Dental Mouth Gag 4.5 inch, Net Weight of Instrument 3.17 oz.: Mouth Gag is a device used to hold the patient's mouth open when working in the oral cavity, or to force the mouth open when it cannot open naturally because of forward dislocation of the jaw joint's intraarticular cartilage pad. Use of a mouth gag instrument to facilitate bite block insertion and prevent finger and probe bites during Examination. It is a surgical device fitting between the upper and lower jaws to prevent the mouth from closing during operative procedures of the mouth or throat.