Dentine Dr Firas Alsoleihat, BDS, PhD Department of Conservative Dentistry

Lecture Outline Physical properties. Chemical composition. Dentine tubules. Intratubular dentine. Dentinal tubules contents. Regional variations in dentine: mantle dentine, interglobular dentine, granular layer, hyaline layer, circumpulpal dentine, predentine. Structural lines in dentine. Age related and post-eruptive changes: Secondary, tertiary and sclerotic dentine and dead tracts Clinical considerations.

Dentine Forms the bulk of the tooth. Large number of parallel tubules in a mineralised collagen matrix. The tubules contain the processes of odontoblasts. A sensitive tissue. Formed throughout life.

Physical Properties Fresh dentine is pale yellow. Harder than bone and cementum. Softer than enamel. Its tubular nature renders it strong (higher compressive, tensile and flexural strength than enamel). Permeable, depending on the patency and size of the tubules (decreases with ageing).

Chemical Composition Dentine is composed of 70% inorganic component, 20% organic component and 10% water by weight. Inorganic composition: Calcium hydroxyapatite Ca10(PO4)6(OH)2. The crystals are calcium poor and carbonate rich. Much smaller than enamel hydroxyapatite. The crystals are found on and between collagen fibrils. Organic composition: Collagen (mainly type I) forms 90%, Dentine phospho-proteins, proteoglycans, gla-proteins, acidic proteins, Growth factors, lipids.

Chemical Composition 35nm 10nm ?

Chemical Composition The Organic Matrix: Over 90% of the organic matrix is made of collagen fibrils, mainly collagen type I. Non collagenous proteins: Phosphophoryn (PP-H): The main phosphoprotein in dentine. The most acidic protein known. Due to its high calcium ion binding properties, it has been implicated in mineralisation.

Chemical Composition proteoglycans The main proteoglycans in dentin are biglycan and decorin. Proteoglycans have an important role in collagen assembly, cell adhesion, migration, differentiation and proliferation. They may also have a role in mineralisation. The main glycosaminoglycans are chondroitin-4- sulphate and chondroitin-6-sulphate.

Chemical Composition Gla proteins -Carboxyglutamate-containing proteins Small proteins present in low amounts in dentine. They bind strongly but reversibly to hydroxyapatite crystals and may have a role in mineralisation.

Chemical Composition acidic proteins Other acidic proteins such as osteonectin, osteopontin are also present in dentine. Their function is not known.

Growth factors: IGF-2 BMP-2 TGF-ß They are absorbed from circulating tissue fluid

Chemical Composition The Organic Matrix: Lipids comprise 2% of the organic content in dentine. Phospholipids may be involved in the formation and growth of apatite crystals.

Dentine Tubules Dentinal tubules extend from the pulp surface to the amelo-dentinal and the cemento-dentinal junctions. Tubules follow a curved sigmoid course.( Primary curvatures).

Dentine Tubules The tubules are circular in cross section. Dentine between tubules is called intertubular dentine. Tubule Intertunular dentin Peritubular dentin

Dentine Tubules The tubules are 2.5μm in diameter at the pulpal end and 1μm or less at the Enamel end. As the odontoblasts retreat inwards, they occupy a smaller area, thus the tubules become closer to each others. 22% of the cross sectional area near the pulp is occupied by dentinal tubules. 2.5% at the enamel-dentine junction.

Dentine Tubules Secondary curvatures, if they coincide in adjacent tubules they give rise to contour lines of Owen.

Dentine Tubules Dentinal tubules branch near the enamel-dentine junction. In the root, the terminal branches loop. More obvious in predentine.

Dentine Tubules The walls of newly formed dentinal tubules at the pulp surface are made of mineralised type I collagen. Maturation of the tubules is associated with the deposition of another type of dentine on the walls. Reduction in the size of the lumen, sometimes complete obliteration. This is called peritubular or intratubular dentine.

Peritubular (Intratubular) Dentine Intratubular dentine lacks a collagen matrix. Lost in deminerlisation Increased radiographic and electron density (~ 10% more mineralised than intertubular dentine).

Ground, partial demenerlisation Demenerlised

Peritubular (Intratubular) Dentine The main protein in intratubular dentine is different from phosphophoryn. The inorganic component is mainly carbonated apatite with a different crystalline form than intertubular dentin. Some hypocalcified areas.

Contents of the Dentinal Tubules Odontoblastic processes. Afferent nerve terminals. Antigen presenting cells processes. Extracellular dentinal fluid.

Variable structure at various tissue levels. Odontoblastic processes Variable structure at various tissue levels. More organelles in the predentine area. Microtubules & intermediate filaments along the process. In the inner layers of dentine, the processes occupy almost the full width, no periodontblast space.

Contents of the Dentinal Tubules Odontoblastic processes Terminal dentinal tubules can contain on of the following: Odontoblastic process Sometimes remnants of the processes (tubulin and microfilaments) can be seen in the peripheral parts of the tubules after the process itself has degenerated. Only peritubular dentin The reason?

3 hypotheses for the withdrawal of odontoblasts: The process remains at the peripheral part. Predetermined length of process and then retreat. Degeneration of the peripheral end.

Contents of the Dentinal Tubules Odontoblastic processes

Contents of the Dentinal Tubules Afferent Nerve Terminals Mainly present in the inner layers of the dentine. Intimate relation with the odontoblastic process. The axons contain mitochondria and vesicles.

Contents of the Dentinal Tubules Sensory Terminals Their extent in the tubules is not certain. Found mostly in coronal dentine beneath the cusps (80% of tubules), sparse in cervical and root dentine. Narrower than odontoblastic process. Contain Microtubules, microfilaments & mitochondria.

Contents of the Dentinal Tubules Antigen Presenting Cells Processes They appear as small processes in the tubules near the pulp. Immunocpmpetent antigen presenting cells. Within and beneath odontoblasts. Processes limited to the predentine. Extend deeper in the tubules under carious dentine

Contents of the Dentinal Tubules Extracellular Dentinal Fluid Unknown composition. Higher potassium and lower sodium ions level in comparison to other fluids. This balance affects the membrane properties of cells. Positive force from pulpal tissue pressure ( defense criteria).

Regional Variations in Dentine Structure and Composition Mantle Dentine. Hyaline layer. Granular layer of Tomes. Predentine. Intermediate dentine. Circumpulpal dentine. Interglobular dentine

Mantle Dentine The most peripheral (first to be formed) layer of dentine. 20-150μm in width Differs from circumpulpal dentine: 5% less mineralised. Collagen fibrils perpendicular on DEJ. Branching of tubules. Different mineralisation process (dentinogenesis).

Mantle Dentine

Mantle Dentine

Interglobular Dentine In dentin minerals deposited as globules (calcospheres) then fuse to form a uniform calcified tissue. failure of fusion beneath mantle dentine produce Undercalcified interglobular areas, appear dark in ground sections viewd under transmitted light. Tubules pass through these areas without deviation neither peritubular dentin.

Interglobular Dentine

Granular Layer of Tome dark granular zone at the peripheral root dentine. Caused by: tubules branch and loop back on themselves creating air spaces in ground sections OR Incomplete fusion of calcospherites?? Tree top appearance of tubules when filled with stain in ground sections. Hypomineralized compared to circumpulpal dentin.

Granular Layer of Tome

Hyaline Layer Outside the granular layer. Obscure origin dentin or cementum. up to 20μm in width. Atubular and structureless. Helps in bonding dentine to cementum.

Hyaline Layer

Circumpulpal Dentine Forms the bulk of the dentine. Uniform in structure except at peripheries; interglobular and predentin.

Predentine Initially laid dentine matrix prior to mineralization. Mineralization front may show a globular or a linear appearance ( dentinogenesis). 10-40μm in width. Thicker in young teeth.

Structural Lines in Dentine Lines associated with the primary curvatures of dentinal tubules. Lines associated with the secondary curvatures of dentinal tubules. Incremental lines: von Ebner’s lines & Andresen lines. All of them are approximatley perpendicular to dentinal tubules

Primary Curvatures Lines Schreger Lines Schreger lines. Longitudinal sections. Peaks of sigmoid primary curvatures coincide. Difficult to see in cross sections.

Secondary Curvatures Lines Contour lines of Owen : Coincidence of secondary curvatures.rare in primary dentin. Exaggerated line on the border of primary and secondary dentine. Neonatal line.Change in composition of matrix and minerlisation

Incremental Lines Short term striations (von Ebner’s lines) & Long term striations (Andresen lines). Seen in: ground, demenerlised sections, under polarised light or microradiographs Cause: Fluctuations in acid-base balance effects the mineral content, thus the refractive index. Change in collagen fibrils orientation in andersen lines make them more marked under polarised light.

Von Ebner’s Lines Cuspal dentine: 4μm separate every 2 lines. Root dentine: 2μm separate every 2 lines.

Von Ebner’s Lines

Andresen Lines 16-20μm apart. 6-10 von Ebner's lines between every 2.suggesting 6-10 days rythem

Andresen Lines Exaggerated neonatal line.

Age Related and Post Eruptive Changes Physiological age changes: Secondary dentine. Translucent dentine. Changes associated with dentinal responses to stimuli: Tertiary dentine. Sclerotic dentine. Dead tracts of Fish.

Secondary Dentine starts to form once the root is completed and the tooth comes into occlusion. Very similar to primary dentine. Sudden change in the tubules direction, owen. Slower deposition, Closer incremental lines. Faster on pulp floor, cause narrowing of chamber and canals with age

Secondary Dentine

Secondary Dentine

Translucent Dentine Obliteration of tubules with intratubular dentine. Root dentine.

Peritubular (Intratubular) Dentine Physiologic ageing in root dentine leads to complete obliteration of the tubules with intratubular dentine. Same refractive index as intertubular dentine. These areas appear translucent when put in water.

Peritubular (Intratubular) Dentine Translucent dentine has a butterfly shape in cross section. This is due to the convergence of the tubules. Increases with age. Forensic dentistry to know age.

Tertiary Dentine External stimuli might induce the pulp to produce more calcified material. Caries, leakage, cavity preperation etc.. Irregular secondary dentine, reparative dentine, reactionary dentine, response dentine and osteodentin. Variable appearance and composition. Mainly tubular, may contain few irregular tubule or some atubular areas.

Tertiary Dentine

Tertiary Dentine

Tertiary Dentine Stimuli induce cells in the pulp to differentiate into “odnontoblasts”. Production of collagen type I and dentine sialoprotein by new odontoblasts Primary odontoblasts might be involved in the early stages.

Sclerotic Dentine Slow going Stimuli like slow caries & attrition induce the deposition of material inside the tubules. Sclerotic dentine is the result. Very similar in appearance to transparent dentine.lack structure Different composition from intratubular dentine. Apatite crystals possibly, octacalcium phosphate crystals. Exposed tubules might contain occluding components from saliva.

Sclerotic Dentine

Dead Tracts of Fish Primary odontoblasts could be killed by external stimuli. They could retreat before the formation of intratubular dentine. This results in empty tubules. Might be sealed at their pulpal end by tertiary dentine. Air filled, thus light will be internally reflected and they will appear dark. Dead tracts is the term given to these air filled tubules.

Dead Tracts of Fish

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