Abstract
ABSTRACTObjective: This study evaluated the force decay and design shape changes caused by stress relaxation in two different orthodontic cantilever configurations. Methods: Eighty cantilevers made of 0.017 x 0.025-in beta-titanium wires were standardized in a passive position, using real scale templates, and randomly divided into two groups (n = 40): Type 1 and Type 2. Each group received a different design (Type 1 with three bends, and Type 2 with two bends), and both were divided in four subgroups (n = 10) according to the evaluation periods: G1 = 24h, G2 = 1 week, G3 = 4 weeks, and G4 = 8 weeks. Mechanical tests were performed immediately after preactivation and at the end of each period, to evaluate force decay. The cantilevers were also scanned and the angles of the bends were measured to assess shape changes. Results: Cantilever forces decayed over time. Type 1 - G1 showed less force decay than Type 2 (10.83 cN vs 17.87 cN). Type 1 cantilevers showed significant force decay only when G4 was compared to G1 (9.05 cN), G2 (11.73 cN), and G3 (9.78 cN). Type 2 cantilevers presented differences when G1 was compared to G2 (9.57 cN) and G3 (7.89 cN). Regarding to the cantilever angle closest to the bracket insertion, Type 1 cantilevers showed significant decrease for G2 (1.58°) and G4 (1.52°). Conclusions: Cantilevers’ design and proximity of the bends influenced force decay pattern overtime. Type 1 cantilevers presented more stable design at the first weeks than Type 2.
Highlights
Orthodontic tooth movement is the result of force application on a tooth
Type 1 cantilevers showed significant force decay only when group 4 (G4) was compared to group 1 (G1) (9.05 cN), group 2 (G2) (11.73 cN), and group 3 (G3) (9.78 cN)
Type 2 cantilevers presented differences when G1 was compared to G2 (9.57 cN) and G3 (7.89 cN)
Summary
Orthodontic tooth movement is the result of force application on a tooth. Primarily, orthodontists generate forces using archwires, springs, and elastics. Anchored at only one end, a cantilever is a beam with which the orthodontist can and accurately predict tooth movement.[1,2,3] By producing effects on the tooth in all three planes, controlling and individualizing the forces applied, cantilevers can be applied to provide intrusion or extrusion of one or several teeth simultaneously They can perform tractions, uprightings, retractions, and early corrections of the deep curve of Spee.[1,2,3,4,5,6] Because of their formability and springback characteristics, titanium-molybdenum alloys, 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] the use of β-titanium alloys enables the construction of cantilevers with simpler designs, saving time during the clinical procedures
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