Surface phenomena in dental caries.

Abstract

ONE of the important characteristics of early carious decay of human dental enamel is that it occurs below the surface and remains covered by a surface layer which is relatively unaffected by the attack. Human tooth enamel is highly calcified, containing 97 per cent mineral hydroxyapatite (which is negatively birefringent) and 3 per cent organic material and water. During carious decay there is an increase in the total pore volume in the tissue and this “mixed body” system1 produces positive form birefringence. When an early lesion of enamel caries is examined between crossed polars after imbibition with a medium having a refractive index remote from that of the enamel—water, for example—the surface zone is seen to retain its negative birefringence while the porous subsurface enamel becomes positively birefringent.