Stability of beta-titanium T-loop springs preactivated by gradual curvature

Sergei Godeiro Fernandes Rabelo CALDAS, Renato Parsekian MARTINS, Marcela Emílio de ARAÚJO, Marília Regalado GALVÃO, Roberto Soares da SILVA JÚNIOR, Lídia Parsekian MARTINS

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.

Keywords: Orthodontics. Tooth movement. Orthodontic wires.

How to cite: 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

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