Its dark blue color contrasts with dentin and is easily distinguished from the pulp.
Carious dentin is made up of two distinct layers.
There is an outer layer of infected carious dentin which is soft, discolored, nonvital, nonsensitive and cannot remineralize. Research indicates that the dye in the caries detector bonds to the denatured collagen which is present in the outer infected dentin but which is not present in the inner uninfected dentin and normal dentin. Only the outer infected dentin is stained. Stains outer infected dentin only. Detects caries in difficult to see places.