Comparison of the force levels among labial and lingual self-ligating and conventional brackets in simulated misaligned teeth

Background/objective: The aim of this study was to evaluate force levels exerted by levelling arch wires with labial and lingual conventional and self-ligating brackets. Materials/methods: The tested orthodontic brackets were of the 0.022-in slot size for labial and 0.018-in for lingual brackets and were as follows: 1. Labial brackets: (i) conventional bracket (GACT-win, Dentsply), (ii) passive self-ligating (SL) brackets (Damon-Q (R), ORMCO; Ortho classic H4 (TM), Orthoclassic; FLI (R) SL, Rocky Mountain Orthodontics) and (iii) active SL brackets (GAC In-Ovation (R) C, DENTSPLY and SPEED (TM), Strite). 2. Lingual brackets: (i) conventional brackets (Incognito, 3M and Joy (TM), Adenta); (ii) passive SL bracket (GAC In-Ovation (R) LM (TM), Dentsply and (iii) active SL bracket (Evolution SLT, Adenta). Thermalloy-NiTi 0.013-in and 0.014-in arch wires (Rocky Mountain Orthodontics) were used with all brackets. The simulated malocclusion represented a maxillary central incisor displaced 2 mm gingivally (x-axis) and 2 mm labially (z-axis). Results: Lingual bracket systems showed higher force levels (2.4 +/- 0.2 to 3.8 +/- 0.2 N) compared to labial bracket systems (from 1.1 +/- 0.1 to 2.2 +/- 0.4 N). However, the differences between SL and conventional bracket systems were minor and not consistent (labial brackets: 1.2 +/- 0.1 N for the GAC Twin and 1.1 +/- 0.1 to 1.6 +/- 0.1 N for the SL brackets with 0.013-in thermalloy; lingual brackets: 2.5 +/- 0.2 to 3.5 +/- 0.1 N for the conventional and 2.7 +/- 0.3 to 3.4 +/- 0.1 N for the SL brackets with 0.013-in Thermalloy). Limitations: This is an in vitro study with different slot sizes in the labial and lingual bracket systems, results should be interpreted with caution. Conclusions/implications: Lingual bracket systems showed higher forces compared to labial bracket systems that might be of clinical concern. We recommend highly flexible nickel titanium arch wires lower than 0.013-in for the initial levelling and alignment especially with lingual appliances.