Expanders and Growth Appliances: What They Are Like

Palatal expanders

The upper jaw is two halves joined at a midline suture that usually fuses during the mid-to-late teens, though the timing varies from person to person. An expander, cemented to the upper back teeth, pushes the halves apart a fraction of a millimetre per turn; the body fills the space with new bone. It is used for a narrow upper jaw with a posterior crossbite, and sometimes to make room for crowded teeth or for an upper canine that is heading the wrong way.

Fitting (30 to 45 minutes)Separators may be placed a week before to make room around the molars. The expander is cemented in; the mouth feels full and the tongue explores it constantly for days.
Days 1 to 5Speech is thick, swallowing feels odd, saliva increases. Soft food. Practise reading aloud; it speeds the adjustment.
Turning phaseA parent inserts the key into the hole in the screw, pushes it toward the back of the mouth until the next hole appears, and removes it. How often, and for how many weeks, is set for your child specifically and given to you in writing — it is not the same for everyone. The child feels pressure across the nose and cheeks for a minute or two. A gap often appears between the front teeth within a week or two: this is the suture opening and is a sign the expander is working.
Holding phaseNo more turns. The appliance stays in while new bone forms across the widened suture. The front gap closes on its own as the teeth drift together. Braces or aligners may start during this time.
Removal (15 minutes)The cement is cracked and the expander lifted off. The palate feels enormous for a day. A retainer with a plate, or the next appliance, holds the width.

Twin blocks and other functional appliances

For a lower jaw that sits well behind the upper (the most common reason for prominent front teeth), a functional appliance holds the lower jaw forward while the child grows, encouraging the bite to correct. Twin blocks are the common removable version: two plastic plates with angled blocks that meet only when the jaw is forward. Fixed versions exist, as does a mandibular advancement feature built into some aligners.

Living with twin blocks

Wear: most of the day and all night, out for eating (sometimes worn while eating, on instruction), for 9 to 12 months. Growth-spurt timing matters, so the orthodontist may wait for it.
First two weeks: tired jaw muscles, a lot of saliva, speech that improves with practice. The bite feels wrong when the appliance is out; that is expected.
Cleaning: brush the appliance with a soft brush and cool water after meals; soak weekly. Keep it in its case, never in a napkin.
Compliance: the appliance only works while it is in. Missed days show at the next visit as no change.
What follows: usually a period of braces or aligners to align the teeth once the jaws fit better.

What growth appliances can and cannot do

Growth appliances: evidence-calibrated expectations
Claim	What the evidence supports
Expansion corrects a posterior crossbite in a growing child	Well supported; one of the best-established early treatments
Expansion makes room for crowded teeth	Partly; it gains a few millimetres, which resolves mild crowding and reduces moderate crowding
Functional appliances correct a Class II bite	Supported in growing patients; the change is mostly in the teeth and bite, with a small skeletal effect; results after full treatment are similar whether treatment is one-phase or two-phase
Early treatment reduces the chance of injury to prominent front teeth	Supported by systematic review
Early treatment avoids extractions or surgery later	Sometimes, in specific cases; not a general promise
Expansion treats breathing or sleep problems	Not an orthodontic outcome to promise. Some studies report changes in nasal dimensions after expansion; whether that improves breathing or sleep in a given child is a medical question for a physician

A note on airway and sleep. Orthodontists assess growth, jaws, bite, arches and habits. Physicians diagnose medical sleep and airway disorders, and orthodontic treatment is not a treatment for sleep apnea, snoring, mouth breathing or attention difficulties. Where a growth pattern or habit may be relevant to breathing, a good assessment says so and suggests a medical referral rather than promising an outcome. For the national evidence summary, see AirwayOrthodontics.ca.

Why this matters clinically

The midline suture of the upper jaw responds to expansion only while it is open, which is why expansion is a childhood and early-teen treatment. Functional appliances depend on the growth spurt to have an effect. Timing and compliance, more than appliance choice, are the variables that most affect whether a growth appliance works, which is why an orthodontist may ask a family to wait a year rather than start now.

Questions people ask

Does turning the expander hurt?

Usually it causes pressure across the nose and cheeks for a minute or two rather than pain; some children find the first turns sore. If a turn causes sharp pain or the key will not go in, stop and call.

The gap between the front teeth is huge. Is that normal?

Yes. It is the sign the suture is opening. It closes on its own during the holding phase.

What if we miss a turn?

Do not double up. Do the next scheduled turn and tell the clinic at the next visit; the schedule can be extended.

Can adults have an expander?

Once the suture has matured, conventional expansion mostly tips the teeth rather than widening the jaw. Adults who need true skeletal width may be offered mini-screw-assisted expansion or surgically assisted expansion, depending on the case.

A twin block appliance in its case beside a toothbrush

References

Agostino P, Ugolini A, Signori A, Silvestrini-Biavati A, Harrison JE, Riley P. Orthodontic treatment for posterior crossbites. Cochrane Database of Systematic Reviews 2014;(8):CD000979. https://doi.org/10.1002/14651858.CD000979.pub2
Batista KBSL, Thiruvenkatachari B, Harrison JE, O'Brien KD. Orthodontic treatment for prominent upper front teeth (Class II malocclusion) in children and adolescents. Cochrane Database of Systematic Reviews 2018;(3):CD003452. https://doi.org/10.1002/14651858.CD003452.pub4
Thiruvenkatachari B, Harrison J, Worthington H, O'Brien K. Early orthodontic treatment for Class II malocclusion reduces the chance of incisal trauma: Results of a Cochrane systematic review. American Journal of Orthodontics and Dentofacial Orthopedics 2015;148(1):47-59. https://doi.org/10.1016/j.ajodo.2015.01.030
Behrents RG, Shelgikar AV, Conley RS, et al. Obstructive sleep apnea and orthodontics: An American Association of Orthodontists White Paper. American Journal of Orthodontics and Dentofacial Orthopedics 2019;156(1):13-28.e1. https://doi.org/10.1016/j.ajodo.2019.04.009
Proffit WR, Fields HW, Larson BE, Sarver DM. Contemporary Orthodontics, 6th edition. Elsevier, 2019.

Expanders and growth appliances: what they are like for a child, and for the parent turning the key

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