RESUMEN
Objective: this study aimed to assess the effectiveness of Passive Ultrasonic Irrigation (PUI) with different so-lutions for calcium hydroxide (Ca(OH)2) removal. Ma-terials and method: forty-eight single-rooted mandibu-lar premolars were prepared and filled with Ca(OH)2. After 15 days, the specimens were randomly divided into four groups according to the method of removal of the intracanal medication (n=12). In Group 1, Ca(OH)2removal was performed through conventional irrigation with 2.5% NaOCl and 17% EDTA combined with the use of the 'master apical file' at working length. Groups 2 and 3 were treated in the same manner as Group 1, following the PUI with 2.5% NaOCl and 17% EDTA, and 2.5% NaOCl and 10% citric acid, respectively. Group 4 served as a control group and received no intracanal medication. The roots were longitudinally grooved and split in two halves. The half with the higher remaining amount was analyzed with a stereomicros-cope, and the percentage of surface area covered by the remaining Ca(OH)2 in relation to the total surface area and the surface area of each third of the root canal was calculated. The results were statistically analyzed with the Kruskal-Wallis Test and Mann-Whitney Test. Null hypothesis was set as 5%. Results: none of the groups tested showed similarity to the control group (P < 0.05)...