Head and Neck Overview: Skull Landmarks, Mandible, Maxilla, and TMJ

Core Review

The Skull: Cranial and Facial Skeleton

The human skull comprises 22 bones divided into the cranial vault (neurocranium) and the facial skeleton (viscerocranium). The cranial bones — frontal, parietal (paired), temporal (paired), occipital, sphenoid, and ethmoid — enclose and protect the brain. The facial bones — nasal (paired), lacrimal (paired), zygomatic (paired), maxilla (paired), palatine (paired), inferior nasal conchae (paired), vomer, and mandible — form the framework of the face and oral cavity.

For the dental hygienist, the sphenoid bone deserves special attention. Its greater wing forms part of the middle cranial fossa and the lateral wall of the orbit. The pterygoid processes descend from the sphenoid body and consist of medial and lateral plates. These processes provide attachment for the medial and lateral pterygoid muscles and serve as critical landmarks for local anesthesia — the medial pterygoid plate guides needle placement for the anterior (greater) palatine nerve block.

The temporal bone houses the structures of the external, middle, and inner ear. Its squamous portion articulates with the parietal bone; the petrous portion contains the internal carotid artery canal; and the styloid process, mastoid process, and zygomatic process serve as attachments for muscles of mastication, facial expression, and neck movement. The stylomastoid foramen, located between the styloid and mastoid processes, is the exit point for the facial nerve (CN VII) — knowledge of this landmark helps in understanding Bell's palsy and parotid surgery complications.

The Mandible

The mandible is the only movable bone of the skull and the strongest facial bone. Its landmarks are among the most tested on the NBDHE.

Body of the mandible: The horizontal portion extending from the symphysis to the angle. The external surface features the mental protuberance (chin), mental foramen (exit of the inferior alveolar nerve's terminal branch — the mental nerve), and the external oblique line (attachment for the buccinator and depressor anguli oris muscles). The internal surface displays the mylohyoid line (attachment for the mylohyoid muscle, forming the floor of the mouth), the submandibular fossa (housing the submandibular gland), the sublingual fossa (housing the sublingual gland), and the genial tubercles (mental spines — attachments for the genioglossus and geniohyoid muscles).

Ramus of the mandible: The vertical portion. Its anterior border forms the coronoid process (attachment for the temporalis muscle), and its posterior border leads to the condylar process (head of the condyle articulating with the temporal bone at the TMJ). The mandibular notch separates these two processes. The lingula, a small bony projection on the medial surface of the ramus, marks the entrance to the mandibular foramen — the target for the inferior alveolar nerve block.

Mandibular foramen and canal: The inferior alveolar nerve (V3) and inferior alveolar artery enter the mandibular foramen and travel through the mandibular canal, supplying the mandibular teeth, periodontium, and supporting bone. Understanding the trajectory and variations of this canal is essential for safe administration of the inferior alveolar nerve block and for recognizing anatomical variants that may affect anesthesia success.

The Maxilla

The paired maxillae form the upper jaw, the floor of the orbit, the lateral walls and floor of the nasal cavity, and the anterior portion of the hard palate. Key landmarks include:

Maxillary sinus (antrum of Highmore): The largest paranasal sinus, pyramidal in shape, occupies the body of the maxilla. Its floor lies in close proximity to the roots of the maxillary posterior teeth — particularly the first and second molars, and occasionally the second premolar and third molar. This relationship has major clinical implications: periapical infection can spread to the sinus (odontogenic maxillary sinusitis), sinus pathology can refer pain to maxillary teeth, and oroantral communications can occur during extractions.

Infraorbital foramen: Located below the infraorbital margin, this foramen transmits the infraorbital nerve (terminal branch of V2), artery, and vein. It serves as the target for the infraorbital nerve block, which anesthetizes the maxillary anterior teeth, periodontium, and upper lip.

Palatine process: The horizontal projection that forms the anterior three-quarters of the hard palate. The incisive foramen, located in the midline behind the central incisors, transmits the nasopalatine nerve and sphenopalatine artery — the target for the nasopalatine nerve block.

Greater palatine foramen: Located medial to the third molar region, it transmits the greater (anterior) palatine nerve and vessels, supplying the palatal gingiva of the posterior teeth.

Maxillary tuberosity: The rounded posterior extension of the maxilla, located behind the third molar region. It contains the posterior superior alveolar foramina, through which the posterior superior alveolar nerves enter. This is the target for the PSA nerve block.

The Temporomandibular Joint (TMJ)

The TMJ is a ginglymoarthrodial (hinge and gliding) synovial joint between the mandibular condyle and the mandibular fossa (glenoid fossa) of the temporal bone. Key structures:

Articular disc: A fibrocartilaginous biconcave disc divides the joint into superior and inferior compartments. The superior compartment allows gliding (translational) movements, while the inferior compartment permits hinge (rotational) movements. The disc is attached anteriorly to the superior head of the lateral pterygoid muscle, posteriorly to the retrodiscal tissue (bilaminar zone), and medially and laterally to the condylar poles.

Joint capsule and ligaments: The fibrous capsule surrounds the joint, reinforced by the lateral (temporomandibular) ligament, which limits excessive retrusion and lateral movement. The stylomandibular and sphenomandibular ligaments provide additional support but are considered accessory ligaments.

Movements of the TMJ:

• Depression (opening): Lateral pterygoid (inferior head) initiates; suprahyoid muscles assist. The condyle first rotates in the inferior compartment, then translates forward along the articular eminence.
• Elevation (closing): Temporalis, masseter, medial pterygoid.
• Protrusion: Lateral pterygoid (both heads), assisted by medial pterygoid.
• Retrusion: Posterior fibers of temporalis; deep masseter.
• Lateral excursion: Contralateral lateral pterygoid (moving the mandible to the opposite side); ipsilateral temporalis for stabilization.

Clinical correlations: TMJ disorders (TMD) affect approximately 5-12% of the population and are more common in women. Signs include clicking/popping (disc displacement with reduction), locking (disc displacement without reduction), crepitus (degenerative changes), pain on palpation, and limited range of motion. Bruxism, malocclusion, trauma, and stress are contributing factors. The NBDHE may ask about the relationship between the disc and lateral pterygoid, the muscles responsible for specific movements, and distinguishing myofascial pain from internal derangement.

Clinical Application

Understanding skull landmarks directly impacts local anesthesia technique. The height of the mandibular foramen relative to the occlusal plane determines needle placement for the inferior alveolar block. The proximity of the maxillary sinus to posterior tooth roots guides extraction planning and endodontic treatment. The TMJ's dual-compartment structure explains why disc displacement can cause both clicking and limited opening — the disc must reduce for full translation to occur.

Common Traps

• Confusing the mental foramen (mandibular premolar region, exit of mental nerve) with the infraorbital foramen (maxillary, below orbit, exit of infraorbital nerve)
• Thinking the mandible articulates with the maxilla — it articulates only with the temporal bone at the TMJ
• Misidentifying which muscles attach to the coronoid process (temporalis) versus the condylar process (none — the lateral pterygoid attaches to the condylar neck and disc)
• Assuming the entire maxillary sinus floor is uniformly distant from tooth roots — individual variation is significant
• Confusing the greater palatine foramen (posterior, near third molar) with the incisive foramen (anterior midline)