Histopathology of Enamel and Dentine Caries

Histopathology of Enamel and Dentine Caries

• GDC Learning Outcomes:
  • Describe oral diseases and their relevance to prevention, diagnosis, and treatment.
  • Explain the aetiology and pathogenesis of oral disease.
  • Describe relevant and appropriate dental, oral, craniofacial, and general anatomy; explain application to patient management.
• Pre-reading:
  • Aetiology of Dental Caries lecture.
  • Histology of enamel and dentine lectures.

Histopathology of Dentine Caries

• Learning Objectives:
  • Describe the clinical appearance of dentine caries.
  • Describe the histology of dentine caries.
  • Identify and name the 4 zones of destruction in dentine caries.
  • Identify mechanisms dentine uses to protect itself and the pulp.

Recap on Caries Aetiology

• As pH lowers, tooth surface (hydroxyapatite) demineralizes, breaking down into component ions.
• Continued demineralization (without neutralization) leads to caries.

ICDAS Scores

• International caries detection and assessment system for clinical research, practice, and epidemiology.
• A clinical scoring system for diagnosing caries.
• Enables caries process detection and characterization at different stages.
• Developed due to inconsistencies in previous caries diagnosis methods.

ICDAS Scores - Moderate Stage Caries

• Code 4: Dark shadow from dentin, with or without enamel breakdown.
• White or brown spot when wet.
• Darkened area of intrinsic shadow (grey, blue, brown).

ICDAS Scores - Extensive Stage Caries

• Code 5: Distinct cavity in opaque/discoloured enamel with visible dentin.
• Visible evidence of demineralization (white or brown walls).
• Code 6: Extensive cavity; visible extension into dentin.

Recap on the Structure of Dentine

• The mineral component of dentin is hydroxyapatite.
• Organic material is collagen.
• Dentin is a vital tissue with dentinal tubules permeated by odontoblast processes.
• Dentin is able to defend itself from assault (alongside the pulp).

Macroscopic Dentine Caries - ICDAS Code 4

• Progression from enamel to dentin shows change in substrate hardness.
• This causes lateral spread of caries under enamel.
• Leads to grey shadowing and eventual crown breakdown.
• Similar to cliff erosion with bacteria as water.

Macroscopic Dentine Caries - ICDAS Code 5/6

• Enamel undermining and breaking away leads to dentin exposure (ICDAS 5).
• This further leads to extensive cavities (ICDAS 6).
• More destruction equates to more difficulty in its restoration.
• Bacterial destruction makes dentin softer.

How does clinical appearance translate to histological appearance?

• Clinical observation corresponds to microscopic appearance.

Microscopic Dentine Caries

• Caries progress along the dentin (deeper).
• 'Undercutting' of enamel with caries progresses.
• Microscopic observations reveal zones.

Microscopic Dentine Caries

• Zones (dentinal-lesion cross sections) are: necrotic, contaminated, demineralized, translucent, tertiary, and hard dentin.

Microscopic Dentine Caries (Affected vs. Infected Zones)

• Affected dentin: changing but without bacteria.
• Infected dentin: penetrated bacteria resulting in destruction.

Zone 1 - Zone of Destruction

• Outermost, necrotic; clinically dark brown, soft, and mushy.
• Rapid caries: soft yellow; slow caries: browner.
• Mineral content dissociated by bacterial acid; collagen denatured.
• High bacterial load, with dentinal tubule destruction and liquefaction foci.
• Transverse clefts are formed.

Zone 1 - Zone of Destruction

• Cannot be repaired.
• Weak surface for bonding.
• Poor sealing ability.
• Inadequate restoration support.

Zone 2 - Zone of Penetration/Bacterial Invasion

• Dentinal tubule structure still exists.
• Tubules invaded by bacteria that decalcify through acid.
• Dissolving proteins.
• Believed this zone is to be removed (with bur).

Zone 3 - Zone of Demineralization

• Acid spread from upper zones to un-occluded dentinal tubules; demineralizing dentin.
• No bacteria present.
• This is the advancing lesion front (very small, <1 mm).

Zone 3 - Zone of Demineralization

• Can feel softer than sound dentin.
• Can be repaired by the dentin pulp complex.
• Paler brown in appearance.

Zone 4 - Translucent (Sclerotic) Zone

• Acid penetration initiates odontoblast process calcification.
• Tubules 'plugged' with mineral; slows acid/toxin penetration.
• Radiographically: whiter area below caries (hyper mineralization).
• Does not have to be removed.

Zone 5 - Tertiary Dentine

• Formed away from the lesion (not a zone though).
• New dentin laid down along pulp-dentin border.
• This increases dentine between lesion & pulp for pulp protection.

Zone 5 - Tertiary Dentine

• Produced when pulp inflammation (by advancing acid).
• Irregular tubular structure with types.
• Reactionary (mild irritant): deposited by surviving odontoblasts.
• Reparative (strong irritant): deposited after odontoblast death or cell death.

Zone 5 -Tertiary Dentine

• Diagram showing mechanisms of formation with mild/intense injury and corresponding dentine types.

Video for Review

• This video summarizes the process. Please view from 4:40.
• [YouTube link].