Histology of Dentine

Histology of Dentine

• Dentine is a hard, yellowish tissue that forms the bulk of a tooth.
• It's located between the enamel and the pulp.
• It has 3 types: primary, secondary, and tertiary.

Intended Learning Outcomes

• Students should be able to describe the composition and structure of dentine.
• They should be able to differentiate among the 3 types of dentine.
• They should be able to explain how the structure of dentine relates to its function.
• Students should be able to apply this knowledge to understand the clinical relevance of dentine in health and disease.
• This is based on GDC Learning Outcomes 1 1 5.

Tissues of Teeth and Supporting Structures

• Enamel
• Dentine
• Pulp
• Cementum
• Alveolar bone
• Periodontal ligament
• Gingiva

Refresh Prior Knowledge

• Students should know the location of dentine.
• Learners need to understand dentinogenesis (how dentine forms).
• They should recall the embryonic origin of dentine.
• Review previous lectures on oral embryology and tooth morphology for these topics.

Why Know About Dentine?

• Knowledge of dentine is crucial for clinical assessment, diagnosis, and management.
• It helps interpret dentine hypersensitivity, restorative materials, caries, affected and healthy dentine, and pathology and repair linked to pulp.
• Examples include using radiographs and interpreting the results.

Key Features: Dental Tubules - Composition and Structure

• Dentine is approximately 70% inorganic minerals (calcium hydroxyapatite), 20% organic material (primarily collagen), and 10% water.
• Dentine differs from enamel in its composition and quantity.
• The composition affects dentine's properties, like its resistance to fracture and ability to absorb shock.

Structural Features - Dentine Tubules 1-3

• Based on the minute tubules that permeate dentine, extending from the DEJ (dentinoenamel junction) to the pulp chamber.
• Peritubular/intratubular dentine surrounding the tubules is highly calcified, low in collagen.
• Intertubular dentine is between tubules, less calcified, containing more collagen.

Structural Features - Dentine Tubules 4

• Odontoblast process extends into the tubules.
• Periodontoblastic space surrounds the odontoblast process, containing fluid—understanding this is key to dentine hypersensitivity.

Structural Features - Interglobular Dentine

• Areas of unmineralized or hypomineralized dentine in the circumpulpal dentine.
• This is often found just beneath the mantle dentine.
• Occurrence may be linked to vitamin D deficiency or high fluoride exposure during dentinogenesis.

Structural Features - Sclerotic Dentine

• Dentine tubules can calcify via mineral deposition.
• Most prevalent apically in the root and midway in the crown - increases with age.
• Calcification reduces permeability and may be linked to protection from further damage.

Structural Features - Dead Tracts

• Empty dentine tubules where the odontoblastic process has retracted or died.
• Result of physiological or pathological processes, increasing with age.

Structural Features - Incremental Lines 1 and 2

• Incremental lines in dentine are similar to enamel lines, visible under a microscope.
• Lines of Von Ebner represent dentinogenesis increments.
• Contour lines of Owen are more distinct at the junction of primary and secondary dentine, delineated by changes in dentine tubule direction.

Structural Features - Granular Layer of Tomes

• A narrow dentine layer with granular appearance.
• Located in root dentine beneath the cemento-dentinal junction.
• More numerous towards the apex.
• A result of interference with dentine mineralisation by the dental sac.

Types of Dentine Overview

• Dentine is heterogeneous, with 3 main types based on formation location and timing.
• Mantle dentine forms first and outlines the dentine, adjacent to enamel and cementum.
• Circumpulpal dentine forms the bulk of the dentine.
  • Contains dentine tubules, located between the mantle and pre-dentine.
  • Pre-dentine is adjacent to the pulp chamber.

Primary Dentine

• The major part of dentine, formed before root completion.
• Composed of mantle and circumpulpal dentine.

Secondary Dentine

• Forms after root completion, slowly throughout life.
• Concentrated over the pulp roof and floor, reducing the pulp chamber size over time.
• Structurally similar to primary dentine, but less regular.

Tertiary Dentine

• Also called reactionary or reparative dentine.
• Forms in response to various stimuli (e.g., caries, attrition, abrasion) and is usually localized to the area where the stimuli occurs.
• Its structure varies according to the intensity and duration of the stimulus.

Clinical Significance of Tertiary Dentine

• Tertiary dentine formation is a response to various stimuli, like caries, abrasion, and attrition, affecting pulp shape.
• Clinical assessment includes identifying the type of stimuli and the impact on the pulp.

Reactionary vs Reparative Tertiary Dentine

• Reactionary: deposited by pre-existing odontoblasts.
• Reparative: deposited by newly differentiated odontoblast-like cells, forming part of the pulp.

Functions Linked to Dentine Structure

• Dentin functions for support, protection, communication, and repair of the tooth structure.
• Functions depend on its structure, like the dentin tubules housing fluid allowing communication with the pulp.

Dentine Colour

• In health, dentine is more yellowish, less mineralised, and absorbs more light than enamel.
• In disease, dentine colour changes to brown or other colours, influencing crown appearance to a greyish tone.
• The various colour changes are used clinically to detect disease and monitor treatment.

Dentine Permeability

• Dentine tubules and organic content make dentine permeable to varying degrees.
• Permeable regions are higher apically and closer to the pulp, related to disease progression.
• Understanding this is important, because caries and sensitivity are affected by permeability.

Dentine Communication

• Dentine tubules and odontoblast process facilitate communication with the pulp.
• This allows the transmission of sensations (e.g., temperature, pressure).

Fluid Content and Dentine Hypersensitivity

• Dentine fluid in tubules can influence sensitivity when exposed via irritation from pressure (e.g. biting).
• This impacts restorative procedures requiring minimal or no anaesthetics.

Radiographic Appearance of Dentine/Caries

• Dentine is radiopaque on radiographs.
• Diseased dentine, like caries, appears radiolucent compared to enamel and healthy dentine on X-Rays.