Rectangular loops in inconsistent force systems: a laboratory investigation.

Abstract

MATERIAL AND METHOD: [corrected] The force system delivered by the rectangular loop (R-loop) was the subject of this in-vitro investigation. The correction of a first-order irregularity was simulated in an inconsistent force system. Three types of R-loop made of 0.017" x 0.025" TMA wire but differing in length and insertion system were tested in a 3D strain gauge (Hottinger, Darmstadt, Germany). The buccal segment consisted of one molar and two bicuspids, with the first bicuspid as an active unit scheduled to be moved buccally into the dental arch. RESULTS: The first R-loop tested revealed too high a force magnitude to be recommended for clinical use. A loop connecting only two teeth and bypassing the second premolar delivered a favorable initial force of 85 cN with a drop of 20 cN per 1 mm deactivation. In order to achieve a translatory tooth movement, a buccal root torque must be bent in addition into the short horizontal leg of the R-loop. The use of a transpalatal arch is indispensable if adverse side effects are to be avoided.