Teeth can move after braces, a phenomenon known as relapse. After investing time and resources into straightening teeth, it can be frustrating to learn that alignment is not permanent. Teeth have a natural tendency to shift back toward their original positions or drift over time. Understanding the biological forces and external factors that cause this movement is essential for protecting your orthodontic results.
Why Teeth Are Not Static
The underlying reason teeth move is that they are not rigidly fused to the jawbone. Each tooth is held in its socket by the periodontal ligament (PDL), a network of fibers that allows for slight movement during chewing. When braces move a tooth, the PDL fibers are stretched on one side and compressed on the other. This action triggers a biological response known as bone remodeling.
Bone remodeling involves two types of cells: osteoclasts that resorb bone and osteoblasts that deposit new bone. This continuous process allows the tooth to travel through the jawbone to its new location. Once braces are removed, the PDL fibers and surrounding gum tissues possess a “memory.” They try to pull the tooth back to its previous position, and it takes months or years for the surrounding bone and soft tissues to fully stabilize around the new alignment.
Specific Triggers for Relapse
Beyond the biological memory of the PDL, several external and internal factors push teeth out of alignment after treatment. One significant factor is the continued maturation and growth of the jaws, particularly in younger patients who finish treatment before skeletal maturity. This ongoing growth can change the shape of the dental arches and lead to crowding, especially in the lower front teeth.
Teeth also have a lifelong tendency to slowly migrate forward, a process called mesial drift. Habitual factors place external forces on the teeth, acting like small, constant orthodontic appliances. These habits include chronic teeth grinding or clenching (bruxism), which applies intense, repeated pressure. Other common triggers are an incorrect swallowing pattern known as a tongue thrust or habitually resting the tongue improperly against the teeth.
The Essential Role of Retention Devices
Retention is the stage where corrected tooth positions are stabilized, and it is the most important factor in preventing relapse. The primary goal of a retention device is to hold the teeth in their final position, allowing the bone and soft tissues to fully reorganize around the roots. Failure to wear the retainer as instructed is the most frequent cause of teeth shifting.
There are three main types of retainers, each providing a different approach to stability.
Hawley Retainers
Hawley retainers are a classic choice, featuring a metal wire that wraps around the teeth and is embedded in a custom-molded acrylic base. They are durable, easily adjustable for minor movement, and removable for cleaning. However, the wire is visible.
Vacuum-Formed Retainers
Another popular choice is the vacuum-formed retainer, often called an Essix retainer. This is a clear, thin plastic tray that fits snugly over the entire arch of the teeth. These are highly aesthetic and nearly invisible, making them a favored option for many adults. They are less durable than Hawley retainers and may need replacement more frequently due to wear or cracking.
Bonded Retainers
A third option is the bonded, fixed, or lingual retainer. This consists of a thin wire permanently cemented to the tongue-side of the front teeth, most commonly on the lower arch. This option offers continuous retention without requiring patient compliance. However, it demands meticulous oral hygiene to prevent plaque buildup around the wire. Orthodontists typically prescribe full-time wear initially, transitioning to lifelong nightly use to ensure stability.
Addressing Minor Shifting
Even with diligent retainer wear, minor shifting can sometimes occur due to natural aging or a temporary lapse in compliance. If you notice a small change, contact your orthodontist immediately, especially if your retainer feels tighter than usual. For very minor movements, increasing the wear of your existing retainer back to full-time for a few weeks may be enough to gently push the teeth back into alignment.
When movement is too significant for the original retainer to correct, other options are available that do not necessitate a return to full braces. Minor tooth movement can often be addressed with a series of passive aligners, sometimes called a clear aligner “touch-up.” This limited re-treatment uses a small number of custom-made trays to quickly reposition the affected teeth. Seeking early intervention is recommended, as addressing minor relapse promptly is easier and less costly than waiting until full re-treatment is required.