Dentine Histology and Composition

Histology of Dentine

• Key features: Dental Tubules.

Composition of Dentine

• Approximately 70% inorganic minerals, specifically calcium hydroxyapatite (smaller than enamel).
• Contains roughly 20% organic material, which is mostly collagenous rich matrix (18%), and a minority of non-collagenous matrix proteins and lipids (<2%).
• Consists of approximately 10% water.

Structural Features – Dentine Tubules

• Dentine Tubules are the main structural unit of dentine.
• Minute tubules permeate the dentine structure, extending from the DEJ to the border of the pulp chamber.
• Tubules traverse the dentine in an S-shape in the cusps, incisal edges and at the root tip they appear almost straight.
• Tubules have a tapered outline, being more widely separated near the DEJ compared to near the pulp.
• The wall of the tubules is called peritubular/intratubular dentine, which is highly calcified with minimal collagen.
• The dentine inbetween the tubules is called intertubular dentine; it is less calcified and more collagenous, making up the bulk of dentine.
• An odontoblastic process is a cytoplasmic extension of the odontoblast that can be found in the dentine tubule.
• The periodontoblastic space surrounds the odontoblastic process and is filled with fluid.
• Periodontoblastic space is key for understanding dentine hypersensitivity

Structural Features – Interglobular Dentine

• Interglobular dentine consists of unmineralized (hypomineralised) areas that failed to fuse during the zones of minerialisation of dentinogenesis.
• Often found in the circumpulpal dentine just below the mantle dentine.
• Prevalent in teeth with vitamin D deficiency or high fluoride exposure during maturation of dentinogenesis.
• The structure of dentine is normal, less mineralised, and does not include peritubular dentine.

Structural Features – Sclerotic Dentine

• Dentine tubules can calcify, resulting in sclerotic dentine through mineral deposition.
• This calcification commonly occurs in the apical third of the root, and midway in the crown between the DEJ and pulp.
• The amount of sclerotic dentine increases with age, reducing the permeability of dentine.

Structural Features – Dead Tracts

• Empty dentine tubules where an odontoblastic process has died or retracted, and is sealed off, are known as dead tracts.
• May result from physiological or pathological processes.
• Dead tracts are the first part of sclerotic dentine and increase with age, reducing dentine permeability.

Structural Features - Incremental Lines

• Incremental lines are similar to enamel and can be be viewed under a microscope in dentine.
• Reflect the pattern of dentinogenesis laid in increments called Lines of Von Ebner; are visible and difficult to visualise (4um).
• A more distinct incremental line is known as the Contour Lines of Owen; viewed at the inter-face between primary and secondary dentine
• Delineated by a change in direction of the dentine tubules.

Structural Features – Granular Layer of Tomes

• The Granular Layer of Tomes is a narrow layer of dentine with a granular appearance.
• Present only in root dentine beneath the cemento-dentinal junction.
• More numerous towards the apex and only visible in ground sections.
• Granular Layer of Tomes, thought to be caused by interference with the mineralisation of dentine by the inner layer of the dental sac.

Types of Dentine

• The structure of dentine contains different types of dentine (heterogenous) according to the location and timing of formation (dentinogenesis).
• Mantle dentine is the initial formed which outlines the periphery of the dentine adjacent to the enamel and cementum.
• Circumpulpal dentine is is the bulk of the dentine and contains the dentine tubules, lying between the mantle and pre-dentine.
• Pre-dentine (dentine matrix) surrounds the pulp chamber to enable dentinogenesis to continue throughout the tooth's life.
• Primary dentine is the bulk of the dentine within the tooth, forming prior to root formation completion; contains both mantle and circumpulpal dentine.
• Secondary dentine formation begins after root formation is complete; forms slowly throughout life and is concentrated over the roof and floor of the pulp.
• Pulp recession is the process of secondary dentine reducing the size of the pulp chamber over time.
• Similar in structure to primary dentine with tubules, secondary dentine is less regular and visible histologically.
• Tertiary dentine, also known as reactionary or reparative, forms in response to stimuli and is localised to the area of stimulus.
• Can have tubules continuous with secondary dentine, or may appearing in an irregular arrangement.
• A histological distinction exists between reactionary tertiary dentine which is deposited by pre-existing odontoblasts.
• Reparative tertiary dentine is deposited by newly differentiated odontoblast-like cells from the ectomesenchyme of the pulp; cells may become trapped in the matrix forming osteodentine.

Clinical Significance of Secondary Dentine

• Over time the formation of secondary dentine changes pattern.
• As people age, the pulp essentially shrinks protecting itself.
• In restorative dentistry, a carious or incidental pulpal exposure is MORE likely in younger teeth because of the prominent pulp horns.

Function Linked to Structure

• Dentine has various functions, including support, protection, communication, and repair.
• The structure of dentine consists of the bulk of the tooth crown and root, fluid-filled dentine tubules, proximity to pulp, odontoblastic process and rigid yet flexible secondary and tertiary dentine.
• Dentine structure is rigid (70% mineralised) yet elastic (collagen 20%), enabling it to absorb shock.

Colour of Dentine

• The colour of dentine in health is yellow in comparison to white enamel because it is less mineralised and absorbs more light than enamel.
• In disease, the colour of dentine changes to brown (or other colours), altering the appearance of the crown.
• Changes in tooth colour are essential for detecting disease (caries, tooth surface loss, pulpal involvement).
• Changes in tooth colour also essential for reassuring health (yellowing of teeth with age, new adult teeth are yellow compared to primary teeth, canines more yellow).

Permeability

• Dentine tubules and organic content make dentine permeable, with permeability varying within the structure.
• Tubules at the EDJ are the least permeable (narrower tubule diameter), with those above the pulp being more permeable (wider diameter).
• Permeability affects the progression of caries, because caries progress quicker and are more extensive, plus Innervation of dentine, because communication with the pulp enabled by porous tubules.

Fluid Content in Dentine

• Dentine hypersensitivity arises from the movement of fluid as a result of pressure changes triggering sensitivity or pain when dentine is exposed.
• Restorative procedures for etching and bonding plastic materials to dentine are also affected.

Radiographic Appearance of Dentine

• Dentine appears distinctly visible on radiographs as a radio-opaque structure.
• In disease, once caries has reached the dentine, it is a more visible radiolucent area.

This lesson covers the histology and composition of dentine. It discusses the key features of dentine, including dental tubules. It also details the organic and inorganic components of dentine, as well as its structural features.