Which muscle is primarily responsible for mouth closure?

The muscle primarily responsible for mouth closure is the orbicularis oris. This muscle is a circular band of muscle fibers surrounding the mouth and plays a critical role in actions such as puckering the lips, closing the mouth, and facilitating movements involved in speaking, eating, and facial expressions. Its unique structure allows it to contract and constrict the mouth effectively, making it essential for maintaining the integrity of the oral cavity during various activities.

In contrast, the zygomaticus major is primarily involved in smiling and elevating the corners of the mouth rather than closing it. The frontalis muscle is located on the forehead and is involved in raising the eyebrows and wrinkling the forehead, not in actions surrounding the mouth. The orbicularis oculi, meanwhile, encircles the eye and is responsible for closing the eyelids, therefore, does not play a role in mouth closure. Hence, the orbicularis oris is the key muscle for this specific function.