title: Force system generated by an adjustable molar root movement mechanism.
abstract: BACKGROUND
  Tooth movement simulation is important for planning the optimal force system and appliance design to correct a specific malocclusion. Experimental verification of a 3-dimensional force system is described for a unique molar root movement strategy that can be adapted to many clinical scenarios.
  
  
  METHODS
  The force system was measured for molar root movement springs that had adjustable alpha (anterior) and beta (posterior) moments. A 3-dimensional transducer assessed moments and forces in 3 planes during deactivation and simulated molar rotation. Two experimental situations were compared by using 10 springs in each group: spring reactivation was performed to compensate for changes in the force system caused by molar movement, or there was no reactivation.
  
  
  RESULTS
  Without reactivation, the force system becomes unfavorable after approximately 5 degrees of molar movement (rotation). With reactivations, a favorable force system through 20 degrees of molar movement is maintained.
  
  
  CONCLUSIONS
  Present root-movement appliances require periodic adjustment to achieve optimal tooth movement. Additional studies are needed to design orthodontic appliances for delivering optimal force systems for the entire range of tooth movement.
authors.affiliation: Department of Orthodontics and Oral Facial Genetics, Indiana University School of Dentistry, Purdue School of Engineering and Technology, Indianapolis, IN 46202, USA. rviecill@iupui.edu
authors.forename: Rodrigo F
authors.initials: RF
authors.lastname: Viecilli
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Katona
authors.forename: W Eugene
authors.initials: WE
authors.lastname: Roberts
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation; D008954:Models, Biological; D008963:Molar / Q000473:pathology*; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D010347:Patient Care Planning; D012399:Rotation; D013314:Stress, Mechanical; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*; D014092:Tooth Root / Q000473:pathology*; D014159:Transducers