Hawley: a retainer made of metal wire and plastic. The metal wire typically surrounds the six anterior teeth and helps keep them in place. The advantage to these types of retainers is that the metal wire can be adjusted to finish treatment and continue minor movement of the anterior teeth as needed.
Essix: these vacuum-formed, transparent retainers are molded around your teeth and are similar in appearance to Invisalign aligners.
Fixed Retainer: these retainers are minimally compliant, because they are bonded to the back of the lower front teeth, which means you never have to worry about losing it or not wearing it. Additionally, teeth naturally shift as we age, so a fixed retainer typically provides a better long-term result for teeth straightening than a removable retainer.