Frictional Resistance in Conventional, Active and Passive Self-ligating Brackets

Objectives: To compare the frictional resistance between conventional, passive self-ligating and active self-ligating brackets by Finite Elements Analysis (FEA).
Methods: 79 sliding experiments were made by combining conventional brackets, 0.018” stainless steel archwire and 0.010” ligature in an INSTRON 3345 load system. The average maximum static frictional resistance (MSFR) was obtained. MSFR value was compared with the FR (frictional resistance) obtained by simulations using the same combination of brackets and archwire by FEA. Once FEA was validated, CAD (Computer Aided Design) models of conventional, active and passive self-ligating brackets and archwires were created. A comparison of the MSFR was made between these brackets in combination with different archwire alloys (NiTi, Stainless Steel, TMA) and cross-sectional sizes (0.018", 0.019" x 0.025", 0.020" x 0.020").
Results: Experimental MSFR was 2.42 N (p=0.05) and FEA MSFR was 2.44 N, which resulted in the validation of FEA. The simulation showed the lowest MSFR in the passive self-ligating bracket, followed by conventional and active self-ligating brackets. With respect to the archwire dimension, the minimum stress occurred with the 0.018" archwire, followed by the 0.019" x 0.025" archwire and the maximum stress was observed with the 0.020" x 0.020" archwire. However, the active self-ligating bracket with 0.020" x 0.020" archwire produced less stress when compared to the 0.019" x 0.025" archwire.
Conclusions: FEA is an alternative for predicting the MSFR in various combinations of brackets and archwires. According to the FEA, passive self-ligating bracket produced the lowest MSFR, followed by conventional brackets. The highest MSFR was produced by the active self-ligating bracket. The greater contact area between the archwire and the bracket slot resulted in greater frictional resistance. The active self-ligating bracket produced a high frictional force in all combinations of bracket and archwire due to its larger contact area and the spring clip.