Mandible

The mandible is the only freely moving bone in the skull and makes up the entire lower face. It has joints on both sides of the head with the temporal bone. It houses the lower teeth and this combination of teeth and movement allows mastication. Being unsupported by other bones it has thick cortical plates and dense spongy bone to resist the forces created on it by the strong muscles of mastication. Even so some bending of the bone occurs when opening wide.

Parts – The mandible has a horizontal section that is known as the body. The superior surface of the body which houses the teeth is called the alveolar process just as in the maxilla. Like the maxilla this is dependent on teeth being present and if the teeth are removed this area of the mandible resorbs, weakening the bone considerably over time. On either side of the midline along the inferior border are protuberances known as the mental tubercles. Starting from these tubercles an initially faint line runs obliquely along the mandible to the vertical section becoming more prominent as it proceeds more posteriorly and superiorly. This is known as the external oblique line. It acts as an attachment for several muscles, the most important being the buccinator. There is a corresponding line internally known as the internal oblique line by the radiography department but the anatomists generally refer to it as the mylohyoid line which is the attachment point for the mylohyoid muscle that forms the floor of the mouth. On either side of the midline on the inferior and lingual portion of the bone are two projections known as the genial tubercles which act as muscle attachment points.

Figure 24.

Figure 24.

Figure 25.

Figure 25.

Figure 26.

Figure 26.

The vertical portion of the mandible is known as the ramus. The area where the ramus and body meet is known as the angle of the mandible. The ramus itself splits at its superior extent into two processes. The anterior process known as the coronoid process is the attachment point for the temporalis muscle. The posterior process is known as the condylar process as it ends at the mandibular condyle which is the articular surface (above) of the bone. Attached anterior at the superior end of the process is the lateral pterygoid muscle. Between the two processes is a notch known as the mandibular notch or is some texts as the sigmoid notch.

Openings – There are two important openings in the mandible and they are connected by and internal canal known as the mandibular canal. The proximal end of the canal is the "mandibular foramen which is located on the inner surface of the ramus centered between the body and the mandibular notch superior-inferiorly and aligned with the depth of the notch. It is the point where the inferior alveolar nerve enters the mandible and as such is the area where local anesthesia can be administered to anesthetize all the hard tissues of the body of the mandible plus some of the soft tissue. At this point there is also a bony projection, the lingula, that covers the medial side of the opening and attaches one of the ligaments that stabilizes the temporomandibular joint (TMJ).

At the other end of the canal is the mental foramen. This allows passage of the nerve and blood vessels that supply the soft tissues of the chin, lip and the buccal gingiva of the lower anterior teeth. You can often palpate this on yourself.