Orthodontics is based on the principle that if prolonged force is applied to a tooth, tooth movement will occur. The force creates pressure that causes the bone around the tooth to remodel. Remodeling is a process where bone is selectively removed in some areas and added in others. The remodeling of bone is controlled by the periodontal ligament (PDL). The PDL is a dynamic collection of fibers surrounding the root of the tooth, which serves many purposes.

• The PDL houses the cells that make bone (osteoblasts) or destroy bone (osteoclasts) around the tooth.
• The PDL provides the fibers that attach the tooth to the bone.
• The PDL houses the vascular and nervous tissue for the tooth.

How Do Teeth Move?

Under ideal circumstances, teeth move 3 mm per month. In reality, teeth move 1.5 mm per month

• Factors Affecting Movement
• Types of Forces