The application of braces moves the teeth as a result of force and pressure on the teeth. There are four basic elements that are needed in order to help move the teeth. In the case of traditional metal or wire braces, one uses brackets, bonding material, arch wire, and ligature elastic, also called an “O-ring” to help align the teeth.
The teeth moves when the arch wire puts pressure on the brackets that are attached to the teeth. Sometimes springs or rubber bands are used to put more force in a specific direction. Braces have constant pressure, which over time, move teeth into their proper positions. Occasionally adults may need to wear headgear to keep certain teeth from moving. When braces put pressure on your teeth, the periodontal membrane stretches on one side and is compressed on the other. This movement needs to be done slowly otherwise the patient risks losing his or her teeth. This is why braces are commonly worn for approximately one and a half years and adjustments are only made every three or four weeks. This process loosens the tooth and then new bone grows in to support the tooth in its new position which is technically called bone remodeling.
Bone remodeling is a biomechanical process responsible for making bones stronger 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. Two different kinds of bone resorption are possible which are called direct resorption, starting from the lining cells of the alveolar bone, and indirect or retrograde resorption, which takes place when the periodontal ligament has become subjected to an excessive amount and duration of compressive stress.
Another important factor associated with tooth movement is bone deposition. Bone deposition occurs in the distracted periodontal ligament and without bone deposition, the tooth will loosen and voids will occur distal to the direction of tooth movement. A tooth will usually move about a millimeter per month during orthodontic movement, but there is high individual variability. Orthodontic mechanics can vary in efficiency, which partly explains the wide range of response to orthodontic treatment.