A scanning electron microscope study of the effect of etching time and mechanical pre-treatment on the pattern of acid etching on the enamel of primary teeth.

Eighty-five deciduous teeth, divided into five groups, were examined using a scanning electron microscope. The first two groups were etched for 60 and 120 sec respectively; the third and fourth groups were lightly milled and then etched for 60 and 120 sec respectively. In the first two groups, etching produced very few histological modifications. In the milled groups removal of the prismless enamel exposed the prisms to dissolution by the phosphoric acid. It was found that pretreatment and an etching time of 120 sec produced a constant and regularly distributed loss of inter- and intraprismatic substances.

Morphology of the aprismatic enamel: a SEM study of different etching.

Using the SEM, 55 longitudinally sectioned deciduous teeth were examined. The specimens were treated with a 37% solution of phosphoric acid and subsequently subdivided into groups in order that they could undergo etching for 1 min., 2 mins., 1 min. + 1 min. A minimal change was obtained with an etching time of 1 min., while an etching time of 2 mins. produced large porosity and deep, evenly distributed fossae. No important differences were seen following intermediated washing.