Braces correct misaligned teeth by applying gentle, continuous pressure, which triggers a controlled biological response that allows teeth to move through the jawbone. This process relies on the body’s natural ability to remodel the bone surrounding the tooth roots. Understanding this transformation reveals the balance between the hardware that generates the force and the cellular activity that permits the movement. The journey involves detailed phases, ensuring the movement is safe, predictable, and stable.
The Components That Generate Force
The hardware of fixed braces functions as a precise system designed to deliver light, sustained force. Brackets are small square attachments bonded directly to the tooth surface, acting as handles with a slot that accepts the archwire. The archwire is the engine of the system, running through the slots of all brackets and connecting them into a single unit.
Early in treatment, the archwire is often made of nickel-titanium, prized for its super-elasticity and “shape memory.” When bent to fit crooked teeth, the wire constantly attempts to return to its original, ideal arch shape, applying a light and consistent force.
As teeth straighten, nickel-titanium wires are replaced with stiffer archwires, like stainless steel, for more complex movements. Small elastic loops (ligatures) or fine wires secure the archwire into the bracket slots. The force applied must be light and continuous, as excessive force can damage the tooth root or cause tissue damage.
The Biological Engine of Tooth Movement
Tooth movement is fundamentally a biological process driven by the periodontium, the tissue surrounding the tooth root. The Periodontal Ligament (PDL) is a fibrous structure connecting the tooth root to the alveolar bone of the jaw. When the archwire applies pressure, the PDL translates the mechanical force into a biological signal.
On the side facing the direction of movement, the PDL is compressed against the bony socket wall. This compression triggers a response that recruits specialized cells called osteoclasts. Osteoclasts are responsible for bone resorption; they dissolve the bone tissue directly in the path of the moving tooth, creating space for the root to travel.
Simultaneously, the PDL is stretched on the opposite side of the tooth, causing tension. This tension stimulates osteoblasts, which are bone-forming cells, to migrate to the area. Osteoblasts begin new bone deposition, laying down a fresh bone matrix to fill the space behind the moving tooth root.
This synchronized cycle of bone breakdown (resorption) on the pressure side and bone rebuilding (deposition) on the tension side is known as bone remodeling. The tooth slides through the jawbone as bone is selectively removed ahead of it and rebuilt behind it. The speed of movement is regulated by the rate of this cellular remodeling, typically progressing about one millimeter per month.
Key Phases of Orthodontic Treatment
Orthodontic treatment is divided into three main phases. The first is Leveling and Alignment, which focuses on correcting rotations and vertical discrepancies. This phase uses flexible nickel-titanium archwires to gently move the crowns of the teeth onto the same plane.
The treatment then moves into the Working Phase, focusing on correcting the bite relationship between the upper and lower arches. The orthodontist replaces the flexible wires with stiffer, rectangular stainless steel archwires to better control root position. Bite issues, such as overbites or underbites, are corrected using elastics or springs to apply forces between the jaws.
The final stage is Finishing and Detailing, where minor adjustments perfect the alignment. The goal is optimal occlusion, ensuring the upper and lower teeth fit together precisely for efficient chewing. This phase involves small bends and loops in the archwires to achieve ideal root parallelism before the braces are removed.
Maintaining the New Position
After braces are removed, the surrounding tissues are not yet stable. The bone and Periodontal Ligament need time to reorganize and solidify around the relocated tooth roots. This stabilization is accomplished through a retainer, making the retention phase a necessary part of the process.
Retainers, which can be fixed (bonded to the back of the teeth) or removable, hold the teeth firmly in place while this biological reorganization occurs. Without retention, teeth tend to shift back toward their original positions, a phenomenon known as relapse. The bone tissue, temporarily softened during remodeling, gradually hardens and matures, permanently securing the new alignment.
Wearing a retainer, often lifelong, protects the investment made during active treatment. By maintaining the achieved position, the retainer ensures the long-term success of the orthodontic correction and stabilizes the new smile.