| Field | Value |
|---|---|
| ID | OA-0326 |
| Type | expander |
| Category | expander |
| Fixed/removable | fixed |
| Primary function | mandibular arch expansion; molar uprighting |
| Malocclusion target | lower arch constriction; posterior crossbite; crowding |
| Inventor | various (1970s adaptation) |
| First year | 1970s |
| Period | modern |
| Status | current |
| Wire gauge | 0.036″ stainless steel |
| Uses TADs | no |
The Bi-Helix is a fixed mandibular expander constructed from a single 0.036″ SS wire with two posterior helical loops, connected to lower first molar bands. It is the mandibular equivalent of the Quad Helix (Quad Helix): the two helical loops store elastic energy and deliver light, continuous buccal forces to the lower posterior teeth, producing gradual dentoalveolar arch widening. Because the mandible has no symphyseal suture in patients past early childhood, all expansion is dentoalveolar (tooth tipping and alveolar bending). The Bi-Helix is preferred over a jackscrew lower expander when lighter, more continuous forces are desired or when a patient cannot tolerate the bulk of an acrylic-based design.
The pre-activated helical loops try to return to a wider position, pressing the wire arms against the lingual surfaces of the posterior teeth. This produces buccal tipping of the lower molars and premolars and mild arch widening. Simultaneously, the design helps upright mesiolingually-rotated lower molars. Force delivery is continuous and light — the Bi-Helix can be reactivated chairside by spreading the helical loops with a three-prong plier. Expected expansion per activation: 2–4 mm over several weeks per cycle.
Mild lower arch constriction requiring modest arch width increase; lower posterior crossbite correction; lower molar uprighting; cases where the lighter force of a spring-type expander is preferred over a jackscrew; patients with skeletal open bite tendency where heavy vertical forces should be avoided (jackscrew designs can open the bite more). Often used in conjunction with an upper RPE or Quad Helix to coordinate upper and lower arch widths.
Not a skeletal expander — produces purely dentoalveolar changes. Significant lower arch constriction (> 5 mm needed) is better addressed with orthopedic expansion or extraction. Patients must maintain good hygiene around the lingual wire. Cannot be adjusted for asymmetric expansion as easily as a jackscrew.
vs. four for Quad Helix)
lingual to premolar/canine region
The two helices must be symmetric and equal — asymmetric loops deliver uneven force. The anterior arms should contact the lingual surface of the lower teeth 1–2 mm off tissue. Solder the wire ends into the lingual aspect of the molar bands with hard solder; joint strength is critical. Pre-activate the appliance 3–4 mm beyond passive width before soldering — this is the stored activation delivered on seating. CFL's Bi-Helix is entry-level; the "Transverse" variant likely represents a heavier-gauge or wider-activation version.
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alternative. See Lower lingual expander.
Lab](https://www.ddslab.com/orthodontics/arch-development/bi-helix/)
Lab](https://uniortholab.com/us/portfolio-item/bi-helix-lower/)
Lab](https://www.qcortho.com/expansion-and-arch-development.html)
business notes.