The mandible forms the lower third of the facial skeleton and is respon­sible for the lower transverse facial width. It has a number of power ful muscles inserted along its length. These include the muscles of mastica­tion (temporalis, masseter, medial, and later al pterygoid), and the supra­hyoid muscles (digastric, geniohyoid, and mylohyoid). These muscles can generate considerable biting forces and are an important cause of man­dibular fracture displacement. The mandible also receives the inser tion of genioglossus (which forms the bulk of the tongue). Loss of support for this muscle can place the airway at risk. Morphologically, the mandible can be considered as a U- shaped long bone articulating at each end with the skull at the TMJs. Anatomically it is dividedinto:

The ver tical ramus suppor ts the condyle (which articulates with the gle­noid fossa) and the coronoid process (which receives the insertion of the temporalis muscle). The condylar head is supported on a relatively slen­der neck— a frequent site of fracture. On the medial side of the r amus, the inferior alveolar (inferior dental— ID) ner ve and vessels enter the bone via the mandibular (lingula) foramen, passing forward through the ‘ID’ canal. These provide sensor y innervation and nutrition to the lower teeth. The mental ner ve, a terminal branch, exits the mandible through the mental foramen in the premolar region. This provides sensation to the lower lip. Numbness of the lower lip may therefore signify fracture or pathology anywhere along the course of this nerve. High- energy blows to the side of the lower jaw can result in signicant displacement of frac­tures involving the ID canal. This may result in stretching (or even avul­sion) to the ner ve itself, adversely aecting its likelihood of recovery. Make sure you record any numbness. This is a common source of litigation following injuries as well as dental treatment/ surger y (notably removal of wisdom teeth).