Mouth spreader

What is a mouth spreader?

A mouth spreader (in English also mouth gag) is a tool that holds the mouth open instead of filling it. There are two build types: a ring the teeth sit behind, and a screw or ratchet spreader out of surgery. A mouth spreader makes the mouth accessible; it silences no one.

Where the mouth spreader comes from

From the operating room, and the design has barely changed.

The instrument was designed to hold a patient’s mouth open during an operation, and to stop someone biting the breathing tube and cutting off the supply. It came in handy for removing tonsils too.

The design is by the British surgeon William Fergusson (1808–1877), who drew it in 1876. The grooved jaws that close against the teeth were added later, by the British dentist William Robert Ackland (1863–1949). Anyone who buys a spreader with a ratchet today is buying a nineteenth-century surgical instrument with a different box around it.

The two build types

One is a size, the other a setting, and that difference decides everything.

1. The ring. A metal or silicone ring behind the teeth, with a strap around the head. The opening is fixed by the size you buy. A spider gag is the same ring with little hooks on the side, so the ring cannot tilt.
2. The screw or ratchet spreader. Two jaws you turn apart step by step. Adjustable, and harder for exactly that reason: you can crank it open further than the jaw goes on its own.

Why people use a mouth spreader

For the impossibility of closing your mouth.

A filled mouth is passive, a held-open mouth is not: it stays open even when you want to shut it, and that difference is exactly the point. Whatever else happens is secondary, because the spreader itself is already the scene.

Everything stands or falls on the clock. There is a moment where your jaw stops experiencing this as play and starts experiencing it as work, and that moment barely announces itself.

What to watch with a mouth spreader

The degrees, because the joint has no brake.

Bruno Bordoni and Melina Brizuela call the jaw joint ginglymoarthrodial in their StatPearls chapter on that joint: it hinges and it slides. After about ten degrees of mouth opening it is the sphenomandibular ligament that has to check the forward slide of the head. Everything you force above that hangs on a ligament and not on bone.

In practice: pick a size or setting your jaw can take without pushing, agree on a hand signal before the instrument goes in, and take it out at the first tremor rather than the last.

Where this fits on this site

This variant belongs to the bondage part of an evening, provided we set a time and a signal in advance. How that preparation runs is on the BDSM date.

Sources

• Anatomy, Head and Neck, Temporomandibular Joint. Bruno Bordoni & Melina Brizuela, StatPearls Publishing, NCBI Bookshelf (NBK538486), updated 8 September 2025. Provides the classification of the jaw joint as a diarthrosis and more precisely as a ginglymoarthrodial joint, so hinging and sliding, and the finding that the sphenomandibular ligament protects the joint after about ten degrees of mouth opening against excessive forward slide of the joint head.

This page too is listed as a tool term and leaves the source exemption unused: anyone who claims something about a joint should back it up.

Related terms

A mouth spreader is the mouth-opening kind within the gag, the page with the full breakdown.

• Jaw clamp. The same object under a word that in medicine means exactly the opposite.
• Gag. The English umbrella word, which also covers the filling and covering kinds.
• Mouth gag. The filling counterpart, where nothing more can fit.
• Bitgag. Half open instead of all the way, with a bar between the molars.
• Deep throat. What the access is usually meant for.
• Bondage. The practice this instrument is part of.
• Check-in. The signal that replaces your voice once the mouth is held open.