title: Human tooth movement by continuous high and low stresses.
abstract: OBJECTIVE
  To compare three-dimensional tooth movements resulting from relatively higher and lower stresses in a split-mouth design.
  
  
  METHODS
  Eight volunteers whose maxillary first premolars were removed for orthodontic treatment participated. Each subject's maxillary canines were retracted by randomly assigned constant stresses of 78 kPa and 4 kPa via segmental mechanics. Dental casts depicting 8-10 visits per subject over 84 days and a three-axis microscope were used to measure movements serially. Descriptive statistics and mixed linear modeling were applied for data analyses (α = .05).
  
  
  RESULTS
  Teeth moved by 78 kPa had significantly faster (P = .0005) distal movement (0.066 ± 0.020 mm/day) compared to teeth moved by 4 kPa (0.031 ± 0.012 mm/day). Lateral movement and distopalatal rotation were also significantly faster (fourfold and 10-fold, respectively) with higher than with lower stress (P < .0001). Average extrusion-intrusion, crown torque, and tip were small (≤ |0.25| mm, |2.29|°, and |1.98|°, respectively), fluctuated, and not significantly different between high and low stresses. No lag phase of tooth movement was evident.
  
  
  CONCLUSIONS
  Maxillary canines were retracted faster by 78 kPa than by 4 kPa. Controlled translation was possible with 4 kPa, but 78 kPa outstripped appliance constraints, causing distopalatal rotation.
authors.affiliation: a  Dental Student, University of Missouri-Kansas City (UMKC) School of Dentistry (SOD), Kansas City, Mo.
authors.forename: Whitney N
authors.initials: WN
authors.lastname: Deforest
authors.forename: Jodi K
authors.initials: JK
authors.lastname: Hentscher-Johnson
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.forename: Hongzeng
authors.initials: H
authors.lastname: Liu
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Nickel
authors.forename: Laura R
authors.initials: LR
authors.lastname: Iwasaki
mesh_terms: D000293:Adolescent; D001641:Bicuspid / Q000601:surgery; D001696:Biomechanical Phenomena; D002648:Child; D003481:Cuspid / Q000473:pathology; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008437:Maxilla / Q000473:pathology; D003765:Models, Dental; D016382:Orthodontic Appliance Design; D009969:Orthodontic Wires; D010865:Pilot Projects; D012399:Rotation; D013314:Stress, Mechanical; D013997:Time Factors; D019228:Tooth Crown / Q000473:pathology; D014081:Tooth Extraction; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*; D019415:Torque; D055815:Young Adult