We know what braces do – they move and straighten teeth – but do we know how they work? Yes, braces put force on teeth over time, causing them to shift position, but there’s more to it than that. Today we’re going to talk about exactly how and why braces work as well as they do.
How Brackets and Wires Work Together
Braces are a “fixed appliance,” meaning they are attached to the teeth and can’t be taken out by the patient like a removable retainer.
With traditional kinds of braces (that is, not Invisalign or other aligners), individual brackets are bonded to the surface of the teeth. These brackets vary in shape and size depending on the width, curvature, and desired angulation of each tooth.
Each bracket has a slot for the arch-wire, which stretches across the brackets from one side of the mouth to the other. There are different ways of keeping the wire attached to the bracket. Some braces rely on elastic ligatures, which are little rubber bands that come in many colors. Twisted steel ligatures can be used instead of elastic ligatures, which do the same thing but keep the wire in place even tighter. Other types of braces, called self-ligating braces, have a door or gate that hold the wire secure.
The arch-wire is the crucial part of the braces that provide the force to the teeth, causing them to move over time. It’s first shaped like the arch of the patient’s mouth before it’s attached to the brackets. This shape provides a track the teeth can move along to get into position. When the wire is placed in the mouth and attached to the brackets, it naturally picks up the shape of the misaligned teeth at first. After a while, though, as the body warms the wire up, the wire “remembers” and returns to its original shape, moving the teeth along with it.
Beyond Brackets and Wires
The description above shows how braces work at the most basic level. There are other things that help the brackets and wires do their jobs, including elastics and coil springs.
Elastic chains look like a strip of colored elastic circles. Each circle goes around a bracket and the elastic is stretched across multiple braces. These can be used to help close spaces between certain teeth or to move several teeth together as a group.
Elastics and rubber bands of varying sizes and strengths can be used to apply force, too. They often stretch between the lower and upper jaw to correct an overbite, underbite, or cross-bite. Rubber bands may be used throughout treatment but are especially common towards the end of treatment to help shape the final movements in the mouth.
Coil springs look like tiny metal springs and may be placed on or near the arch-wire. They are used to create space between teeth when, for example, space needs to be reserved for a future implant, or a canine tooth is blocked and needs space to come in between the two adjacent teeth.
Osteoclasts and Osteoblasts
If teeth stopped right at the gum line, it wouldn’t take so long to move them with braces. But the changes aren’t happening on the surface, they’re happening down below the surface in the bones of the jaw.
The force of the wire against the crown of the tooth is distributed into the root, which itself is embedded in bone in a sling called the periodontal ligament. The force on the tooth causes specialized cells called osteoclasts to dissolve bone on the side where the tooth is moving too, creating space for it. What happens to the newly made gap on the other side of the tooth, where it’s moved from? Specialized cells called osteoblasts create new bone on that side at the same time.
This process is called “remodeling” and takes around four to six weeks to complete. In the meantime, the tooth has moved a small distance. Then the process is repeated again, and again. This is why it takes several months for braces to work.
The Human Element
Another component of effective treatment with braces is the patient. It’s important for them to be an active part of their treatment and help get the best outcomes by taking care of their braces, avoiding foods that can damage their braces, wearing elastics as directed, and going to orthodontist appointments as scheduled. With the patient’s involvement, the braces can work their magic to create a healthy, beautiful smile.