The Heister mouth gag is a surgical instrument used to keep a patient's mouth open during oral and maxillofacial procedures, providing clear access to the oral cavity and improving visibility for the surgeon. 
During anesthesia the muscles in the back of the mouth, throat and jaw relax, sometimes causing the airway to the lungs to become obstructed.
The gag features jaws with serrations that interlock with the teeth, ensuring a secure and stable grip. The straight arms of the device allow for broad opening angles, maximizing exposure.