Palatal expansion

The palatal expansion concept

The way the top teeth come together with the bottom teeth is called occlusion. For this occlusion to be normal, the upper teeth and molars must come into contact with those on the bottom when they bite; they must also overlap them slightly. In other words, all of the upper teeth must be visible outside the lower teeth.

Expansión palatina

When this relationship is reversed, i.e. the top teeth come down inside the lower teeth, the condition is called crossbite. This can be anterior, posterior, or can affect both at the same time.

Posterior crossbite (which occurs when the premolars and/or molars are crossed), can in turn occur on one or both sides. In both cases the palate will be narrow. This means that, to make it fit the jaw properly, the palate must be expanded, a process known as superior maxillary expansion.

Expansion mechanism and anatomy

The hard palate is made up of bone from both sides of the palate, right and left. This is known as palatal apophysis of the upper right and left maxillaries and is where the left and right palates come together in the centre to form the mid-palatal suture. This suture runs from front to back, from the joint between the two front or central upper incisors to the uvula.

In children, this suture or joint is still cartilage (it has not yet closed), i.e. it still hasn’t turned into bone. While the ossification process has begun in adolescents, at the age of 25 ossification is still only around 5%. Given that the suture is still soft, it can be broken and opened to widen the palate. Because this is a slow process, the mucous round the bone adapts without tearing.

We can apply palatal expansion until a patient is 25 years old.

Nevertheless, we can try it, without a complete guarantee of success, up to the age of 30. However, if expansion is not carried out at the right age, the process would require surgical assistance.

Types of palatal expansion

There are three types of expansion: slow, rapid and surgically assisted.

Slow expansion

This is achieved with a removable resin palatal expander. This expander takes the shape of a pink (although it can be in another colour) resin plate, 1 mm thick and split in two at the centre, running from front to back, and which covers the whole palate. It has a central screw which turns to separate the parts and open the expander. The screw is given a quarter turn with each expansion.

The expander is removed to eat; when inserted into the palate, it is held in the place with flexible wires around the molars. Although the mid palatal suture does widen the palate, part of the expansion will cause an outwards tilting of the molars. Also, while it does straighten the bite, the tendency is for the crossbite to reappear since the molars tend to tilt back inwards over time.

It has the drawback that, being easy to remove, the patient must cooperate in its use. And in the case of children and adolescents, we must keep a close watch over them to ensure that they use it and don’t lose it. Sometimes they take it out to eat and forget to put it back in or even misplace It.

The best known slow expanders are: Schwartz, Quad Helix, Franckel and Bionator.

Rapid Palatal Expander (RPE)

This is a resin plate 2mm thick which covers the whole palate and fits over the masticatory surface of the premolars and molars. It is fixed to the teeth with a special glue. It comes with a fitted central resin screw which separates the two halves of the expander when turned, widening it and expanding the palate.

It is turned every day (a quarter of a turn), obtaining a ¼ of a millimetre expansion each time. It is expanded to the extent required to straighten the bite. Often an expansion of 4 or 5 mm is required, or 16 or 20 turns of the screw over the corresponding number of days.

It has the advantage of not requiring the patient’s cooperation to use or wear it.

The patient can eat with the expander in and there is absolutely no need to remove it during treatment. Besides, given that the upper molars are prevented from fully contacting with those at the bottom by their cusps and grooves, they don’t catch on one another, so that straightening is easier.

Advantages of rapid expansion over slow expansion

Rapid expansion produces greater change in the skeletal bone. As well as expanding the palate, it also expands the side walls of the nasal pits and improves breathing.

Rapid expansion straightens the teeth better and causes less tilting of the teeth.

Furthermore, if the Rapid Palatal Expander is used with a face mask (an apparatus worn outside the mouth to bring the upper jaw forward) the process will be more effective. The face mask is used in patients with class III malocclusion. In other words, when the jaw is too far forward and prominent in comparison to the upper maxilla.

In the majority of cases the jaw is normal. But the upper maxilla is narrower in the case of crossbite, and is set backwards from the rest of the face. Using the rapid palatal expander together with the mask widens the maxilla and brings it forward. This kind of bone combination is found rather frequently in the Basque Country.

Surgically assisted rapid palatal expansion

When the Rapid Palatal Expander fails to work it may be because the patient is an adult over the age of 20, whose mid palatal suture has ossified and can no longer be opened. On other occasions we may find that the rapid expander doesn’t work because the patient had used the slow expander as a child, but not continually. In such cases, the surgeon uses a chisel to open the mid palatal suture and separate the upper maxilla down the middle. The expansion can then continue using the rapid palatal expander.

Maintaining the expansion obtained

Once the rapid expansion has been completed, the expander will be left in the mouth passively, i.e. without turning the screw, for 3 months.

After this time, the rapid expander is removed, and a so-called Transpalatal Arch or space maintainer is fitted, which will remain in place for two or three years. This consists of metal bands or rings fitted around the first superior molars on both the right and the left. These are connected by a thick wire or bar fixed to the palate and stretching from right to left, welded to said bands or rings.

In children, the arch is left in place for the time it takes for all of their teeth to grow into the right place. However, if the patient is an adolescent or adult with a short and narrow maxilla, the teeth will have had no space to grow in and will have created a crossbite. In these cases, while the expander remains in place, we also use orthodontics with brackets to align their teeth.

Thanks to the expander, there is no need for the maxillofacial surgery which would otherwise be required. As well as an aesthetic improvement, we correct their masticatory function.