impressive little gadgets. Over time, they move your teeth.
But how do they do it?
four basic parts (more are shown in this photo):
made of metal or ceramic. A bracket is attached to each tooth.
material (glue) or a metal band. This is what attaches the bracket
to the tooth.
Arch Wire, which is a thin metal wire that runs from bracket to
bracket and puts pressure on the teeth.
The Ligature Elastic
(also called an "o-ring"). This is a small
colored elastic that holds the bracket onto the arch
wire. The ligatures are usually changed at each
adjustment visit. Some types of brackets do not need
elastic ligatures (they are called "self-ligating").
teeth move when the arch wire puts pressure on the brackets
and teeth. Sometimes, springs or rubber bands are used exert
more force in a specific direction. Braces exert
constant pressure, which over time, move
teeth into their proper positions. Occasionally adults may
need to wear headgear to keep certain teeth from moving (see A
Few Words About Headgear for more information).
teeth are surrounded on top by gum tissue (also called Gingiva).
Under the gum tissue, the Periodontal Membrane (sometimes
called the Periodontal Ligament or PDL) encases the bottom
portion of the tooth. Next to that lies Alveolar Bone.
When braces put
pressure on your teeth, the periodontal membrane stretches on
one side and is compressed on the other. This loosens the
tooth. The bone then grows in to support the tooth in its new
position. Technically, this is called bone remodeling.
Through Bone Remodeling
Bone remodeling is a biomechanical process responsible for making bones
in response to sustained load-bearing activity and weaker in
the absence of carrying a load. Bones are made of cells called
osteoclasts and osteoblasts.
remodeling works like this: increase the load on a bone and
osteoclasts are created which break it down in response to the
load. Remove the load and osteoblasts are created which create
new bony cells. Repeat the process through repetitive motion
and eventually the bone density increases.
Your teeth are socketed in bone (your maxilla
for the upper teeth, and your mandible for your lower teeth).
As mentioned, surrounding each tooth is a Periodontal Ligament
attaches it to the surrounding bone.
The PDL as a sort of messenger between the
teeth and surrounding bony sockets. Pressure between the PDL and
bone causes the bone to create osteoclasts and breakdown the
bone to restore the normal spacing between the teeth and bone.
The corresponding tension on the PDL behind the movement
causes the bone to create osteoblasts, effectively building
new bone to fill in the difference and restore the normal
spacing between teeth and bone. Not a whole lot of force is
necessary, only "some" force which is not normally
Enter the brackets and arch
wire - the artificial force
needed to create and sustain the pressure.
Arch wires are interesting things in that they tend to want
to retain their normal shape. They are also made of materials
activated by body heat to increase stiffness. The wire you
have presently is what is called a twist wire which is like a
small cable. It wants to remain straight. When it is put onto
your teeth which as a braces patient are all over the place,
and activated by the heat of your mouth which is 20-25 degrees
above room temperature, its desire to remain straight
provides the forces necessary to get the biomechanical process
of bone remodeling to begin and continue.
The solid wires which come later are made of a
nickel-titanium alloy and while so flexible that you can tie a
knot in it, once activated by body heat becomes quite stiff.
The strategic placement of brackets on teeth and tying of
those brackets to this wire complete the transmission of
forces from the arch wire to the teeth and sustained result in
the awesome process of bone remodeling as your teeth are moved
to new positions in your mouth.
The osteoclast (breakdown)
process takes about 72 hours to
get fully going, the osteoblast (rebuild) process about 90
days. Stabilizing the result takes about 10 months (which is
why it is important to wear your retainer to avoid a relapse
of the original or some intermediate positions).
Thanks to Kevin
from Michigan for the technical info on bone remodeling.
on this page from http://www.vtbraces.com/general_info.htm,
http://www.aim.gr and http://www.stlaurentdental.com/implants.html