There is no reliable evidence from the trials included in this review that any specific initial arch wire material is better or worse than another with regard to speed of alignment or pain. There is no evidence at all about the effect of initial arch wire materials on the important adverse effect of root resorption. Further well-designed and conducted, adequately-powered, RCTs are required to determine whether the performance of initial arch wire materials as demonstrated in the laboratory, makes a clinically important difference to the alignment of teeth in the initial stage of orthodontic treatment in patients.
Efficiency of multi-strand steel, superelastic Ni-Ti and ion-implanted Ni-Ti archwires for initial alignment.
In a clinical trial involving 155 dental arches with irregularity > 5 mm, the rate of alignment was used to compare the alignment efficiency of 16 mil superelastic Ni-Ti versus 17.5 mil triple-stranded steel archwires, and to determine whether ion implantation of the Ni-Ti wire improved its performance. Subjects were randomly assigned to archwire types; both 18 and 22 slot edgewise appliances were employed. Pre-treatment equivalence of the experimental groups was verified. Anterior irregularity was determined monthly (using Little's irregularity index) until it decreased below 2 mm, and the elastomeric ligatures were replaced at each appointment. Effective tooth movement occurred with each of the archwire types. There were no significant differences among wires, but the rate of alignment was significantly faster in the lower arch for subjects with the 22 slot appliance.