Influence of second-order bracket-archwire misalignments on loads generated during third-order archwire rotation in orthodontic treatment.
OBJECTIVE
To investigate the influence of a rotational second-order bracket-archwire misalignment on the loads generated during third-order torque procedures. Specifically, torque in the second- and third-order directions was considered.


METHODS
An orthodontic torque simulator (OTS) was used to simulate the third-order torque between Damon Q brackets and 0.019 × 0.025-inch stainless steel archwires. Second-order misalignments were introduced in 0.5° increments from a neutral position, 0.0°, up to 3.0° of misalignment. A sample size of 30 brackets was used for each misalignment. The archwire was then rotated in the OTS from its neutral position up to 30° in 3° increments and then unloaded in the same increments. At each position, all forces and torques were recorded. Repeated-measures analysis of variance was used to determine if the second-order misalignments significantly affected torque values in the second- and third-order directions.


RESULTS
From statistical analysis of the experimental data, it was found that the only statistically significant differences in third-order torque between a misaligned state and the neutral position occurred for 2.5° and 3.0° of misalignment, with mean differences of 2.54 Nmm and 2.33 Nmm, respectively. In addition, in pairwise comparisons of second-order torque for each misalignment increment, statistical differences were observed in all comparisons except for 0.0° vs 0.5° and 1.5° vs 2.0°.


CONCLUSIONS
The introduction of a second-order misalignment during third-order torque simulation resulted in statistically significant differences in both second- and third-order torque response; however, the former is arguably clinically insignificant.
a  Postdoctoral Fellow, School of Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Dan L
DL
Romanyk
b  Undergraduate Research Assistant, Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada.
Andrew
A
George
c  Graduate Student, Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, Alberta, Canada.
Yin
Y
Li
d  Associate Professor, School of Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Giseon
G
Heo
e  Professor and Associate-Dean (Programs and Planning), Faculty of Engineering, University of Alberta, Edmonton, Alberta, Canada.
Jason P
JP
Carey
f  Professor and Chair, School of Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Paul W
PW
Major
D003722:Dental Alloys; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D012399:Rotation; D013193:Stainless Steel; D019415:Torque
D003722:Dental Alloys; D013193:Stainless Steel
Biomechanics; Orthodontic torque simulator; Orthodontics; Third-order torque