SEM–EDX study of prepared human dentine surfaces exposed to gingival retraction fluids

Objectives To evaluate the effects of gingival retraction fluids (GRF) on prepared dentine surfaces, and to test the null-hypothesis that prior exposure of dentine surfaces for prolonged period to any of the fluids evaluated does not influence acid-etching of the exposed surfaces. Methods The investigation was carried out using SEM and energy-dispersive X-ray analysis (EDX). The GRF studied were Hemodent™ (HMDT), Astringedent® (AST) and Ultradent® buffered 25% Aluminium Chloride (ULTB). Longitudinal sections of 220-grit ground dentine surfaces were exposed to GRF for 0.5-, 1-, 2- and 5-min (n=4 each). Another group of samples was produced by 20 s application of 35% phosphoric acid (PA) on GRF-pretreated dentine. Control samples were not exposed to GRF. Differences in etching effect—a function of the Ca-contents detected by EDX, were analysed using Friedmanʹs and Wilcoxonʹs rank test (P<0.05). Results The SEM demonstrated the presence of a relatively non-porous amorphous dentine matrix, but many of the dentine tubule orifices remained occluded. Granular precipitates, which remained even after acid-etching, were noted on surfaces exposed to Hemodent™ for 5 min. Characteristic crystal growth was observed on surfaces exposed to Astringedent® for 1- or 2-min prior to acid-etching. The EDX data demonstrated that there were differences in resulting Ca-content; ULTB >AST>HMDT>ULTB+PA>HMDT+PA>AST+PA>PA, but AST and HMDT were not significantly different. Conclusions The exposure of dentine prepared surfaces to these three GRF altered its morphology and reduced the dentineʹs susceptibility to acid-etching, thus the null-hypothesis is rejected.