The effects of archwire forces on incisor intrusion.

The forces exerted by archwires were measured in association with both Begg and Straight-Wire attachments. Seven stainless steel and three nickel-titanium wires were tested at vertical deflections equivalent to 20, 30, and 40 degrees, these being incorporated via anchor bends or reverse curve of Spee as appropriate to each system. All seven brands of stainless steel arches demonstrated similar performance. An increase in archwire diameter from 0.016 to 0.018 inch increased intrusive forces by 64 per cent for stainless steel and 58 per cent for nickel-titanium. Increasing anchor bend or reverse curve of Spee produced considerable force increases across the range of specimens. Begg archforms produced more force than Straight-Wire archforms of similar deflection when attached to molars only. Attachment of archwires to second premolars in addition to molars reduced the intrusive forces produced by Begg arches, but increased the forces of Straight-Wire arches.