Oral and Maxillofacial Anatomy and Histology
What this domain tests
Anatomy and histology questions in the Cambodian exit exam are rarely pure recall: they ask you to connect a structure to a clinical risk - which nerve runs where, which tissue layer is being cut, which developmental stage explains an anomaly.
Core rules
- Tooth development passes through bud, cap and bell stages. The enamel organ has four layers: outer enamel epithelium, stellate reticulum, stratum intermedium and inner enamel epithelium. Only the inner enamel epithelium differentiates into ameloblasts.
- Ameloblasts secrete enamel matrix (amelogenin, ameloblastin, enamelin) and then retreat; enamel is acellular and cannot regenerate. Odontoblasts persist and secrete dentine throughout life.
- Hertwig's epithelial root sheath maps root number and shape and induces root dentine; its remnants become the epithelial rests of Malassez.
- Principal periodontal fibres: alveologingival, dentogingival, dentoperiosteal, circular, transseptal, horizontal, oblique (most numerous), apical, interradicular. The oblique group resists axial loading.
- Maxillary (V2) teeth are supplied by posterior, middle and anterior superior alveolar nerves; mandibular (V3) teeth by the inferior alveolar nerve, which exits at the mental foramen and continues as the incisive nerve.
- The lingual nerve lies close to the lingual plate below the third molar; the chorda tympani joins it, carrying taste from the anterior two-thirds of the tongue.
Worked example
After a lower third molar extraction a patient has tongue numbness and loss of taste on that side. Reasoning: one lingual nerve injury explains both signs, because chorda tympani fibres travel with it. Inferior alveolar nerve injury would numb the lip and chin instead, with no taste change.
Traps
Calling the stellate reticulum the enamel-forming layer; confusing chorda tympani (taste and parasympathetic) with lingual general sensation; forgetting that the mental nerve supplies the lower lip and chin, not the tongue.