An Essix retainer is a clear, almost invisible style of retainer that is similar in appearance to Invisalign. The Essix retainer is a name most modern dental offices are familiar with, but it’s really a brand of vacuum-formed retainers. Essix retainers are one brand of plastic retainers. When your braces are off and your teeth look straight and beautiful, but how do you make sure they stay that way? Retainers are an important part of orthodontic treatment. No matter what type of braces you had, you will need to wear a retainer. The retention phase of orthodontic treatment lasts a lifetime. The only way to prevent teeth from shifting and becoming crooked again is to wear the retainer your orthodontist has prescribed.