Observations with the scanning electron microscope on trauma-induced micro-cavities in human enamel

Abstract

Seven small carious micro-cavities, situated in the approximal surface enamel of human molars and premolars, were examined by scanning electron microscopy. A series of laminations were seen within a cavity at different levels corresponding with striae of Retzius, along which fracture had apparently occurred. The appearance of each lamina was of a honeycomb because the fractured end of each prism was in the form of a depression. Thus, fractured carious enamel bears a resemblance to normal enamel after it has been etched with acids. Most of the depressions were no more than 5μ deep; a few were much deeper, 15–20μ, but apart from these there was no evidence of prisms being hollowed out into tube-like structures. Nevertheless, the peripheral region of a prism has some property enabling it, more readily than the central region, to retain structural integrity after fracture in carious enamel and after acid-etching in normal enamel. The texture of carious enamel was unlike both fractured normal enamel and acid-etched enamel so that its character may be determined partly by secondary processes such as “remineralization”. On the surface enamel covering white-spot lesions, shallow depressions of prism endings were observed, some of which contained bacteria. Others were bacteria-free and showed a central pitting as if the prisms were eroding away centrally.