Alobeid A, et al. – The present investigation was designed to assess force levels exerted by levelling arch wires with labial and lingual conventional and self–ligating brackets. According to the findings obtained, lingual bracket systems demonstrated higher forces compared to labial bracket systems that might be of clinical concern. The authors suggested highly flexible nickel titanium arch wires lower than 0.013–in for the initial levelling and alignment, particularly with lingual appliances.