root canal dressings are used usually during the endodontic treatment of teeth with 
 apical periodontitis .
calcium hydroxide is considered the standard intracanal medication 
 because of its antibacterial effect . 

however , clinical studies have shown that it is not possible to sterilize the root 
 canals in necrotic teeth even using calcium hydroxide dressings . 

for these reason , new compounds as chlorhexidine , antibiotics , and natural compounds as 
 propolis has been suggested to be used as alternative intracanal medications .
propolis in its crude form , as an extract , is not ideal for the endodontic use , 
 therefore shows characteristic resinous and sticky .
( 2009 ) reached a 
 propolis paste formulation for endodontic use using the lowest concentration of crude 
 extract of propolis which retains its biological activity .
other authors have shown that 
 propolis can be useful as a root canal dressing due to its low toxicity and broad 
 antibacterial spectrum .
in addition to the antimicrobial properties , intracanal medications must be easily 
 removed from the root canal walls .
the obstruction of dentinal tubules , by 
 either smear layer or intracanal medication can impair the performance of the endodontic 
 sealers .
the penetration of the sealers into dentinal tubules improves the seal by 
 increasing the contact surface to the root canal walls .
the purpose of this study was to evaluate the cleaning of the root canal walls after the 
 placement of calcium hydroxide- or propolis - based intracanal medications , using scanning 
 electron microscopy ( sem ) .
twenty freshly extracted single - rooted human teeth from the department of dental 
 materials , restorative dentistry and endodontics , bauru school of dentistry , brazil , 
 were used .
conventional pulp chamber access procedures using spherical diamond and endo 
 z drills ( dentsply ind . e com .
petrpolis , rj , brazil ) were used and the working 
 length determination was established at 1 mm from the apical foramen using a 10 k - file . 

cleaning and shaping of the root canals was performed until the diameter of a 60 k - file 
 using 1 ml of 1% sodium hypochlorite .
a final rinse with 2 ml of 17% edta for 3 min and 
 finally 1 ml of 1% sodium hypochlorite were used .
the root canals were dried using 
 conventional paper points , and the teeth were divided into four experimental groups 
 ( n=5 ) .
group i - no drug ( control ) , group ii - calcium hydroxide / distilled water paste , 
 group iii - propolis paste a70d , group iv - propolis paste d70d .
the pastes were 
 introduced into the root canals using an engine driven lentulo instrument ( dentsply ind . 
 e com .
, the medications were removed using a k- file and 5 ml of 1% 
 sodium hypochlorite .
finally , the canals were flushed with 2 ml of 17% edta for 3 min , 
 and final irrigation was performed with 1 ml of saline . for sem analysis ,
the crowns of teeth were removed and the roots were cleaved using a 
 hammer and chisel .
the root segments were sputter - coated with gold in a sputter - coating 
 unit ( denton vacuum inc . , morristown , nj , usa ) and
the middle third of the root canal 
 walls examined at 750x with a scanning electron microscope ( jsm , 220a , jeol tokyo , 
 japan ) .
cleaning of the root canal walls was analyzed with regard to the number of 
 patent dentinal tubules using the image tool 3.1 software ( uthscsa , san antonio , texas , 
 usa ) ( figure 1 ) .
statistical analysis was performed to show differences 
 in the number of open dentinal tubules among the four analyzed groups using anova and 
 tukey 's test ( p<0.05 ) .
red points : open dentinal tubules ( image 
 tool software ) . scanning electron microscopy
cleaning of the root canal walls was indicated by the mean of number of patent dentinal 
 tubules .
the non - medicated control group was significantly cleaner than the others , with 
 a larger number of patent dentinal tubules ( 229.842.04 ) ( p<0.05 ) .
there was no statistically significant difference ( p>0.05 ) among the other groups - 
 group ii ( calcium hydroxide : 142.367.02 ) , group iii ( propolis paste a70d : 12711.69 ) 
 and group iv ( propolis paste d70d : 147.336.51 ) -showing that cleaning of the root canal 
 walls decrease after the use of the intracanal medications .
a panel of representative sem micrographs of the four experimental groups is shown in 
 figure 2 .
scanning electron microscopy micrographs representative of the four groups : a  
 control ( no drug ) ; b 
interference of the smear layer or intracanal medications decrease the sealing ability 
 of endodontic sealers , and it is 
 basically due to the difficulty to remove them from the root canal walls , as 
 demonstrated by porkaew , et al . 
 ( 1990 ) and calt & serper ( 1999 ) . 
 as propolis paste is an experimental drug , it was necessary to know the performance of 
 this material , after its introduction and removal from root canals .
the choice for the use of sodium hypochlorite and edta , as a final rinse , was based on 
 previous studies .
the analysis 
 of the middle root canal third was defined by the findings of other authors , who described the facility to view the 
 dentinal tubules at the middle and cervical third due to the larger these regions in 
 comparison to the apical third , allowing greater movement of irrigating solutions 
 facilitating the removal of smear layer and consequently the intracanal medication .
the results of this study confirmed the findings of the literature about the difficulty 
 of cleaning the root canal walls after use of calcium hydroxide dressing .
in contrast , 
 when the root canals did not receive the intracanal medication , only final cleaning with 
 sodium hypochlorite and edta , the dentinal tubules were cleaner without the presence of 
 smear layer in comparison to the groups that received medication .
the difficulty to 
 eliminate the experimental propolis pastes was similar to that observed for calcium 
 hydroxide and , in some cases , it was observed the presence of precipitations , as 
 reported by giamalia , et al .
it should be noted the effect of edta on the intracanal medicaments because the findings 
 of a pilot - study showed that without its use the canal walls were completely 
 smear - covered with no patent dentinal tubules . since there was no difference between the two propolis pastes in this experimental 
 study , the election of one of the pastes over the other will depend on their performance 
 in biological studies , which are currently being developed .
removal of experimental propolis pastes from the root canals was difficult and similar 
 to that observed for calcium hydroxide paste , which is a standard intracanal dressing . 

therefore , the experimental propolis pastes a70d and d70d presented acceptable physical 
 characteristics to be used as intracanal medicaments .
 objetives the aim of this study was to investigate through scanning electron microscopy 
 ( sem ) the cleaning of root canal walls after the use of experimental propolis or 
 calcium hydroxide root canal dressings . 
 material and methods twenty single - rooted teeth were used . 
 after conventional cleaning and shaping 
 procedures and removal of the smear layer with 17% edta , the teeth were divided 
 into four groups according to the medication used ( n=5 ) : group i ( control ) - no 
 drug , group ii - calcium hydroxide dressing , group iii - propolis paste a70d and 
 group iv - propolis paste d70d . 
 the medications were introduced into the root 
 canals and maintained for 7 days , then removed with a k - file and 5 ml of 1% sodium 
 hypochlorite irrigation . finally , the canals were flushed with 2 ml of 17% edta 
 for 3 min . for sem analysis 
 , the roots were cleaved and microphotographs from the 
 middle third of the root canal were taken at 750x . 
 the cleaning of the root canal 
 walls was determined by the number of open dentinal tubules as verified with the 
 software image tool 3.1 . 
 the statistical analysis was performed by anova and 
 tukey 's test ( p<0.05 ) . 
 results the results showed no statistically significant difference between the calcium 
 hydroxide and propolis groups . 
 conclusions the experimental propolis pastes presented acceptable physical characteristics to 
 be used as intracanal medicaments . 