The effects of third-order torque and self - Saint Louis University
The effects of third-order torque and self - Saint Louis University
The effects of third-order torque and self - Saint Louis University
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test-archwire in place <strong>and</strong> ligated, the simulated dental<br />
segment was mounted to the fixed head <strong>of</strong> a universal<br />
testing machine (Model 1011, Instron Corporation, Canton,<br />
MA) with the posterior, held end <strong>of</strong> the archwire oriented<br />
vertically. A custom attachment was fastened to the<br />
moveable head <strong>of</strong> the Instron testing machine (Figure 3-10),<br />
equipped with a ten-pound load transducer. This attachment<br />
was fabricated with a four-pronged “pencil chuck,” by which<br />
one posterior end <strong>of</strong> the test-wire was grasped. <strong>The</strong><br />
testing machine <strong>and</strong> an attached chart rec<strong>order</strong> (Model 2310-<br />
069, Instron Corporation) were turned on simultaneously.<br />
<strong>The</strong> wire was pulled posteriorly through the crown-<br />
attachments at a rate <strong>of</strong> one millimeter per minute for 90<br />
seconds while the chart rec<strong>order</strong> produced a force-versus-<br />
displacement plot. Testing was performed in the dry state<br />
<strong>and</strong> at room temperature. <strong>The</strong> load range was set at 0 to<br />
1000 grams. <strong>The</strong> testing machine was initially calibrated<br />
<strong>and</strong> checked after changes <strong>of</strong> crown-attachment sets. From<br />
each test the mean load, which was virtually equal to the<br />
frictional-force magnitude, was determined from ten plot-<br />
points taken at six-second intervals between the 30-second<br />
<strong>and</strong> 90-second marks on the plot.<br />
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