Histology of Dentine

Histology of Dentine

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 knowledge to interpret the clinical significance of dentine in health and disease

Tissues of the Teeth

• Enamel, dentine, pulp, cementum, bone (alveolar), periodontal ligament, and gingiva make up the tissues

Prior Knowledge

• Dentine location
• Dentinogenesis
• Embryonic origin

Composition of Dentine

• Dentine is composed of approximately 70% inorganic minerals (calcium hydroxyapatite), 20% organic material (collagenous matrix, non-collagenous matrix proteins, and lipids), and 10% water

Structural Features: Dentine Tubules

• The main structural units are dentine tubules, which are minute tubules that permeate the dentine structure

Dentine Tubules Shape

• Tubules traverse the dentine in an S-shape
• Tubules are almost straight underneath the cusps, incisal edges, and at the root tip
• They have a tapered outline, being more widely separated near the DEJ compared to near the pulp
• The odontoblasts' path during dentinogenesis reflects this pattern

Dentine Tubule Walls

• The walls of the tubules are called peritubular/intratubular dentine and are highly calcified with minimal collagen
• In contrast, the dentine in between the tubules is intertubular dentine, less calcified, and more collagenous

Odontoblastic Process

• The dentine tubule contains an odontoblastic process, a cytoplasmic extension of the odontoblast
• The periodontoblastic space surrounding the odontoblastic process is filled with fluid and is key for understanding dentine hypersensitivity

Interlobular Dentine

• Interglobular dentine are areas of unmineralized dentine (hypomineralized) that have failed to fuse together at the zones of mineralization
• Interglobular dentine is often found in the circumpulpal dentine just below the mantle dentine

Teeth and Vitamin D

• Interglobular dentine is prevalent in teeth where a vitamin D deficiency or high fluoride exposure has occurred during the maturation stage of dentinogenesis
• The structure of dentine, the dentine matrix, is normal, less mineralized, and does not include peritubular dentine

Sclerotic Dentine

• Dentine tubules can calcify, which is known as sclerotic dentine; it occurs via a physiological process of mineral deposition
• Most common in the apical third of the root and midway in the crown between the DEJ and pulp
• Amount increases with age, thus reducing permeability of dentine

Dead Tracts

• Dead tracts are empty dentine tubules 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, increase with age, and reduce the permeability of dentine

Incremental Lines

• Incremental lines can be viewed under a microscope in dentine, similar to enamel
• They reflect the pattern of dentinogenesis laid in increments called Lines of Von Ebner
• They are very close together and difficult to visualize (4 um)

Contour Lines

• A more distinct incremental line is viewed at the interface between primary and secondary dentine and is known as the Contour Lines of Owen
• These are delineated by a change in direction of the dentine tubules

Granular Layer of Tomes

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

Types of Dentine

• Dentine contains different heterogenous types based on location and timing of formation (dentinogenesis)
• Mantle dentine: initial formed dentine that outlines the periphery of the dentine adjacent to the enamel and cementum
• Circumpulpal dentine: The bulk of the dentine, it contains the dentine tubules and lies 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

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

Secondary Dentine

• Secondary dentine formation begins after root formation is complete and it forms slowly throughout life
• It forms concentrated over the roof and floor of the pulp
• Over time, secondary dentine reduces the size of the pulp chamber, causing pulp recession
• Structurally similar to primary dentine with tubules, however, it is less regular and visible histologically

Clinical Significance: Secondary Dentine

• Secondary dentine's pattern of formation occurs over time
• As people age, the pulp shrinks, protecting itself
• More likely for carious or incidental pulpal exposure in younger teeth because of the prominent pulp horns in restorative dentistry

Tertiary Dentine

• Tertiary dentine is known as reactionary or reparative and forms in response to various stimuli
• It is usually localized to the area of stimulus
• Structure varies in accordance with the intensity and duration of stimulus, which may affect the odontoblasts if the stimulus is strong enough
• It may have tubules continuous with secondary dentine or may be irregular in arrangement

Clinical Significance: Tertiary Dentine

• Caries, attrition, and abrasion from a toothbrush are examples of stimuli that initiate tertiary dentine

Reactionary Dentine

• It is deposited by pre-existing odontoblasts

Reparative Dentine

• It 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

• The functions of dentine are to provide support and protection, communicate, and repair

Function Linked to Structure

• The dentine structure is rigid (70% mineralized) yet elastic (collagen 20%), therefore it can absorb shock

Dentine Functions and Structure

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

Color of Dentine

• More yellow in health compared to white enamel because it is less mineralized and absorbs more light than enamel
• In disease, it changes colors to brown

Clinical Significance: Color of Dentine

• Changes in the color of teeth are essential for detecting disease and reassuring health

Permeability

• Affected by the dentine tubules and organic matter within them
• The permeability structure varies
• Tubules at the EDJ are least permeable because they have smaller diameter
• Those above the pulp are more permeable because they have wider diameter

Progression of Caries

• Quicker and more extensive

Innervation of Dentine

• "Porous" tubules allow communication with the pulp

Communication Via Dentine Tubules

• Communication with the pulp is enabled by the tubules and odontoblastic processes
• Sensations are triggered and it can 'feel'
• This has clinical implications for restorative procedures without local anesthetic and dentine hypersensitivity

Fluid in Dentine Tubules

• Movement of fluid triggers dentine hypersensitivity
• Implicated in restorative procedures for etching and bonding plastic materials to dentine

Radiographic Appearance of Dentine

• Visibly distinct as a radio-opaque structure

Radiographic Appearance of Caries in Dentine

• In disease, once caries has reached the dentine, it becomes more visible radiographically as a radiolucent area in dentine