A rapid palatal expander (RPE) almost always causes a temporary space, known as a diastema, to form between the two upper front teeth. This noticeable gap is a physical sign that the appliance is working exactly as intended to widen the upper jaw. The presence of this gap confirms that the treatment is successfully achieving the desired skeletal correction. This cosmetic change is not permanent and is a predictable part of the process before the teeth are fully aligned.
The Mechanism Behind Gap Formation
The formation of a gap is a direct consequence of the expander’s primary goal: to widen the upper jaw (maxilla) at a skeletal level. The maxilla is composed of two halves joined down the center of the roof of the mouth by the mid-palatal suture. In children and adolescents, this suture is made of flexible connective tissue before it fully fuses, usually in late adolescence.
The RPE is a fixed appliance that attaches to the upper back teeth and has a central screw mechanism. When this screw is turned, it exerts continuous outward pressure on the two halves of the jaw. This controlled force physically separates the mid-palatal suture, widening the arch of the jaw. Since the two upper central incisors are anchored on either side of this separating suture, they are pulled apart as the bone widens beneath them, creating the noticeable space.
The rapid appearance of the gap, often within the first few days, confirms that the skeletal separation is occurring, which is the most effective way to correct issues like a narrow palate or a crossbite. An expansion rate of about 0.5 millimeters per day is common during the active phase.
How Long the Gap Lasts
While the gap may grow prominent during the active expansion phase, its duration is relatively short before it begins to close on its own. The active turning phase usually lasts only a few weeks until the desired jaw width is achieved. Once active turning stops, the RPE remains cemented in place for a passive retention phase necessary for stabilization.
During the retention phase, the tension from the fibers in the gum tissue surrounding the front teeth begins to pull the central incisors back toward each other. This natural biological process causes the gap to gradually shrink and often close completely, even while the expander is still fixed in the mouth.
The expander is typically kept in place for an additional three to six months after the last turn to allow new bone to solidify within the separated mid-palatal suture. This bone consolidation is essential to ensure the widened jaw remains stable and does not relapse to its original narrow width. By the time the expander is removed, the large gap that formed initially is usually gone, or only a very minor space remains.
What Happens After Expansion
The expander phase is usually the first step in a comprehensive orthodontic treatment plan. The appliance is removed only after the jaw has been adequately widened and the bone has stabilized. After the expander is taken out, the patient transitions to the next stage of treatment, which is most often traditional braces or clear aligners. These appliances refine the alignment of all the teeth.
While the expander closes the large gap between the two front teeth, subsequent treatment is required to fine-tune the bite and ensure all teeth are properly positioned. Braces or aligners will fully close any remaining small gaps and correct the rotational or positional issues of the front teeth that were slightly tipped by the expansion process. This second phase of treatment solidifies the improvements made by the RPE and achieves the final straight, functional smile.