The effect of bracket position and location of the point of force application on tooth movement. In the labial system, the intrusive force against the incisors is applied anterior to the center of resistance and therefore the incisors tend to tip forward as they intrude. Lingual intrusive force is applied close to the center of resistance of the incisors and the incisors are well intruded with little flaring. The possibility of flaring of the incisors is lower with lingual than labial mechanisms.

CR, Center of resistance; Fa, labial intrusive force; Fb, lingual intrusive force; m and M, moment.