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

Abstract

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.

Effects of stress relaxation in beta-titanium cantilevers used in orthodontic mechanics

“…These angle changes show the over time deactivation of the cantilevers, noticed as the decrease of forces. Beyond the force decay of the preactivated loops, some studies 7 , 9 , 10 stated that the sharpness of the bend influences the final angles of the spring’s structure. In addition, concentrated bends are also responsible for relaxation and/or plastic deformation over time.…”

“…Structural areas of the springs can be affected by the proximity of the bends and/or stress-relaxation, as previously reported by the literature using “T” loop shape designs. 7 , 9 , 10 …”

“…[1][2][3][4][5][6] Because of their formability and springback characteristics, titanium-molybdenum alloys, also called β-titanium, are often used for the manufacturing of cantilevers. [1][2][3][4][5][7][8][9][10] This alloy in straight-wire applications can be deflected 105 percent more than stainless steel without permanent deformation, and its stiffness makes it ideal in applications where less force is required but a lower modulus of elasticity would be inadequate to develop the required force magnitudes. 11 Therefore, the use of β-titanium alloys enables the construction of cantilevers with simpler designs, saving time during the clinical procedures.…”

“…The choice of the design of the segmented arch, material, and the way that it is bent has direct influence on how forces decay through time during clinical use. [7][8][9][10] The shape of the cantilever as well as its activation are individual choices of each orthodontist, and often the simpler shapes are more frequently used. However, the impact of a cantilever's design on the delivery of forces is a variable that is more frequently studied in more complex designs, and there is a lack of evidence for those with simpler designs, as well as which is the best form of use during orthodontic treatment.…”

Orthodontic force prediction model of T-loop closing spring based on dynamic resistance model

“…But the research is aimed at the measurement of static orthodontic force. Caldas et al 39 found that the orthodontic process of T-loop was dynamic. So static orthodontic force measurement cannot meet the clinical needs.…”