it has been proven that the quality of the permanent coronal restoration has a great influence on the overall prognosis of endodontically treated teeth.15 in contemporary dental practice , the opportunity of restoring such teeth with resin composite has been increased as a result of the continuous revolution in the adhesive systems formulation . bonded resin restorative materials permit transmission of functional stresses across the bonded interface to the tooth , with the potential to reinforce the weakened tooth structure.6,7 nevertheless , chemical irrigants employed during root canal treatment to provide gross debridement , lubrication , destruction of microbes , and dissolution of tissues , result in alteration of the chemical and mechanical characteristics of dentin , which affects its interaction with the restorative materials used for coronal sealing.8 the most commonly used irrigating solutions are sodium hypochlorite ( naocl ) and chlorhexidine gluconate ( chx ) . naocl has a unique tissue solvent ability in addition to its well documented potent antimicrobial activity . while chx , being similarly antibacterial and relatively non - toxic to the periapical tissues forms an alternative irrigant to sodium hypochlorite.9 the adverse effects of naocl on resin - dentin bond have been investigated previously.8,1014 although the effect of chx on resin / dentin adhesion is still unclear,15 recent studies reported that chx could prevent the degradation of the collagen fibres and preserve the integrity of the hybrid layer.1618 the self - etching approach is based on simultaneous conditioning and priming of dentin with incorporation of the smear layer within the hybridized complex.19,20 the single - step self - etching adhesives are less technique sensitive and less time consuming compared with their multi - step counterparts . this might be of an importance , especially for the busy dental practitioners.21 the permanent restoration can be applied immediately after completion of endodontic treatment , or can be postponed for some time and a temporary restoration is used to seal the access cavity . the question then arises : would such a delaying in the bonding procedures affect the resin / dentin bond strength ? the purpose of this study is to evaluate the outcome of either immediate or delayed application of a single - step self - etching adhesive to coronal dentin after the application of different endodontic irrigants . the null hypothesis tested is neither irrigating solutions nor application time has an influence on the shear bond strength of the single - step self - etching adhesive to coronal dentin . thirty five human molars extracted for periodontal reasons , and stored in 0.5% thymol solution at 4c for not more than one month were used in this study . twenty eight teeth were used for shear bond strength testing and seven teeth were used for sem evaluation . each tooth was sectioned mesio - distally down to the root using a diamond disc mounted on a low speed contra angle with a copious air - water spray . the experimental specimens were subdivided into three equal groups representing the three tested irrigants ; 0.9% physiologic saline solution ( ns , al mottahedoon pharma , 10 ramadan city , cairo - egypt . lot # 61212 ) , 2% chlorhexidine gluconate in water solution ( chx , cairo pharmaceuticals , cairo - egypt , lot # 2005323 ) , and 2.5% commercially used sodium hypochlorite solution . each group was further subdivided into two equal subgroups according to the adhesive application time , either immediate or delayed for one week after completion of the irrigating procedures . each specimen was encircled with a rectangular mould ( figure 1a ) into which auto - cured acrylic resin ( acroston , under exclusive license of acroston dental company - cairo , egypt ) was poured . the control specimens were fixed on the base of the mould from their dentin side using a double face adhesive tape . while the experimental specimens were fixed using a double layer of pink wax in order to create artificial side walls ( figure 1b ) . after setting of the acrylic material , the coronal dentin was wet ground using a high speed abrasive bur ( 016 , 6835 kr . komet , usa ) with gentle pressure for 5 seconds in one direction to create a smear layer . the dentin surfaces were rinsed with copious air - water spray for 10 seconds and the specimens were stored in distilled water at room temperature . the coronal dentin of the control specimens were restored directly without the use of the different irrigants . a single - step self - etching adhesive , clearfil s bond in a single - dose form , ( kuraray medical inc , okayama , japan . the self - etching adhesive was applied with gentle agitation using the supplied micro - brush and left undisturbed for 20 seconds . the adhesive was then air - dried with high pressure oil - water free compressed air for 5 seconds and light cured for 10 seconds using a halogen light curing unit ( cromalux - e , meca - physik dental division , rastatt , germany ) with an output of 600 mw / cm . the solution was renewed every 2 minutes so that the dentin surface was kept moist throughout this period . after being rinsed with 10 ml distilled water , half of the specimens received immediate adhesive application as for the control specimens , while the other half were sealed with sterile cotton and a temporary restorative material ( coltosol , coltene g , altsatten , sweitzerland ) and kept in an incubator in 100% relative humidity at 37c for one week . after this period the temporary restorations were removed , the specimens were rinsed using copious air / water spray for 10 seconds and gently air dried for 5 seconds , before the application of the adhesive . the irrigation and bonding procedures are summarized in table 1 . a transparent polyvinyl tube ( 3 mm in diameter and 2 mm in length ) was filled with resin composite material ( tph spectrum , shade a3 , dentsply , konstanz , germany , lot # e617014 ) , placed over the cured adhesive , and the composite material was cured for 40 seconds . after curing of the composite material , the polyvinyl tube was cut using bard parker blade # 15 and the specimens were stored in distilled water for 24 hours . for shear bond strength testing , 8-specimens form each group each specimen was mounted to a universal testing machine ( lloyd instrument lr5k series- london , uk ) and a chisel bladed metallic instrument was positioned as close as possible to the composite / dentin interface from the occlusal enamel side , in which no artificial acrylic wall was present ( figure 1c ) . the test was run at a crosshead speed of 0.5 mm / minute until failure . the load recorded in newton was divided over the surface area and the shear bond strength was calculated in megapascal ( mpa ) . for sem evaluation , 2- specimens were used from each group . after curing of the adhesive , a composite block approximately 2 mm in thickness was used to restore the coronal dentin and was cured for 40 seconds . each half was sectioned cervical to the composite block to separate the dentin surface with its attached composite material from the acrylic block . this procedure was done using diamond disc rotated at low speed with a copious air - water spray . each separated half was further sectioned occluso - cervically into two halves , producing 4 specimens per group . the evaluated dentin surfaces were wet ground using 600 , 1000 and 1200 grits sic . the surfaces were acid etched using 35% phosphoric acid for 10 seconds , rinsed for 15 seconds and gently air dried . the samples were then immersed in 5.25% sodium hypochlorite for 120 seconds , washed under running water for 120 seconds and dried in ascending concentration of alcohol series of 50% , 70% , 90% for 20 minutes each and in 100% for one hour . the specimens were fixed with double - faced stickers on specimen holders , gold sputtered ( bal - tec , scd 005 sputter coater , germany ) , and examined under sem ( philips xl30 , holland ) , operated at 30 kv . all data were expressed as meanstandard deviation ( sd ) in mpa and were analyzed using one - way analysis of variance ( anova ) followed by tukey kramer multiple - comparison post hoc test , which was used to compare the shear bond strength between groups . thirty five human molars extracted for periodontal reasons , and stored in 0.5% thymol solution at 4c for not more than one month were used in this study . twenty eight teeth were used for shear bond strength testing and seven teeth were used for sem evaluation . each tooth was sectioned mesio - distally down to the root using a diamond disc mounted on a low speed contra angle with a copious air - water spray . the experimental specimens were subdivided into three equal groups representing the three tested irrigants ; 0.9% physiologic saline solution ( ns , al mottahedoon pharma , 10 ramadan city , cairo - egypt . lot # 61212 ) , 2% chlorhexidine gluconate in water solution ( chx , cairo pharmaceuticals , cairo - egypt , lot # 2005323 ) , and 2.5% commercially used sodium hypochlorite solution . each group was further subdivided into two equal subgroups according to the adhesive application time , either immediate or delayed for one week after completion of the irrigating procedures . each specimen was encircled with a rectangular mould ( figure 1a ) into which auto - cured acrylic resin ( acroston , under exclusive license of acroston dental company - cairo , egypt ) was poured . the control specimens were fixed on the base of the mould from their dentin side using a double face adhesive tape . while the experimental specimens were fixed using a double layer of pink wax in order to create artificial side walls ( figure 1b ) . after setting of the acrylic material , the coronal dentin was wet ground using a high speed abrasive bur ( 016 , 6835 kr . komet , usa ) with gentle pressure for 5 seconds in one direction to create a smear layer . the dentin surfaces were rinsed with copious air - water spray for 10 seconds and the specimens were stored in distilled water at room temperature . the coronal dentin of the control specimens were restored directly without the use of the different irrigants . a single - step self - etching adhesive , clearfil s bond in a single - dose form , ( kuraray medical inc , okayama , japan . the self - etching adhesive was applied with gentle agitation using the supplied micro - brush and left undisturbed for 20 seconds . the adhesive was then air - dried with high pressure oil - water free compressed air for 5 seconds and light cured for 10 seconds using a halogen light curing unit ( cromalux - e , meca - physik dental division , rastatt , germany ) with an output of 600 mw / cm . the solution was renewed every 2 minutes so that the dentin surface was kept moist throughout this period . after being rinsed with 10 ml distilled water , half of the specimens received immediate adhesive application as for the control specimens , while the other half were sealed with sterile cotton and a temporary restorative material ( coltosol , coltene g , altsatten , sweitzerland ) and kept in an incubator in 100% relative humidity at 37c for one week . after this period the temporary restorations were removed , the specimens were rinsed using copious air / water spray for 10 seconds and gently air dried for 5 seconds , before the application of the adhesive . a transparent polyvinyl tube ( 3 mm in diameter and 2 mm in length ) was filled with resin composite material ( tph spectrum , shade a3 , dentsply , konstanz , germany , lot # e617014 ) , placed over the cured adhesive , and the composite material was cured for 40 seconds . after curing of the composite material , the polyvinyl tube was cut using bard parker blade # 15 and the specimens were stored in distilled water for 24 hours . each specimen was mounted to a universal testing machine ( lloyd instrument lr5k series- london , uk ) and a chisel bladed metallic instrument was positioned as close as possible to the composite / dentin interface from the occlusal enamel side , in which no artificial acrylic wall was present ( figure 1c ) . the test was run at a crosshead speed of 0.5 mm / minute until failure . the load recorded in newton was divided over the surface area and the shear bond strength was calculated in megapascal ( mpa ) . for sem evaluation , 2- specimens were used from each group . after curing of the adhesive , a composite block approximately 2 mm in thickness was used to restore the coronal dentin and was cured for 40 seconds . each half was sectioned cervical to the composite block to separate the dentin surface with its attached composite material from the acrylic block . this procedure was done using diamond disc rotated at low speed with a copious air - water spray . each separated half was further sectioned occluso - cervically into two halves , producing 4 specimens per group . the evaluated dentin surfaces were wet ground using 600 , 1000 and 1200 grits sic . the surfaces were acid etched using 35% phosphoric acid for 10 seconds , rinsed for 15 seconds and gently air dried . the samples were then immersed in 5.25% sodium hypochlorite for 120 seconds , washed under running water for 120 seconds and dried in ascending concentration of alcohol series of 50% , 70% , 90% for 20 minutes each and in 100% for one hour . the specimens were fixed with double - faced stickers on specimen holders , gold sputtered ( bal - tec , scd 005 sputter coater , germany ) , and examined under sem ( philips xl30 , holland ) , operated at 30 kv . all data were expressed as meanstandard deviation ( sd ) in mpa and were analyzed using one - way analysis of variance ( anova ) followed by tukey kramer multiple - comparison post hoc test , which was used to compare the shear bond strength between groups . the results of this study ( table 2 ) , showed that irrigation with ns , chx , or naocl followed by immediate adhesive application resulted in a reduction in the shear bond strength values recorded and this was statistically significant in comparison with the control group ( p<.05 ) . however , delaying the adhesive application resulted in a statistically significant ( p<.05 ) improvement in the shear bond strength recorded in specimens irrigated with ns and chx only . representative sem images for groups g1 , g3 , g4 and g6 are presented in figures 2 , 3 , 4 and 5 , respectively . resin composite restorations are used to restore the access cavity or to function as a foundation restoration in endodontically treated teeth . in both clinical cases it is very important to achieve an excellent bond with dentin.11 loss of endodontically treated teeth due to improper coronal restoration has been reported to be more than the actual failure of the endodontic treatment.3 although immediate sealing using restorative materials after completion of the endodontic treatment is a powerful tool in preventing early coronal leakage,1517,22 the effect of delayed placement of adhesive restorations on the dentin bond strength was not discussed extensively in the literature . this is an important gap in our knowledge ; as such delaying process would affect the resin / dentin bond . the use of self - etching adhesives offers some advantages over the use of the etch and rinse counterparts . self - etching adhesives have weak acids in their primer composition , leading to less change in dentinal wall structure than the strong acids in the etch and rinse systems . also collagen fibril collapse as a result of the air drying procedure after rinsing of acid is eliminated.23,24 following the results of this study , the null hypothesis is rejected . the irrigating solutions and the time of adhesive application influenced the shear bond strength of clearfil s bond to coronal dentin . clearfil s bond is a mild single - step self - etching adhesive21,25,26 with ph2.21 when the coronal dentin was irrigated with the different irrigating solutions used and received immediate adhesive application , the bond strength was adversely affected . ns precipitates sodium and chlorine ions on dentin surface27 which might interfere with the bonding efficiency and resin infiltration of the clearfil s adhesive . the significant improvement in the shear bond strength when the adhesive application was delayed could be attributed to the presence of numerous resin tags infiltration ( figure 3 ) , which resisted the acute debonding stresses22 which could be occurred during bond strength testing . the presence of these numerous resin tags might be due to the elimination of the effect of the precipitated sodium and chlorine ions . as chx is a strong dicationic base with 2 positive charges on either side of the hexamethylene bridge,28 a strong electrostatic bond with the phosphate group of the hydroxyapatite might be formed.29 white et al30 and leonardo et al31 have demonstrated that chx adsorbs to and is released from dentin as long as 48 to 72 hours . the contamination of the dentin surface with irrigating residues and by - products might interfere with resin penetration into the demineralized dentin.32 this explanation confirmed our results , as the adsorption of chx onto dentin interferes with immediate resin infiltration ( figure 4 ) . this is in disagreement with santos et al20 who reported that chx did not affect the bond strength of the self - etch adhesive , clearfil se bond , to the pulp chamber dentin because it is a non - oxidizing agent . in this study , santos et al20 compared the effect of chx with ns as a control , which is not the condition in our study . as adsorption and release of chx from tooth surface takes as long as 4872 hours , with the possible degradation of chx , delaying of adhesive application for one week might negate its interfering action . this result is in consistence with previous studies.1014 the presence of  protein chloramine - derived radicals19 in naocl - irrigated dentin might result in premature chain termination and incomplete resin polymerization10 which leads to reduction in bond strength . although some resin tags were observed in specimens irrigated with naocl that received immediate bonding ( figure 5a ) , these tags showed a porous structure ( figure 5b ) . this porous structure might be attributed to the interfering action of naocl with resin polymerization . inadequately polymerized resin could be evaporated during sem preparation leaving the resin tags with porous structure . delaying the adhesive application for one week this could clarify that the action of these protein chloramine - derived radicals persisted for more than one week . within the limitations of this study , delaying the bonding procedures for one week appeared to be beneficial in improving the shear bond strength for the tested single - step self - etch adhesive to coronal dentin especially when ns and chx were used as endodontic irrigants . naocl proved to be an incompatible irrigant when used prior to the application of such adhesive . further studies should be conducted to evaluate the effect of the different irrigants on the resin / coronal dentin bond strength of the contemporary available adhesives . from the results of this study , if clearfil s bond is intended to be used for restoring endodontically treated teeth , it is preferable to postpone the restorative procedure for one week .
objectives : the aim of this study was to evaluate the outcome of immediate or delayed bonding of a single - step self - etch adhesive to coronal dentin after the application of different endodontic irrigants.methods:thirty five human molars were used . 
 the coronal dentin was irrigated with either 0.9% physiologic saline ( ns ) , 2% chlorhexidine gluconate ( chx ) or 2.5% commercially used sodium hypochlorite ( naocl ) . 
 composite cylinders were bonded with the coronal dentin using the clearfil s3 bond , which was applied either immediately or after one week storage time following the irrigation procedures . shear bond strength testing 
 was performed at a cross - head speed of 0.5 mm / min , and the resin / dentin interface was evaluated using sem.results:irrigation with ns , chx , or naocl followed by immediate adhesive application resulted in a reduction in the shear bond strength values recorded and this was statistically significant in comparison with the control group ( p<.05 ) . however , delaying the adhesive application resulted in a statistically significant ( p<.05 ) improvement in the shear bond strength recorded in specimens irrigated with ns and chx only.conclusions:delaying the bonding procedures for one week appeared to be beneficial in improving the shear bond strength of clearfil s3 bond with coronal dentin especially when ns and chx were used as endodontic irrigants . 
 naocl proved to be an incompatible irrigating solution when used prior to the application of such adhesive .