Properties of crimpable archwire hooks: a laboratory investigation

The aim of the present study was to utilize a strain gauge, which enabled t he force applied to produce firmly attached crimpable hooks to rectangular stainless steel archwires, to be measured. In vitro testing of two hooks, A merican Orthodontic (AO) and TP Orthodontic (TP), and two dimensions of sta inless steel archwire, 0.019 x 0.025 and 0.018 x 0.025-inch, was carried ou t using an Instron Universal Testing machine. The results demonstrate that there was a significant difference in the beha viour of the two types of crimpable hooks, with almost twice the force need ed to dislodge the TP hooks compared with the AO hooks (11.7 and 6.22 N, re spectively). When using TP hooks attached to either 0.019 x 0.025 or 0.018 x 0.025-inch stainless steel wires, the archwire size makes little differen ce to the force required to produce movement. The clinical significance of these findings is discussed.