Retainer (orthodontics)

The underneath surface of an upper Wrap Around Hawley retainer resting on top of a retainer case

The best-known removable retainer is the Hawley retainer, which consists of a metal wire that typically surrounds the six anterior teeth and keeps them in place. Named for its inventor, Dr. Charles A. Hawley, the labial wire, or Hawley bow, incorporates 2 omega loops for adjustment. It is anchored in an acrylic baseplate that sits in the palate (roof of the mouth). The advantage of this type of retainer is that the metal wires can be adjusted to finish treatment and continue minor movement of the anterior teeth as needed.[3] It also benefits from being robust and rigid, easy to construct and allows prosthetic tooth/teeth to be added onto. The main disadvantages of this type of retainer is its inferior aesthetics, interference with speech, risk of fracture and inferior retention of lower incisors in comparison to vacuum-formed retainers.[1]

Recently, a more aesthetic version of the Hawley retainer has been developed. For this alternative, the front metal wire is replaced with a clear wire called the ASTICS. This retainer is intended to be adjustable similarly to the traditional Hawley retainer, which is not practical with vacuum-formed retainers.

Another common type of removable retainer is the vacuum formed retainer (VFR). This is a polypropylene or polyvinylchloride (PVC) material. This clear or transparent retainer fits over the entire arch of teeth or only from canine to canine (clip-on retainer) and is produced from a mold. The retainer is virtually invisible and clear when worn. Hence, it can provide aesthetics value to the patient. VFRs, if worn 24 hours per day, do not allow the upper and lower teeth to touch because plastic covers the chewing surfaces of the teeth. Some orthodontists feel that it is important for the top and bottom chewing surfaces to meet to allow for "favorable settling" to occur. Besides that, it is advisable to wear VFRs only at night, every night.[1] When eating is necessary, the retainer is removed to allow natural consumption and to avoid the crushing of the VFR. Patient should be informed never to drink, especially cariogenic or fizzy drinks, with VFR in situ as it will lead to substantial loss of tooth surface and dental caries. The retainer can behave like a reservoir, enclosing the incisal edges and cuspal tips with the cariogenic drink, leading to decalcification of teeth.[1] VFRs are less expensive, less visible, and easier to wear than Hawley retainers; however, for patients with disorders such as bruxism, VFRs are prone to rapid breakage and deterioration, especially if the material is PVC, a short chain molecule which breaks down far more quickly than polypropylene, a long chain molecule.[4]

A fixed retainer typically consists of a passive wire bonded to the tongue-side of the (usually, depending on the patient's bite, only lower) incisors. Unlike the previously-mentioned retainer types, fixed retainers cannot be removed by the patient. Some doctors prescribe fixed retainers regularly, especially where active orthodontic treatments have affected great changes in the bite and there is a high risk for reversal of these changes. While the device is usually required until a year after wisdom teeth have been extracted it is often kept in place for life. Fixed retainers may lead to tartar build-up or gingivitis due to the difficulty of flossing while wearing these retainers. As with dental braces, patients often must use floss threaders to pass dental floss through the small space between the retainer and the teeth.