A retainer is a custom-made oral appliance worn after orthodontic treatment to maintain the new alignment of the teeth. The retention phase is a continuation of the overall process, protecting the significant time and financial investment made in braces. Retention is non-negotiable because the biological structures supporting the teeth are temporarily destabilized during orthodontic movement. Without a retainer, the teeth almost immediately begin to shift back toward their original positions, a phenomenon known as relapse.
The Biological Drive for Dental Relapse
The immediate tendency for teeth to move back is driven by the “memory” of the periodontal ligaments (PDL). These ligaments are a network of fibers that anchor the tooth root to the surrounding alveolar bone. During orthodontic treatment, the continuous force from the braces stretches and compresses these fibers as the tooth is moved into a new location.
When the braces are removed, these stretched PDL fibers act like microscopic, elastic bands, exerting a strong, immediate pull to revert the tooth to its former position. This tissue rebound is the primary biological justification for why a retainer must be worn full-time immediately following the removal of braces. The retainer acts as a physical barrier against this inherent elastic recoil.
While the PDL fibers are a major factor, the gingival fibers (connective tissues in the gums) also contribute significantly to relapse. These fibers, particularly the transseptal fibers that run between the teeth, have a slower rate of remodeling compared to the PDL. They remain stretched and retain their memory for a longer period, sometimes months, exerting a persistent force that tries to rotate or move the teeth back.
Allowing Bone and Tissue Stabilization
Beyond the immediate elastic pull of the ligaments, retention is necessary to allow the supporting bone structure to solidify around the newly positioned teeth. Orthodontic movement involves a continuous process of bone remodeling, where bone tissue is resorbed (broken down) and deposited (built up) to allow the tooth to move through the jaw.
At the end of active treatment, the alveolar bone surrounding the roots is less dense and structurally immature, having been actively broken down and rebuilt. The bone needs time, often many months, to fully mature, calcify, and structurally stabilize the teeth in their new positions.
The retainer holds the teeth in place while this long-term maturation process occurs. Research shows that bone density around the teeth can significantly increase during the retention period, sometimes recovering to near-original levels after 20 to 22 months of retention. If retention is discontinued too soon, the immature bone cannot withstand the forces of chewing and soft tissue memory, leading to a gradual shift.
Choosing the Right Retention Method
The practical solution to preventing relapse involves choosing a suitable retention device and following a prescribed wear schedule. Retainers fall into two main categories: removable and fixed.
Removable Retainers
Removable retainers, such as the clear plastic Essix style or the acrylic and wire Hawley appliance, offer the benefit of being taken out for eating and oral hygiene. The clear Essix retainer is often favored for its near-invisibility and its ability to hold the teeth firmly on all sides. The Hawley retainer is more durable and adjustable, though the wire across the front of the teeth makes it more noticeable. Both types typically require full-time wear for the first several months, transitioning to a nighttime-only schedule as the supporting tissues stabilize.
Fixed Retainers
Fixed, or bonded, retainers consist of a thin wire permanently cemented to the tongue-side of the teeth, usually across the lower front teeth. The main advantage is that they are compliance-free, meaning they continuously hold the teeth in position without the patient needing to remember to wear them. However, a fixed wire can make flossing more challenging, requiring the use of floss threaders or specialized tools to maintain hygiene and prevent plaque buildup.
The choice of retainer is highly individualized, and retention is generally considered a lifetime commitment to ensure the stability of the orthodontic result.