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The effect of off-center positioning on the force system produced by segmented 0.017 × 0.025-inch TMA T-loops was measured. A T-loop was designed to produce equal and opposite moments in the centered position. The spring was tested in seven positions, centered, 1, 2, and 3 mm toward the anterior attachment, and 1, 2, and 3 mm toward the posterior attachments. The horizontal force, vertical force, and alpha and beta moments were measured over 6 mm of spring activation. The results showed that the alpha/beta moment ratio was dependent only on the spring position, and independent of spring activation. Eccentric positioning of T-loop springs effectively produces a consistent moment differential through the range of spring activation. (Am J Orthod Dentofac Orthop 1997;112:12-8.) |
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