August 14th, 2017
“Can we use an expander?”
“The dentist said he might need expansion…”
“Some of her friends at school had expanders. Will she need one?”
The parents of many young patients that come to us ask questions like this, especially if their son or daughter’s primary care dentist is paying close attention to the growth of the jaws and permanent teeth, or if they’ve been talking to friends whose children had some sort of orthodontic treatment. Like everything in orthodontics, the answer varies depending on the individual.
Generally speaking, an expander is an appliance designed to expand the dental arch. The reasons and treatment objectives for doing so can vary, but generally one or both of the arches is narrower than desired. Expanders are most commonly used on the upper jaw (called palatal or maxillary expanders) but can be used on the lower teeth as well.
There are several different reasons for using an expander. The maxilla, or upper jaw, may be too small to fit well with the mandible, or lower jaw. Sometimes the lips smile much wider than the teeth, showing a lot of dark space at the corners of the smile. Sometimes the growing front teeth get hung up in the bone because there isn’t enough room in the front of the jaw for them to come in. In all of these situations, widening the maxilla can reduce or resolve the problem.
Before getting into how expanders work, it’s important to understand some background of how the upper and lower jawbones grow and develop. The maxilla is made of two bones – one on either side – and these bones are the skeleton of the middle of the face. In fact, they not only form the upper jaw, but also the floor and sides of the nasal cavity, and the bottom of the eye socket! If you’ve ever looked at a skull in a museum or even in a cartoon, you may have noticed that only the mandible seems to move compared to the rest of the head. That’s because even though our heads have many different bones in them, they are joined at special seams called sutures. As we grow throughout childhood and adolescence, the bones both grow apart at the sutures and also grow larger as the body adds new bone on the surfaces that are growing outward.
That seam on the roof of your mouth? That’s a remnant of how the upper jaw formed before birth, and the midpalatal suture where the bottom of the two maxillary bones join is just underneath the gums there. While someone is still growing, maxillary or palatal expanders work by gradually increasing the pressure on the midpalatal suture to the point where the two bones separate. The expander is most commonly a metal framework attached to the teeth with a specially designed screw in the middle; sometimes plastic is added to put pressure on the sides of the roof of the mouth as well. The screw is usually designed to open at the rate of ¼ millimeter for each turn, so over the course of several weeks of turning, 6-7mm of extra width can be developed. As the pressure from the expander increases, the midpalatal suture opens, and the soft immature bone between the two growing halves of the upper jaw gets stretched out before hardening and maturing into new bone. As wild as it sounds, most patients describe the process as pressure only without any significant discomfort! Since the expander is actually pushing the bones apart at the level of the mouth (and sometimes slightly at the nose) it’s common to see space between the two front teeth increase as the bones carry the teeth away from each other. Since the gums get stretched out just like the immature growing bone between the two bones of the upper jaw, the front teeth will start moving back toward each other on their own in most cases. That stretching is also why the expander is commonly left in place for several months after the turning is finished – so that the new bone formed can mature and harden, and the gums that have been stretched out given some time to relax and remodel.
The mandible, on the other hand, forms as one single bone and can’t be widened without surgically cutting it in the middle. However, it’s still possible to use an expander in the lower arch to push the teeth out to the side and increase the space available for the teeth. Fortunately, it is much more common for the upper jaw to be smaller, or the lower jaw to be larger than the upper in these situations, so the need to widen the lower jaw bone rarely presents itself.
So now that we have some idea of how expanders work, when is the best time to use one, if it’s needed? The answer to that again varies depending on each individual. For a young child without all of his or her permanent teeth, an expander can be beneficial if space is needed for the permanent front teeth to erupt, or to align them if the bite is bad enough that it might be risky to the health of the permanent teeth to wait.
Many times, though, even when the need for expansion at some point is clear, it can be better to wait until all the permanent teeth come in – when the expander can be done in conjunction with alignment of all the teeth in one single course of orthodontic treatment during adolescence. This usually means fewer office visits and less time wearing orthodontic appliances overall, which is why it’s often preferable to wait when the problems we can see aren’t likely to cause any problems to oral health while our patient grows and the teeth and jaws develop for a few more years.
Are you curious whether an expander is going to be needed for your child? We offer free consultations, so please get in touch to schedule an appointment. I would love to take a look and discuss the orthodontic options available!
-Darren C. Pakravan, DDS, MS