Four zones are clearly distinguishable, starting from the inner advancing front of the lesion. These are the (1) translucent zone, (2) dark zone, (3) body of the lesion and (4) surface layer.
Zones of enamel caries Translucent zone {TZ)
First recognizable zone of alteration
Advancing front of the lesion
Half the lesions demonstrate TZ, not always present
Seen in longitudinal ground sections in clearing (quinoline – RI – 1.62)
TZ appears structureless
Pore volume – I% (compared to 0.1 % of sound enamel)
Dark zone
Lies adjacent and superficial to the translucent zone Positive zone
Shows positive birefringence (in contrast to sound enamel.
Pore volume of 2-4% (polarized light)
Presence of small pores; large molecules of quinoline are unable to penetrate
Micropore system – gets filled with air and becomes dark
Medium like water may penetrate
Body of the lesion
Between unaffected, surface and dark zone
Area of greatest demineralization
Pore volume – 5% in periphery and 25% in centre
Quinoline imbibition – body appears transparent
Water imbibition – positive birefringence compared to sound enamel Striae of Retzius – prominent
Surface zone
Quantitative studies – partial demineralization of 1-10% • Pore volume – less than 5% of the spaces
Negative birefringence – water imbibition
Positive birefringence – porous subsurface
All the four zones of enamel caries cannot be seen with same immersion medium.
REFERENCE – Shafers textbook of oral pathology 8th edition
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