Biomagnetics is an interdisciplinary field were magnetics, biology and medicine overlap. Recent advances in biomagnetics are reviewed in this paper. This paper focuses on transcranial magnetic stimulation, biological effects of magnetic and electromagnetic fields, magnetic orientation of biological cells, medical applications of biomagnetic effects, magneloencephalography, impedance and neuronal current MR imaging techniques.
Magnetic resonance imaging is a widely accepted modality for providing anatomical information. Current research involves extending MRI methods to provide information about biological function, in addition to the concomitant anatomical information. This paper reviewed recent clinical applications of MR medicine in muscle and brain.
Phosphorous magnetic resonance spectroscopy (31P-MRS) has proved to be a reliable and noninvasive tool to explore muscular metabolism. Due to the chemical shift of the phosphorus containing metabolites, the relative distribution of the central intramuscular compounds phosphocreatine, inorganic phosphate, adenosine triphosphate, phosphomonester, and phosphodiester can be assessed. 31P-MRS can be used to obtain information indirectly on the muscle fiber composition because the distribution of muscle fibers assumed to be one of the physiologic factors which might influence relative PCr (PCr/ATP, PCr/Pi, etc).
Newly developed magnetic resonance techniques offer non-invasive tools for functionality analysis in humans, namely, BOLD (blood oxygen level dependent) functional magnetic resonance imaging (fMRI). Since BOLD contrast depends on the state of blood oxygenation, physiological events that change the oxy/dexyhemoglobin ratio should lend themselves to noninvasive detection through the accentuation of BOLD contrast. The technique makes use of changes in regional deoxyhemoglobin concentration associated with brain function.
Magnetic attachment is an effective retainer that can be used for various clinical applications. Even now, new types of magnetic attachments have been introduced, while I think that there are common points to success in dental clinic using magnetic attachment as coping. Those are the form of coping and the procedure setting magnetic assemblies in dentures.
My clinical reports are presented, using magnetic attachments and pins is one of useful prostheses to vital abutment teeth.
Yoshinobu Tanaka, Kazumoto Hoshiai, Takeshi Kanazawa, Yoshinori Nakamura, Yoshinori Desaki, Kenji Tsuda, Toshikiyo Miyata, Sachiko Okazaki, NaokoMuraji, Michio Okada* and Tomohiko Ishigami**
A magnetic attachment is now a very popular prosthodontic procedure contributing greatly to improve the standard of health science in Japan. So far, more than 1,000,000 magnetic attachments have been delivered to Japanese dental clinics. The reason why it has gained peoples' confidence in a comparatively short time since its introduction into the Japanese market, is that people realized that it has various clinical advantages over conventional mechanical retainers such as clasps.
We developed our original magnetic attachment and various accessories in the 1990's.Through trial and error, we are continuing to develop many additional goods and methods to make clinical procedures using our magnetic attachment easier and more reliable.
In this paper, the outline of our basic philosophy in regards to the latest denture design with magnetic attachments was presented. In addition several promising trial products were introduced. They include a "Keeper Tray", a "Housing Dummy", an "Extracoronal Keeper Tray", a "Magnotelescopic Crown", and an "Implant Keeper". We, also, introduced the "CAD/CAM method in Magnoprosthestics". In addition, some mention of our expectations and anxieties about an ultimate magnetic attachment using some type of film magnet was made.
As a final step, we should confirm that our magnetic attachment perform well in clinical situations through large-scale field tests and patient feedback.
Magnetic measurement system using a method combining BPNN (Back Propagation Neural Networks) with NLS (Nonlinear Least - Squares) is described in this paper. The mandibular movements can be measured by estimating the position and orientation of two small permanent magnets attached on the maxilla and mandible separately. Although a BPNN method can solve this typical inverse problem fast enough for real time measurement, the accuracy may be not high enough. The problem of using a NLS method is that the solution may be trapped in the local minima of an error function or be not converged. The authors propose a method combining BPNN with NLS. The new methods show how to estimate an approximate solution of the inverse problem by the BPNN method, and how to select the initial value of the NLS method due to the results of BPNN to obtain the optimum solution, where the problem is solved by Gauss - Newton iteration algorithm. This system is proven to be accurate and fast enough for the application to diagnosis by a simulation for the practical mandibular movements.
Due to extensive and spreading clinical uses of magnetic attachments, various types of magnetic attachment as to size, shape and retention property are required clinically to improve the effectiveness of the attachment. Magnetic retention property of the attachment depends on the magnetic structure of a magnetic assembly. The magnetic attachment should have a large magnetic force, e.g. more than 600gf, at zero gap between a magnetic assembly and a keeper. On the other hand, a restoring force which is required at a small gap, e.g., 0.1mm, should controlled depending on the state of abutment teeth. For poor conditioned abutment teeth, a magnetic attachment having a small restoring force is suitable to avoid excessive compulsory force to the abutment. A new magnetic attachment with such a property has been developed here, using a cylinder magnet magnetized in unidirection. As a result of analyzes on this cylinder typed magnetic attachment using a magnetic moment method, the attachment has a high retentive force more than 800gf and a low restoring force, e.g., less than10% of the retentive force at a gap of 0.1mm. By use of the attachment, poor state teeth may be possible to be used as abutment teeth.
Because magnetic fields are generally said to have the effect of improving blood circulation, various types of magnetic rings, necklaces and earrings have come on to the market. Therefore, utilizing a noncontact blood flow meter, we investigated whether changes in blood flow occur when magnetic attachments are used in the mouth. Magnetic attachments are used in the mouth in contact with keeper, and it is said that leakage of the magnetic field under these circumstances is very small. However, we found that blood flow was increased depending on the type of magnetic attachment. Therefore, it is necessary to investigate this issue further.