Oral Biology
Oral Biology examines the structure, composition and function of teeth, periodontium, oral mucosa, saliva and oral biofilm. The exam tests how microscopic structure explains clinical behavior: why enamel cracks propagate, why dentin is permeable, and how plaque ecology shifts toward disease.
Core concepts
- Enamel is about 96% mineral by weight, organized into rods and interrod enamel; rod direction determines the pattern of caries and fracture.
- Dentin is about 70% mineral, 20% organic (mostly type I collagen) and 10% water. Tubules run from pulp to the dentinoenamel junction; tubule density and diameter are greatest near the pulp, making deep dentin more permeable.
- Pulp is a low-compliance space; inflammation raises tissue pressure and can compromise blood flow.
- Periodontal ligament principal fibers resist forces; oxytalan fibers may support vessels.
- Cementum is avascular; acellular extrinsic fiber cementum attaches principal fibers, while cellular cementum forms after injury and with age.
- Saliva contains bicarbonate buffer, amylase, mucins, lactoferrin, secretory IgA, statherin and proline-rich proteins. Flow drops at night.
- Biofilm: early colonizers are streptococci; later anaerobes and fusobacteria increase in inflammation.
Worked example
A patient has a white spot on a smooth surface. Reasoning: this is subsurface enamel demineralization with an intact surface layer. It can remineralize with fluoride and plaque control; cavitation means irreversible loss and restoration.
Traps
Enamel does not contain collagen and cannot regenerate. Do not call all cementum acellular; cellular cementum is common apically. Do not treat saliva as sterile or constant; flow and composition vary.