title: Effects of mechanical stress and growth on the velocity of tooth movement.
abstract: BACKGROUND
  In this study, we investigated the effects of the magnitudes of applied stress and growth status on the speed of tooth movement.
  
  
  METHODS
  Eighty-two maxillary canines in 41 subjects were retracted for 84 days by estimated stresses of 4, 13, 26, 52, or 78 kPa applied continuously via segmental mechanics. Dental impressions made at intervals of 1 to 14 days resulted in 9 or 10 dental casts per subject. Three-dimensional tooth movements were quantified using these casts, custom reference templates, and a measuring microscope. Serial height and cephalometric measurements determined growth status.
  
  
  RESULTS
  Distal tooth movement was linear with no lag phase in 96% of the teeth. Speeds averaged 0.028, 0.040, 0.050, 0.054, and 0.061 mm per day (standard errors, ± 0.004) for 4, 13, 26, 52, and 78 kPa, respectively. The maximum difference in speed between teeth was 9:1. Teeth moved significantly faster (P <0.0001) in growing compared with nongrowing subjects, on average by 1.6-fold. Stress and speed of tooth movement were logarithmically related in growing (R(2) = 0.47) and nongrowing (R(2) = 0.34) subjects. Other tooth movements were relatively small, except for the distopalatal rotation of teeth moved by 78 kPa that averaged more than 19°.
  
  
  CONCLUSIONS
  The speed of retraction was logarithmically related to the applied stress and was significantly faster in actively growing subjects compared with those who were not growing.
authors.affiliation: Associate professor, Departments of Orthodontics & Dentofacial Orthopedics and Oral & Craniofacial Sciences, School of Dentistry, University of Missouri, Kansas City, Mo. Electronic address: nickeljc@umkc.edu.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Nickel
authors.affiliation: Postdoctoral fellow, Departments of Orthodontics & Dentofacial Orthopedics and Oral & Craniofacial Sciences, School of Dentistry, University of Missouri, Kansas City, Mo.
authors.forename: Honzeng
authors.initials: H
authors.lastname: Liu
authors.affiliation: Professor, Department of Statistics, University of Nebraska, Lincoln, Neb.
authors.forename: David B
authors.initials: DB
authors.lastname: Marx
authors.affiliation: Associate professor, Leo Rogers Chair of the Department of Orthodontics & Dentofacial Orthopedics; joint appointment, Department of Oral & Craniofacial Sciences, School of Dentistry, University of Missouri, Kansas City, Mo.
authors.forename: Laura R
authors.initials: LR
authors.lastname: Iwasaki
mesh_terms: D000293:Adolescent; D000328:Adult; D002508:Cephalometry; D002648:Child; D003481:Cuspid / Q000254:growth & development*; D003735:Dental Casting Technique; D003799:Dental Stress Analysis / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008437:Maxilla / Q000254:growth & development*; D008962:Models, Theoretical; D013314:Stress, Mechanical; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*