Tomiyuki Ushita

Studies on the Sm-Co Magnet as a Dental Material

The Sm-Co magnet has superior and convenient magnetic properties as compared with conventional ones used hitherto in prosthesis, and even very small pieces can provide the force necessary in dentistry. Also, the magnet has high corrosion resistance and is innocuous to tissues. Therefore, it can be used as a dental material, overcoming the limitations in past applications.

Pd-Co Dental Casting Ferromagnetic Alloys

Three kinds of Pd-Co alloys have been newly developed. Their magnetic and physical properties and corrosion resistances have been examined. As a result, it was found that they are available as the dental casting ferromagnetic alloy which can be used in combination with Sm-Co magnets, overcoming such problems as non-castability and brittleness.

Sectional prostheses connected by samarium-cobalt magnets

Large acquired defects with undercuts can be restored with sectional prostheses. Sections of the prosthesis can be connected with small Sm-Co magnet pairs. The advantages of Sm-Co magnets are that (1) sections of prostheses can be connected by magnets less than 1 cm in size, (2) they can be embedded in thin sections of acrylic resin, (3) they are easy to place, (4) insertion is easy (magnetic attraction enhances), (5) hollow obturators can be used, and (6) tissue undercuts can be used for additional retention of prostheses.

Optimization and Design of Permanent Magnet Devices for Retaining Dental Prosthetic Appliances

Attraction between a pair of rare earth-cobalt magnets is very useful for retention of dental prosthetic appliances. In these applications, the space available for embedding magnets is very narrow. Therefore, the magnets must have those optimum dimensions which cause the mximum attraction. The optimum dimensions are calculated for a rectangular or disk magnet pair utilizing the axial or radial attraction. In order to maximize the axial attraction of a magnet pair in small separation, the rectangular magnet must be slender and the square or disk magnet must have a size ratio of about OA, which is defined as the ratio of thickness to length of edge or diameter of the magnet. In the case of radial attraction, the optimum disk magnet has a little larger size ratio, e.g., about 0.55 in zero separation. Based on these theoretical analyses, the method of designing the optimum magnets with a required attraction is proposed.

A neural network model composed of multioscillators to generate low—frequency biological rhythms

The biological system has low-frequency rhythms, such as a circadian rhythm. In general, it is considered that the source of the circadian rhythm is mostly the neural system, such as optic lobe and suprachiasmatic nucleus. This paper proposes a neural network model which can generate the low-frequency biological rhythm, and discusses its characteristics. The model is composed of the set of neural oscillators composed of excitatory-inhibitory neuron pairs, together with a neuron taking the sum of the oscillator activities. By feeding back the activity of the summing neuron to the oscillators by a suitable magnitude, the proper frequency of the whole model is decreased, realizing the low-frequency rhythm. The generation condition for the low-frequency rhythm is derived through the approximate analysis of the model and the computer simulation. The properties of the generated rhythm are discussed.