Fundamental Research On The Biological Effects Of The Static Magnetic Field Of The Magnetic Attachment On Human Gingival Fibroblasts And Human Periodontal Ligament Fibroblasts

With the progress of magnetic materials and the applying of finite element analysis in magnetic field, several types of dental magnetic attachments have been introduced into prosthetics to aid the retention of prosthesis. Magnetic attachments have flux leakages, thus they will exert certain magnetic fields on the adjacent tissues when used in the oral cavity. The biological effects of magnetic fields are still unclear and controversial. There are few research reports on the characteristics of the magnetic fields generated by magnetic attachments and on their biological effects on the human body. Thus it's necessary to research the magnetic fields of magnetic attachments and their biological effects on the adjacent tissues.The present research aimed to measure and analyze the static magnetic fields (SMF) around two types of commonly used dental magnetic attachments,and to develop a cellular SMF exposure system according to the results of SMF analysis. By using this system, the in vitro cultured human gingival fibroblasts (HGF) and human periodontal ligament fibroblasts (HPDLF) were exposed to SMF of different intensities with different time. Then the effects of SMF on morphologies, proliferations and intracellular Ca²⁺ concentrations of the HGF and HPDLF were investigated, thus to research the biological effects of the SMF of magnetic attachments and to guide the clinical applying of magnetic attachments.The flux densities of the SMF around two types of commonly used dental magnetic attachments (MAGNEDISC 800 and MAGFIT EX600W) were measured in the present research. Results showed that there were flux leakages under both the open-field circuit and closed-field circuit of the two types of magnetic attachments. The flux leakages under closed-field circuit were smaller than those under open-field circuit. The flux leakage of magnetic attachments would increase in clinical situations as it's difficult to attach the magnet and the keeper accurately.A cellular SMF exposure system, which could produce constant and adjustable SMF was developed. The system has a small size and is able to exert SMF of different strengths to cells in vitro for different time.Trypsin and type I collagenase two step digestive method was introduced to culture the HGF and HPDLF in vitro. The cultured cells were passaged and were found to be typical HGF and HPDLF with steady proliferation speeds.According to the results of the SMF analysis and the clinical circumferences of magnetic attachments, SMF of 120mT and 10mT were produced by the cellular SMF exposure system to simulate the SMF of the open-field andclosed-field magnetic attachments respectively. Cultured HGF and HPDLF were exposed to SMF simulating those of magnetic attachments in the cellular SMF exposure system and the effects of the SMF on the morphology, proliferation and the intracellular free Ca²⁺ concentrations of the HGF and HPDLF were inspected.Results showed that the SMF of magnetic attachments could lead to certain changes in the cellular shape and size, surface ultrastructure, morphology and structure of cytoskeleton, cell vitality and proliferation activity of human periodontal cells. The cellular changes induced by 120mT SMF were more prominent than those by 10mT SMF. Besides, 120mT SMF could induce cell apoptosis. These indicated that SMF of relatively high strength had unfavorable eflFects on the morphology and proliferation of human periodontal cells. The open-field magnetic attachment has relatively high amount of flux leakage and exerts SMF of relatively high flux density on periodontal tissues, thus it may be unfavorable for the health of periodontal tissues and should be used with caution. The closed-field magnetic attachment should be carefully designed and manufactured to minimize the SMF leakage. In clinical manipulation, the magnet and keeper should be attached accurately to minimize the SMF strength exerted on the periodontal tissues. The intracellular free Ca²⁺ concentrations of HGF and HPDLF increased for a certain extent after exposed to 10mT and 120mT SMF for 12 to 60 hours, this may be related to the changes of cellular shape and size, cytoskeleton, cell vitality and cell apoptosis rate of HGF and HPDLF after SMF exposure. On the basis of the present cellular research, there should be further animal experiments to investigate the biological effects of SMF on organism tissuesmore deeply.