Torque moments and stress analysis in two passive self-ligating brackets across different incisor inclinations: A 3-dimensional finite element study

Abstract

Objective: To compare torque expression characteristics between rectangular slot (0.022″ x 0.028″) Damon Q passive self-ligating brackets (Ormco, Glendora, Calif) and square slot (0.021″ x 0.021″) Pitts 21 brackets (OC Orthodontics) using 0.019″ x 0.025″ Stainless Steel and 0.020″ x 0.020" Titanium Molybdenum alloy wires at various incisal inclinations using finite element analysis. The null hypothesis was that there were no differences in torque expression in both tested groups.

Methods: Reporting guidelines for in-silico studies using finite element analysis in medicine (RIFEM) were used. Damon Q and Pitts 21 brackets were scanned and 3D models generated. Brackets were placed on a 3-D model of a maxillary central incisor with its long axis inclined at 0⁰,5⁰,10⁰,15⁰ and 20⁰ to the occlusal plane. Final 0.019″ x 0.025″ SS and 0.020″ x 0.020" TMA archwires were inserted into slots of both tested brackets. Geometric models were converted into finite element models. Material properties were assigned for involved structures with automatic meshing performed by software. Torque movements were simulated with the FE program Ansys Space claim R 22.

Results: Torque moment values, torque expression and Von - Mises stress was higher in Pitts 21 than Damon Q at all inclination angles. There was a gradual increase in the magnitude of values with decrease in incisal inclination.

Conclusion: Square slot passive self-ligating brackets show superior torque expression characteristics as compared to rectangular wire-rectangular slot combinations. The FEM results should be validated with in-vivo studies in order to confirm the findings.

Keywords: FEM; Rectangular slot; Square slot; Tooth inclination; Torque.

Graphical abstract

Fig. 1

Methodology: A) Solid model of Damon Q bracket with 0.019″x0.025″ SS wire, B) Solid model of Pitts 21 bracket with 0.020″x0.020″ TMA wire, C) Meshing of Damon Q bracket with nodes, D) Meshing of Pitts 21 bracket with nodes, E) Boundary conditions of Damon Q, F) Boundary conditions of Pitts 21, G) Bracket placed at different inclinations of maxillary central incisor.

Fig. 2

Assessment: A) Torque moment in Damon Q, B) Torque moment in Pitts 21, C) Total deformation in Damon, D) Total deformation in Pitts 21, E) Von -Mises Stress in Damon Q, F) Von -Mises Stress in Pitts 21.

Fig. 3

Comparison of torque moments between Damon Q and Pitts 21 at different incisal inclinations.

Fig. 4

Comparison of total deformation (tooth movement) with Damon Q and Pitts 21 at different inclinations.

Fig. 5

Comparison of Von-Mises stress between Damon Q and Pitts 21 at different incisal inclinations.