title: Selective use of hand and forearm muscles during bone screw insertion: a natural torque meter.
abstract: OBJECTIVE
  To compare the maximum torque produced by different muscle groups and its influence on mini-implant insertion torque and fracture prevention.
  
  
  METHODS
  Eighty-seven professionals were evaluated for the maximum torque produced on a screwdriver by a combined action between the thumb and index finger (maximum digital torque [MDT]) and by the forearm supination movement (maximum brachial torque [MBT]). Ninety mini-implants distributed among 9 different diameters were fractured to determine the fracture torque (FT). The fracture resistance index (FRI) was obtained from: FRI_MDT = FT/MDT and FRI_MBT = FT/MBT. Analysis of variance and t tests were used to compare the groups.
  
  
  RESULTS
  The MDT was smaller than the MBT, and the 2 measurements were smaller in female subjects. The FT increased for each 0.1-mm increment in diameter. The FRI_MDT was greater than FRI_MBT for all diameters. An FRI_MDT greater than 1 was found when the diameter was greater than or equal to 1.5 mm. An FRI_MBT greater than 1 occurred with diameters equal to or greater than 1.7 mm for female subjects and 1.8 mm for male subjects.
  
  
  CONCLUSIONS
  The digital torque was 42% smaller than the brachial torque, and it was mechanically safer and biologically more compatible, allowing the prevention of the fracture of mini-implants with a diameter 1.5 mm or thicker owing to an insertion torque limitation at 15 N-cm.
authors.affiliation: Department of Orthodontics, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil. sergioestelita@yahoo.com.br
authors.forename: Sérgio Estelita
authors.initials: SE
authors.lastname: Barros
authors.forename: Guilherme
authors.initials: G
authors.lastname: Janson
authors.forename: Kelly
authors.initials: K
authors.lastname: Chiqueto
authors.forename: Eduardo Silveira
authors.initials: ES
authors.lastname: Ferreira
authors.forename: Marcos
authors.initials: M
authors.lastname: Janson
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001863:Bone Screws; D004868:Equipment Failure; D005260:Female; D005542:Forearm / Q000502:physiology*; D006225:Hand / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D011446:Prospective Studies; D015203:Reproducibility of Results; D012727:Sex Characteristics; D018709:Statistics, Nonparametric; D019415:Torque