Wires

Also called

Vertical bowing

What happens

The light wire cannot hold its shape against the closing force: it bends, and the teeth beside the space tip into it instead of moving bodily. A round wire carries none of the brackets' torque, so the incisors retrocline as they come back.

What you see

A lateral open bite at the extraction site, a deeper overbite and curve of Spee, and upright incisors; with a high canine, the neighbours dip toward it and the occlusal plane can cant.

Wire choice

Close on rectangular steel — 19×25 in the textbook's space-closure rationale, 16×22 or 17×25 in practitioner sequences. Chain on a light round or NiTi wire is the classic trigger.

Evidence: Both layers describe it. The textbook's remedies are convention and its account of the mechanism is ungraded; no source gives a measured size for the effect.

What happens

A distal force at the incisor brackets acts occlusal to the teeth's centre of resistance, so the crowns tip lingually around a centre of rotation near the apex. Swinging back on that arc lowers the incisal edges, like a drawbridge coming down: the incisors retract and extrude together, and the bite closes.

What you see

Incisors uprighting and coming down as the space closes, more overbite, and often a more consonant smile arc.

Wire choice

It needs the incisors free to tip; a rigid rectangular wire holding their torque works against it.

Evidence: The textbook states the mechanism without the nickname, as a deliberate open-bite treatment (convention); the nickname comes from the published literature.

What happens

Practitioner experience says chewing moves the teeth slightly up and down; each bite bends the passive laceback for a moment across the extraction space, shortening it and pulling the canine back a little, repeated with every meal.

What you see

Practitioner experience says the canine moves back between visits although no force was added at the visit.

Wire choice

Practitioner experience says move to a .018 or .020 round steel wire soon after lacebacks go on, rather than staying long on flexible heat-activated NiTi.

Evidence: Practitioner experience only: no textbook card describes it, and the published literature calls it a hypothesis, not a measured effect.

What happens

Seen from the front, the incisors sit on an arc like the spokes of a wheel. Torque and tip are coupled on that arc: adding palatal root torque takes away mesial crown tip, and over-proclined incisors bring their root apices together.

What you see

Incisor roots converging or crowding in the finished case, and apices close together on a periapical film — which matters before space closure or a prosthesis next to them.

Wire choice

It follows the torque actually expressed, so it shows on rectangular steel finishing wires; practitioner experience says rectangular NiTi only begins torque control.

Evidence: The textbook describes the arc and the converging apices but gives no ratio (convention). The often-quoted 4° of torque cancelling 1° of tip is practitioner-only. Practitioner sources also note an upside: more torque, less mesial tip, less anchorage demand.

Also called

Archwire bowing

What happens

The wire bends between its supports instead of holding its shape, so the reaction lands on the teeth nearest the load. Bent vertically, it is the roller-coaster pattern, which practitioner sources call vertical bowing. Bent within the arch, the neighbouring teeth tip toward the load and the arch form flattens.

What you see

Teeth beside the load tipping toward it — for a palatal canine, its neighbours moving into crossbite — and a flatter arch form. A torquing spring on the incisors can bow the front segment mildly too.

Wire choice

A rigid steel base wire for sliding and for traction — 19×25 in the textbook's space-closure rationale — with flexible wires kept for alignment.

Evidence: The textbook describes wire bending under load in braces (convention) but has no card on a named bowing effect for them; its card on bowing is about aligner plastic sagging at extraction sites, an aligner question answered in Q&A.