Materials and appliances in orthodontics: brackets, arch wires, and friction.

The focal point for any orthodontic patient is the form and comfort of his or her appliance. To the practitioner, both can influence the function of the arch wire-bracket combination. The most critical interaction that occurs within the so-called couple is friction. When friction is high, sliding is hampered, as the efficiency and reproducibility of the appliance may be impaired. In this review, the recent advances to control friction and to modify the arch wire-bracket combination are reviewed.