Head& neck anatomy
Dr. Hatem A Hatem
By the end of your review, you may be able to address the following items:
Bony features of head and neck of interest to the dentist:
I- Describe the morphology, relations and ossification of the maxilla and mandible.
II- Identify general arrangement and major relations of other cranial bones.
As a dentist, you will have a detailed knowledge of the structure of the maxilla and mandible. Other bones are important as much as they facilitate understanding of soft tissue anatomy.
Familiarize yourself with the key features of each bone and the articulated skull views. These features will be mentioned repetitively in later sections of head and neck soft tissue anatomy and you can always go back to their definitions while reading.
MOST RELEVANT KEY FEATURES OF THE SKULL
Spheno-occipital synchondrosis: cartilaginous joint of the basiocciput that is responsible for bone growth that modulates the facial appearance. It closes at early adulthood.
Lesser wing: Optic canal.
Greater wing :
Superior orbital fissure: between the greater wing below and lesser wing above.
Foramen rotundum: communicates the middle cranial fossa with the pterygopalatine fossa.
Foramen ovale: communicates the middle cranial fossa with the infratemporal fossa. It transmits the mandibular (V) and lesser superficial petrosal (IX) nerves, the accessory middle meningeal artery and an emissary vein.
Forame spinosum: just behind and lateral to the foramen oval for the middle meningeal artery.
Foramen venosum (of Visalius): inconstant. Medial to foramen ovale for an emissary vein.
Spine of sphenoid: just behind foramen spinosum for the attachment of the sphenomandibular ligament.
Medial pterygoid plate
Lateral pterygoid plate
Pterygoid notch: in between the diverging lower ends of the two pterygoid plates where the pyramidal process of the palatine bone is insinuated.
Pterygoid hamulus: spine at the lower end of the medial pterygoid plate.
Pterygoid fossa: the surface between the two pterygoid plates.
Scaphoid fossa: depression at the root of the medial pterygoid plate
Pterygoid (Vidian) canal: communicates the foramen lacerum with the pterygopalatine fossa.
Palatovaginal groove: forms a canal with the corresponding groove of the palatine bone.
Infratemporal crest: the sharp edge between the inferior and lateral aspects of the greater wing of the sphenoid.
Mastoid notch: medial to the mastoid process. Origin to posterior belly of digastric.
Styloid process; anteromedial to the mastoid process
Stylomastoid foramen: in between the mastoid and styloid processes. Exit for facial nerve.
Squamotympanic fissure: suture between the tympanic and squamous parts of the temporal bones.
Tegmet tympani: a ridge of bone that makes a partition in the medial part of the squamotympanic fissure
Pterotympanic and pterosquamous fissures: the medial part of the squamotympanic fissure.
Mandibular fossa: articulates with the head of the mandible with the articular disc in between.
Articular eminence: in front of the mandibular fossa.
Tympanic canaliculus: between the carotid and jugular foramena. Inlet for the tympanic branch of the glossopharyngeal nerve.
Key Features of the Palatine bone
Lesser palatine canal
Lesser palatine foramen
Posterior nasal spine
MANDIBLE AND MAXILLA
Alveolar process of each jaw bone is the bony plate that carries the teeth.
The root of each canine makes a smooth elevation on the outer surface of the bone. The depression medial to it is the incisive fossa.
Alveolar process is more dense in the mandible "especially at the molars" than in the maxilla.
Local anesthetics may infiltrate the alveolar process to reach the maxillary but not the mandibular molars where nerve block is mandatory.
In general, the mandible is the strongest bone of the facial skeleton.
In edentulous people the alveolar process is partially resorbed which makes it more vulnerable invasion of adjacent soft tissue infection or malignancy.
Key features of the Mandible
Symphesis menti: ossified junction of two halves of the mandible at the midline.
Mental protuberance: an elevation on either side of the symphesis.
Mental foramen: gives exit to the mental nerve. It is situated midway between the upper and lower margins of the body of the mandible in-between the premolars. It is directed backwards in adults.
Coronoid process: the triangular process at anterosuperior end of the ramus.
Mandibular (Coronoid) notch: on the upper border of the ramus.
Condyle of the mandible
Neck of the condyle
Pterygoid fovea: at the anterior surface of the neck.
Angle of the mandible.
External oblique line.
Mandibular foramen: Is found on the medial surface of the ramus midway between the anterior and posterior borders.
Lingula: Spine of bone hanging in front of the mandibular foramen
Myelohyoid line: gives attachment to the myelohyoid muscle.
Myelohyoid groove: extends below the mandibular foramen parallel and posterior to the myelohyoid line.
Submandibular fossa: below the myelohyoid line
Sublingual fossa; above the myelohyoid line.
Torus mandibularis: Excess bone formation that may be present opposite the canine area.
Retromolar triangle: Area of bone behind the last molar which is enclosed by the diverging tendon of the temporalis muscle.
Mental spines (Genial tubercles): paramedian attachment for genioglossus above and geniohyoid below.
The mandibular ramus is tightly plastered with muscles (masseter laterally and medial pterygoid medially) to the extent it may not need fixation if fractured (see figure).
Body segment fractures will be stable or otherwise depending on the effect of the muscles pull on the fracture segments. This has an impact on surgical procedures involving resection or fixation of the body of the mandible.
In general the mandible is a strong bone that can resist invasion due to thick trabeculae and good blood supply from the attached muscles.
The weak points of the mandible are:
1. The edentulous alveolar process.
2. The retromalar trigone.
3. The mandibular canal from the mandibular foramen to the mental foramen.
Thrombosis of the inferior alveolar artery may occur leading to osteonecrosis.
The age changes of the morphology of the mandible are relevant to several clinical situations.
Mandibular angle tends to be more obtuse at the extremes of age than in adulthood.
The mandibular canal acquires a relatively higher position with advance of age.
Examine the inner side of the mandible. Noticethat the myelohyoid line extends downwards and forwards. This line corresponds to the attachment of the myelohyoid muscle which separates the sublingual space above from the submandibular space below. You may notice that deciduous teeth have shorter roots that will be almost always above the line.
Permanent anterior teeth will have their roots above the line while molar roots will be below it. Accordingly molar infections may potentially extend to the submandibular space causing the risky Ludwig’s angina. This complication is rather rare nowadays.
The lingual nerve passes downwards from the infratemporal fossa to enter the mouth just under the edge of the superior constrictor of the pharynx. The nerve is in a vulnerable position just under the mucosa of the oral cavity below the last molar where it is liable to injury.
Anterior nasal spine
Canine eminence: produced by the root of the canine.
Incisive fossa: medial to the eminence.
Canine fossa: lateral to the eminence.
Infra-orbital foramen: above the canine fossa.
Maxillary tuberosity: the lower end of the posterior surface behind the last molar.
Alveolar foramina (2:3)
Maxillary ostium: communicates the maxillary antrum with the nasal cavity.
Lacrimal sulcus: lodeges the nasolacrimal duct.
Conchal crest: for articulation with the inferior concha.
Incisive foramen: for the sphenpalatine nerve.
Torus palatinus: median "or symmetrically paramedian" excessive bone formation that may be found in the hard palate.
Think of the maxilla as a cube (though it is actually more like a pyramid). The posterior surface is the anterior wall of the pterygo-palatine fossa, the upper is the floor of the orbit, the medial surface is the lateral of the nasal cavity, the inferior surface is the roof of the mouth and the anterior surface is in the face. The inside of the cube is the maxillary antrum.
The maxillary nerve in the pterygo-palatine fossa is related to the posterior surface of the maxilla where it gives the posterior superior alveolar nerve which inters the bone through a separate foramen in the posterior wall. The maxillary nerve then passes from the fossa to the orbit through the inferior orbital fissure. The nerves continues forwards on the superior surface of the maxilla in a groove that turns into a complete bony canal i.e. the nerve sinks in the bone. In this infraorbital canal the maxillary nerve gives the anterior superior alveolar nerve that passes laterally in its own canal ‘sinus canal’. Lastly the maxillary nerve exits the anterior surface of the bone through the infraorbital foramen as the infraorbital nerve. The maxillary nerve surely deserves its name. The nerve acquires the name of infraorbital at the inferior orbital fissure in some textbooks. The posterior alveolar nerves may be duplicated.
There may be a middle branch in the posterior part of the infraorbital canal. Alveolar nerves communicate with one another.
The root of the last molar is separated from the maxillary antrum by a narrow rim of bone.
Affection of either entity by the pathology of the other is not unlikely. Notice the independent opening of the maxillary antrum on the medial side of the bone. This may make the antrum more liable to infection due to poor drainage. The size of the hiatus is highly variable.