Sliding mechanics with heavy exedgewise forces

A wide range of treatment mechanics was evaluated during the 1970s, in the early days with the preadjusted bracket system. Attempts were made to apply traditional edgewise force levels (500-600 gm) to the new brackets. It was found that heavy space closure forces (for example using steel Pletcher springs on .018/ .025 steel wires) caused unwanted tip, rotation, and torque changes (Figs 9.8-9.11).

When these heavy forces were used for space closure, there was therefore a need for extra tip, rotation control, and torque control. This additional control could be achieved by designing extra tip, rotation, and torque into the brackets. This was the background to the 'extraction series' or 'translation series' brackets developed by Andrews.2 I lowever, such brackets retained the extra features through to the end of treatment (unlike standard edgewise, where anchor bends, for example, could be adjusted in the final stages). Cases treated with extraction series brackets and heavy forces therefore placed heavier demands on anchorage early in the treatment, and often had over-corrected tooth positions at the end of treatment (Fig. 9.12).

Normal space closure I " Too rapid space closure

Fig. 9.7 Closing loop archwires were part of traditional edgewise treatment mechanics. They were individually made for each patient, and had a limited range of action before the omega loop came into contact with the molar tube.

Fig. 9.8 Too rapid incisor retraction can leave the incisors with inadequate torque.

Fig. 9.10 In response to too rapid space closure, there is an increased tendency for rolling in of teeth adjacent to extraction sites.

Normal space closure Too rapid space closure isl Too rapid space closure

Fig. 9.9 Too rapid space closure also allows unfavorable torque effects on upper and lower molars. The movements shown are not favorable for proper functional chewing movements, and molars in this position require additional torque to reach ideal position.

Fig. 9.10 In response to too rapid space closure, there is an increased tendency for rolling in of teeth adjacent to extraction sites.

Normal space closure Too rapid space closure isl Too rapid space closure

Fig. 9.11 Unwanted effects of over-rapid space closure include lower molar tipping, with extrusion of the distal cusps, especially in high-angle cases. Also, excessive soft tissue build-up can occur, which sometimes prevents proper space closure, or causes re-opening of extraction space.

Fig. 9.12 This patient was treated using upper canine brackets with 11° of tip, leaving the upper canine roots in close proximity to the premolar roots.

Fig. 9.11 Unwanted effects of over-rapid space closure include lower molar tipping, with extrusion of the distal cusps, especially in high-angle cases. Also, excessive soft tissue build-up can occur, which sometimes prevents proper space closure, or causes re-opening of extraction space.

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