Abstract: 　　　[Abstract] Objective To research effective endodontic irrigation protocols on smear layer removal from curved canals.Methods Forty mandibular first molars with curved mesial root canal were selected,decoronated. Mesiobuccal root canal was instrumented to F3 using handed Protaper system,and randomly divided into four groups according to final irrigation protocols. They are group A:syringe irrigation;group B:#30K File agitation;group C:passive ultrasonic irrigation (PUI);group D:combination of #30K File agitation and PUI. Ultrasonic file was located within 0.5mm coronally from start of the curvature. All root canal were mesio-distally split,snicked at start of the curvature and 2mm apically from start of the curvature ,and divided into three sections.They are Ⅰ,Ⅱ,Ⅲfrom coronally to apically. Smear layer of each section of root canal was examined under scanning electron microscope(SEM). Result Group D presented small amounts of scattered or thin smear layers and obtaind the lowest score at each section of root canal wall. At sectionⅠandⅡ,there was not significant difference for smear layer score between Group D and Group C ,and they were both lower than Group A,B(P<0.05); At section Ⅲ, Group D showed lower score than Group A,B,C, while Group B,C were lower than Group A (P<0.05). Conclusion When ultrasonic file was located coronally from start of the curvature, to apply K File which was the same size as dimension of apical portion preparation to agitate and PUI can remove smear layer from curved canals efficiently.

Key words: 　root canal preparation, curved canals, smear layer, apical portion preparation, passive ultrasonic irrigation