A clinical investigation into the behaviour of crimpable archwire hooks

The objective of this study was to measure the force applied to attach crimpable hooks securely to rectangular stainless steel archwires, both inside and outside the mouth. A specially designed strain gauge was utilized to measure the force applied by each operator. In vitro testing of the attached hooks was carried out using an Instron Universal Testing Machine. Two operators crimped a total of 80 TP Orthodontic crimpable hooks to 0.019 x 0.025-inch stainless steel archwires. For one operator there was a significant difference between the intra- and extra-oral forces used to produce firmly attached crimpable hooks (P = 0.03). However, in vitro testing demonstrated no statistically significant difference between the force levels required to displace the crimped hooks for either operator. The clinical significance of these findings is also discussed. Better reliability of crimpable hooks may be achieved by placing them out of the mouth.