Citric acid is a biologic organic acid used in the endodontic, periodontics and dentistry therapies. Preliminary experimental researches have demonstrated the low irritating potential of this acid when compared with chelating agents. Concentration is an important factor associated with efficiency and biocompatibility of the acids. Objective: the aim of this study was to evaluate, by the Evans blue test, the irritating potential of citric acid (pH 1.0) in different concentrations (1%, 5%, 10% and 25%). Method: eight adult male Wistar rats, per group, were anesthetised (ketamine/xylazine) and four experimental sites were designed in their backs. Injections of 2% Evans blue (20mg/kg) were given intravenously into the lateral caudal vein. 0,1mL of the solutions tests was injected intradermally into the experimental sites. The animals were killed 30 minutes, 1, 3 and 6 hours after injection of the solutions, and each piece of skin containing the lesion was submerged in formamide (10mL) and incubated at 45oC for 72h. After filtration, the optical density was measured in a spectrophotometer (A620). The data were statistically analysed by 2-way non-parametric test (Friedman Repeated Measures Analysis of Variance on Ranks). Results: there was no statistical difference between all solutions at the 30min., 3h and 6h times studied (p<0.05). At 1h time, there was statistical difference between 10% and 25% (p<0.05), but not between 1% and 5% groups. The highest median values were observed at 3h time specimens. When comparing the substances in each time period, the 5% and 25% groups had similar results. At 10% group was noted statistical difference between 3h and the other period of time (p<0.01). No differences were found between the specimens in the 1% group. Conclusion: the results showed the similarity of citric acid irritating potential in different time periods despite the increasing of concentration. Supported by FAPESP 01/10672-9.

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