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Short answer: A mouth gag is a surgical device placed between the upper and lower jaw to keep the mouth from closing during operations on the mouth or throat. In the United States the FDA lists it under product code KBN as "Gag, Mouth", a Class I ear, nose and throat device regulated under 21 CFR 874.4420 and exempt from 510(k) premarket notification (FDA Product Classification, checked 2026-10-30).
This page is general product information for lab, clinic and supply staff. It is not medical advice and does not describe how to use the device on a patient.
Definition and scope
A review in the Journal of Maxillofacial and Oral Surgery describes mouth gags as surgical devices placed between the upper and the lower jaw to prevent the mouth from closing during operative procedures of the mouth or throat (Hoefert, 2012, checked 2026-10-30).
The FDA regulation that names the device, 21 CFR 874.4420, covers ear, nose, and throat manual surgical instruments, defined as "one of a variety of devices intended for use in surgical procedures to examine or treat the bronchus, esophagus, trachea, larynx, pharynx, nasal and paranasal sinus, or ear." A mouth gag appears by name in that regulation’s list of instruments (eCFR, checked 2026-10-30). Other items on the same list include the metal tongue depressor and the oral screw; see the guide to ENT surgical instruments for the wider group.
How it is used in practice
The published review describes the purpose rather than a technique: the gag holds the jaws apart so the operating field in the mouth or throat stays open. Historically the jaw-opening function also served examination, feeding and dental care in patients whose mouths would not open, for example in tetanus (Hoefert, 2012). The same author notes that the development of general anaesthesia after 1846 increased demand for jaw-opening devices.
Some designs are used with a tongue depressor or tongue plate attached. For the separate tongue-depressor device see what is a tongue depressor. Placement, positioning and removal belong to the surgical team and the manufacturer’s instructions for use, and are not covered here.
Types of mouth gag
Hoefert (2012) reports that a wide variety of models has been invented, "with or without tongue depressors or plates, one- or double-sided". The table below keeps only the distinctions that review states.
| Design family | What the source says | Reported limitation |
|---|---|---|
| Screw-type (Heister) | Lorenz Heister developed a screw-like device to open the mouth in trismus; the review calls it the classic prototype for most later models. His eccentric-pattern gag was introduced in 1714. | Not stated in the review. |
| One-sided, eccentric pivot | Most mouth gags in use are single-sided and employ an eccentric pivot. The Denhart gag is the one-sided model the review modifies; Molt and Boyle-Davis are among the named models in its table of gags. | Slipping, sliding and dislocation in the mouth, especially with one-sided gags; discussed since the nineteenth century. |
| Double-sided | Gags that engage both sides of the mouth. | Size and difficulty in positioning. |
| With tongue plate | Some models carry or accept a tongue depressor or plate; the modified Denhart-Hoefert gag described in the paper allows one to be fixed to it. | Not stated in the review. |
The Denhart-Hoefert gag in that paper is the author’s own modification with pivotal pads, reported by the author as showing less sliding and dislocation than the original Denhart; it was developed with a manufacturer and is a single-author report, not a comparison across brands.
Where it matters for labs, clinics and supply decisions
For anyone documenting or sourcing the item, the regulatory identity is the part that can be checked against official records. These are the FDA fields for product code KBN (FDA Product Classification database, checked 2026-10-30; openFDA classification record, last updated 2026-10-19).
| Field | FDA record |
|---|---|
| Device name | Gag, Mouth |
| Product code | KBN |
| Regulation number | 21 CFR 874.4420 |
| Review panel | Ear, Nose and Throat |
| Device class | Class I (general controls) |
| 510(k) premarket notification | Exempt, subject to the limitations in 21 CFR 874.9 |
| GMP exempt | No |
| Implanted / life-sustaining | No / No |
| Summary malfunction reporting | Eligible |
Practical checklist drawn from those fields, for reading a product listing or specification sheet:
- Does the listing identify the device as a mouth gag and match product code KBN and 21 CFR 874.4420?
- Is the manufacturer an FDA-registered establishment? The FDA classification page notes that 510(k)-exempt manufacturers still register their establishments.
- Does the manufacturer’s instructions for use say whether the instrument is reusable or single-use, and how it is reprocessed? Reprocessing rules differ by device; see medical device reprocessing.
- Does the listing show any exemption limitation claimed? The FDA page advises confirming exemptions and limitations against 21 CFR 862-892.
Common misunderstandings
Class I and 510(k) exempt do not mean unregulated
Class I devices remain subject to general controls. The FDA record for KBN shows the device is not GMP exempt and that exempt manufacturers still register establishments. For how classes and pathways relate, see FDA medical device classification.
A mouth gag is not a retractor or a tongue depressor
The regulation lists the three as separate named instruments. A gag holds the jaws apart; a surgical retractor holds tissue aside; a tongue depressor presses the tongue. Some gags accept a tongue plate as an attachment.
Newer designs are not shown here to be better
The review documents recurring problems of slipping and dislocation across designs, and one author’s modification. It does not rank commercial products.
FAQ
What is a mouth gag?
A surgical device placed between the upper and lower jaw to keep the mouth open during operative procedures of the mouth or throat (Hoefert, 2012).
What are the types of mouth gag?
The literature distinguishes screw-type gags (Heister), one-sided gags with an eccentric pivot (such as Denhart), double-sided gags, and designs with or without a tongue plate (Hoefert, 2012).
Is a mouth gag regulated by the FDA?
Yes. It is a Class I device, product code KBN, regulated under 21 CFR 874.4420 and exempt from 510(k) premarket notification, with establishment registration still applying (FDA, checked 2026-10-30).
What is the difference between one-sided and double-sided mouth gags?
The review reports slipping and dislocation as the notable problem of one-sided gags and size and positioning difficulty as the problem of double-sided gags.
Sources
- FDA, Product Classification, product code KBN, "Gag, Mouth": accessdata.fda.gov, checked 2026-10-30.
- FDA openFDA device classification API, product code KBN, last updated 2026-10-19: api.fda.gov, checked 2026-10-30.
- 21 CFR 874.4420, Ear, nose, and throat manual surgical instruments: ecfr.gov, checked 2026-10-30.
- Hoefert S. The Evolution of Mouth Gags. Presentation of a New Modificated Denhart Mouth Gag. J Maxillofac Oral Surg 2012;12(4):475-479, doi:10.1007/s12663-012-0417-z: PMC3847009, checked 2026-10-30.
