3-D experimental identification of force systems from orthodontic loops activated for first order corrections

Intrd-arch irregularities can be corrected using wire of low stiffness, wir es of increasing stiffnesses, or by the activation of loops built into the appliance. While the orthodontist controls only the magnitude of force when leveling with continuous arches, the configuration and positioning of loop s offer the possibility of controlling the type and direction of force. In the present study, force systems developed by the L-loop, the T-looy, and t he rectangular (R-) loop were analyzed with respect to the force systems ac ting for first order irregularities, buccolingual movement, and rotation al ong the long axis of the tooth. An interbracket distance of 21 mm was chose n, and the loops were analyzed in a testing machine that made it possible t o register forces and moments simultaneously in three planes of space. The activations included a symmetrical translation of 1 mm made in steps of .2 mm, corresponding to a buccolingual movement, and 10-degree rotations clock wise and counterclockwise in steps of one degree. Force systems were record ed during activation and de activation. Loops made of TMA wire delivered 40 % of the force delivered by the same loops made of stainless steel wire. Th e T-loop generated a force system that deviated qualitatively only slightly from that delivered by a straight wire, The L-loop generated a force syste m that was dependent on orientation; constancy was better corresponding to the anterior part of the loop. It was evident that the rectangular loop was capable of generating any desired moment-to-force ratio, and the R-loop de monstrated a high degree of constancy of the force system. Rectangular loop s should, therefore, be preferred for making first order corrections.