Oral Basic Sciences: Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology
Oral Basic Sciences covers tooth and periodontal development, oral histology, oral physiology and oral microbiology - the substrate for endodontics, periodontics and oral pathology questions.
Development and histology
- Enamel is ectodermal (ameloblasts from inner enamel epithelium); dentine, pulp, cementum and alveolar bone are ectomesenchymal. Enamel therefore cannot regenerate.
- Amelogenesis passes through secretory, transition and maturation stages; reduced enamel epithelium later forms the eruption pathway and Nasmyth's membrane.
- Hertwig's epithelial root sheath determines root form; its remnants persist as epithelial rests of Malassez, the origin of radicular cysts.
- Dentinal tubules converge pulpally and are S-shaped in coronal dentine; peritubular dentine is more mineralised than intertubular.
- The principal fibres of the periodontal ligament are Sharpey's fibres; the oblique group is most numerous and resists axial load.
Oral microbiology and physiology
Supragingival biofilm is streptococcus-dominant (S. mutans, S. sanguinis); mature subgingival plaque shifts to Gram-negative anaerobes - Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola (red complex) and Aggregatibacter actinomycetemcomitans in aggressive forms. Resting saliva is hypotonic; stimulated saliva is bicarbonate-rich and buffers acid.
Worked example
A child has thin, yellow-brown, chipped enamel on all erupted teeth; radiographs show normal dentine thickness and normal pulp chambers. Because the defect is confined to the enamel organ with normal dentine, this is amelogenesis imperfecta. Dentinogenesis imperfecta would show bulbous crowns, obliterated pulp chambers and opalescent dentine. Chronological hypoplasia would affect only teeth forming at the time of the insult.
Traps
Equating every enamel defect with fluorosis; calling a radiolucency a cyst before histology; assuming plaque quantity rather than composition drives periodontitis; confusing primary, secondary and reparative dentine.