▁time ▁being ▁longer ▁when ▁self ▁lig ated ▁orth od ont ic ▁brackets ▁are ▁used ▁compared ▁to ▁conventional ▁orth od ont ic ▁brackets . ▁ ▁Fr iction ▁ ▁A ▁system atic ▁review ▁done ▁by ▁E hs ani ▁et ▁al . ▁in ▁ 2 0 0 9 , ▁stated ▁that ▁self - lig ating ▁brackets ▁produce ▁lower ▁fr iction ▁when ▁couple d ▁with ▁small ▁round ▁arch w ires ▁in ▁the ▁absence ▁of ▁t ipping ▁and / or ▁tor que ▁in ▁an ▁ide ally ▁aligned ▁arch . ▁However , ▁sufficient ▁evidence ▁was ▁not ▁found ▁to ▁claim ▁that ▁with ▁large ▁rect angular ▁w ires , ▁in ▁the ▁presence ▁of ▁t ipping ▁and / or ▁tor que ▁and ▁in ▁arch es ▁with ▁considerable ▁mal oc clusion , ▁self - lig ating ▁brackets ▁produce ▁lower ▁fr iction ▁compared ▁with ▁conventional ▁brackets . ▁Other ▁studies ▁also ▁agree ▁that ▁round ▁w ires ▁produce ▁less ▁fr iction ▁than ▁the ▁rect angular ▁w ires . ▁They ▁also ▁stated ▁that ▁most ▁of ▁the ▁evaluated ▁studies ▁agreed ▁that ▁fr iction ▁of ▁both ▁self - lig ated ▁and ▁conventional ▁brackets ▁increased ▁as ▁the ▁arch wire ▁size ▁increased . ▁However , ▁a ▁study ▁done ▁by ▁P izz oni ▁et ▁al . ▁stated ▁that ▁self - lig ating ▁brackets ▁had ▁a ▁marked ly ▁lower ▁fr iction ▁than ▁conventional ▁brackets ▁at ▁all ▁ang ulations . ▁ ▁Active ▁vs . ▁Pass ive ▁brackets ▁ ▁Self - lig ating ▁brackets ▁can ▁be ▁of ▁two ▁types . ▁Active ▁self - lig ating ▁brackets ▁have ▁a ▁clip ▁that ▁works ▁to ▁press ▁on ▁the