A mouth corset is a type of neck corset that covers both the neck and the mouth.
Incorporating a gag into a neck corset presents a few safety issues: should the wearer begin to choke, it is not easy to remove the gag quickly. For this reason, most mouth corsets use a simple muzzle gag that merely covers the mouth and does not force anything into the mouth, thus minimising the risk.
Despite not forcing anything into the mouth, mouth corsets are usually very effective in gagging the victim due to the fact that the chin piece prevents the wearer from opening their mouth and dislodging the gag and the lacing at the back of the corset holds the gag tighly against the mouth making a very effective seal. Also, the cheeks are compressed.