RESUMEN
AIM: The aim of this study was to evaluate the efficacy of different lengths of time of passive ultrasonic irrigation (PUI) in removing calcium hydroxide (CH) paste from root canal, using scanning electron microscopy and energy dispersive spectrometry (SEM/EDS). MATERIAL AND METHODS: Fifty-four human premolars were used. After coronal access, a size #15 K-file was used to obtain apical patency. Root canal preparation was performed using WaveOne 40.08 instruments. CH paste was placed into the root canal. Specimens were stored in a humid environment, and after seven days, they were divided into five groups (n=12) according to the irrigation protocols: Manual a size #40 K-file; PUI/1 1 min; PUI/2 2 min; PUI/3 3 min; and Control without CH paste. An elementary chemical microanalysis (SEM/EDS) was performed to quantify the presence of calcium on the dentinal walls. RESULTS: The percentage of calcium was higher in all experimental groups when compared to the control group (P < 0.05); but no differences among them were found (P > 0.05). CONCLUSION: The amount of calcium hydroxide paste on the dentinal walls was not dependent on length of time of ultrasonic activation. SEM/EDS analysis seems to be a reliable method to assess CH paste removal from the root canals.