关键词: 玷污层, 扫描电镜, 超声波, Nd：YAG激光

Abstract: Objective    To compare the ability of five techniques on cleanness at the apical third of root. Methods    Sixty extracted single-rooted human teech ，randomly distributed into 6 groups ，were prepared by using Protaper rotary instruments and subjected to different techniques on removal of smear layer；hydrogen peroxide and normal saline（ group A）； 5.25%sodium hypochlorite（NAOCL） and ethylenediamine tetraacetis（EDTA） gel （group B），irrigation with ultrasonics（group C）； with Nd：YAG laser（ group D）， EDTA gel and ultrasonics with normal saline irrigation （group E）；EDTA gel and ultrasonics with 5.25% NAOCL irrigation （ group F）. Samples were examined under the scanning electron microscope （SEM） and scored for cleanness at the apical third of root and the condition of dentin tubule. Results    In group A the apical root and dentine tubules were covered by smear layer. The smear layer of the other 5 groups were cleared partly.There were significant difference bwteen group A and other groups（P < 0.05）. There were no significant difference between the group D and group E（P > 0.05）. There were significant difference among  the other tested groups（P < 0.05）. Conclusion    the smear layer at the root tip can be removed effectively  by using chemical ，ultrasonics and Nd：YAG laser. EDTA gel combined with ultrasonics and 5.25% NAOCL irrigation （group F） was best.

Key words: smear layer, scanning electron microscope（SEM）, ultrasonics, Nd：YAG laser