Comparison of slot deformation in stainless steel and ceramic brackets during torque - A finite element analysis

Introduction: Torque in orthodontics is vital in final positioning of the teeth during fixed appliance therapy. Torqueing of archwires is a significant factor in transferring the applied forces to the bracket which might cause deformation of the slot. Any deformation in the bracket slot can vary the torque prescription and thus can affect the tooth position. Aim: To evaluate and compare the deformation of stainless steel (SS) and ceramic bracket slots during torque, using finite element analysis. Materials and methods: A maxillary right central incisor bracket (0.022 x 0.028 inch) dimensions were measured using a profile projector, and a finite element (FE) model was constructed. Bracket materials considered were stainless steel (SS) and ceramic. An SS rectangular archwire (0.019 x 0.025 inch) with angles of twist ranging from 5° to 40° was theoretically converted into torque. The bracket slot deformation was obtained at the top, middle and bottom locations using FE analysis. Results: There is a uniform increase in deformation in the bracket slot walls from torque of 9.7 to 77.62 Nmm except that there is a 100 percent increase in deformation when the torque changed from 38.81 to 48.51 Nmm. The top location in the gingival slot wall showed maximum deformation compared with middle and bottom slot positions in both the materials. The deformation of SS bracket slot was more than the ceramic bracket slot. Conclusion: This study showed that the bracket slot walls of both SS and ceramic brackets are subjected to deformation by application of torque and the maximum deformation was in the upper part of the bracket slot. Corresponding Author: Pandurangan Harikrishnan Teeth”N”Jaws Center, 600034 Chennai, India e-mail: [email protected] Comparison of slot deformation in stainless steel and ceramic brackets during torque A finite element analysis Original Article INTROdUCTION In fixed appliance therapy, there is transfer of force from the archwire to the teeth through the bracket. In this force transfer mechanism especially during torque, there is a possibility of bracket deformation. It is necessary to study the bracket deformation, in order to understand the effective torque. Torque is the ability of force to rotate an object around an axis or pivot. In orthodontics, torque is a moment generated by the torsion of a rectangular wire in the bracket slot. The terms “moment”, “torsional moment”, “couple”, “biomechanical torque”, “thirdorder torque” is often used in the orthodontic literature indicating the same loading conditions. 1 The variables in the expression of torque include the stiffness of wire alloys, the play between wire and slot, the ligation modes, and the bracket design. 2 The rectangular archwire bracket slot relationship establishes the stability of tooth root position. Incisor torque is important to get the proper interincisal angle, overjet and for optimal posterior teeth occlusion as well. Experimental studies available for predicting the orthodontic bracket behavior for an applied torque needs extensive instrumentation. 3-6 Moreover, they do not allow a graphical display of the deformation and stress distribution for the clinicians to visualize. Prior deformation studies have been limited to tie wing displacement. 6-8 The finite element (FE) method is an approximation technique used by numerical equations. This technique can be used to model the physics of complex structures. 9 The development of a numerical model makes it possible to quantify and evaluate the effects of torsional forces applied to achieve tooth movement.10 Finite element method is suggested by many authors for deformation and stress studies.11-12 Harikrishnan P, Magesh V, Kingsly Jeba Singh D. Comparison of slot deformation in stainless steel and ceramic brackets during torque A finite element analysis. South Eur J Orthod Dentofac Res. 2017;4(1):5-8. Submitted: August 25, 2016; Revised: February 24, 2017; Published: April 19, 2017 5 South Eur J Orthod Dentofac Res Harikrishnan P. et al. Slot deformation during torque