Periodontal Anatomy & the Healthy Periodontium MCQ

Periodontics begins with knowing what healthy looks like. The periodontium is four tissues working together (the gingiva, the periodontal ligament, the cementum, and the alveolar bone), joined at the junctional epithelium that seals the gingiva to the tooth. Every periodontal measurement, every diagnosis, and every treatment plan is read as a change from this baseline. The single most clinically loaded concept is the supracrestal attachment (formerly biologic width): the junctional epithelium plus the connective tissue attachment above the alveolar crest, about 2 mm, that must be respected by every restoration. Violate it and the periodontium fights back with chronic inflammation, recession, or bone loss.

The Gingiva

• The gingiva has a free portion (the unattached marginal cuff around the tooth, forming the wall of the sulcus) and an attached portion (firmly bound to underlying bone and cementum), separated by the free gingival groove.
• The attached gingiva ends at the mucogingival junction, beyond which the alveolar mucosa is movable and non-keratinized.
• Healthy gingiva is coral pink, stippled (orange-peel surface from connective-tissue rete pegs), with a knife-edge marginal contour and a scalloped course around the teeth.
• A network of gingival fibers (including dentogingival, circular, transseptal, and alveologingival groups) supports the marginal gingiva and helps it return to position around the tooth.

The Periodontal Ligament

• The periodontal ligament (PDL) suspends the tooth in its socket, distributes occlusal load, and supplies sensation; its rich proprioception is why a tooth still 'feels' bite even after root canal therapy removes the pulp.
• PDL collagen fibers embed in cementum on one side and alveolar bone on the other as Sharpey's fibers, anchoring the tooth to the bone.
• The principal fiber groups are alveolar crest, horizontal, oblique (the largest group, resisting axial load), apical, and interradicular (between roots of multirooted teeth).
• The PDL is approximately 0.15 to 0.38 mm wide, and it appears as a thin radiolucent line between the tooth and the lamina dura on radiographs.

Cementum and the Cementoenamel Junction

• Cementum is the mineralized tissue covering the root surface; it anchors PDL fibers (Sharpey's fibers) to the tooth and is essential for periodontal attachment.
• Acellular (primary) cementum covers most of the cervical two-thirds of the root and contains no cells; cellular (secondary) cementum is found mainly at the apex and in furcations and can repair.
• Cementum is laid down throughout life by cementoblasts and lacks its own blood supply, making it more resistant to resorption than bone.
• At the cementoenamel junction, three relationships occur (in roughly 60 to 30 to 10 percent): cementum overlapping enamel, edge-to-edge meeting, and a small gap with exposed dentin at the CEJ.

Alveolar Bone

• The alveolar process is the part of the maxilla and mandible that contains and supports the tooth sockets; alveolar bone proper lines the socket and is where Sharpey's fibers from the PDL insert.
• Bundle bone (the layer of alveolar bone proper containing inserted Sharpey's fibers) is also called the cribriform plate; it appears as the radiopaque lamina dura on radiographs.
• Cortical plates form the buccal and lingual surfaces of the alveolar process; cancellous bone with marrow lies between them.
• Alveolar bone is tooth-dependent: it forms with the tooth, is maintained by the tooth's function, and resorbs after extraction (ridge atrophy).

Junctional Epithelium and the Supracrestal Attachment

• The junctional epithelium (JE) is a thin band of stratified squamous epithelium that seals the gingiva to the tooth at the base of the sulcus by hemidesmosomes; it has a remarkably high turnover rate and is the gatekeeper against bacterial entry into the deeper periodontium.
• The supracrestal attachment (formerly called biologic width) is the junctional epithelium plus the connective tissue attachment above the alveolar crest, totaling roughly 2 mm.
• A restorative margin that violates the supracrestal attachment (placed too far subgingivally, encroaching on this zone) produces chronic gingival inflammation, recession, or bone loss until equilibrium is restored.
• Crown lengthening (surgical removal of soft tissue and bone, or orthodontic extrusion) reestablishes the supracrestal attachment and creates restorative space, allowing margins to be placed where they belong.