Histopathology of Enamel Caries

Histopathology of Enamel and Dentine Caries

• Histopathology of enamel and dentine caries is a focus of study
• This covers the aetiology and pathogenesis of oral disease, as well as clinical and histological appearances of enamel caries
• Learning outcomes include describing oral diseases and their relevance to prevention, diagnosis and treatment, explaining aetiology and pathogenesis of oral disease, relevant anatomy, and its application to patient management
• A pre-reading lecture on 'Aetiology of Dental Caries' suggests various causative factors (time, plaque bacteria, fermentable carbohydrate, susceptible tooth surface)
• Pre-reading material also includes 'Histology of enamel and dentine' lectures

ICDAS Score

• The International Caries Detection and Assessment System (ICDAS) is a clinical scoring system for diagnosing caries
• ICDAS allows for caries detection throughout different stages and characterises the carious activity of the lesion
• ICDAS was developed for use in clinical research, clinical practice and epidemiological purposes

ICDAS Score- Clinical Appearance in relation to stage

• Score 0: Clinically sound tooth. No caries evidence. No change in appearance, whether when surface is wet or dry

• Score 1: Initial stage caries. No clinical signs of caries when the tooth surface is wet to the touch, but visual signs are evident after drying. White spot and/or brown spots/discolourations are present.

• Score 2: Initial stage caries. Distinct visual changes in enamel. These changes are visible both upon wet and dry surfaces

• Score 3: Moderate stage caries. Localised enamel breakdown without dentine exposure visible when the tooth surface is wet or dry. Prolonged drying of the surface reveals loss of enamel integrity

• The progression of caries is highlighted clinically by the distinct visual changes

Recap on Caries Aetiology

• As the pH of the tooth surface decreases, hydroxyapatite demineralises, breaking down into component ions
• If pH does not neutralise, this demineralization over time leads to caries
• Ca 10 (PO4)6 (OH)2 (hydroxyapatite) breaks down into calcium ions, phosphate ions, and hydroxyl ions

Histological Appearance of Enamel Caries

• Every carious process begins with slight etching of the enamel surface under the dental plaque
• This is reversible
• Under cariogenic circumstances, the tooth dissolves further, resulting in micro porosities in the enamel surface
• These are typically located at prism boundaries
• The first clinical signs are white spots due to a greater portion of incoming light being scattered, compared to surrounding enamel. This happens because mineral is lost from enamel. Air or electrolytes in these porosities have different refractive index which is different from sound enamel
• Where these porosities occur, white spot lesions can incorporate exogenous pigmentation. This makes the lesion appear brown.
• This suggests longer lesion presence

Established Enamel Caries Histology

• Established enamel caries (still within enamel, not extending into dentine) has 4 distinct zones:

  • Surface Zone: Relatively unaffected, able to remineralise. Has a relatively high mineral content. Pore volume below 5%.
  • Body of the Lesion: Largest area and an area of demineralisation. Pore volume varies from 5-25%. Appears translucent with striae of Retzius well marked
  • Dark Zone: Does not transmit light, appears dark under microscopy. Also shows some remineralisation. Pore volume is 2-4%.
  • Translucent Zone: Advancing edge of the lesion. Pore volume 1%

• These present as a 'wedge' shaped lesion with the point towards the dentine in smooth surface caries, and towards the enamel surface in pit and fissure caries

Identifying Histological Zones

• Samples are cleared using a clearing agent (quinoline) which has identical refractive index to enamel to ensure correct identification of all zones.
• Classical zones of enamel caries are identified due to differences in the amount and size of porosities. Transmission light microscopy is used
• Different clearing mediums and polarised light microscopy allow for measurement of pore size and volume.