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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difference in rate <strong>of</strong> tooth movement on the side with ion-<br />
implanted ß-titanium alloy wires engaged. 43<br />
Cross-sectional Shape <strong>and</strong> Size<br />
Many studies have suggested that the cross-sectional<br />
size <strong>of</strong> an archwire <strong>and</strong> frictional-resistance potential may<br />
be directly related. 5,23,31,34,36,44,45 In 2003 Smith, Rossouw<br />
<strong>and</strong> Watson 34 found significantly greater friction with<br />
larger archwires than smaller ones, <strong>and</strong> they attributed<br />
this difference to greater flexural stiffnesses <strong>of</strong> the<br />
wires having larger cross-sections.<br />
Rectangular wires permit the orthodontist to exert<br />
<strong>third</strong>-<strong>order</strong> control during treatment. <strong>The</strong>se wires are<br />
stiffer than round wires with similar cross-sectional<br />
dimensions. 46 <strong>The</strong> shape <strong>of</strong> the archwire cross-section<br />
influences its bending characteristics. Changes in shape<br />
from round to square to rectangular (e.g., while<br />
maintaining second-<strong>order</strong> slot-clearance), <strong>and</strong> the<br />
corresponding increases in stiffnesses, can cause increases<br />
in frictional resistance. Frank <strong>and</strong> Nikolai 5 found,<br />
however, that the smaller contact areas between the wire<br />
<strong>and</strong> bracket-slot with binding angulations in 0.020-inch<br />
round wires produced greater friction than the stiffer<br />
rectangular wires. <strong>The</strong>y suggested that the point-contacts<br />
14