title: A study on the changes in attractive force of magnetic attachments for overdenture.
abstract: OBJECTIVE
  Although magnetic attachment is used frequently for overdenture, it is reported that attractive force can be decreased by abrasion and corrosion. The purpose of this study was to establish the clinical basis about considerations and long term prognosis of overdenture using magnetic attachments by investigating the change in attractive force of magnetic attachment applied to the patients.
  
  
  METHODS
  Among the patients treated with overdenture using magnetic attachments in Dankook University Dental Hospital, attractive force records of 61 magnetic attachments of 20 subjects who re-visited from July 2013 to June 2014 were analyzed. Dental magnet tester (Aichi Micro Intelligent Co., Aichi, Japan) was used for measurement. The magnetic attachments used in this study were Magfit IP-B Flat, Magfit DX400, Magfit DX600 and Magfit DX800 (Aichi Steel Co., Aichi, Japan) filled with Neodymium (NdFeB), a rare-earth magnet.
  
  
  RESULTS
  Reduction ratio of attractive force had no significant correlation with conditional variables to which attachments were applied, and was higher when the maintenance period was longer (P<.05, r=.361). Reduction ratio of attractive force was significantly higher in the subject group in which attachments were used over 9 years than within 9 years (P<.05). Furthermore, 16.39% of total magnetic attachments showed detachment of keeper or assembly.
  
  
  CONCLUSIONS
  Attractive force of magnetic attachment is maintained regardless of conditional variables and reduction ratio increased as the maintenance period became longer. Further study on adhesive material, attachment method and design improvement to prevent detachment of magnetic attachment is needed.
authors.affiliation: Department of Prosthodontics, College of Dentistry, Dankook University, Cheonan, Republic of Korea.
authors.forename: Han-Wool
authors.identifier: 0000-0001-7084-5218
authors.initials: HW
authors.lastname: Leem
authors.affiliation: Department of Prosthodontics, College of Dentistry, Dankook University, Cheonan, Republic of Korea.
authors.forename: In-Ho
authors.initials: IH
authors.lastname: Cho
authors.affiliation: Department of Prosthodontics, College of Dentistry, Dankook University, Cheonan, Republic of Korea.
authors.forename: Jong-Hyuk
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Prosthodontics, College of Dentistry, Dankook University, Cheonan, Republic of Korea.
authors.forename: Yu-Sung
authors.initials: YS
authors.lastname: Choi
keywords: Attractive force; Magnetic attachment; Overdenture