Anatomy (head and neck, histology, embryology)
Anatomy: what is tested
This domain integrates regional head-and-neck anatomy, oral histology, and embryology. Questions usually link a structure to its nerve, pharyngeal-arch origin, or microscopic layer rather than asking isolated names.
Pharyngeal arch derivatives
- Arch 1: mandible, maxilla, malleus, incus; muscles of mastication, mylohyoid, anterior digastric, tensor tympani, tensor veli palatini; nerve V3.
- Arch 2: stapes, styloid process, lesser horn of hyoid, stylohyoid ligament; facial-expression muscles, posterior digastric, stylohyoid, stapedius; nerve VII.
- Arch 3: greater horn of hyoid and stylopharyngeus; nerve IX.
- Arch 4/6: laryngeal cartilages and pharyngeal constrictors; vagus, with superior laryngeal for arch 4 and recurrent laryngeal for arch 6.
- Tongue: anterior two-thirds from arch 1 (V3 general sensation, chorda tympani taste); posterior third from arch 3 (IX for both).
Tooth development and histology
- Enamel organ is ectodermal; dental papilla and follicle are ectomesenchymal (neural crest).
- Hertwig epithelial root sheath sets root number and shape; rests of Malassez persist in the periodontal ligament.
- Enamel rods run roughly perpendicular to dentin; enamel is aprismatic at the dentinoenamel junction and cervical region.
- Dentinal tubules converge toward the pulp; peritubular dentin is more mineralized than intertubular dentin.
- Principal periodontal fibers: alveolar crest, horizontal, oblique (most numerous), apical, interradicular.
Worked example
A patient has complete right facial palsy after parotid surgery but normal taste and lacrimation. Reasoning: the lesion is distal to the stylomastoid foramen. Chorda tympani and greater petrosal branches leave the facial nerve proximal to that point, so anterior-tongue taste and lacrimal flow are spared. The injury is therefore in the extratemporal trunk.
Traps
- Assigning arch-1 structures to VII instead of V3.
- Claiming enamel regenerates after acid demineralization.
- Forgetting that posterior tongue is arch 3/IX.
- Confusing dental papilla (dentin and pulp) with dental follicle (cementum, periodontal ligament, bone).