A retainer (synonyms: tooth stabilizer, retention device) is a removable or fixed orthodontic appliance worn to stabilize the long-term success of orthodontic therapy after it is completed. In the course of orthodontic treatment, teeth are moved in the jawbone, optimizing their position. This is possible by applying precisely measured forces. As a result, bone is removed from the side of the tooth toward which it is to be moved, while new bone is formed on the other side. Since these processes are not tied to growth phases, teeth can be moved even in adulthood. The tooth movements stretch tissues and exert traction on connective tissue fibers of the periodontium (periodontium). If the orthodontic appliance is no longer worn, there is a risk of recurrence (return to the original position). Up to four years after a fixed multiband treatment, the teeth still show increased degrees of loosening. The incomplete growth in adolescents and unbalanced muscle forces can also have a negative effect on the treatment result. In certain cases, there is even a lifelong risk of recurrence, whereby genetically determined anomalies are in principle more prone to recurrence than acquired malocclusions. Therefore, even after the actual orthodontic treatment has been completed, the teeth must be held in their new position for as long as possible using special aids – retainers. The longer the retention phase (holding phase after completion of treatment), the better the result will be. As a rule of thumb, the retention phase must last at least as long as the active treatment, but often longer. In certain cases, even lifelong permanent retention must be recommended. Retainers are available both as removable appliances (passive plate appliances or deep-drawing splints), which stabilize the teeth of one jaw at a time, and in the form of fixed wires, which are usually fixed to the lingual surface (the surface facing the tongue) of the anterior teeth. Understandably, after several years of orthodontic treatment, the patient’s compliance, i.e. his or her willingness to take responsibility for the success of the treatment, inevitably decreases. It is therefore not surprising if one or the other removable appliance ends up in the drawer permanently, even though it only has to be worn once or twice a week at night after a weaning phase. Fixed retainers therefore significantly reduce the risk of recurrence.
I. Lingual retainer
Lingual retainers (adhesive retainers) are usually made of drawn or stranded stainless steel wire or hard gold alloys. A nearly invisible alternative, but one that lasts only a few months, is a fiberglass “wire” in a polymer resin bonding agent (Ever Stick Ortho). In addition, more elaborate constructions with lingual adhesive brackets on the terminal teeth or lingual retainers made by casting are also used. These are bonded to the lingual surfaces not at points, but over their entire extent. Adhesive retainers made of wire lie delicately on the lingual surfaces (surfaces facing the tongue) of the teeth and are selectively bonded to each tooth using the etch-adhesive technique (adhesive technique in which the luting resin forms a micromechanical bond with the enamel surface). They are usually placed from canine to canine (3-3 retainers) in both the maxilla and mandible, but more extensive or smaller retainers – e.g., between two central incisors after diastema closure (anterior gap) – are also conceivable.
Indications (areas of application)
- For stabilization of the achieved tooth position in the anterior region – e.g. after closure of a diastema mediale (synonyms: trema, gap between the central incisors) or after gap closure of an unattached lateral incisor.
- After derotations (turning out) of the incisors.
- After resolution of an anterior tooth crowding, especially in the lower jaw.
- For stabilization after vertical tooth movement (intrusion: elongated tooth was moved into the jaw and thus shortened; extrusion: tooth was elongated).
- After transverse extension (distance between the canine and posterior teeth was increased in the transverse direction when the jaw was too narrow).
- In case of lack of compliance for a removable retainer.
- For permanent retention
The procedure
- Impression taking with alginate impression material can be done in this procedure even before the orthodontic appliance is removed, as it does not cover the lingual surfaces of the teeth.
- Production of plaster models based on the impressions.
- Individual adaptation of the wire by bending it to the contours of the lingual surfaces. The wire must fit the surfaces without tension.
- Manufacture of a key, e.g., from silicone, which facilitates the transfer and fixation of the wire in the patient’s mouth.
- Cleaning the lingual surfaces of the teeth
- Conditioning – The lingual surfaces of the teeth are chemically roughened with 35% phosphoric acid for 60 seconds. Rinse off the acid for at least 20 seconds and dry with air.
- Putting the key together with the wire on the teeth. The key leaves the lingual surfaces of two teeth free, over which the first fixation of the wire by means of low viscosity composite (plastic) by light curing.
- After removing the key, the wire can be fixed to the remaining teeth in the same way.
- Instruct the patient on dental hygiene with interdental brushes used between the gingiva (gum) and retainer in a horizontal direction from labial to lingual (from the lip to the tongue side).
After the procedure
According to Harzer, the retention phase with a lingual retainer should last at least five years and should continue beyond the eruption of the wisdom teeth, unless they were removed anyway for orthodontic reasons. The retention phase is followed by the orthodontist at longer intervals.
II. passive plate appliance
They are visually similar to removable orthodontic therapy appliances that actively exert forces on the teeth. Unlike these, however, plate appliances for retention only rest passively against the teeth, i.e., without the application of force and thus without tension. If tension builds up, this is the sign of a recurrence, which must be counteracted by wearing the retainer more frequently. One advantage of plate appliances is that they can be extended with active elements if there are signs of recurrence that cannot be counteracted by wearing the retainer more consistently. Different design principles are available for passive plate appliances, depending on the initial findings and the course of therapy: For example, if tooth movements in the vertical direction are to be made possible during the retention phase, the design must be free of metal elements on the occlusal surfaces concerned (Hawley retainer or wrap-around). This is also achieved by a spring retainer which extends only over the anterior teeth and encloses them with plastic shields through which a stabilizing wire runs. Extensive anterior movements or derotations (rotations out) require the labial surfaces (anterior sides of the teeth) of the anterior teeth to be physically restrained by a resin-sheathed labial arch, to name a few examples.
Indications (areas of application)
- Stabilization of vertical tooth movements
- Free space for vertical tooth movements (Hawley, wrap-around, spring, etc.)
- Stabilization of all teeth of a jaw in their final position.
- After derotations and extensive movements in the anterior region with plastic-coated labial bow.
Contraindications
- Lack of patient compliance with regard to required wearing times.
The procedure
- Impression taking usually with alginate impression material immediately after removal of the fixed multiband appliance.
- Fabrication of plaster models based on the impressions.
- Manufacture of the plate in the dental laboratory from individually bent retaining elements (clasps, button anchors, etc.) and PMMA-based plastic (polymethymethacrylate), in which they are anchored.
- Insertion of the retainer on the patient – the retention of the plate is done via clasps and/or button anchors and can be influenced by their de-/activation.
- Instructing the patient regarding the wearing times.
III. miniplast splint
According to the manufacturing process also called thermoforming splint, it is made of thermoplastic clear acrylic plastic.It encloses all the dental crowns of a jaw up to just below the respective dental equator (widest protrusion of the dental crowns), under which it snaps in, providing support without additional clasps. A special form of the deep-drawn splint is the Essix splint: The thermoplastic properties of the material allow grooves and nubs, which are inserted into the splint with the help of special preheated pliers, to cause minor positional corrections.
Indications (areas of application)
- Stabilization of vertical tooth movements
- Stabilization of all teeth of a jaw in their final position by physical enclosure.
Contraindications
- Lack of patient compliance with regard to required wearing times.
The procedure
- Immediately after removal of the multiband appliance, impression taking with alginate impression material.
- Fabrication of plaster models based on the impressions.
- Undergoing areas under the tooth equators are blocked out on the plaster model.
- Heating of a plastic plate, initially 1-2 mm thick, until it is plasticized to the extent that it can be “deep-drawn” over the jaw model in the vacuum of a thermoforming device, following the contours of the tooth crowns.
- After cooling, the acrylic returns to its solid state. The plastic is separated just below the equators of the teeth, the edges are reworked so that the splint fits without interference for the soft tissues of the lips and cheeks.
- Incorporating the splint on the patient – too strong hold on the teeth can still be reduced here if necessary.
- Practicing the insertion and removal with the patient.
After the procedure
According to Harzer, the wearing times of a removable retainer should follow the following schedule:
- Three months day and night
- Three months half day and night
- Six months at night
- Continue to wear every other night, then every third night, finally once a week and continue to “fit”, ie: If the retainer starts to jam, this is a sign of tooth migration, so the wearing frequency must be increased again.
The retention phase is accompanied by the orthodontist at increasingly longer intervals of check-up appointments.
