Braces move teeth by applying constant, gentle pressure that triggers your body to remodel the bone around each tooth. This isn’t a simple mechanical push. It’s a biological process where bone dissolves on one side of the tooth and rebuilds on the other, gradually shifting each tooth into a new position over months or years.
The Parts That Generate Force
Every set of braces has three core components working together. Brackets are the small attachments bonded to the front of each tooth. They have a built-in slot designed to control both the direction and angle of movement. An archwire, a thin metal wire shaped in the ideal curve your teeth should follow, threads through those slots. The gap between where the wire wants to sit and where the tooth currently is creates the force that drives movement.
Ligatures hold the wire in place inside each bracket. These are either tiny elastic bands (the colored rings you see on most braces) or thin stainless steel ties twisted around the bracket. Without ligatures, the wire would simply pop out of the slot and stop transmitting force. The choice of archwire changes throughout treatment. Early wires are flexible and produce lighter forces suited for initial alignment. Later wires are stiffer, delivering more precise control for fine-tuning tooth positions.
What Happens Inside Your Jawbone
The real work of braces happens in the thin layer of tissue between each tooth root and the surrounding bone, called the periodontal ligament. This tissue is about 0.15 to 0.38 mm thick and acts like a shock absorber, connecting the tooth to the bone with thousands of tiny fibers. When braces push a tooth in one direction, the periodontal ligament gets compressed on the side the tooth is moving toward and stretched on the side it’s moving away from.
That compression and tension send chemical signals to two types of specialized bone cells. On the compressed side, cells called osteoclasts activate. They release enzymes that dissolve the hardened bone, leaving microscopic pits and clearing a path for the tooth to move into. On the stretched side, cells called osteoblasts deposit a mix of proteins, calcium, and other minerals that hardens into new bone, filling in the space the tooth left behind. This paired process of dissolving and rebuilding is what allows your teeth to physically relocate within solid bone without leaving gaps or weakened spots behind them.
The Three Phases of Tooth Movement
Teeth don’t move at a steady rate. The process unfolds in three distinct phases, and understanding them explains why treatment sometimes feels like nothing is happening.
Initial Phase
This happens immediately after force is first applied. The tooth shifts rapidly within the periodontal ligament, and the surrounding bone flexes slightly. You typically see about 0.4 to 0.9 mm of movement within the first week. This early shift is mostly the tooth rocking into the compressed ligament space rather than true bone remodeling, which is why it happens so quickly.
Lag Phase
After that initial burst, movement slows dramatically or stops entirely. During this phase, areas of the compressed periodontal ligament lose their blood supply and form patches of dead tissue. The body has to clear this tissue before bone remodeling can begin in earnest. Lighter orthodontic forces produce less of this dead tissue, so the lag phase tends to be shorter. Heavier forces create more damage and a longer stall. A patient’s age and bone density also affect how long this phase lasts.
Post-Lag Phase
Once the dead tissue is cleared, osteoclasts begin resorbing bone directly along the root surface, and steady tooth movement resumes. This is the phase where most of the meaningful repositioning happens. Movement accelerates and becomes more consistent, as the biological machinery is now fully engaged and cycling through rounds of bone removal and bone formation.
How Much Force Braces Actually Use
You might expect there’s a precise, agreed-upon number for how much force is ideal. There isn’t. A systematic review in The Angle Orthodontist found no scientific consensus on optimal force levels. Studies on human teeth used initial forces ranging from roughly 18 to 1,500 centinewtons, a massive spread that reflects how much force requirements vary depending on the type of movement, the specific tooth, and the individual patient.
What orthodontists do agree on is the principle: lighter forces generally produce more efficient movement with less tissue damage. Heavy forces crush more of the periodontal ligament, extending the lag phase and potentially harming the tooth root. So while there’s no universal number, the clinical goal is always the minimum force needed to trigger bone remodeling without overwhelming the tissue.
Why Roots Can Shorten During Treatment
One side effect of orthodontic treatment that rarely gets discussed upfront is root resorption, where the tips of tooth roots gradually shorten. A 2024 study found that roughly 73% of orthodontic patients showed some degree of root shortening by the end of treatment, with the upper lateral incisors (the teeth next to your front teeth) most frequently affected.
For most people, the amount of shortening is minor and causes no long-term problems. But certain factors increase the risk of more significant loss. Teeth that already have short roots before treatment are more vulnerable. Treatment duration matters: the longer you’re in braces, the more cumulative resorption occurs. Fixed appliances (traditional braces) carry a higher risk than removable ones. Certain tooth characteristics like unusually narrow crowns or ectopic positioning (teeth that erupted in the wrong spot) also correlate with greater root shortening.
This is one reason orthodontists take periodic X-rays during treatment. If significant root shortening shows up, they can adjust the treatment plan, reduce forces, or wrap up treatment earlier to limit further loss.
Why It Takes So Long
The average orthodontic treatment runs 18 to 24 months, and the biology explains why shortcuts are difficult. Bone remodeling is inherently slow. Osteoclasts need time to dissolve bone at the leading edge, osteoblasts need time to build new bone at the trailing edge, and the body cycles through lag phases and active phases repeatedly as forces are adjusted at each appointment. Every time the orthodontist places a new, stiffer wire or adds an elastic, the three-phase cycle essentially restarts for whatever new movement is being introduced.
The process also isn’t just about getting teeth into position. New bone needs time to mature and harden. This is why retainers are necessary after braces come off. The bone around your newly positioned teeth is still relatively soft and actively remodeling for months. Without a retainer holding everything in place, teeth can drift back toward their original positions before the bone fully solidifies around them.