[Scanning and transmission electron microscopy study of the effects of a citric acid solution on the human root dentine].

After removal of the cementum layer, the buccal surface of human roots was been treated in vitro for 60, 120 and 180 seconds with a gel solution of 50% citric acid (pH 2.1). These surfaces were prepared for observation in the scanning electron microscope (SEM) and ultra-thin sections of the treated areas were studied in the transmission electron microscope (TEM). The SEM results showed that application of an acid solution revealed fibrous like structures on the dentinal surface after 60 and 180 seconds of treatment. A correlation between the results obtained in SEM and TEM is not always evident. The ultra-thin sections showed, in the superficial dentine, three distinct zones at the three time intervals chosen: from outside to inside, a very thin crust, a demineralized zone with collagen fibres and a deep dentine zone could be observed. After 120 seconds, the collagenous matrix seemed to be totally freed from the inorganic part.