Periodontal Anatomy, Histology, and Physiology
Periodontal Anatomy, Histology, and Physiology
This domain tests whether histologic fact can be turned into a clinical decision: where the attachment truly lies, what a probing depth measures, and which structures return after surgery.
Structural layers
- Gingiva comprises marginal (free) gingiva, attached gingiva and interdental papillae; the free gingival groove and mucogingival junction are the surface landmarks.
- Sulcular epithelium is non-keratinized; junctional epithelium (JE) is only 0.25–0.35 mm long, 15–20 cells coronally and 1–3 cells apically, attaching by hemidesmosomes to the internal basal lamina on the tooth.
- Gargiulo's dimensions: sulcus 0.69 mm, JE 0.97 mm, connective tissue attachment 1.07 mm - the supracrestal attached tissues total about 2.04 mm.
- PDL: ~0.2 mm wide, with alveolar crest, horizontal, oblique, apical and interradicular fiber groups; oxytalan fibers run cervically.
- Bone: bundle (cribriform) plate, cancellous trabeculae and cortical plates; the interdental septum is the key radiographic landmark.
Physiology
Oblique fibers convert axial load into tension and drive remodeling; the PDL provides proprioception; gingival crevicular fluid starts as a transudate and becomes an inflammatory exudate with disease.
Worked example
A buccal site has PD 4 mm and 3 mm recession. CAL = 4 + 3 = 7 mm; the 4 mm is not the attachment loss. If only 2 mm of keratinized tissue remains, a subgingival margin placed 1 mm into the sulcus risks encroaching on the supracrestal attachment.
Traps
Confusing histologic sulcus depth with probing depth; assuming transseptal fibers are permanently lost (they regenerate from the gingiva); forgetting that JE is the most permeable and least resistant seal.