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.