Even though some children may benefit from early treatment, the optimal age to treat most children is about 11-12 years of age, that is, at the end of the mixed dentition when most of the permanent teeth have erupted. Commencing treatment at this age which is around the time of pre-pubertal growth spurt may enhance jaw growth and optimise your orthodontic result.
In teenagers, we generally use fixed appliances also called train-tracks (plain metal or with colours). Sometimes, train tracks are supplemented by removable appliances.
Recently we have started to use Invisalign Teen which is Invisalign for teenagers.