• The Journal of Korean Academy of Prosthodontics
• /
• v.40 no.5
• /
• pp.470-483
• /
• 2002

The purpose of this study was to investigate further the mechanics of failure of magnets used for denture retention. Dyna magnets were retrived from denture that had failed after 34 months of clinical use. The magnets were observed and sectioned in order to analyse with high resolution scanning electron microscope. From this study, corrosion behaviors of used magnetic attachment were analysed. The results were as follows ; 1. In Nd-Fe-B based magnetic materials, the erosion-corrosion was started at ununiformed part of stainless steel cover. 2. Corrosion was initiated at weared stainless steel surface and then magnetic materials were spalled by corrosive solution. 3. Spatting was occurred in Nd-Fe-B magnet materials due to corrosion products and then corrosion rate was increased drastically. 4. Corrosion started from ununiformed stainless steel surface as well as welded zone. In conclusion, the failure of magnets may occur by either breakdown of the welding or breakdown of the encapsulating material. So, it is considered that the corrosion problem of dental magnetic materials could be solved to some extent with surface treatment of dental magnetic materials.

• The Journal of Korean Academy of Prosthodontics
• /
• v.37 no.1
• /
• pp.1-22
• /
• 1999

In order to investigate various physical and biological properties of dental magnetic attachments studies on retentive characteristics, corrosion properties, cytotoxicity of different magnetic systems for dental applications were done. For the study of retentive characteristics changes of retentive force by increasing air gap, wear properties of various attachment systems and loss of magnetic force by heat treatment were measured. Forte study of corrosion property of magnet covering metal electrochemical corrosion was done in artificial saliva and 0.9% NaCl solution between $-1,000mV_{SCE}\;and\;+1,000mV_{SCE}$. Anodic polarization curves are obtained about 6 types of samples and 2 types of solution. Corroded surfaces were examined with metallurgical microscope, scanning electron microscope and surface profilometer. For the study of cytotoxicity of magnetic attachment and its field cell growth and agar overlay test were done. The results of this study were as follows. 1. In Magnetic attachments using closed circuit retentive force at zero air gap was greater than magnets using open circuit, but decrease of retentive force by increasing air gap was also greater than open systems. 2. After 40,000 cycles of wear test all mechanical attachment resulted in varing degree of retention loss but in magnetic attachments no loss of retentive force was observed. 3. The magnetic attachment using Neodymium magnet showed early loss of retentive force about $200^{\circ}C$ but attachment using Samarium magnet showed some resistance to heat treatment and complete retention loss was observed about $500^{\circ}C$. The keeper was not influenced by heat treatment in retention. 4. In electrochemical corrosion test Dyna magnetic attachment covering metal showed the highiest corrosion resistance and Shiner magnet covering metal showed the least corrosion resistance and examination of corroded surface with metallurgical microscope, scanning electron micro-scope and surface profilometer also showed same results with anodic polarization corves. 5. The result of cell culture tests on the magnet covered with metal showed least recognizable cytotoxicity.