Histopathology of Enamel and Dentine Caries

Histopathology of Enamel and Dentine Caries

• Topic: Histopathology of enamel and dentine caries
• Subject: Oral and Dental Science
• Presenter: Josh Hudson

GDC Learning Outcomes

• Describe oral diseases & their relevance to prevention, diagnosis, and treatment
• Explain the aetiology and pathogenesis of oral disease
• Describe appropriate dental, oral, craniofacial, and general anatomy, and explain their application to patient management

Pre-reading: Aetiology of Dental Caries

• Key factors for dental caries: Time, plaque bacteria, fermentable carbohydrates, susceptible tooth surface

Pre-reading: Histology of Enamel and Dentine Lectures

• Topic: Histological study of enamel and dentine

Histopathology of Enamel Caries

• Topic: Study of enamel caries

Learning Objectives

• Describe the clinical appearance of enamel caries
• Describe the histology of enamel caries
• Identify and name the 4 zones of destruction in enamel caries
• Describe the clinical appearance of enamel caries in relation to its histopathology

Recap on Caries Aetiology

• As pH lowers, the tooth surface (hydroxyapatite) demineralizes, breaking down into component ions
• If pH does not neutralize, demineralization leads to caries
• Chemical equation for demineralisation: Ca10(PO4)6(OH)2 → Ca2+, PO43− + OH− (hydroxyl ion)

How do we know this is happening clinically?

• Topic: Clinical methods to identify caries

ICDAS Score

• International caries detection and assessment system
• ICDAS was developed for clinical research, clinical practice, and epidemiological purposes.
• A clinical scoring system for diagnosing caries
• Allows detection of the caries process at every stage and characterisation of the carious activity of the lesion
• Developed due to inconsistencies in caries diagnosis

ICDAS Score - Score 0

• Sound tooth
• No evidence of caries when tooth surface is wet
• No evidence of caries when tooth surface is dry
• Tooth clinically sound

ICDAS Score - Code 1 (Initial Stage Caries)

• No evidence of caries when tooth surface is wet
• First visual signs (white spot and/or brown discolouration) after air drying
• Initial stage caries

ICDAS Score - Code 2 (Initial Stage Caries)

• Distinct visual changes in enamel
• Visible when wet and dry

ICDAS Score - Code 3 (Moderate Stage Caries)

• Localized enamel breakdown without visible dentine exposure
• Visible when wet and dry
• Prolonged drying reveals loss of enamel integrity

How does this apply to the histological appearance?

• Topic: Relation between clinical and histological view of caries

Enamel Caries Microscopic Appearance

• SEM (scanning electron microscope) images of enamel caries

Enamel Caries Microscopic Appearance

• Caries process starts with slight etching of enamel surface under dental plaque
• This is reversible and occurs frequently
• Healthy enamel beside etched enamel
• Microscopic view of enamel caries-induced microporosities

Enamel Caries Microscopic Appearance (Continued)

• Under cariogenic circumstances, tooth dissolving results in microporosities in enamel surface
• Typically located at prism boundaries

Enamel Caries Micro/macroscopic Appearance

• First clinical signs: white spots (greater proportion of incoming light is scattered compared to surrounding enamel)
• Elevated porosities due to mineral loss
• Air (or electrolyte) in porosities has different refractive index compared to sound enamel

Enamel Caries Micro/macroscopic Appearance

• White spot lesions can incorporate exogenous pigmentation, making them appear brown
• This may suggest a longer lesion duration, but does not guarantee it

Established Enamel Caries Histology

• Established enamel caries (still within enamel, not extending into dentine) has four distinct zones
• Surface zone (relatively unaffected, remineralization-able)
• Body of the lesion (largest demineralization area)
• Dark zone (cannot transmit light, some remineralization and demineralization occurs)
• Translucent zone (advancing edge of lesion, initial area of destruction)

Established Enamel Caries Histology (Continued)

• Description of each zone in relation to its characteristic(s): pore volume, visibility, and remineralization potential
• Wedge-shaped lesions of smooth surface caries and pit/fissure caries

Established Enamel Caries Histology (Continued)

• Samples need to be cleared using quinoline for identifying histological zones
• Differences based on amount and size of porosities are observed using transmitted light microscopy
• Varying clearing mediums of different optical refractive indices used for pore volume/size determination using transmitted/ polarized light microscopy

1. Surface Zone

• Outermost zone of the lesion
• Also called pseudo-intact surface or intact surface
• High mineral content
• Pore volume below 5%
• Remineralize ability due to its contact location with saliva or plaque

2. Body of the Lesion

• Area below the surface zone
• Visible in conventional radiographs
• Demonstrates porosities of varying size
• Pore volume from 5-25%
• Translucent with Retzius striae

3. Dark Zone

• Thin layer below the body of the lesion
• Called dark zone due to small porosities (clearing medium cannot enter)
• Dark appearance under light microscopy
• Pore volume 2-4%
• Possibly due to lipid and protein presence that hampers mineral precipitation
• Suggests remineralization

4. Translucent Zone

• Layer at the advancing edge of the lesion
• Initial area of destruction as part of the carious process
• Pore volume of 1% (sound enamel: 0.1%)
• Demineralization
• Initial dissolution along gaps between rods

Video for review

• This video summarises the process: https://www.youtube.com/watch?v=Y_o0ygwA6CI (from 4:40)