Braces straighten teeth by applying constant, gentle pressure that triggers your body to remodel the bone surrounding each tooth. This isn’t a mechanical process like bending metal. It’s a biological one: the pressure creates changes in living tissue that allow teeth to shift through solid bone at a rate of roughly one millimeter per month. Understanding how this works explains why treatment takes so long, why it hurts, and why retainers matter afterward.
How Pressure Reshapes Bone
Each tooth sits in a socket of jawbone, held in place by a thin layer of connective tissue called the periodontal ligament. This ligament acts like a hammock, suspending the tooth and cushioning it against chewing forces. When braces apply pressure in a specific direction, they compress the ligament on one side of the tooth and stretch it on the other.
The compressed side triggers your body to break down bone (a process driven by cells called osteoclasts), creating space for the tooth to move into. The stretched side triggers new bone formation (driven by osteoblasts), filling in the gap left behind. This cycle of destruction and rebuilding is what actually moves teeth. It’s the same remodeling process your skeleton uses throughout your life, just directed by the orthodontic force.
This is why braces can’t work faster than your biology allows. Teeth safely shift about one millimeter every four weeks, with clinical studies showing a range of 0.55 to 2.44 millimeters per month depending on the tooth and the type of movement. Pushing harder doesn’t speed things up. Excessive force can damage tooth roots or kill the compressed tissue entirely, which actually stalls movement until the area heals.
What Each Component Does
The brackets bonded to your teeth don’t move anything on their own. They’re handles, giving the system something to grip. The real engine is the archwire, a curved metal wire that threads through every bracket and acts as a track or rail. When the wire is bent to fit your crooked teeth, it “wants” to return to its original shape, and that stored energy is what pushes or pulls each tooth toward its target position.
Early in treatment, orthodontists typically use nickel-titanium wires. These have a remarkable property: they can be bent dramatically (up to 7 to 8 percent strain, roughly forty times the flexibility of stainless steel) and still spring back to their programmed shape. More importantly, they deliver force at a nearly constant level as they unwind, which keeps pressure gentle and steady rather than spiking and fading. Body heat from your mouth actually activates this shape memory, so the wire works continuously.
As treatment progresses, stiffer stainless steel wires replace the flexible ones. These allow more precise control for closing gaps and fine-tuning positions. Loops bent into the wire can target specific teeth with customized force. Springs threaded onto the wire push teeth apart or together along its length. Elastic bands hooked between upper and lower brackets correct bite alignment by connecting the two arches.
The Four Stages of Treatment
Orthodontic treatment follows a predictable sequence, and knowing where you are in it helps explain why certain months feel different from others.
Leveling and aligning comes first. This is when the most visibly crooked teeth start to straighten. A series of progressively stiffer wires brings all teeth to the same height and into a smooth arch shape. This phase typically produces the most dramatic visible change and also the most soreness, since teeth may be moving the greatest distances.
Space closing follows once the teeth are roughly aligned. If teeth were extracted to make room, or if gaps exist naturally, the wire and elastic chains draw teeth together to eliminate spaces. Teeth slide along the archwire during this phase, which is why low friction between the bracket and wire matters for efficiency. Self-ligating brackets (the kind without traditional rubber band ties) are designed to reduce this friction.
Detailing and finishing is the fine-tuning stage. Individual tooth positions are adjusted so upper and lower teeth mesh together properly when you bite. Small bends in the wire, repositioned brackets, or short-term elastic wear handle these corrections. Progress may feel slow because changes are subtle, but this phase determines how well your bite functions long-term.
Retention begins the day braces come off, when you switch to a retainer. This phase is arguably the most important, because the tissues holding your teeth haven’t finished adapting to their new positions.
Why Braces Hurt
The soreness you feel after adjustments isn’t just from pressure on your teeth. It’s from inflammation in the periodontal ligament, which is the same tissue doing the work of remodeling bone. When orthodontic force compresses the ligament, it restricts blood flow in that area and triggers a cascade of inflammatory signaling molecules. These molecules are essential for recruiting the bone-remodeling cells that make movement possible, but they also activate pain-sensing nerve fibers in and around the tooth.
The nerve fibers in your periodontal ligament and tooth pulp detect this inflammation and send pain signals that typically peak 24 to 72 hours after an adjustment, then gradually fade. The inflammation also causes the ligament to swell, which is why teeth can feel “too tall” or sensitive to biting pressure. Over-the-counter pain relievers that block the inflammatory pathway (like ibuprofen) are effective precisely because they interrupt this process. However, because inflammation is what drives tooth movement, there’s a theoretical trade-off: suppressing it too aggressively could slow treatment slightly.
The cycle repeats with each wire change or adjustment. As teeth get closer to their final positions and need less movement, the inflammation is milder and discomfort typically decreases.
Why Teeth Try to Move Back
One of the least intuitive parts of orthodontics is that straightened teeth actively try to return to their original positions. This tendency, called relapse, has multiple causes, and it’s why retainers aren’t optional.
The most immediate cause involves the fibers in the periodontal ligament. During treatment, fibers on the tension side of a moving tooth get stretched and embedded in newly deposited bone. After braces come off, these stretched fibers pull back toward their original configuration. According to research on post-treatment changes, the principal ligament fibers drive most of the initial relapse tendency. After about a month, a different set of fibers in the gum tissue becomes the dominant force pulling teeth back.
Gum fibers are particularly stubborn. Unlike the ligament fibers deeper in the socket, gum fibers have a slower turnover rate and aren’t anchored in bone that remodels quickly. After a tooth is rotated, for example, the surrounding gum fibers remain stretched and unremodeled for at least five months, generating a constant pull back toward the old position. Fibers connecting neighboring teeth can also try to reestablish the original spacing between them.
Beyond the fibers, your lips, tongue, and cheek muscles exert forces on teeth every day. If the new tooth positions don’t balance perfectly with these muscle forces, the teeth drift. Continued jaw growth (especially in younger patients) and habits like tongue thrusting add further instability. This is why many orthodontists now recommend long-term or indefinite retainer wear rather than a fixed endpoint. The retention period needs to last at least until the fiber systems fully reorganize and the surrounding tissues regain their normal structure, and some of those changes may never fully complete.
What Affects How Long Treatment Takes
Most braces treatments last 12 to 24 months, but the range can be wider depending on what needs to happen. The biology of bone remodeling sets a hard speed limit, so the main variable is distance: how far teeth need to travel and how many different corrections are required.
Simple crowding where teeth just need to rotate or tip into place moves faster than cases requiring bodily movement, where an entire tooth (root and all) must shift in the same direction. Closing extraction spaces takes time because teeth may need to travel several millimeters through solid bone. Bite corrections that involve repositioning the upper and lower arches relative to each other add complexity and duration.
Age plays a role too. Children and teenagers have denser blood supply to the bone and faster cellular turnover, which generally means quicker remodeling. Adults can achieve the same results, but the biological response is typically slower, and the denser, more mineralized bone of an adult jaw doesn’t remodel as readily. Compliance also matters: if you’re prescribed rubber bands and don’t wear them, the forces needed to correct your bite simply aren’t being applied, and that phase stalls until you do.