Certain cases, it is observed by the orthodontist that the teeth once aligned and positioned correctly, will need some additional and perhaps, prolonged support to maintain them in the corrected position.
In such cases, (unless the patient resolves to be extremely particular with removable retainers), the Orthodontist advises Fixed retainers as the solution. The Fixed Retainer is made of Stainless Steel, or Titanium wire contoured as per the inside surfaces of the front teeth, fixed on the inside of the front four to eight teeth (varies case to case) with a special dental adhesive.
Though not compulsory, it is always prudent on the part of the patient and Orthodontist to give an additional BACK UP removable retainer to the patient along with the fixed retainer.( In effect the patient gets two retainers per jaw - One - fixed, the other - removable). The Back up retainer is to be worn only at nights.
The rationale behind a Back up removable retainer : If ever the adhesive holding the wire in place comes off, or, the wire breaks, the patient may not realise it. He/She would come to know of the damage only after he/she observes the tooth out of line. If the patient , however, was wearing the Back up retainer every night, the tooth would not move out of place and the damage can be detected by the Orthdontist on the patient's annual follow up visit and repaired easily.