title: The force-distance properties of attracting magnetic attachments for tooth movement in combination with clear sequential aligners.
abstract: BACKGROUND
  The demand for clear sequential aligner therapy has increased dramatically in recent years. An improved system utilising small neodymium-iron-boron (NdFeB) magnetic attachments has been proposed to enhance appliance capabilities.
  
  
  OBJECTIVE
  The aim of the investigation was to analyse the force system diagrams produced by small attracting NdFeB magnets to determine, 1) whether the force levels were sufficient to induce tooth movement, 2) the effect of magnet morphology on force characteristics and, 3) the most appropriate magnet dimensions that could be utilised for this application.
  
  
  METHODS
  Twenty-nine NdFeB rectangular magnets of varying dimensions were tested. A Mach-1 universal testing machine (Biosyntech Inc, Quebec, Canada) was used to measure the attractive force of pairs of magnets. Measurements commenced with a magnetic pair in contact and subsequently vertically separated a distance of 10 mm at a speed of 12 mm/minute. For all magnetic configurations four repeat measurements were performed on five magnetic pairs of the same size.
  
  
  RESULTS
  The force-distance diagrams for all magnet configurations demonstrated a dramatic decrease in force with increasing magnet separation. Rather than a suggested inverse square law, the experimental data followed an inverse fourth law when an offset determined by a regression analysis was applied to the distance. For the majority of magnets, insignificant forces were attained beyond 2 mm of separation. Magnets with large pole face areas and longer magnetic axes provided the greatest force.
  
  
  CONCLUSIONS
  A select range of magnet configurations exhibited suitable and reliable attractive forces and therefore could be advocated for prescribed clinical application.
authors.affiliation: Discipline of Orthodontics, Faculty of Dentistry, University of Sydney, Sydney, Australia.
authors.forename: Angie
authors.initials: A
authors.lastname: Phelan
authors.forename: Peter
authors.initials: P
authors.lastname: Petocz
authors.forename: William
authors.initials: W
authors.lastname: Walsh
authors.forename: M Ali
authors.initials: MA
authors.lastname: Darendeliler
mesh_terms: D000497:Alloys / Q000737:chemistry; D001895:Boron / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D003970:Diastema / Q000628:therapy; D006801:Humans; D007180:Incisor / Q000473:pathology; D007501:Iron / Q000737:chemistry; D060526:Magnetic Fields; D008280:Magnetics; D008437:Maxilla; D009354:Neodymium / Q000737:chemistry; D016382:Orthodontic Appliance Design; D013314:Stress, Mechanical; D013499:Surface Properties; D014087:Tooth Movement Techniques / Q000295:instrumentation*
chemical_list: D000497:Alloys; D009354:Neodymium; D007501:Iron; D001895:Boron