Objective: Compare the area of calcium hydroxide (Ca(OH)2) remaining in the apical third of curved canals after sonic and ultrasonic activation using Scanning Electron Microscope (SEM). Methodology: Permanent mandibular molars were collected. Were included mesial roots that radiographically presented a curvature between 15° and 30°. 39 mesiolinguales root canal were instrumented rotary ProTaper and filled with Ca(OH)2 mixed with propylene glycol. They were randomly divided into 3 groups according to the type of removal. Group I, three inserts with lime F2 irrigating with 2 mL of sodium hypochlorite (NaOCl) 5.25% for each insertion. Group II, three sonic activations, irrigating with 2 mL 5.25% NaOCl between activations. Group III, three ultrasonic activations irrigating with 2 mL 5.25% NaOCl between activations. were left 3 root canal and other 3, unfilled and with total filling respectively as positive and negative controls. After longitudinally fractured obtaining two sections, the apical third of the root canal of each section is microfotografio SEM and then in an area of 100.000 um2, the surface with Ca(OH)2 remaining in both sections is measured using ImageJ 1.47. Were analyzed with one-way ANOVA using GraphPad Prism 5.01. Results: The percentage of area with Ca(OH)2 remaining in group I was 62.93%. Group II, 51.77%. Group III 58.90%. There was no significant difference between the three groups (P> 0.01) Conclusion: No significant differences in the percentage of area with Ca(OH)2 remaining in the apical third of curved canals, comparing sonic ultrasonic activation using SEM. Keywords: Endodontics, Calcium Hydroxide, Removal, Sonic, Ultrasonics. Activacion sonica versus ultrasonica en remocion de hidroxido de calcio en conductos curvos: estudio in-vitro. Objetivo: Comparar el area de hidroxido de calcio (Ca(OH)2) remanente en el tercio apical de conductos curvos, tras activacion sonica y ultrasonica, utilizando Microscopio Electronico de Barrido (MEB).Metodologia: Se recolectaron molares mandibulares permanentes. Se incluyeron los que en la raiz mesial presentron radiograficamente una curvatura entre 15o y 30°. Se instrumentaron 39 conductos mesiolinguales con ProTaper rotatorio y se rellenaron con Ca(OH)2 mezclado con propilenglicol. Se dividieron aleatoriamente en 3 grupos de acuerdo al tipo de remocion. Grupo I: tres inserciones con lima F2 irrigando con 2 mL de hipoclorito de sodio (NaOCl) 5.25% entre cada insercion. Grupo II: tres activaciones sonicas, irrigando con 2 mL NaOCl 5.25% entre activaciones. Grupo III: tres activaciones Ultrasonicas irrigando con 2 mL NaOCl 5.25% entre activaciones. Se dejaron 3 conductos sin rellenar y otros 3 con relleno total como controles positivo y negativo respectivamente. Luego se fracturaron longitudinalmente obteniendo 2 secciones, se microfotografio el tercio apical del conducto radicular de cada seccion con MEB y posteriormente en un area de 100.000 um2, se midio la superficie con Ca(OH)2 remanente de ambas secciones usando ImageJ 1.47. Se analizo con ANOVA de una via usando GraphPad-Prism 5.01.Resultados: El porcentaje de area con Ca(OH)2 remanente del grupo I fue 62.93%. Grupo II, 51.77%. Grupo III 58.90%. No hubo diferencia significativa entre los tres grupos (P>0.01)Conclusion: No hay diferencias significativas en el porcentaje de area con Ca(OH)2 remanente del tercio apical de conductos curvos, al comparar la activacion sonica con la ultrasonica, utilizando MEB. Palabras clave: Endodoncia, Hidroxido de Calcio, Remocion, Sonico, Ultrasonico.