Sequential observations followed by acid etching on the enamel surfaces of human teeth under scanning electron...

A scanning electron microscope equipped with a low vacuum specimen chamber and a Robinson's backscattered electron detector was employed to observe the natural surfaces of human buccal enamel before and after 30 percent phosphoric acid etching sequentially up to 90 sec at the same sites with no coatings. Furthermore, successive etching patterns were compared between deciduous and permanent teeth. On the imbrication lines of young permanent teeth, prism-end pits surrounded with a "prismless" structure occasionally disappeared after acid etching and became a prismless enamel. Sequential etching caused the prismless areas and the areas of a type 1 etching pattern to decrease, and a cone-shaped prism structure and a complex type of the type 1 and type 2 etching pattern (type 1-2) to appear. The former was a transitional type between the prismless enamel and type 2 prisms. These etched surfaces show type 2 prisms after deeper etching. Small dome-shaped structures, slightly elevated on the attrited enamel surfaces, were found only in deciduous teeth. After acid etching, such areas which retained the prismless enamel rose to the underlying surfaces of cone-shaped prisms.