Lecture 6 (Mandible and Muscles of Mastication) PDF

MANDIBLE AND MUSCLES OF MASTICATION  The Mandible The mandible is the largest and strongest bone of the human skull. It is commonly known as the lower jaw and is located inferior to the maxilla. It is composed of a horseshoe- shaped body which lodges the...

MANDIBLE AND MUSCLES OF MASTICATION  The Mandible The mandible is the largest and strongest bone of the human skull. It is commonly known as the lower jaw and is located inferior to the maxilla. It is composed of a horseshoe- shaped body which lodges the teeth, and a pair of rami which projects upwards to form a temporomandibular joint Body The body of the mandible is curved, and shaped much like a horseshoe. It has two borders: Alveolar border (superior) – contains 16 sockets to hold the lower teeth. Base (inferior) – site of attachment for the digastric muscle medially  The body is marked in the midline by the mandibular symphysis. This is a small ridge of bone that represents the fusion of the two halves during development. The symphysis encloses a triangular eminence – the mental protuberance, which forms the shape of the chin. Lateral to the mental protuberance is the mental foramen (below the second premolar tooth on either side). Rami There are two mandibular rami, which project perpendicularly upwards from the angle of the mandible. Each ramus contains the following bony landmarks: Condylar process formed of : Head – situated posteriorly, and articulates with the temporal bone to form the temporomandibular joint.  Neck – supports the head of the ramus, and site of attachment of the lateral pterygoid muscle. Coronoid process – site of attachment of the temporalis muscle Foramina A foramen refers to any opening through which neurovascular structures can travel. The mandible is marked by two foramina. The mandibular foramen is located on the internal surface of the ramus of the mandible. It serves as a conduit for the inferior alveolar nerve and inferior alveolar artery. They travel through the mandibular foramen, into the mandibular canal, and exit at the mental foramen. The mental foramen is positioned on the external surface of the mandibular body, below the second premolar tooth. It allows the inferior alveolar nerve and artery to exit the mandibular canal. When the inferior alveolar nerve passes through the mental foramen, it becomes the mental nerve (innervates the skin of the lower lip and the front of the chin).  The Muscles of Mastication There are four muscles: Masseter. Temporalis. Medial pterygoid. Lateral pterygoid.  Temporalis. Masseter.  Lateral pterygoid Medial pterygoid The masticatory muscles attach to the mandible, and thus produce movements of the lower jaw at the temporomandibular joint (TMJ) to enable functions such as chewing and grinding. These movements include: Protrusion (protraction), which moves the mandible forwards. Retraction, which pulls the mandible backwards. Elevation, which elevates the mandible and closes the mouth. Depression, which depresses the mandible and opens the mouth. Rotation, which produces side-to-side movements of the mandible.