| Field | Value |
|---|---|
| ID | OA-0194 |
| Type | component |
| Category | component |
| Fixed/removable | fixed (on archwire between hooks) |
| Primary function | pull teeth together; close space |
| Uses TADs | no |
A closed coil spring (tension coil) is stretched and attached between two hooks or stops on the archwire — one hook closer to the midline and one distally — and contracts to deliver a continuous closing force. In contrast to power chains (which lose force rapidly due to elastic relaxation), NiTi closed coil springs provide a more constant, predictable force over a longer period without requiring frequent replacement. Typical force range: 50–200 g depending on coil diameter and activation. Used for: extraction space closure, diastema closure, canine retraction, and molar mesial movement.
A closed coil spring rests on the archwire in a stretched state between two points of attachment (typically two hooks). As it contracts toward its natural length, it pulls the attachment points together. Force is determined by the spring's extension beyond its natural length and its stiffness constant.
Extraction space closure: Closed coil springs between the canine hook and the molar hook provide continuous retraction force during anterior segment retraction. They deliver a more consistent force over time than power chain, which degrades rapidly.
Canine retraction: A common use is single-tooth canine retraction during the space-closure stage after extraction, using a spring from the canine hook to the molar tube hook.
Alignment of displaced teeth: A spring laced to an auxiliary archwire can draw an impacted or severely displaced tooth into the arch.
NiTi closed coil springs deliver near-constant force over a wide range of extension — a significant clinical advantage over steel springs, which show a steep force-deflection curve. The typical target force for canine retraction is 150–200 g. Force should be checked at each appointment as the teeth move and the spring extension decreases.
Spring length is selected to fit the span without over-extension. Inner diameter must clear the archwire. NiTi is preferred for space closure; stainless is used when higher force or more predictable activation is needed.
Over-extension beyond 3× natural length risks permanent deformation. Poorly crimped hooks allow springs to dislodge. Like open coil springs, anchorage control must be planned — without TAD or adequate posterior anchorage, the whole posterior segment moves mesially during retraction.
No lab fabrication. Manufactured product; placed chairside.
Appliances that incorporate this component. ★ = fabricated by Clear Fusion Lab.
Bonded lingual retainer (space closure adjunct)
TAD-based distal jet
common; 150 g – 250 g load range
closure in extraction cases
space closure
specific force ratings (150 g, 200 g, 300 g) for predictable force delivery
JCO](https://www.jco-online.com)
AJO-DO](https://www.ajodo.org)
Orthodontics 6th ed.](https://www.elsevier.com)