Retainer (orthodontics)

Top (left) and bottom (right) retainers
Vacuum form retainer in the foreground (used on upper); illustration of an early Hawley retainer in the background

Orthodontic retainers are custom-made devices, usually made of wires or clear plastic, that hold teeth in position after surgery or any method of realigning teeth. Once a phase of orthodontic treatment has been completed to straighten teeth, there remains a lifelong risk of relapse (a tendency for teeth to return to their original position) due to a number of factors: recoil of periodontal fibres, pressure from surrounding soft tissues, the occlusion and patient’s continued growth and development. By using retainers to hold the teeth in their new position for a length of time, the surrounding periodontal fibres are allowed to adapt to changes in the bone which can help minimize any changes to the final tooth position after the completion of orthodontic treatment.[1]

Retainers can be removable or fixed. The four types of retainers typically prescribed by orthodontists and dentists are Hawley, Essix, Zendura, and Bonded (Fixed) retainers. A review of the evidence suggests that removable retainers are only required to be worn part-time (at night) and that overall there is still insufficient evidence to recommend one type of retention procedure over another.[2]

Hawley retainer

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. The original clear bow named QCM, was developed to eliminate the look of wire across the facial surface of the arch. Excessive breakage has made this impractical for younger patients.

Vacuum-formed (Essix) retainer

Another common type of removable retainer is the vacuum formed retainer (VFR). This is a polypropylene or polyvinylchloride (PVC) material, which is more economical and faster to make, typically .020" or .030" thick. Essix (invented by Dr. John Sheridan) and Zendura are the brand names commonly associated with this retainer. 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. It is similar in appearance to Invisalign trays, though the latter are not considered "retainers." 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.[4] 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.[4] 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.

Most removable retainers are supplied with a retainer case for protection. During the first few days of retainer use, many people experience extra saliva in their mouth. This is natural and is due to the presence of a new object inside the mouth and consequent stimulation of the salivary glands. It may be difficult to speak for a while after getting a retainer, but this speech difficulty should go away over time as one gets used to wearing it.

Zendura clear retainer material
Zendura Dental Appliance Material with Thermoformed Clear Retainers.

Fixed retainers

An entirely different category of orthodontic retainers are fixed or bonded retainers. There are many different types of fixed retainers, which include :

· Reinforced fibres

· Fixed canine and canine retainer (only bonded to canine teeth)

· Multi-strand retainers (bonded to every tooth)

The most preferred bonded retainer is the multi-strand stainless steel wire type as it is bonded to every tooth in the labial segment, using composite resin or acid-etch composite bonding. For fixed canine and canine retainer, it is only bonded to the canine teeth and hence often cause relapse of the incisors ; and for the reinforced fibre retainers, they tend to fracture commonly. In order to prevent minor unwanted tooth movement, the fixed retainer must be passive.[4]

A fixed retainer typically consists of a passive wire bonded to the lingual-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.

References

  1. 1 2 Mitchell, Laura. An Introduction To Orthodontics. 1st ed. Oxford: Oxford University Press, 2007. Print.
  2. ↑ Littlewood, Simon J et al. "Retention Procedures For Stabilising Tooth Position After Treatment With Orthodontic Braces". Cochrane Database of Systematic Reviews (2016)
  3. ↑ S., Lynn. "Part Six: After the Braces Come Off". Braces 101: a primer for adults new to braces. Retrieved 2008-08-26.
  4. 1 2 3 Mitchell, Laura (2013). "16". An Introduction to Orthodontics. pp. 199–200. ISBN 978-0-19-959471-9.
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