Orthodontic treatment with fixed braces can last from three months to correct just one tooth up to three years for very complex treatment. The average duration for orthodontic treatment in adults is probably around 24 months.
On the other hand, the duration of treatment with lingual braces can be 10 – 20% longer, depending on the skill and experience of the orthodontist. The best orthodontists can achieve shorter treatment times using lingual braces than average orthodontists can with labial braces (i.e. fixed to the outside of the teeth).
To summarise, it can be said that, given that the training and treatment methodology is good, there is very little difference between the length of treatment with labial braces and that of lingual braces.