to realize any function within a short processing time. Computer simulations are used for evaluating measurement accuracy. From the results, we obtained an average error of 7 micron for position and 0.004 degree for angular orientation. These estimation accuracies are satisfactory enough to measure a boundary movement, conditions of occlusion and kinetic characteristics.

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

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A Split Pole Type of Magnetic Attachment and its Characteristics

Yoshinori Tegawa and Yohsuke Kinouchi^*

School of Medical Sciences, The University of Tokushima
^*Faculty of Engineering, The University of Tokushima

It is required to develop a magnetic attachment which has large restoring force to resist the reduction of magnetic retention due to deformation of the alveolar ridge and dentures. Two types of split-pole magnetic attachment are proposed here. Theoretical analysis and experiments show that one of the magnetic attachments consisting of three magnets has large restoring force (more than two times) as compared with usual attachments on the market. Therefore, the new split-pole type of magnetic attachment proposed here will supply an useful retention in magnetic prostheses.

Keywords : magnetic attachment, denture, magnet, magnetic moment method, magnetic force

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A New Adhesive Method of Magnetic Keeper for Home Dental Care

Masami Hattori, Haruhiko Asai, Katsuhiko Kattoh, Toyozo Kawaguchi, Yuuichiro Amano^*, Makoto Miyamae^* and Yoshinobu Tanaka^*

The Second Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University
^*The First Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University

Several types of dental magnetic attachments are commercially available of which two have been put on the market in Japan. They work by means of the keeper which is cast-weld in the root cap with general dental alloys. That root cap fits accurately onto the tooth and prevent decay. But with the cast-weld technique a patient needs at courses of dental treatment. Since such is too hard for an old bedridden person, we have therefore developed a method of adhesive for home dental care. The keeper was cemented to a tooth using an adhesive cement, then magnetic attachment was inserted in the denture base.

We applied this method to 7 patients and obtained a good prognosis. This method is thus useful in home dental care.

Keywords : adhesive fixed method, magnetic attachment, magnetic keeper, home dental care

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New Surgical Template by using Magnetic Attachment for Oral Implant Treatment

Tomohiko Ishigami, Chiaki Ohsaki^*, Kenichi Kurita^**, Munetaka Naitoh^***, Yoshinobu Tanaka and Kenji Hiranuma

The First Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University
^*The Laboratory of Dental Hospital, School of Dentistry, Aichi-Gakuin University
^**The Second Department of Oral and Maxillofacial Surgery, School of Dentistry, Aichi-Gakuin University
^***Department of Oral and Maxillofacial Radiology, School of Dentistry, Aichi-Gakuin University

A surgical template for implant surgery is presented. This consisted of three parts that are guide pins indicating starting points for drilling, drilling direction indicators and a base. The magnetic attachments are buried in the base and the other two parts can be detached during surgery if they obstruct surgical maneuver.

Keywords : surgical template, oral implant, magnetic attachment

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Influences of Heat Treatments on Attractive Force of Magnetic Attachments

Kazuo Nakamura, Hiroshi Mizutani, Naoki Fukazawa, Tomoko Morita and Minoru Ai

The First Department of Prosthodontics, Faculty of Dentistry, Tokyo Medical and Dental University

Magnetic Assemblies of dental magnetic attachments are often exposed heat in the process of the clinical and laboratory procedures.

The purpose of this study was to evaluate the effects of heat procedures, i.e. heat curing of acrylic resin and sterilization, on attractive force of two types of magnetic attachments; the HICOREX MD 400 (containing the SmCo₅ magnet) and HICOREX SUPER J (containing the Nd-Fe-B magnet).

The results were as follows.

1. Attractive force of the HICOREX MD decreased after its magnetic assembly was directly heated over 360°C.

2. Attractive force of the HICOREX SUPER J decreased after its magnetic assembly was directly heated over 190 °C.

3. After curing procedure of acrylic resin, attractive force of each magnetic assembly was unchanged.

4. After sterilizing procedure by autoclave, attractive force of each magnetic assembly was unchanged.

5. After sterilizing procedure by dry air sterilization, attractive force of the HICOREX MD was unchanged, but that of the HICOREX SUPER J decreased by 30gf.

Keywords : dental magnetic attachment, a heat-resistance test, Nd-Fe-B magnet

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