The muscles that form the oral group of facial muscles move the lips and cheeks. They include the orbicularis oris and buccinator, as well as other facial muscles that can be divided into two groups - lower and upper groups of oral muscles.

Many of these muscles intersect immediately lateral to each corner of the mouth at a structure that is known as the modiolus.

Orbicularis oris

The orbicularis oris is a facial muscle that is located in the thickness of the lips. It surrounds the oral opening. The main function of the orbicularis oris is to close the mouth.

This muscle is composed of two parts:

• Marginal part - consists of longitudinal fibers;
• Labial part (peripheral part) - made of circular fibers.

Buccinator

The buccinator is a facial muscle that forms the anterior part of the cheek. It originates from the alveolar processes of the maxilla and mandible at the region of the first and second molar teeth, and the pterygomandibular raphe.

The buccinator inserts into the angle of the mouth, also radiating into the fibers of the orbicularis oris muscle. This muscle participates in forming the lateral wall of the oral vestibule.

The buccinator pulls the angle of the mouth laterally, presses the cheeks to the teeth, thus decreasing the oral vestibule. Contractions of the buccinator produce facial expressions presenting satisfaction, as well as laughing and crying.

Lower group of oral muscles

The lower group of oral muscles includes the following muscles:

• Depressor anguli oris
• Depressor labii inferioris
• Mentalis

The depressor anguli oris is responsible for pulling the angle of the mouth downward, thus enabling a facial expression associated with frowning.

The depressor labii inferioris is a facial muscle of the chin area that pulls the lower lip downward and forward.

The mentalis is also located in the chin area. It produces small dimples in the chin. Contractions of the muscle can produce facial expression presenting doubt and indecision.

Upper group of oral muscles

The upper group of oral muscles consists of the following muscles:

• Risorius
• Zygomaticus major
• Zygomaticus minor
• Levator labii superioris
• Levator labii superioris alaeque nasi
• Levator anguli oris

The risorius is located immediately lateral to the mouth opening. It pulls the angle of the mouth to the lateral side.

The zygomaticus major extends between the zygomatic bone and the corner of the mouth. It is one of the two zygomatic muscles. They lie next to each other in the cheek area. An activated zygomaticus major is involved in creating a facial expression known as a smile.

The zygomaticus minor lies medially to the zygomaticus major, and it belongs to the lip elevators.

The levator labii superioris is another facial muscle that lifts the upper lip.

The levator labii superioris alaeque nasi is a relatively long muscle of facial expression, and it is found around the oral and nose openings. It widens the nostrils and elevates the upper lip, thus enabling the "snarl" expression in the face.

The levator anguli oris is a facial muscle that lifts the angle of the mouth.