This type of retainer is made of molded clear plastic and resembles an Invisalign aligner. People like this type of retainer because it is less noticeable than a Hawley retainer. However, it doesn’t allow your top and bottom teeth to touch in a natural way. Because of this, some orthodontists don’t like this type of retainer. Essix retainers also have a shorter lifespan than Hawley retainers. On average, they begin to wear out after a few years, and then need to be replaced.