Most of the time the retainers have to be worn for then 6 months. For initial 6 months they are worn day and night and after that they are worn for either alternate days or only at night.Some times they have to be worn for the life time and in that case the fixed retainers are given.he retainers are the ones that are going to keep your teeth just the way you wanted them and that is long after the braces are off. Although not many people are aware of this, they are considered to be the most important aspect of the treatment in teeth braces.