Periodontal Anatomy, Histology, and Biology
What this domain tests
Periodontal anatomy, histology, and biology underpin every clinical measurement. The exam expects you to connect microscopic structure with probing, attachment loss, and mucogingival surgery.
Structural rules
- Gingiva has marginal, attached, and interdental components. Attached gingiva extends from the free gingival groove to the mucogingival junction and is keratinized; alveolar mucosa is not.
- The dentogingival unit is the junctional epithelium plus gingival fibers. Junctional epithelium is nonkeratinized, 15–30 cells coronally tapering apically, and attaches by hemidesmosomes to an internal basal lamina and to enamel.
- Gingival fibers: dentogingival, dentoperiosteal, circular, transseptal.
- PDL fibers: alveolar crest, horizontal, oblique (most numerous; principal support), apical, interradicular.
- Cementum: acellular extrinsic fiber cementum provides attachment; cellular intrinsic fiber cementum appears in repair and apical areas.
- Alveolar bone proper is the cribriform plate; bundle bone is the tooth-related layer.
Worked example
Mid-buccal probing depth is 3 mm. The gingival margin sits 2 mm coronal to the CEJ. CAL = PD + distance from CEJ to margin = 3 + 2 = 5 mm. If the margin is 2 mm apical to the CEJ (recession), CAL is still 3 + 2 = 5 mm, because recession is recorded as a positive value. Only when the margin is exactly at the CEJ does CAL equal PD.
Traps
- Equating pocket depth with attachment loss.
- Describing sulcular epithelium as keratinized; it is nonkeratinized.
- Forgetting that the biologic width concept is now called supracrestal attached tissues.
- Assuming attached gingiva is uniform in width; it is narrowest on the lingual of mandibular incisors and absent in some edentulous sites.