Craniofacial and Dental Development

Question 1

What is the significance of the neural crest?

Answer 1

Neural crests differentiate into a wide array of tissues during embryonic development:

• Cartilage/bone of the skull
• Cartilage of the pharyngeal arches
• Bones of the facial skeleton
• Odontoblasts

Question 2

When does embyronic development of the head and neck begin, and what does this result in?

Answer 2

Weeks 4-5 in utero.

Results in growth of mesenchymal tissue (connective tissue), the cranial region results in the growth of pharyngeal arches, clefts, and pouches.

Question 3

Describe the structure of the pharyngeal arches.

Answer 3

Bi-lateral pharyngeal arches form in mesenchymal region of the embryo.

Clefts seperate the arches on the ectodermal surface (external)
Pouches seperate the arches on the endodermal surface (internal)
The pouches appear on the lateral wall of the pharynx.

Question 4

How many pharyngeal arches are there?

Answer 4

Six, but the fifth regresses soon after formation.

Question 5

Give for the first pharyngeal arch:

• The skeletal/cartilaginous components
• The cranial nerve
• The muscular component
• The vascular components

Answer 5

The maxillary prominence becomes:
- The future maxilla
- Zygomatic bone
- Part of the temporal bone
- Maxillary cartilage (gives rise to the incus)
- External auditory meatus

The mandibular prominence becomes:
- The future mandible
- Is associated with Meckel’s cartilage (gives rise to malleus, and sphenomandibular ligament

The artery becomes terminal portion of maxillary artery (branch of external).

Associated with the trigeminal nerve CN V.

Gives rise to MoM, ant. belly of digastric, tensor veli palatini, tensor tympani.

Sensory skin of the face, lining of mouth and nose, general sensation to ant. 2/3 of tongue.

Question 6

What are the two parts of the first pharyngeal arch?

Answer 6

Maxillary prominence (dorsal portion)
Mandibular prominence (ventral portion)

Question 7

Give for the second pharyngeal arch:

• The skeletal/cartilaginous components
• The cranial nerve
• The muscular component
• The vascular components

Answer 7

Reichart’s cartilage, which is a precursor to the stapes, styloid process, stylohyoid ligament, parts of the hyoid bone.

Cranial nerve is facial nerve CN VII, innervates muscles of facial expression and the stapedius, stylohyoid, platysma, post. belly of digastric.

Associated muscles are the stapedius, stylohyoid, platysma, post. belly of digastric.

Taste sensation to ant. 2/3 of tongue via chorda tympani.

Associated arteries are stapedial artery and hyoid artery.

Question 8

Give for the third pharyngeal arch:

• The skeletal/cartilaginous components
• The cranial nerve
• The muscular component
• The vascular components

Answer 8

Gives rise to lower body and greater horn of hyoid

Glossopharyngeal nerve CN IX. Sensory function, taste and general sensation to post. 1/3 of tongue.

Stylopharyngeus muscle.

Becomes the common carotid artery.

Question 9

Give for the fourth pharyngeal arch:

• The skeletal/cartilaginous components
• The cranial nerve
• The muscular component
• The vascular components

Answer 9

Gives rise to laryngeal cartilage (namely the thyroid, corniculate, and the cuneiform.

Nerve is the superior laryngeal branch of Vagus nerve CN X. Innervates constrictors of the pharynx, levator palatini, and cricothyroid. Innervation to root of the tongue.

Right side develops into proximal portion of subclavian artery.
Left side develops into aortic arch.

Question 10

Give for the sixth pharyngeal arch:

• The cranial nerve
• The muscular component
• The vascular components

Answer 10

Nerve is the recurrent laryngeal nerve of the Vagus nerve CN X. Innervates intrinsic muscles of the larynx, not the cricothyroid.

Sensory innervation of the:
- Epiglottis
- Pharynx
- Efferent limb of gag reflex
- Parasympathetic innervation to the viscera

Question 11

What are the derivatives of the first pharyngeal pouch?

Answer 11

Eustachian tube and middle ear cavity

Question 12

What are the derivatives of the second pharyngeal pouch?

Answer 12

Lining of the palatine tonsils

Question 13

What are the derivatives of the third pharyngeal pouch?

Answer 13

Dorsal - inferior parathyroid glands
Ventral - thymus gland (lymphatic)

Question 14

What are the derivatives of the fourth pharyngeal pouch?

Answer 14

Dorsal - superior parathyroid glands
Ventral - Ultimobranchial body (C cells)

Question 15

How can a pharyngeal (branchial) cyst arise?

Answer 15

If the pharyngeal clefts aren’t obliterated by the second pharyngeal arch, they arise at any point along the anterior border of the SCM.

Question 16

What are odontoblasts and what is their function?

Answer 16

Tooth forming cells derived from the ectomesenchyme, and migrated from nerual crest.

Their function is dentinogenisis.