Dentine Structure and Composition

• Histology of Dentine
• Dentine is the material in the tooth located between the enamel and the pulp
• Intended learning outcomes:
• Describe the composition and structure of dentine
• Distinguish between the 3 types of dentine (primary, secondary and tertiary)
• Describe how the structure of dentine relates to its function
• Apply this knowledge to interpret the clinical significance of dentine in health and disease
• GDC Learning Outcomes: 1.1.5, 1.1.6
• Histology of the tissues of the teeth and supporting structures includes: enamel, dentine, pulp, cementum, bone (alveolar), periodontal ligament and gingiva
• Location of dentine – It is found in both the crown and the root of teeth
• Knowing about dentine is important for: Dentine hypersensitivity and management, Restorative and bonding materials, Identification of caries - infected, affected and healthy dentine, Radiographs, Pathology and repair of dentine linked to pulp
• This knowledge is important for clinical assessment, diagnosis, management and advice

Composition of Dentine

• Approximately 70% inorganic minerals: calcium hydroxyapatite (smaller than enamel)
• Approximately 20% organic material: Majority collagenous rich matrix (18%), Minority non-collagenous matrix proteins and lipids (<2%)
• Approximately 10% water

Structural Features - Dentine Tubules

• Dentine tubules are the main structural unit of dentine
• They are minute tubules that permeate the dentine structure
• They extend from the DEJ to the border of the pulp chamber
• The tubules traverse the dentine in an S-shape
• Underneath the cusps, incisal edges and at the root tip they are almost straight
• They are more widely separated near the DEJ compared to near pulp thus have a tapered outline
• The pattern of the tubules reflects the path of odontoblasts
• Odontoblasts become crowded during dentinogenesis so some will die off to make space
• The wall of the tubules is called peritubular/intratubular dentine that is highly calcified with minimal collagen
• The dentine between the tubules is less calcified and more collagenous, called intertubular dentine, and makes up the bulk of dentine
• An odontoblastic process is a cytoplasmic extension of the odontoblast
• The periodontoblastic space that surrounds the odontoblastic process is filled with fluid
• The dentinal fluid filled tubules are the key for understanding dentine hypersensitivity

Structural Features - Interglobular Dentine

• Interglobular dentine are areas of unmineralized dentine (hypomineralised) that have failed to fuse together at the zones of mineralisation during dentinogensis
• They are often found in the circumpulpal dentine just below the mantle dentine
• Prevalent in teeth where a vitamin D deficiency or high fluoride exposure has occurred during the maturation stage of dentinogenesis
• The structure of dentine is normal (dentine matrix), less mineralised and does not include peritubular dentine

Structural Features - Sclerotic Dentine

• Dentine tubules can calcify and is known as sclerotic dentine
• Sclerotic dentine development is a physiological process of mineral deposition
• Sclerotic dentine is most common 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 thus reducing the permeability of dentine

Structural Features - Dead Tracts

• Dead tracts are known as empty dentine tubules where an odontoblastic process has died or retracted and is sealed off
• This may result from physiological or pathological processes
• They are thought to be the first part of sclerotic dentine and increase with age and reduce the permeability of dentine

Structural Features - Incremental Lines

• Similar to enamel, incremental lines can be viewed under a microscope in dentine
• Incremental lines reflect the pattern of dentinogenesis laid in increments called Lines of Von Ebner
• They are very close together and difficult to visualise (4um)
• A more distinct incremental line can be viewed at the inter-face between primary and secondary dentine known as the Contour Lines of Owen
• Contour Lines of Owen are 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
• It is found only in root dentine beneath the cemento-dentinal junction
• The Granular Layer of Tomes is more numerous towards the apex
• It is only visible in ground sections
• It's development is thought to be a result of interference with the mineralisation of dentine by the inner layer of the dental sac

Types of Dentine Overview

• The structure of dentine contains heterogenous types of dentine according to the location and timing of formation (dentinogenesis)
• Mantle dentine is initial formed dentine, outlining the periphery of the dentine adjacent to the enamel and cementum
• Circumpulpal dentine is the bulk of the dentine, containing dentine tubules that lies between the mantle and pre-dentine
• Pre-dentine (dentine matrix) surrounds the pulp chamber to enable dentinogenesis to continue throughout the teeth’s life

Primary Dentine

• Primary dentine is the bulk of the dentine within the tooth that forms prior to completion of root formation
• It is made up of both mantle and circumpulpal dentine

Secondary Dentine

• Formation of secondary dentine begins after root formation is complete
• It forms slowly throughout life
• Formation is not even, It is concentrated over the roof and floor of the pulp
• Over time, secondary dentine reduces the size of the pulp chamber (pulp recession)
• The structure is similar to primary dentine with tubules however it is less regular and a distinction is visible histologically

Clinical Significance of Secondary Dentine

• The formation of secondary dentine changes over time
• 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

Tertiary Dentine

• Tertiary dentine is also known as reactionary or reparative dentine
• It forms in response to various stimuli and it's localized to the area of stimulus
• The structure varies in accordance with the intensity and duration of stimulus – may affect the odontoblasts if strong enough
• It may have tubules continuous with secondary dentine or it may not, and may appearing irregular in arrangement

Clinical Significance of Tertiary Dentine

• Examples of stimuli initiating tertiary dentine: caries, attrition, and abrasion from a toothbrush

Reactionary vs Reparative Tertiary Dentine

• There is a histological distinction between the two types reaction and reparative dentine
• Reactionary dentine is deposited by pre-existing odontoblasts
• Reparative dentine is deposited by newly differentiated odontoblast-like cells from the ectomesenchyme of the pulp
• The cells forming reparative dentine may become trapped in the matrix forming osteodentine.
• Dentine:
• provides support
• protects
• allows communication
• provides repair

Function of the Tooth Linked to Structure

• Dentine structure is rigid (70% mineralised) yet elastic (collagen 20%) therefore it is able to absorb some degree of shock
• Dentine supports: bulk of tooth crown and root
• Dentine Protects due to: fluid filled dentine tubules, proximity to pulp and odontoblastic processes
• Dentine communicates due to: Proximity to pulp and an Odontoblastic process
• Dantine can be repaired by: Rigid but flexible secondary/tertiary dentine

Colour and Permeability of Dentine

• The color of dentine in health is more yellow in comparison to white enamel because it is less mineralised and absorbs more light than enamel
• In disease, the color of dentine changes to brown (or other colors) that then changes the appearance of the crown to a grey shadowing appearance
• Changes in the colour of teeth are essential for detecting disease (caries, tooth surface loss, pulpal involvement)
• Changes in the colour of teeth are essential for reassuring health by yellowing of teeth with age, new adult teeth are yellow compared to primary teeth, canines more yellow because thicker tooth and reflects light differently
• It's Permeable: Dentine tubules and the organic content make dentine permeable to some extent and this permeability varies within the structure
• The tubules at the EDJ are the least permeable (narrower tubule diameter) and those above the pulp are the more permeable (wider diameter)
• Affects:
• Progression of caries as it is quicker and more extensive
• Innervation of dentine as the 'porous' tubules allow communication with the pulp

###Communication and Fluid Content in Dentine

• The dentine tubules and the odontoblastic process enable communication with the pulp
• The pulp triggers sensations and enables teeth to 'feel'
• This can have clinical implications for restorative procedures without local anaesthetic and dentine hypersensitivity
• The fluid content in dentine tubules has clinical implications in sensitivity & restorative procedures
• Dentine hypersensitivity can occur when the dentine is exposed, movement of fluid occurs due to pressure changes triggering sensitivity or pain
• Restorative procedures effect the etching and bonding plastic materials to dentine

Radiographic Appearance

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

Explore the composition of dentine, including the percentage of inorganic minerals and the main organic component. Review different types of dentine and the function of dental tubules. Understand the clinical relevance of dentine structure knowledge.