| Field | Value |
|---|---|
| ID | OA-0202 |
| Type | component |
| Category | component |
| Fixed/removable | component in removable appliance |
| Primary function | slow maxillary arch expansion |
| Malocclusion target | mild maxillary transverse deficiency |
| Uses TADs | no |
The Coffin spring (W-spring) is a heavy-gauge (1.0–1.25 mm SS) omega-shaped spring lying in the palate of a divided removable plate. The spring bridges the gap between the two halves of the plate; as it opens (is activated), it pushes the two halves of the appliance apart, transmitting slow transverse expansion force to the teeth and palate. Activation is typically 1 mm every 2–3 weeks. The Coffin spring predates the modern expansion screw; it is less precise but still used in some systems. More commonly seen in UK and European removable appliance traditions.
The coffin spring (palatal spring) is a large omega-shaped or horseshoe-shaped midline spring embedded in the baseplate of a removable expander. When compressed laterally, it tries to return to its wider natural shape, applying a slow, continuous expansion force to the palatal baseplate and, through the baseplate and clasps, to the posterior teeth. The force is distributed broadly across the arch rather than concentrated at specific teeth, making it a gentle, tissue-borne expander.
The coffin spring is the active element in Coffin-plate expanders and many Schwarz appliance designs. It is used for slow maxillary expansion in growing patients — typically 0.5–1 mm of expansion per month, compared to 0.5 mm per day for rapid palatal expanders. Indications include mild to moderate posterior crossbite in the mixed dentition, arch perimeter gain for space management, and palatal constriction associated with mouth-breathing habits. Unlike the RPE, the coffin spring does not require daily patient activation — the spring's elastic properties deliver continuous force.
Heavy gauge wire (1.0–1.25 mm SS) is required to generate sufficient expansion force across the width of the palate. The spring is activated by spreading the arms slightly at each appointment — typically 2–3 mm every 4–6 weeks. Activation is performed chairside with pliers.
Coffin spring expanders are limited to dentoalveolar expansion — they cannot open the midpalatal suture in a clinically meaningful way (unlike the RPE). They are indicated for mild crossbites with dentoalveolar component; moderate to severe skeletal crossbites require an RPE or MARPE. Compliance-dependent: the appliance must be worn full-time for expansion to occur.
Lab-bent from 1.0–1.25 mm SS wire; spring is incorporated midline in divided acrylic baseplate.
Appliances that incorporate this component. ★ = fabricated by Clear Fusion Lab.
appliance
appliance
symmetric bilateral expansion
activation forces
activation range
incorporated into split-plate for combined expansion + other tooth movement
(constant force); screw is activated incrementally; Coffin preferred for slow, continuous expansion in very young patients
Manual](https://www.aapd.org)