Effect of stress relaxation in two different preactivation methods of beta-titanium T-loops: bends vs. continuous curvature

• Published in: Journal of the world federation of orthodontists 2017-09, Vol.6 (3), p.98-104
• Main Authors: Caldas, Sergei Godeiro Fernandes Rabelo, Martins, Renato Parsekian, de Araújo, Marcela Emílio, Galvão, Marília Regalado, Reis, José Maurício dos Santos Nunes, Martins, Lídia Parsekian
• Format: Article
• Language: English
• Subjects: Beta-titanium; Preactivation; Stress relaxation; T-loop
• ISSN: 2212-4438; 2212-4438
• DOI: 10.1016/j.ejwf.2017.08.002

Assess the changes in the force system of T-loop springs (TLSs) preactivated by bends and curvature, when secured in place with a constant strain over time. A total of 120 TLSs with dimensions 6 x 10 mm, produced out of 0.017 × 0.025-inch TMA, were randomly divided into two groups of 60 TLSs, each according to what preactivation was going to be used, concentrated bends or gradual curvature. Subgroup 1 was tested immediately and the remaining subgroups were tested after they were secured at 5-mm activation for different periods of time in an interbracket distance of 23 mm. Subgroups 2, 3, 4, 5, and 6 were kept activated for 24, 48, and 72 hours, 1 and 2 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 (MF) ratios were recorded. Both groups showed a decrease in force levels over time (P < 0.001 and 0.005 for bend and curvature preactivation, respectively), but with different behaviors. The group preactivated by bends showed a reduction in moments over time (P < 0.001), whereas the group preactivated by curvature did not (P = 0.410). The MF ratio has not changed over time in either group. The stress-relaxation effect is more evident on group preactivated by bends. •The T-Loops Spring can be preactivated by concentrated bends and curvature.•The changes in the force system of preactivated T-Loops Spring were evaluated.•The tested preactivations suffer stress relaxation over time.•The preactivation by concentrated bends showed an abrupt load decrease.•The moment-to-force ratio has not changed over time in both groups.