A retainer is a fixed or removable orthodontic appliance, custom-fit to the patient. Retainers are mainly used to hold a patient’s teeth in the positions to which they’ve been moved by treatment, usually with braces but sometimes with surgery. In some patients, retainers are used to control tongue thrusting or to prevent grinding of teeth. The focus of this review is retention after orthodonture.
WHAT ARE THEY GOOD FOR?
Understanding why retainers are needed after the braces come off invites us to look more closely at the way braces work in the first place. It’s pretty obvious that the appliances an orthodontist attaches to a patient’s teeth apply constant pressure, and that this pressure slowly moves the patient’s teeth to the desired positions and alignment. Gums are soft, it’s easy to see how they wouldn’t put up much resistance to the pressure applied by braces. If teeth were like plastic tabs stuck in clay gums, they’d stay where they were moved to. A closer look shows why teeth that have been repositioned by braces have a tendency to move back toward their previous positions.
The roots of a tooth fit into a socket in the alveolar bone of the jaw, and the tooth is sealed and supported there by the surrounding gum tissue. Teeth are anchored to the jaw bone by a ligament, and like other ligaments in the body, the periodontal ligament is flexible and tough. The periodontal ligament connects the tooth’s root to the alveolar bone, securing the tooth in its socket. The flexibility of the periodontal ligament allows for limited, near-microscopic freedom of movement for the tooth, “give”, which provides shock absorption during chewing and protects the tooth from breaking.
Braces apply pressure to a tooth in the desired direction of movement. The jaw bone, periodontal ligament, and gums slowly adapt by “remodeling”. Bone is removed on the side of the socket toward which the tooth is pressured, and added on the other side. The periodontal ligament and gums also remodel to accommodate the tooth’s movement.
This brings us to the main reason retainers are needed after braces have moved teeth to their new positions. Braces move teeth slowly, imperceptibly, but the movement is faster than the remodeling processes of the affected tissues. When the braces come off, these adaptations are not complete. There are still pressures urging the teeth back toward their original positions. The job of a retainer is to counter these pressures, and permit continued remodeling.
We’ll review the several types of retainers, and discuss caring for them and living with them, but first The Question must be addressed: how long? How long must a patient wear retainers after the braces come off? The best answer is one that’s not too satisfying: it depends!
All other things being equal, it would seem that a patient should be able to stop wearing a retainer when remodeling of bone, gum, and the periodontal ligament is completed. There should no longer be any pressures pushing teeth back to their previous positions.
In theory, it’s true. It’s thought that the alveolar bone remodeling completes within a year after teeth are moved to their final positions. Indeed, some orthodontic patients are able to toss their retainers after a year or so without experiencing a significant relapse.
In life, though, other things are not always equal. Most orthodontic patients are kids. Kids grow, and the shape and geometry of their jaws change over time. When a child or adolescent finally gets to de-banding day and the braces come off, it’s highly likely that the oncoming years of growth will see natural remodeling of the structures impacted by his or her orthodontic treatment. Retainers will be in the picture until things stabilize.
Adults are a fast-growing segment of the orthodontic patient community, and on their side of the life cycle, there’s also movement. Adults’ jaws, gums, and teeth are continuously adapting to the forces acting on them. Ongoing and changing stresses due to eating habits and wear on teeth stimulate remodeling. There are long-term remodeling trends due to normal aging, too. Adults’ jaw length decreases as they move toward middle age when jaw height also begins to decrease. There’s an overall decrease in jaw volume, which encourages crowding of teeth. All these factors make adults candidates for long-term retainer use after braces.
This brings us to a review of the types of retainers used in contemporary orthodontic practice. There are removable retainers, inserted and removed at will by patients themselves, and fixed (bonded) retainers which are installed and removed after longer periods, by the orthodontist.
Perhaps the most familiar removable retainer is the Hawley type, with the plastic shell that fits to the roof of the patient’s mouth. A wire runs over his or her front teeth. The plastic shell is acrylic, custom-molded to the patient’s mouth. It’s adjustable, so the orthodontist can tune it for optimum effectiveness and comfort. The downsides are cosmetic because the wire is conspicuous and some patients tend to lisp at least initially. They’re removable, which is convenient for cleaning teeth, but they won’t work unless they’re put back in. It falls on the patient to be disciplined about wearing it per the orthodontist’s instructions.
The Essix removable retainer is a different design concept. They look a bit like transparent versions of the tooth guards worn by athletes in contact sports, only much more refined and delicate. Essix retainers fit over the teeth. They solve the cosmetic problem by being virtually invisible. Downsides include relative short lifetime, perhaps six months as opposed to many years for the Hawley type. There may be dental hygiene issues, too, as the interior surfaces of these retainers are hard to clean and can trap decay-promoting liquids against tooth surfaces. Lastly, Essix retainers interfere with normal bite, since they don’t allow upper and lower teeth into direct contact with each other.
Finally, fixed or “bonded” retainers are glued by the orthodontist to the back of the teeth, usually the lower front teeth. Like the Essix removable type, bonded retainers are invisible to onlookers. They also relieve the patient of the burden of remembering his or her duty, since they stay in place until the orthodontist removes them. They’re applied to front teeth, and so cannot directly address stabilization of the other areas of a patient’s mouth. Since Hawley retainers are applied to the upper teeth, bonded retainers are sometimes installed for use in conjunction with a Hawley type, to cover all the bases.
LIFE GOES ON
The requirement for a retainer to stabilize orthodontic outcomes is long-term, but nearly always diminishes over time. A patient will likely have to wear a retainer 24/7 for the first year or so after de-banding, but then the orthodontist may recommend nighttime-only, and at a later stage, occasional wear. People are very good at adapting to retainers and find ways to minimize any inconvenience or discomfort. The retainer quickly vanishes into the background noise of everyday life.
Retainers are going to be in the lives of orthodonture patients, younger and older, for a long time. How long depends on the factors we reviewed earlier, but never less than a year after braces come off. Some patients will be best served by wearing retainers, though perhaps only at night and not every night, for the rest of their lives. Our bodies are in constant change throughout our lives, but retainers, thankfully, retain the value of our investment in orthodonture. They keep us in good shape.