Influence Of The Root Canal Instrumentation Size On The Disinfection Of Intracanal Microbe By Er:YAG Laser

Objectives:The purpose of this study was to evaluate the influence of the different root canal instrumentation size on the disinfection of intracanal E. faecalis and C. albicans of dental root canal by using Er:YAG laser combination of 3% Na OCl,17% EDTA and 0.9% saline.Methods:368 extracted human anterior teeth with single straight root were randomly divided into 8 groups of 46 roots each. They were instrumented with K3 Ni-Ti files as follows:group A1 and group B1(#25/0.06)?group A2 and group B2(#30/0.06)?group A3 and group B3(#35/0.06)?group A4 and group B4(#40/0.06). After prepared and sterilized by autoclaving,group A were inoculated with Enterococcus faecalis for 4 weeks, and group B were inoculated with Candida albicans for 3 weeks. After inoculation of intracanal E.faecalis and C.albicans were finished, all groups were irrigated as follows: Er:YAG laser+3% Na OCl,Er:YAG laser+17% EDTA and Er:YAG laser+0.9% saline. Then the numbers of microbe on the surface of root canal walls were counted a fter the treatment, the absolute reduction of CFUs and the relative residual rate of CFUs in the individual group was determined. An additional 4 samples were random drawing from group A and group B,Samples were processed then submitted to scanning electron microscopy so that we could evaluate the morphological changes of apical third of root canals.Results:Levels of disinfection on E.faecalis and C.albicans increased when root canals were enlarged; #40/0.06 shows the best disinfection,#35/0.06 shows a significantly better disinfection than #30/0.06 and #25/0.06. Substantial reduction of microbe was obtained in #35/0.06 and #40/0.06 compared with #25/0.06 and #30/0.06(P < 0.05). Scanning electron microscopy examination demonstrated that improved cleaning root canal surfaces and exhibited open dental tubules were increased when root canals were enlarged,however,scattered residual debris remain on the root canal surface and in tubules.Conclusion:Within the root canal size of #25/0.06~#40/0.06,under the conditions of Er:YAG laser combination of 3% Na OCl,17% EDTA and 0.9% saline,it was concluded that the reduction of Enterococcus faecalis and Candida albicans of the anterior straight root canals could be predicted by increasing the root canal instrumentation size large than #30/0.06.