Enamel Organ, Dentin, Pulp, and Periodontium

Flashcards covering the physical properties, microscopic structures, and clinical considerations of enamel, dentin, pulp, and the periodontium based on Lecture 7 notes.

Hydroxyapatite

A crystalline form of calcium phosphate with the formula $Ca_{10}(PO_4)_6(OH)_2$ that makes up approximately $96\%$ of enamel and is also found in bone, dentin, and cementum.

Enamelin

The organic component of enamel that is similar to the protein keratin found in skin.

Enamel Rod formation

A structure formed by four ameloblasts: one forming the rod head, parts of two forming the neck, and a fourth forming the tail.

Rod Sheath

The surface of an enamel rod that contains more organic material than the core.

Rod Core

The center of an enamel rod that is more sensitive to demineralization than the peripheral hydroxyapatite.

Hunter-Schreger Bands

Light and dark bands produced by groups of enamel rods bending at slightly different angles, extending through one-half to two-thirds of the enamel thickness.

Striae of Retzius (Incremental lines)

Lines resulting from the rhythmic recurrent deposition of enamel, appearing as the enamel matrix mineralizes following deposition patterns.

Neonatal line

An accentuated incremental line of Retzius caused by environmental and nutritional changes at the time of birth; it separates prenatal enamel from postnatal enamel.

Enamel Lamellae

Visible leaf-like cracks in the enamel surface that may form during development or due to stress from temperature changes, serving as a possible avenue for caries.

Enamel Tufts

Projections located at the DEJ that extend one-tenth to one-fifth of the way to the outer surface, filled with organic enamelin.

Enamel Spindles

Short extensions of dentinal tubules that arise at the DEJ and extend into the enamel, sometimes containing living odontoblastic processes.

Perikymata (imbrication lines)

Fine ridges on the enamel surface that are the external manifestation of the striae of Retzius, most prominent near the cervical region.

Prismless enamel

A $20$ to $40\,\mu m$ thick zone of structureless microcrystalline enamel near the outer surface where Hunter-Schreger bands are not found.

Microlamellae

Minute spaces located between or around enamel rods and through crystal spaces within the rods.

Dentin

A hard yellowish substance composed of $70\%$ inorganic hydroxyapatite, $20\%$ organic material, and $10\%$ water.

Predentin

The initial nonmineralized collagen fiber matrix laid down by odontoblasts during dentinogenesis.

Odontoblasts

Cells originally from the outer dental papilla that produce dentin; their cell bodies remain in the pulp while their cytoplasmic extensions stay in the dentin.

Globular dentin

Lighter, rounded areas of dentin where both primary and secondary mineralization have occurred with complete fusion.

Interglobular dentin

Dark, arch-like areas in dentin where only primary mineralization occurred and globules failed to fuse completely.

Dentinal tubules

Long tubes extending from the DEJ or DCJ to the outer wall of the pulp, containing dentinal fluid, an odontoblastic process, and possibly an afferent axon.

Primary curvature

The large S-shaped curve of the overall course of a dentinal tubule.

Secondary curvature

Small delicate curves within the primary curvature of dentinal tubules, reflecting daily changes in odontoblast direction.

Peritubular dentin

The highly mineralized dentin that creates the wall of the dentinal tubule.

Intertubular dentin

Dentin found between the tubules that is highly mineralized, though less so than peritubular dentin.

Mantle Dentin

The first predentin to form and mature, characterized by higher levels of mineralization and more peritubular dentin.

Secondary dentin

Dentin formed after the completion of the apical foramen, which continues to form throughout life and is less mineralized than primary dentin.

Tertiary dentin (Reparative dentin)

Dentin formed quickly in localized regions in response to injury, characterized by an irregular tubule pattern.

Sclerotic dentin

Dentin in which odontoblastic processes have died, leaving vacant tubules that become retrofilled and occluded with mineralized substance.

Imbrication lines of von Ebner

Incremental lines or bands in dentin that run at right angles to the tubules, similar to the growth rings in enamel.

Contour lines of Owen

A series of dark bands in stained dentin representing a number of adjoining parallel imbrication lines caused by a metabolic disturbance.

Tomes’ granular layer

A spotty area found in the peripheral dentin beneath the root's cementum, adjacent to the DCJ.

Pulp stones (denticles)

Calcified masses of dentin with tubules and processes that may be attached or free within the pulp chamber.

Odontoblastic layer

The outermost zone of the pulp, closest to the dentin, containing cell bodies capable of forming secondary and tertiary dentin.

Cell-free zone

The zone inward from the odontoblastic layer that contains fewer cells but houses a nerve and capillary plexus.

Periodontium

The supporting soft and hard dental tissues including cementum, alveolar bone, and the periodontal ligament (PDL).

Cementum

A dull, pale yellow hard tissue covering the root that is $65\%$ mineralized; it attaches the teeth to the alveolar bone via the PDL.

Sharpey’s fibers

Portions of collagen fibers from the PDL that are partially inserted at $90^{\circ}$ angles into both the cementum and the alveolar bone.

Cementocytes

Cementoblasts that have become entrapped in the lacunae of the cementum they produced.

Acellular cementum (Primary cementum)

The first layer of cementum deposited at the DCJ, which contains no embedded cementocytes and maintains a constant width.

Cellular cementum (Secondary cementum)

Layers of cementum containing embedded cementocytes, deposited over acellular cementum mainly in the apical third of the root.

Hypercementosis

The excessive production of cellular cementum, usually occurring at the apex due to occlusal trauma or pathology.

Alveolar bone proper

The compact bone lining the tooth socket (alveolus), also called the cribriform plate or lamina dura on radiographs.

Alveolar crest

The cervical rim of the alveolar bone proper, located $1$ to $2\,mm$ apical to the CEJ in a healthy state.

Cortical bone

Plates of compact bone on the facial and lingual surfaces of the alveolar bone.

Trabecular bone

Cancellous (spongy) bone located between the alveolar bone proper and the cortical plates.

Periodontal ligament (PDL)

An organized fibrous connective tissue that maintains the gingiva and transmits occlusal forces from teeth to bone.

Epithelial rest of Malassez

Groups of epithelial cells found in the mature PDL that remain after the disintegration of Hertwig’s root sheath.

Alveolodental ligament

The main principle fiber group of the PDL, consisting of alveolar crest, horizontal, oblique, apical, and interradicular groups.

Oblique group

The most numerous fiber subgroup of the PDL, covering the apical two-thirds of the root and resisting rotational and intrusive forces.

Interdental ligament (transeptal ligament)

Fibers that travel from cementum to cementum of neighboring teeth without bony attachment, resisting rotational forces.