Aim: Different variables that may affect the results of orthodontic shear bond strength tests have been under investigation. One of these variables has been the crosshead speed. But studies which have evaluated the effect of crosshead speed have came up with interestingly opposite results. The details of these studies show that other parameters might have a confounding effect. One could be the type of load cell. Therefore the purpose of this study was to observe whether different load cells (wire loops and shearing blades) could interact with the results of crosshead speed studies.
Materials and Methods: Stainless steel central incisor edgewise brackets were bonded to forty eight bovine incisors using Transbond XT adhesive system. After embedding in self curing acrylic, the specimens were randomly assigned to one of the four study groups: 1)wire loop load cells and 5 mm/min crosshead speed 2)wire loop load cell and 0.5 mm/min speed 3) Shearing blade load cell and 5 mm/min speed and 4) Shearing blade with 0.5 mm/min speed.
Results: Analysis of variance showed a significant difference between the results obtained from the two blade groups (P=0.003) whereas the difference between the wire loop groups was insignificant (P=0.21).
Conclusion: Force delivery systems appear to act as confounders when delivering force. The wire loop seemed to have acted as a shock absorbing system. This might be the reason that different crosshead speeds show similar results when wire loops are used as load cells. There is a need for standardizing orthodontic shear bond strength tests.