Histology of Dentine

Histology of Dentine

• Dentine is a tissue of the teeth
• It is important for clinical assessment, diagnosis, management and advice

Intended Learning Outcomes

• Students will describe the composition and structure of dentine
• Students will distinguish between the 3 types of dentine (primary, secondary and tertiary)
• Students will describe how the structure of dentine relates to its function
• Students will apply this knowledge to interpret the clinical significance of dentine in health and disease

Tissues of Teeth and Supporting Structures

• Enamel
• Dentine
• Pulp
• Cementum
• Bone (alveolar)
• Periodontal ligament
• Gingiva

Refresh Prior Knowledge

• Location of dentine within the tooth
• Dentinogenesis – how dentine is formed
• Embryonic origin

Composition of Dentine

• Consists of approximately 70% inorganic minerals, specifically calcium hydroxyapatite
• Contains approximately 20% organic material, primarily collagenous matrix (18%) and a small amount of non-collagenous matrix proteins and lipids (<2%)
• Contains approximately 10% water

Structural Features of Dentine: Dentine Tubules

• Dentine tubules are the main structural unit of dentine
• They are minute tubules that permeate the dentine structure, extending from the DEJ to the border of the pulp chamber
• In the dentine, the tubules traverse 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 the pulp, thus having a tapered outline, which reflects the path of odontoblasts during dentinogenesis
• The wall of the tubules is called peritubular/intratubular dentine, which is highly calcified with minimal collagen
• Dentine inbetween the tubules known as intertubular dentine is less calcified and more collagenous, making up the bulk of the dentine
• Dentine tubules contain an odontoblastic process, which is a cytoplasmic extension of the odontoblast
• Dentine is also surrounded by the periodontoblastic space which is filled with fluid, that is key for understanding dentine hypersensitivity

Structural Features of Dentine: Interglobular Dentine

• Interglobular dentine are areas of unmineralized dentine (hypomineralised)
• They failed to fuse together at the zones of mineralization during dentinogenesis
• These are prevalent in teeth with a Vitamin D deficiency or high fluoride exposure during dentinogenesis
• This dentine is often found in the circumpulpal dentine just below the mantle dentine
• The structure of dentine is normal (dentine matrix), less mineralized, and does not include peritubular dentine

Structural Features of Dentine: Sclerotic Dentine

• It is most common in the apical third of the root, and midway in the crown between the DEJ and pulp
• Dentine tubules can calcify, and are known as sclerotic dentine, this is due to a physiological process of mineral deposition
• The permeability of dentine is reduced by sclerotic dentine increasing with age

Structural Features of Dentine: Dead Tracts

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

Structural Features of Dentine: Incremental Lines

• Incremental lines, similar to enamel, can be viewed in dentine under a microscope
• They reflect the pattern of dentinogenesis in increments called Lines of Von Ebner
• These are very close together and difficult to visualise (4um)
• A more distinct incremental line can be viewed at the interface between primary and secondary dentine known as the Contour Lines of Owen
• This is delineated by a change in the direction of the dentine tubules

Structural Features of Dentine: Granular Layer of Tomes

• Granular Layer of Tomes is a narrow layer of dentine with a granular appearance
• Its found only in root dentine beneath the cemento-dentinal junction and is more numerous towards the apex
• It is visible in the ground sections only
• It is thought to be a result of interference with the mineralisation of dentine by the inner layer of the dental sac

Types of Dentine

• The structure of dentine is heterogenous that is categorised according to the location and timing of formation during dentinogenesis
• Mantle dentine is the initial formed dentine that outlines the periphery of the dentine adjacent to the enamel and cementum
• Circumpulpal dentine is the bulk of the dentine and contains the dentine tubules that lie between the mantle and pre-dentine
• Pre-dentine (dentine matrix) surrounds the pulp chamber to enable dentinogenesis to continue throughout the teeths' life

Types of Dentine: 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

Types of Dentine: Secondary Dentine

• The formation of secondary dentine begins after root formation is complete
• It forms slowly throughout life and is concentrated over the roof and floor of the pulp
• Over time, the pulp chamber reduces in size due to secondary dentine
• Its structure is similar to primary dentine with tubules however it is less regular and a distinction is less visible histologically

Clinical Significance of Secondary Dentine

• As people age, the pulp essentially shrinks, protecting itself by the formation of secondary dentine
• In restorative dentistry, carious or incidental pulpal exposure is more likely in younger teeth because of the prominent pulp horns

Types of Dentine: Tertiary Dentine

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

Clinical Significance of Tertiary Dentine

• Stimuli causing tertiary dentine: caries, attrition, abrasion from a toothbrush
• Reactionary dentine is deposited by pre-existing odontoblasts
• Reparative dentine is deposited by newly differentiated odontoblast-like cells from the ectomesenchyme of the pulp These cells may become trapped in the matrix forming osteodentine

Functions of Dentine

• Support
• Protect
• Communicate
• Repair

Functions Linked to Structure

• Support: bulk of the tooth crown and root
• Protect: rigid yet flexible
• Communicate: Fluid, odontoblastic process, proximity to pulp
• Repair: fluid filled dentine tubules, secondary dentine, tertiary dentine

Dentine Colour

• The colour of dentine in health is more yellow, because it's less mineralised, in comparison to white enamel
• In disease the dentine changes to a brown a (or other colours) changing the appearance of the crown to a grey shadowing in appearance

Dentine Colour: Clinical Significance

• Changes in the colour of the teeth are essential for detecting disease such as caries and tooth surface loss
• Colours of the teeth can also be reassuring to assess a patient's dental health
• This includes teeth yellowing with age and distinguishing new adult teeth which are more yellow compared to primary teeth.
• An example is canines which are more yellow because thicker tooth which reflect light differently

Permeability

• The dentine tubules and the organic content make dentine permeable
• The tubules at the EDJ are the least permeable (narrower tubule diameter)
• The tubules above the pulp are the more permeable (wider diameter)

Permeability affects:

• Progression of caries is quicker and more extensive
• Communication with the pulp via porous tubules, also known as its innervation

Communication

• Communication between the dentine and pulp is enabled by dentine tubules and the odontoblastic process
• It triggers sensations
• This can have clinical implications for restorative procedures without local anaesthetic and dentine hypersensitivity

Fluid Content

• When dentine is exposed, the movement of fluid creates dentine hypersensitivity
• This is affected by pressure changes which results in sensitivity and/or pain
• Restorative procedures for etching and bonding plastic materials to dentine

Summary of Dentine Radiographic Appearance

• Dentine is distinctly visible
• It is radio-opaque compared to enamel, alveolar bone and the pulp