Ever wonder how braces work? Very likely you have not. Everyone knows, of course, that braces apply pressure to teeth. The pressure pushes the teeth into the desired positions. This understanding of it satisfies, and so no further inquiry is forthcoming.
This understanding, as far as it goes, is not wrong. However, it is so incomplete as to actually be in the worst case dangerous if a person acts on it. The number of do-it-yourself orthodontic disasters seems to be growing fast. The recent rise of low-cost, at-home aligner treatment startups portends more unfortunate outcomes, too. As this discussion will show, the movement of teeth in response to pressure is not a simple process. Human gums and jaws are not clay. It’s not a simple matter of shoving teeth along. The process is very complex. In fact, we don’t fully understand some aspects of it at the molecular level. Trained orthodontists, however, have a thorough practical knowledge of the process. By the time you finish this article, you’ll see why at-home and DIY orthodontics are so risky.
This discussion uses the term “braces” for convenience. It refers here to all types of braces and also to aligner trays. The technologies are different but the basic principles are the same.
HOW BRACES WORK
At first look, teeth look like a simple business. They’re hard and white. Like some kind of plastic. They’re stuck into gums, which are soft and pink. Moving them seems like an uncomplicated task. Just push ‘em to where you want ‘em. Take care not to push so hard you break a tooth or tear the gums, and you’re golden. Right?
Wrong. It’s not like that at all. First, the structure of the teeth, gums, and jaw bones is much more complex than that. Second, the movement of teeth involves biological processes. It involves the active participation of these living structures. Destruction and rebuilding. We’ll begin with a review of some anatomy.
TEETH, GUMS, AND BONES
First, teeth. Human teeth are not solid chunks of hard white stuff. That description fits the visible outer surfaces of teeth. This enamel is, in fact, the hardest stuff in the human body. Inside are layers of different kinds of tissues. The innermost center of a tooth is a soft, living structure called pulp. The pulp is home to blood vessels and nerves. For this discussion, that’s the important detail about the teeth to keep in mind.
The roots of teeth fit into the jaw bones. This solid base is what enables human teeth to apply the tremendous pressures our jaws can exert while chewing. The average adult, after all, can chew with forces up to 170 lbs.
Gums, in contrast, are soft and not very strong. It should be obvious that gum tissue isn’t nearly strong enough to hold teeth in place under 170 lbs of pressure. Rather, it is a layer of cementum (just like it sounds!) and a strong periodontal ligament that secure teeth in their bone sockets. The gums provide seals to keep stuff out of the sockets.
This simplified tour of oral anatomy makes clear that braces don’t push teeth through gums. The task of orthodontic treatment is, in truth, moving teeth through bone.
MORE ABOUT BONE
Thought experiment. Imagine taking a spare rib and drilling a hole into it. Now, fit a nail tightly into that hole. Your task then to move the nail sideways, 1/8 inch, through the bone. Can you do this?
You can, if you apply enough sideways force. However, you will very definitely crack or break the bone. There is no other way to change the nail’s position. If you apply too little pressure to crack the bone, the nail will never move. No matter how long you keep up the pressure.
See now that moving teeth with braces isn’t so simple after all? How is it even possible? The spare rib and nail example doesn’t hold the key to the mystery. There’s a big difference between that spare rib and a patient’s jaw bones. The patient’s jaw bones are alive. The active response of living jaw bone to pressure on teeth is what makes it possible for braces to work. This response is called bone remodeling.
Bone remodeling is just what it sounds like it is. It means that some parts of a bone are dissolving and other parts are building. Destruction and construction at the same time. All bones in the human body are remodeling all the time. If you think about it, you realize bones must be able to grow new material. Otherwise, no broken bone could ever heal! What’s not so obvious is that bones naturally and constantly undergo destruction and rebuilding.
Orthodontic treatment is the art and science of harnessing this normal process to re-position teeth. That’s what braces do. Let’s dive a little deeper into what happens when braces put pressure on teeth. Into how braces work.
TO THE RIGHT!
Let’s start with a simple case. One front bottom tooth. We want to move it to the patient’s right, to a new position. Therefore, we install very simple “braces” that apply just the right amount of pressure to the left side of that tooth.
This pressure squashes the tooth’s root against the right side of its jaw bone socket. In the direction we want it to move. That side, therefore, we’ll call the compression side. Conversely, the same pressure pulls the root away from the left side of the socket. We’ll call that the tension side. Now, it gets interesting. Let’s look particularly at what happens next on each side of the tooth’s root. This is the key to how braces work.
Our bodies are incredible adapting systems. Where pressures are pulling a tooth root away from the jaw bone socket wall, the body responds. A veritable storm of biochemical and cellular activity kicks up. The body doesn’t like the gap this pressure is trying to create between the tooth root and the bone socket on that side. It acts, therefore, to fill in that gap before it develops. With new bone material! We know in some detail how this happens. That is, we know about many of the adaptive responses the body makes.
Cells called osteoblasts get busy secreting raw material for bone formation. Other cells, fibroblasts, do similar work to build up the soft tissue layer between the bone and the tooth root. Make no mistake about it. The pressure on the tooth is injuring these tissues. A controlled injury, if you will. There is inflammation, regulated by signaling chemicals called cytokines. Other chemicals called growth factors also control the buildup of new bone material. Long story short, the body tries to move the tooth-bone mating structure in the direction of the pressure.This build-up of new bone is called deposition.
Where root is being squashed against the bone socket, the response is more or less the opposite. The body straightaway seeks to relieve the squashing by making room. Thus, cells called osteoclasts break down bone material and release the minerals into the bloodstream. The wall of the bone socket retreats, as it were. As on the tension side, there’s likewise a lot of complex cellular activity and chemical signaling going on to stimulate and control this process of bone resorption.
DON’T TRY THIS AT HOME
So, that’s a very simplified version of how braces work. When a patient’s teeth reach the right alignment, the orthodontist brings the bone remodeling to a controlled stop, over time. We’ve skipped over many details such as optimum pressures, precise direction of pressures, and monitoring of progress. There’s the matter of maintaining results over time. You can see how critical these and other mechanical and biological factors are. It should also be clear that mistakes are not easy to fix.
That’s why orthodontists spend 4 years in college, 4 years in dental school, and then 3-5 years in orthodontics training before opening an office. Next time you see an ad for at-home aligner trays, ask yourself if you really want to try this at home.