Speed of human tooth movement in growers and non-growers: Selection of applied stress matters.

Structured Abstract ObjectivesTo test that the speed of tooth translation is not affected by stress magnitude and growth status. Setting and Sample PopulationAdvanced Education Orthodontic clinics at the Universities of Nebraska Medical Center and Missouri-Kansas City. Forty-six consenting subjects with orthodontic treatment plans involving maxillary first premolar extractions. Materials and MethodsThis randomized split-mouth study used segmental mechanics with definitive posterior anchorage and individual vertical-loop maxillary canine retraction appliances and measured three-dimensional tooth movements. Height and cephalometric superimposition changes determined growing (G) and non-growing (NG) subjects. Subjects were appointed for 9-11 visits over 84days for maxillary dental impressions to measure three-dimensional tooth movement and to ensure retraction forces were continuously applied via calibrated nitinol coil springs. Springs were custom selected to apply two different stresses of 4, 13, 26, 52 or 78 kPa to maxillary canines in each subject. Statistical analyses (=0.050) included ANOVA, effect size (partial (2)) and Tukey's Honest Significant Difference (HSD) and two-group t tests. ResultsDistolateral translation speeds were 0.0340.015, 0.047 +/- 0.019, 0.066 +/- 0.025, 0.068 +/- 0.016 and 0.079 +/- 0.030mm/d for 4, 13, 26, 52 and 78 kPa, respectively. Stress significantly affected speed and partial (2)=0.376. Overall, more distopalatal rotation was shown by teeth moved by 78 kPa (18.03 +/- 9.50o) compared to other stresses (3.86 +/- 6.83o), and speeds were significantly higher (P=.001) in G (0.062 +/- 0.026mm/d) than NG subjects (0.041 +/- 0.019mm/d). ConclusionsStress magnitude and growth status significantly affected the speed of tooth translation. Optimal applied stresses were 26-52 kPa, and overall speeds were 1.5-fold faster in G compared to NG subjects.