Histopathology of Dentine Caries

Histopathology of Enamel and Dentine Caries

• The presentation covers the histopathology of enamel and dentine caries, focusing on the four zones of destruction, the mechanisms of dentine's protection and the ICDAS scoring system.

GDC Learning Outcomes

• Students need to describe oral diseases and their relevance to prevention, diagnosis, and treatment.
• Students need to explain the aetiology and pathogenesis of oral diseases.
• Students need to describe relevant and appropriate dental, oral, craniofacial and general anatomy and explain how it's applied to patient management.

Pre-reading: Aetiology of Dental Caries

• Caries development involves a susceptible tooth surface, plaque bacteria, and a fermentable carbohydrate.
• Time is a crucial factor in the caries development process.

Pre-reading: Histology of Enamel and Dentine

• Lectures on the histology of enamel and dentine are a prerequisite.

Histopathology of Dentine Caries

• This presentation focuses specifically on dentine caries.

Learning Objectives

• Students should describe the clinical appearance of dentine caries.
• Students should describe the histology of dentine caries.
• Students should identify the 4 zones of destruction in dentine caries.
• Students should identify dentine's protective mechanisms against assault.

Recap on Caries Aetiology

• Caries begins when the pH of the oral environment lowers, causing hydroxyapatite (the tooth surface mineral) to demineralize into component ions.
• Ongoing demineralization without neutralization leads to caries.

How do we know this is happening clinically?

• This section describes how clinicians assess caries progression.

ICDAS Scores

• ICDAS is an international caries detection and assessment system.
• It's used in research and clinical practice to assess caries,
• It provides a clinical scoring system for diagnosing caries.
• It identifies and characterizes caries activity at each stage.

ICDAS Scores - Moderate Stage Caries

• Characterised by a dark shadow from dentine, potentially with enamel breakdown.
• Displaying a white or brown color when wet.
• Shows a darkened area of intrinsic shadow (grey, blue, or brown).
• Code 4 represents this stage.

ICDAS Scores - Extensive Stage Caries

• Characterized by a distinct cavity in opaque or discoloured enamel with visible dentine.
• Visible signs of demineralization (white or brown walls).
• Code 5 represents this stage.
• A distinct cavity with visible dentine extension into dentine.
• Code 6 represents this stage.

Recap on the Structure of Dentine

• Dentine is vital tissue with tubules permeated by odontoblast processes.
• It can defend itself and the pulp.
• The mineral component is hydroxyapatite, while collagen is the organic material.

So how does dentine caries progress through each stage to give these ICDAS scores?

• The presentation aims to explain the progression of dentine caries through different stages using ICDAS scores.

Macroscopic Dentine Caries - ICDAS Code 4

• Caries progresses from enamel to dentine resulting in a change in hardness.
• This leads to a lateral spread of caries below the enamel.
• This generates grey shadowing which eventually leads to crown breakdown.

Macroscopic Dentine Caries - ICDAS Code 5/6

• Enamel breakdown leads to dentine exposure.
• The progression to an extensive cavity (Code 6) involves further undermining and increased demineralization.
• Increased destruction makes restoration more challenging.

Macroscopic Dentine Caries - ICDAS Code 5/6

• Dental caries is identified with a sharp probe.
• Intense infection of dentine is characterized by its brown color, and it peels away with an excavator.
• Dentine below is less infected, and firmer.

How does this clinical appearance translate to histological appearance?

• The clinical presentation of caries translates to different histological appearances, including undercutting in the early stages.

Microscopic Dentine Caries

• Microscopic analysis of caries shows undercutting of enamel, softer dentine and progresses through 4 distinct zones.

Microscopic Dentine Caries

• Histological methods detail 4 key zones of a carious lesion (necrotic, contaminated, demineralized, and translucent).
• A fifth zone (tertiary dentine) is formed outside the carious lesion.

Microscopic Dentine Caries

• This area shows caries-affected and infected zones.
• These zones are defined based on macroscopic inability to be observed clinically.

Affected vs Infected Dentine

• The zones of destruction, penetration, demineralization, and translucent zones are detailed.

Zone 1 - Zone of Destruction

• The outermost, superficial, and irreparable area is characterized by necrosis, dark color, and soft, mushy texture.
• It has very high bacterial loads where the mineral content is dissociated, collagen matrix is denatured, and the dentinal tubule structure is destroyed.
• Rapid or slow progression can influence the color, being soft and yellow in the rapid variant, while a slow progression leads to darker, firmer dentine.
• This zone cannot be repaired clinically.

Zone 1 - Zone of Destruction

• This is the infected, easily excavated zone of caries. It cannot be repaired, leading to poor bonding surfaces. Inadequate restoration support is observed in this zone.

Zone 2 - Zone of Penetration/Bacterial Invasion

• Within this zone the tubule structure still exists, but it is heavily populated by bacteria.
• Decalcification and proteolysis are key processes.
• Clinically, this zone needs to be entirely removed with a rose head bur.
• Failure to remove this zone can lead to restoration failure.

Zone 3 - Zone of Demineralisation

• Acid production in higher zones spreads down unoccluded tubules, demineralizing dentin.
• This zone contains no bacteria and is the leading edge of the carious lesion.
• This zone is often very small and may feel softer than normal, but is reparable, and needs no removal.

Zone 3 - Zone of Demineralisation

• Demineralized dentin may feel softer than sound dentin, but may be paler brown in appearance.
• This zone of dentin is considered to be caries-affected and is not required to be removed.

Zone 4 - Translucent (Sclerotic) Zone

• Acid penetration triggers odontoblast processes to build up calcification, resulting in a hyper-mineralised zone.
• This "plugs" the tubules, slowing acid and toxin penetration into the pulp, protecting it.
• It is radiographically observed as a brighter area below the caries, due to hyper-mineralization.

Zone 4 - Translucent (Sclerotic) Zone

• The zone shows radiographically as a whiter area below the caries.
• This zone does not need to be removed.

Zone 5 - Tertiary Dentine

• New dentine formation is laid down at the pulp-dentine border, away from the carious lesion.
• This increases the dentin thickness between the lesion and the pulp as a protective measure.
• Formed when the pulp is mildly inflamed by acid.
• Comes in reactionary (mild irritant) or reparative (strong irritant) subtypes with varying degrees of irregularity.

Zone 5 - Tertiary Dentine

• Teritary dentine is deposited in response to injury, producing different patterns depending on the severity. Both mild (reactionary) and strong (reparative) forms exist and lead to irregular tubular structures.

Video for Review

• A video summarizing the caries process is available at the provided link (4:40 mark onwards).