BDS Oral Embryology Flashcards

24 sample cards from the Oral Embryology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. State the approximate composition of cementum by weight.

   Cementum is about $45\text{-}50\%$ inorganic and $50\text{-}55\%$ organic plus water by weight—the least mineralized of the dental hard tissues, comparable to bone.

2. What are Sharpey's fibers?

   Sharpey's fibers are the terminal portions of principal periodontal ligament collagen fiber bundles that are embedded and mineralized within cementum and alveolar bone, anchoring the tooth in its socket.

3. From which structure does the periodontal ligament develop, and what is its principal function?

   The PDL develops from the dental follicle (dental sac). It is a specialized fibrous connective tissue that attaches the tooth (via cementum) to the alveolar bone, providing support, sensory (proprioceptive), nutritive, and remodeling functions.

4. Name the five principal fiber groups of the periodontal ligament.

   Alveolar crest, horizontal, oblique (most numerous, resist masticatory/axial forces), apical, and interradicular fiber groups.

5. What are the epithelial cell rests of Malassez and their clinical significance?

   They are remnants of Hertwig's epithelial root sheath persisting in the PDL. Clinically they can proliferate to form periapical (radicular) cysts and odontogenic tumors.

6. From which germ layers/tissues does the oral mucosa develop?

   The epithelium derives from ectoderm (anterior/stomodeal region) and endoderm (posterior region, e.g., part of the tongue/pharynx), while the underlying lamina propria derives from ectomesenchyme/mesoderm.

7. Classify the three functional types of oral mucosa with an example location of each.

   Masticatory mucosa (keratinized: gingiva and hard palate), lining mucosa (non-keratinized: cheeks, floor of mouth, ventral tongue, soft palate, lips inner surface), and specialized mucosa (dorsum of tongue with taste papillae).

8. Describe the developmental origin of the tongue, including the germ-layer boundary marked by the terminal sulcus.

   The anterior two-thirds arises from the first pharyngeal arch (tuberculum impar and lateral lingual swellings; ectodermal, general sensation via CN V, taste via CN VII). The posterior third arises from the third arch (hypobranchial eminence/copula; endodermal, CN IX). The sulcus terminalis and foramen cecum mark this junction and the thyroid diverticulum origin.

9. Name the two sets of major salivary glands developing from ectoderm versus the parotid's origin.

   Parotid gland arises from ectoderm (stomodeal epithelium, ~6th week, first to appear but last to become encapsulated). Submandibular (endoderm, ~6th week) and sublingual (ectoderm/endoderm of the floor, ~7th-8th week) complete the three major glands.

10. Describe the general mechanism of salivary gland morphogenesis.

    An epithelial bud grows from the oral epithelium into the underlying ectomesenchyme, then undergoes repeated branching morphogenesis (guided by FGF, EGF, and clefting of the epithelial end buds) to form a ductal tree ending in secretory acini; the lumen then canalizes.

11. Where do minor salivary glands develop and roughly how many are there?

    Minor salivary glands (several hundred, ~600-1000) develop within the submucosa throughout the oral cavity—labial, buccal, palatal, lingual (including von Ebner's serous glands), and glossopalatine regions—by the same epithelial budding/branching mechanism as major glands.

12. List the six pharyngeal (branchial) arches and note that one is rudimentary.

    Arches 1, 2, 3, 4, and 6 (the 5th arch is absent/rudimentary in humans). Each arch has a cartilage, muscle, artery, and cranial nerve component.

13. What derivatives and cranial nerve arise from the first pharyngeal arch?

    First (mandibular) arch: Meckel's cartilage (malleus, incus, template for mandible), muscles of mastication plus mylohyoid, anterior belly of digastric, tensor tympani and tensor veli palatini; nerve is the mandibular division of the trigeminal (CN V3). It forms the maxillary and mandibular prominences.

14. Explain the embryological basis of cleft lip versus cleft palate, and give a classification distinction based on the incisive foramen.

    Cleft lip results from failure of fusion of the maxillary process with the medial nasal process (anterior to incisive foramen). Cleft palate results from failure of the palatal shelves to fuse with each other/nasal septum. Clefts anterior to the incisive foramen (lip, alveolus, primary palate) are 'anterior/primary palate clefts'; those posterior (hard and soft secondary palate) are 'posterior/secondary palate clefts'; both may coexist.

15. Identify the master genes/signaling pathways governing early tooth patterning and morphogenesis.

    Key regulators include the homeobox code (Msx1/2, Dlx1/2, Barx1, Pitx2), and signaling families Shh (Sonic hedgehog), BMP, FGF, and Wnt. Reciprocal epithelial-mesenchymal signaling through these determines tooth initiation, position, type, and cusp patterning via the enamel knot.

16. Name representative genetic anomalies of dental hard tissues and one causative gene each.

    Amelogenesis imperfecta (defective enamel; e.g., AMELX, ENAM, MMP20 mutations); Dentinogenesis imperfecta (defective dentin; DSPP mutation, associated with type I collagen defects/osteogenesis imperfecta). Hypodontia/oligodontia is associated with MSX1, PAX9, and AXIN2 mutations.

17. Define and give examples of anomalies of tooth number and size.

    Anodontia (complete absence), hypodontia/oligodontia (few/many missing teeth) from dental lamina failure; hyperdontia (supernumerary teeth, e.g., mesiodens) from excess lamina activity; microdontia and macrodontia are abnormally small or large teeth.

18. Define fusion, gemination, and concrescence as developmental anomalies of tooth shape.

    Fusion is the union of two adjacent tooth germs by dentin, reducing tooth count. Gemination is incomplete division of a single tooth germ into two, giving a bifid crown with a normal count. Concrescence is the union of two adjacent fully formed teeth by cementum only, occurring after root formation.

19. What are dens invaginatus (dens in dente) and dens evaginatus?

    Dens invaginatus ('tooth within a tooth') is an infolding of the enamel organ into the dental papilla before mineralization, commonly in maxillary lateral incisors. Dens evaginatus is an outgrowth (accessory cusp/tubercle) of enamel and dentin, often on premolar occlusal surfaces (talon cusp on anteriors).

20. What is an odontoma and how is it classified?

    An odontoma is a hamartoma (benign malformation) of odontogenic tissues containing enamel, dentin, cementum, and pulp. Compound odontoma contains multiple small tooth-like structures (denticles); complex odontoma is a disorganized mass of dental tissues.

21. Which prenatal diagnostic techniques are used to detect craniofacial and cleft anomalies?

    Prenatal ultrasonography (2D/3D, can detect cleft lip from ~13-16 weeks), fetal MRI for palatal detail, and amniocentesis/chorionic villus sampling with karyotyping or molecular genetic testing for associated syndromic conditions.

22. Which histological/laboratory techniques are used to study tooth and craniofacial development?

    Ground sections and decalcified (H&E) sections for hard tissue histology, immunohistochemistry and in situ hybridization to localize gene/protein expression, transgenic/knockout mouse models, tissue recombination/organ culture experiments, scanning/transmission electron microscopy, and micro-CT for 3D mineralized-tissue imaging.

23. What are pearls of Serres and their significance?

    After the dental lamina disintegrates, remnants of its epithelium may persist in the gingiva as small clusters called glands (pearls) of Serres. They can give rise to eruption cysts or gingival (odontogenic) cysts of the newborn.

24. Explain the concept of the neonatal line and its diagnostic use.

    The neonatal line is an accentuated incremental line in enamel and dentin of teeth mineralizing at birth (all deciduous teeth and first permanent molars), reflecting the physiologic stress of birth. It is used in forensic odontology to establish whether an infant was born alive and to estimate age.

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