General information about the
Rapid Palatal Expander

Am I a candidate for this? || How do you put this on and what happens after I get it? || What should I expect? || How does it work?


How do I know if I am too old for this to work (am I a candidate for this)?

This appliance works by widening the halves of the upper jaw (see How does it work below). In order for this to work, there has to be a separation between the halves to start with. In growing people (you are young enough that skeletal growth is sill taking place), there is a separation called a suture between the halves. How old is "young enough"? That depends. Age, by itself, is not the best predictor of this. The orthodontist can estimate the amount of skeletal growth you have remaining by taking a Hand-Wrist radiograph, and looking at how developed those bones are to help determine this. For females, your skeletal growth is largely complete by age 14 if you had your first period around age 12-13. For males, your orthodontist may be able to get a sense of how much more skeletal growth you have left by comparing your stature to your parents. In general, I am very wary of using this appliance without surgical assistance in females above age 13 and males above age 15.

The image at the right shows the type of rapid palatal expander that I use on a model. This appliance is also called a "Hyrax" appliance. It consists of a screw that is attached to the teeth by means of bands that go around your teeth. In order to fit you for this appliance, we usually need three visits: 1) a quick (five minutes) visit to put spacers between the teeth that will have bands on them,
2) about 1 week later we see you for a half-hour visit to fit braces around the four teeth and take an impression of your teeth while the braces are on. I will then remove the braces and replace the spacers.
3) about 1 week later, another half-hour visit to put in the expander and give you instructions.
Hyrax on Model
The expander is "activated" by turning the screw. This is done with a "key" (shown on the right). The metal key is attached to a blue safety strap made of elastic material. The end opposite the key is in the form of a loop. Hyrax Key
Since this appliance does not come out of your mouth (until it has done its job), the screw must be turned with the key inside your mouth. The loop is a safety precaution - if you drop the key from between your fingers (see below) it will still be attached to your middle finger and it will not fall down your throat (if your key does not have this safety strap, make sure you tie a piece of dental floss around the key and wrap the other end around your middle finger). So the first thing you need to do is place the loop around your middle finger. Loop around middle finger
You can then hold the key between your index finger and thumb. At this point you should have your child lay on his or her back with his or her head hanging over the end of a bed or couch. This works best where there is adequate lighting, such as near an end table or lamp. You should also have your child open his or her mouth as wide as possible since 1) this makes it easier for you to see what you are doing, and 2) the gag reflex may be evoked by toughing the back of the tongue, and keeping the mouth open very wide minimizes the possibility that you will touch this area while turning the screw.
The key is placed in a hole at the center of the screw. You should be careful not to insert the key too far into the screw. If this happens, you could pinch the roof of your mouth as you turn the screw. I always shorten the length of the metal key before I give it to you to minimize this possibility. You can see arrows on the screw indicating the direction that the screw needs to be turned to activate it (towards the back of your mouth). (the number 13 on this screw means that it can be opened a maximum of 13mm).

Key in Hyarx
The key is then pushed as far back towards the throat as possible. You will feel resistance when the screw cannot be turned any more. You will also be able to see a new hole appear in front of the key for the next activation. To remove the key, you need to push down and back until the key falls out of the hole (its a good thing the safety strap is attached to your middle finger). It is very important that you do not un-turn the screw while you are removing the key. If you do turn back the screw, the next hole at the front of the screw will be obstructed, and you will not be able to insert the key for the next activation. Turn Screw

I will turn the screw once while demonstrating the above to you, and a parent will also turn the screw once, for a total of two turns at the visit that I give the expander to you. Unless I instruct you otherwise, you will then turn the screw one turn starting the following morning, and once at night (two turns per day).

While the screw is being turned, I will see you once per week to ensure that everything is proceeding properly (no loose bands, the space is opening symmetrically, etc.). After we are done turning the screw, I will see you once per month for the three months that I hold the correction before removing the expander.

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What should I expect?

When I put the expander on, it is sometimes uncomfortable until I get it all the way on your teeth. When I turn the screw the first time, you will feel a mild pushing against your teeth. When your parent turns the screw (the second turn) it will feel uncomfortable. It usually doesn't hurt, but you will feel a strong sensation of pushing against your teeth. Over the next 2-3 days, as the screw is being turned, you will feel an uncomfortable pushing feeling. However, once the sutures are opening freely after the first few days, you shouldn't feel anything as the screw is turned.

It is very important that you follow the turning schedule that I have prescribed. If, because it is painful, you decide not to turn for a few days and then start up again, this will lengthen the amount of time you are in pain and it may result in damage to the supporting structures of the teeth. If you do experience pain, please take whatever you usually take for a headache.

After you are done turning the screw, I usually leave the expander in for another 3 months to allow the result to stabilize. Depending upon whether your treatment plan calls for going straight into braces or not, I will either remove the expander (it doesn't hurt to remove it) and give you a retainer, or I will place the braces at the same visit that I remove the expander.

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How does it work?

This function of this appliance is to widen the upper jaw itself. In order for this to happen, your upper jaw must not be rigidly attached to the rest of your skull. If the sutures that attach your upper jaw to the rest of your skull are still open (in females up to around age 13 or so, and in males up to around age 15 or so), this appliance will be able to widen the jaw itself.

The squiggly lines that separate the bones of the skull are called sutures.

If your sutures have already fused, this appliance can only widen the upper jaw if you have had surgery to separate your upper jaw from your skull in key areas.

This is the upper jaw viewed from underneath. You can see the suture that separates both halves of the upper jaw(the squiggly line down the center). This is the suture that opens (and subsequently fills in with new bone) when an RE is used.

In order for teeth to move through the bone, the level of force applied to the teeth must be in a certain "biologic range." If the force level is too low, the teeth will not move. If the force level is too high, the teeth will not move. The way this appliance expands the upper jaw despite the fact that it is attached to teeth, is that the force levels generated by the appliance are too high — they are well above the biologic range for tooth movement. The forces are transmitted through the teeth to the bone, and assuming your upper jaw is not rigidly attached to the rest of your skull, this causes your jawbone itself to widen.

If your jaw is rigidly attached to the rest of your skull, you upper jaw can't widen. In this case, the teeth still move, but not biologically. The only way for the teeth to move under this circumstance is by the bone on the outside surface of the teeth fracturing. The teeth then move outside the supporting bone, and this leads to irreversible recession (the bone and gum tissue shrink up along the root). This is not only unesthetic (the teeth look longer) but it is also can predispose you to losing these teeth.

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