A Jansen mouth gag, also known as a Doyen-Jansen mouth gag, is a surgical instrument used in oral and maxillofacial procedures to hold a patient's mouth open, providing better visibility and access to the teeth and oral cavity for the surgeon. It features curved, serrated blades and an adjustable locking mechanism to maintain a stable opening, and it is made of stainless steel for durability and ease of sterilization. 

Maintaining an open mouth:

The primary function is to keep the patient's mouth open during a procedure, freeing the surgeon's hands.

Improving visibility:

By holding the mouth open, the gag allows for a clear view of the teeth, gums, and other oral structures, which is crucial for complex surgical tasks.

Facilitating surgical access:

It provides necessary access for procedures such as dental extractions, oral surgeries, and other interventions in the oral cavity.