Palatal expansion: the appliance, how long it takes and the right age

When the upper jaw is narrower than the lower jaw, the upper back teeth close inside the lower teeth instead of covering them: this is called a posterior crossbite. In the mixed dentition stage, when baby teeth and adult teeth are in the mouth at the same time, a width problem is the most common bite problem, and correcting it is usually the first step of treatment. Based on the courses of the university diploma in orthodontics and on specialist references (Boileau and Bassigny), this article explains when the upper jaw is widened, how an expander works, how long treatment lasts, and what its limits are. It is for general information only: only a dentist can assess an individual case.

What is a narrow upper jaw?

The diploma courses state that a lack of width of the upper jaw accounts for 8 to 18 percent of bite problems in the mixed dentition stage (according to Raberin), that it appears early, and that it has a strong tendency to relapse. But a "narrow jaw" is not one single thing: it comes in two forms, which are treated differently:

• A narrow bone base: the upper jawbone itself is too narrow, and the teeth stand straight on it or tilt to make up for the lack of width. The usual treatment is opening the palatal suture with a rapid expander.
• Teeth tilted inwards: the bone base has a normal width, but the back teeth and the bony ridges that hold them are tilted towards the tongue. The treatment is a slower dentoalveolar expansion, with an appliance such as a quad helix or a plate with a screw.

Telling these two forms apart is the first thing the dentist decides, because treating a narrow bone simply by tipping the teeth outwards leads, as the courses warn, to relapse and to bite problems.

Signs that may catch your attention

• A crossbite on one side or on both sides.
• A narrow, long upper dental arch, a high, narrow palate, and crowded teeth.
• When smiling, a clear dark space between the teeth and the corners of the mouth.
• In some cases, a long, narrow face, a narrow nose with pinched nostrils, and lips that stay apart.

When the chin shifts to one side on biting

It often happens that, because the upper jaw is narrow, a child has to shift the lower jaw to one side to bring the teeth together. The chin then looks off-centre when the teeth are closed, then goes back to the middle at rest or when the mouth is open. The courses describe this form (crossbite with a functional shift) as the most common. They warn that if this shift is left untreated, it can turn into a true asymmetry of the lower jaw, with effects on the jaw joint (temporomandibular joint), which is why early correction is advised. A problem that is present when the first adult molars come through should not be expected to correct itself.

Causes

The courses state that mouth breathing, a low tongue position, atypical swallowing and sucking habits (such as thumb sucking) often occur together and end up causing a narrow upper jaw. However, Boileau points out that the causal role of mouth breathing in a narrow upper jaw has not yet been proven by scientific evidence. That is why breathing is assessed, when needed, with an ear, nose and throat (ENT) doctor, and widening the jaw is not presented as a treatment for a blocked nose.

The upper jaw expander (Hyrax) and how it works

A rapid expander is a fixed appliance bonded inside the mouth, with a screw in the middle. The courses mention several types:

• Hyrax: metal arms that stay away from the lining of the palate, attached to bands around the molars (two bands), or around the molars and premolars (four bands).
• Haas: arms embedded in resin (acrylic) that touch the roof of the mouth.
• Other forms: a fan-shaped expander, or an appliance with a cap bonded onto the teeth; some have hooks that allow it to be connected to a face mask in some Class III cases.

The appliance works by opening the midpalatal suture, the joining line that divides the roof of the mouth in the middle in children and teenagers, so that the two halves of the upper jaw move apart. One sign of this opening is a gap between the two upper front teeth around day three, which the dentist confirms with an occlusal X-ray. The references explain that this gap sometimes does not appear, and that its absence alone does not mean failure: the X-ray is what decides. This gap is closed later with a simple appliance.

How is the appliance turned?

The screw is turned with a small key, following your dentist's instructions. The protocol used in the diploma courses:

• the first turn on the day after the appliance is bonded;
• a quarter turn twice a day (morning and evening);
• for 5 to 10 days according to one professor, and 8 to 10 days according to another, until the expansion reaches the intended "overcorrection".

Other protocols exist in the references: some start with a week without turning, then an active phase of two to three weeks, and some schools use a slower expansion over 6 to 8 weeks. The dentist chooses the right pace, so do not change the number of turns on your own, and keep the key as you are told.

During this phase, the dentist checks the opening of the suture with regular X-rays (weekly in the diploma courses). If the suture has not opened after two weeks, the courses say to stop turning, because carrying on would only tip the teeth. The palate often needs to be widened by 6 to 8 mm.

The retention phase after expansion

When the turning is finished, the screw is locked, and the appliance stays in place for at least three months according to the main reference, which is the time the suture needs to rebuild itself (about 90 days according to Haas). It is then usually replaced by a simpler retainer (a transpalatal arch or a palatal plate). The durations given by different professors range from one to six months, and the minimum used in the courses is three months.

The right age for upper jaw expansion

Age is a key factor, because the palatal suture becomes more complex and interlocked with age, which makes it harder to open:

Boileau adds that the best time is before or during the growth spurt, and the courses point out that age in years is not enough, so skeletal age is assessed when needed (a hand and wrist X-ray, or the neck vertebrae). The growth spurt happens around age 12 in girls and age 14 in boys.

Slow expansion: the quad helix and the plate with a screw

When the problem is tilted teeth rather than a narrow bone, a slow dentoalveolar expansion is usually enough:

• Removable plate with a screw: turned a quarter turn a week for about three months, before age 9 to 10. Turning it faster makes it lose its grip in the mouth.
• Quad helix: a fixed appliance made of metal wire, activated before it is fitted, then checked and reactivated about every three weeks, with correction within six months at most according to the courses. It is only considered to have an effect on the bone (orthopaedic effect) before about age 10, and under conditions set by the dentist.

Lower jaw expansion: what are its limits?

Many people ask about widening the lower jaw, and the answer in the references is clear: the lower jaw has no suture that can be opened, because its middle fuses around the first year of life. That is why the courses state that widening the lower jaw to make room for crowded teeth is ruled out, because the width between the lower canines goes back to what it was. Lower dentoalveolar expansion is only accepted in special cases, such as lower teeth that are truly tilted inwards. This is why the dentist plans in advance how the lower arch will adapt to the widening of the upper jaw.

In adults: surgically assisted or mini-implant-assisted expansion

Once growth is over, the suture may have fused, and the appliance alone is not enough:

• Surgically assisted expansion: the expander is bonded before the operation, then turned a few days afterwards, following a protocol agreed between the surgeon and the dentist. The courses suggest it when the suture has fused or the narrowing is large (more than 6 mm). Boileau notes that the waiting time before starting and the turning speed vary between teams, and that relapse ranges from 5 to 25 percent.
• Mini-implant-assisted expansion (MARPE is the best-known example): this is not covered in the university diploma courses. It is discussed at the end of the teenage years or in young adults, after the growth spurt, and only for a narrow bone, as an alternative to surgical expansion. It is not an automatic option, and the sources used here do not give a maximum age in figures.

In an adult whose crossbite is caused by teeth tilted on both sides without a shift, orthodontic widening of the teeth is enough, without opening the suture.

Side effects and relapse

• Relapse is common: the Raberin review (2001), cited by Boileau, reports relapse in about half of cases, with the quad helix as well as with the expander. This is an average from a scientific review, not a prediction for an individual case. It is reduced by overcorrection, compulsory retention, and retraining of functions (tongue position, swallowing and breathing).
• Vertical dimension: the courses state that expansion increases the opening of the lower jaw downwards and backwards, and the references describe this effect as small and partly temporary (a backward rotation of the lower jaw of one to two degrees, half of which goes back according to Bassigny). That is why the dentist is careful in people with a long face.
• Teeth and gums: the molars may tilt outwards, and root resorption has been described in the molars that carry the appliance. When expansion is done after growth is over, there may be tipping of the teeth, pain, exposed roots, damage to the lining of the palate, or failure of the suture to open.
• Nose and breathing: opening the suture widens the nasal cavities and may make nose breathing easier, but this change is neither automatic nor quick according to Boileau.

In some Class III cases (when the upper jaw is set back and narrow), expansion is combined with a face mask.

In practice

1. If you notice a crossbite, a chin that shifts to one side when the teeth close, or a very narrow palate in your child, see your dentist without waiting.
2. With an examination and X-rays, the dentist will decide whether the narrowing is in the bone or in the tilt of the teeth, and this decides the type of appliance.
3. Age matters, but the dentist also looks at the growth stage and the state of the suture.
4. Follow the turning instructions exactly, and do not add or skip turns on your own.
5. Attend the check-ups and X-rays on time.
6. A temporary gap between the two front teeth is expected with rapid expansion, so tell your dentist about anything that worries you.
7. Do not neglect the retention phase: relapse is common without it.

Frequently asked questions

Does jaw expansion change the shape of the face?

The references we relied on do not describe a visible change in facial features as an expected result of expansion. What they describe are internal effects: a wider palate and nasal cavities, a small and partly temporary vertical effect on the position of the lower jaw, and a temporary gap between the two front teeth during treatment. As for what to expect in an individual case, ask your dentist.

Can the lower jaw be widened?

Not in the way the upper jaw is widened, because the lower jaw has no suture that can be opened after the first year of life. The courses rule out widening it to make room for the teeth, because it relapses, and only accept dentoalveolar expansion in special cases assessed by the dentist.

What is the right age for upper jaw expansion?

The diploma courses consider the mixed dentition stage to be the best time, with a limit around 14 to 15 years, although professors differ. Boileau considers that there is no consensus, and that the state of the suture on imaging matters more than age alone. Once growth is over, surgically assisted or mini-implant-assisted expansion is discussed.

How long does treatment with an expander last?

The turning itself is short: 5 to 10 days in the main protocol, and it can last a few weeks in other protocols. The appliance then stays locked in place for at least three months for retention, before a simpler retainer. The total duration varies with each case and with the treatment that follows the expansion.

Is the Hyrax expander painful?

The sources we relied on do not give a general description of pain during expansion in children; they mention pain among the complications of late expansion, after growth is over. Ask your dentist what to expect in your case, and tell them about any unusual pain.