The effects of third-order torque and self - Saint Louis University

wire at one or both of its contact points with the edge of
the slot, known as mechanical notching, can occur, further
adding to the resistance to sliding. 70,94 In a clinical
study, this damage to the archwire was found to be related
to the design of the orthodontic bracket. 95 The main effect
of archwire-notching on friction is the creation of
“obstacles” that impede relative wire-slot sliding. 96 It
appears that notching may be a function of the materials in
contact. Kusy et al. 30 found that ceramic brackets cause
more notching than stainless steel brackets. Similarly,
Articolo’s group 96 found that notching of archwires was
three times more prevalent and severe with ceramic brackets
than with stainless steel brackets.
Third-Order Torque
The term “third-order torque” in orthodontics pertains
to the rotational control and movement of a tooth crown or
root faciolingually. This type of tooth movement can occur
subsequent to twisting a square or rectangular archwire
along its longitudinal axis, required to place it into the
slot of a crown-attachment. In this process, two contact
forces acting on the occlusal and gingival walls of the
slot by partial archwire deactivation create a third-order
30