The right and left portions of the mandibular arch are joined at the symphysis in the first year of life, forming a unique horseshoe-shaped skeletal component, whose attachment to the cranium is formed only by muscles and ligaments.

Fig. 11.1 Mandible with periodontium, nerve exit orifices, and course of the inferior alveolar nerve.

The inferior alveolar nerve exits the mandibular body between the root tips of the first and second premolars as the mental nerve, providing sensation to the lower lip. Before leaving the mandibular body, it branches off into other nerve branches for the canines and frontal incisors. The distance between nerve canal and root tips or buccal cortical bone varies, but is on average around 5 mm.

The lingual nerve runs near the inferior wisdom tooth, close to the mandible and sometimes separated from it only by the periosteum.

Fig. 11.2 Section showing the temporomandibular joint and anatomic structures (modified from Richter 1992). 1 Mandibular condyle, 2 cancellous bone in the mandibular condyle, 3 articular fossa (temporal bone), 4 articular cartilage of the mandibular condyle/articular fossa, 5 articular disc, 6 joint capsule with lateral ligament, 7 lateral pterygoid muscle, 8 styloid process.

The joint capsule is relatively loose. Its attachment to the temporal bone surrounds the articular tubercle and extends posteriorly to the petrotympanic fissure. The joint capsule is attached to the articular disk. The mandibular portion of the capsule extends far beyond the condyle down to the condylar neck.

The articular ligaments are not very pronounced. Nonetheless, the following ligaments can be distinguished:

temporomandibular ligament;

sphenomandibular ligament;

stylomandibular ligament;

pterygomandibular ligament.

Between the articular fossa and condyle lies the biconcave fibrocartilage articular disk. The articular disk is attached around its entire periphery to the joint capsule, dividing the temporomandibular joint into a superior and inferior space, and forming the functional articular fossa. The gliding motion of the joint occurs in the superior chamber, between the articular disk and skull base, while rotational movement of the mandibular condyle is possible in the inferior chamber. The physiologic motion of the temporomandibular joint is a rotational-gliding motion, which is directed by the coordination of the muscles of mastication (stomatognathic system). Because each of the two temporomandibular joints is rigidly connected to the other via the mandible, any movement occurring on one side necessarily affects the joint on the other side.

Mandibular fractures occur as simple, double, or multiple factures, often together with midfacial fractures. They are caused by direct and indirect trauma:

Direct trauma is generally the cause of injury to the chin region and the area around the canine teeth and fractures involving the alveolar process and teeth; it is less often the mechanism of injury in the mandibular angle region.

Injuries and fractures of the condylar neck and temporomandibular joint are almost without exception caused by indirect trauma.

Displacement of fragments is caused, on the one hand, by traumatic force and on the other by the pull of muscles. Remember the closing muscles of the jaw are much stronger than the opening muscles. Thus, the orientation of the fracture line can be considered either favorable or unfavorable for displacement.

Diagnosis of mandibular fractures is often possible on the basis of clinical symptoms. A search should be made for specific and unspecific signs of fracture:

Certain fracture signs:

– deformity of the fractured bone with displacement;

– abnormal mobility of the fragments;

– crepitus.

Uncertain fracture signs are often found in mandibular fractures, but they can also have other sources:

– hematomas and swelling;

– tenderness and compression pain around the fracture;

– abnormal function and sensory disturbances.

The upper and lower jaws meet in a special position because of the dental arches. Normally the maxillary and mandibular teeth of a closed jaw fit together perfectly (occlusion), and there are no step-offs in the dental row. As fracture often causes step-offs in the dental row, malocclusion and step-offs in the dental row are important signs of mandibular fracture. However, they are also observed in isolated dental luxation and fractures of the alveolar process.

In fractures involving the extremities, deformity of the fractured bone is frequently visible as abnormal bending or angulation. In mandibular fractures, angulation is often obscured by soft tissue swelling.

Because of the firm attachment between the mucosa of the alveolar process and the bone (attached gingiva), displacement can cause gingival laceration over the fracture site.

Detection of mandibular fractures of the ramus, including intraarticular fracture, is not possible based on abnormal mobility. Segmental mandibular fractures (symphyseal fracture with basal triangle) with unfavorable fracture lines can result in complete loss of mandibular continuity and stability.

Crepitus describes a grating sound heard when broken bone ends rub together. Mandibular fracture surfaces are often smooth so that there is minimal crepitation.

Fig. 11.3 Segmental mandibular fracture with considerable displacement. Swelling of the tongue and floor of the mouth can pose a risk of airway obstruction.

Considerable bleeding in the floor of the mouth, cheeks, soft tissue of the chin, and, less frequently, the tongue and pharyngeal soft tissue results from fracture and traumatic tearing of the soft tissue. There is also concomitant posttraumatic edema. The skin in the affected region is taught and elastic; step-offs are hardly palpable through the swelling. Even palpation of the margin of the mandible is often impossible.

Tenderness to palpation is found with nearly every fracture. However, it is also a sign of inflammation and occasionally tumor. Lacking tenderness to palpation tends to support a cause other than fracture.

Mild pressure applied to the longitudinal axis of the mandible with a tap on the chin elicits pain at the fracture site. Looking for signs of longitudinal compression pain is especially useful for diagnosing fractures of the mandibular ramus, and the condylar process in particular. Compression pain is also present, however, with contusion, distortion, and inflammation of the temporomandibular joint.

Mandibular fractures restrict chewing, speaking, and swallowing functions. Trismus, lockjaw, or lateral deviations on opening the mouth are signs of fracture, but are also observed in other disorders (dislocation, abscess, and tumor).

Mental Nerve (Inferior Alveolar Nerve)

Fractures of the mandible between the mandibular foramen and the mental foramen regularly traverse the alveolar canal. Lesions of the inferior alveolar nerve are caused by direct tear, crushing force, or hematoma. Hypesthesia, anesthesia, or occasionally paresthesia, occur distal to the injury in the nerve distribution area, predominantly affecting the lower lip. Sensation in the teeth and gingiva is impaired or lost.

Sensory disturbances in the nerve distribution area of the mental nerve can be observed, however, after shearing injuries involving soft tissue in the chin area and following extensive hematoma—without the presence of fracture.

Lingual Nerve

Sensory disturbances involving lingual nerve distribution seldom occur as a direct result of trauma. The lingual nerve can be injured by bone fragments in mandibular angle fractures or by extensive hematoma in the floor of the mouth.

Under physiologic conditions the teeth of the upper and lower jaw fit together in a specific position (normal occlusion), whereby there can also be individual interdigitation (individual occlusion). Wear facets are often observable on the corresponding surfaces of opposing teeth.

Any deviation without plausible explanation from this specific and routinely reproducible occlusion must be considered—with an appropriate patient history—a sign of fracture. This is especially true for unilateral malocclusion.

Survey radiographs of the cranium are less useful in evaluating mandibular fractures, especially intraarticular fracture, as there is often superimposition of structures. Conventional radiography should always use the posterior-anterior (p.-a.) view for evaluating the facial skeleton, as only those structures close to the film are sharply imaged (film is closest to the face).

Axial views are generally used for evaluating injury. Coronal reconstructions are possible using small slice thicknesses on axial CT. However, visualization of structures is less exact than on direct coronal views.

For specific clinical questions, such as diagnosis and treatment planning in temporomandibular fractures, coronal views are superior. Evaluation requires a special, hyperextended position and can only be performed after spinal injury has been ruled out.

Magnetic resonance imaging can offer high quality imaging of changes in position or injury of the articular disk as well as changes in the joint capsule. Early detection of inflammatory complications such as osteitis at the fracture gap or osteomyelitis is possible. Orbital soft tissue structures can be shown on high-quality images without adverse radiation effects.

Fig. 11.4 Typical localization of mandibular fractures (from Schwenzer and Ehrenfeld, Vol. 2, 2002). 1 Alveolar process, 2 within the dental row (transverse fracture), 3 outside of the dental row in a fully dentate jaw, 4 outside of the dental row in a partially edentulous jaw, 5 comminuted fracture, 6 in ramus of mandible (oblique fracture), 7 in ramus of mandible (longitudinal fracture), 8 condylar process, 9 coronoid process, 10 condylar head.

Symphysis or Parasymphyis Fracture

Fig. 11.5 Mandibular fracture with dentoalveolar involvement.

a Considerable displacement in a mandibular parasymphysis fracture with step-offs between teeth 41 and 42.

b Step-off between teeth 41 and 42 (orthopantomogram).

Lateral Incisor Region

panorama projection (orthopantomogram [OPG]);

mandibular posterior-anterior, half-axial view (Clementschitsch)—film is closest to the face;

half-lateral/lateral views of the mandible;

computed tomography;

dental films to determine the relationship between root and fracture gap and to detect or exclude dental root fracture.

Nondisplaced Fractures

Management can be conservative using splinting of the mandible and maxilla and intermaxillary immobilization (rigid elastic bands or loop wiring) for 4–6 weeks. An alternative is osteosynthesis using miniplates or, if necessary, compression plates.

Fig. 11.6 Mandibular fracture in the lateral incisor region. a Considerably dislocated mandibular fracture in the right canine region with complete occlusion. Dislocation of the fragments is mimicking a gap between teeth 43 and 42.b Marked displacement in a parasymphyseal fracture on the right (panorama view). c Displaced mandibular parasymphysis fracture on the right (arrow; axial computed tomography).

Displaced Fractures

Displaced fractures should be reduced. Conservative management following reduction employs splinting of upper and lower jaw and intermaxillary immobilization (rigid elastic bands or loop wiring) for 4–6 weeks. Osteosynthesis is usually the preferred method.

Teeth in the Fracture Line