Edition V22N06 | Year 2017 | Editorial Original Article | Pages 61 to 67
Objective: Evaluate changes in the force system of T-Loop Springs (TLS) preactivated by curvature, due to stress relaxation. Methods: Ninety TLSs measuring 6 x 10 mm, produced out with 0.017 x 0.025-in TMA® wire and preactived by gradual curvature, were randomly distributed into nine groups according to time point of evaluation. Group 1 was tested immediately after spring preactivation and stress relief, by trial activation. The other eight groups were tested after 24, 48 and 72 hours, 1, 2, 4, 8 and 12 weeks, respectively. Using a moment transducer coupled to a digital extensometer indicator adapted to a universal testing machine, the amount of horizontal force, moment and moment-to-force ratios were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation, in an interbracket distance of 23 mm. Results: The horizontal forces decreased gradually among the groups (p < 0.001) and the moments showed a significant and slow decrease over time among the groups (p < 0.001). All groups produced similar M/F ratios (p = 0.532), with no influence of time. Conclusions: The TLSs preactivated by curvature suffered a gradual deformation over time, which affected the force system, specifically the moments, which affected the horizontal forces produced.
Orthodontics, Tooth movement, Orthodontic wires,
Caldas SGFR, Martins RP, Araújo ME, Galvão MR, Silva Júnior RS, Martins LP. Stability of beta-titanium T-loop springs preactivated by gradual curvature. Dental Press J Orthod. 2017 Nov-Dec;22(6):61-7. DOI: https://doi.org/10.1590/2177-6709.22.6.061-067.oar