Sunday, August 8, 2010
Orthodontic braces are often used in conjunction with other orthodontic appliances to widen the palate or jaws or otherwise shape the teeth and jaws. While they are mainly used on children and teenagers, adults can also use them.
Teeth move through the use of force. The force applied by the archwire pushes the tooth in a particular direction and a stress is created within the periodontal ligament. The modification of the periodontal blood supply determines a biological response which leads to bone remodeling, where bone is created on one side by osteoblast cells and resorbed on the other side by osteoclasts.
Two different kinds of bone resorption are possible. Direct resorption, starting from the lining cells of the alveolar bone, and indirect or retrograde resorption, where osteoclasts start their activity in the neighbour bone marrow. Indirect resorption takes place when the periodontal ligament has become subjected to an excessive amount and duration of compressive stress. In this case the quantity of bone resorbed is larger than the quantity of newly formed bone (negative balance). Bone resorption only occurs in the compressed periodontal ligament. Another important phenomenon associated with tooth movement is bone deposition. Bone deposition occurs in the distracted periodontal ligament. 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.