the success of root canal therapy depends on the method and the quality of instrumentation , irrigation , disinfection , and three - dimensional obturation of the root canal .
endodontic instrumentation using either manual or mechanized techniques produces a smear layer and plugs of organic and inorganic particles of calcified tissue .
the smear layer contains additional organic elements such as pulp tissue debris , odontoblastic processes , microorganisms , and blood cells in the dentinal tubules .
a smear layer can create a space between the inner wall of the root canal and the obturating materials , thus preventing the complete locking and adherence of the root canal filling materials into the dentinal tubules .
it also contains bacteria and bacterial by - products and thus must be completely removed from the root canal system . in addition , removal of the smear layer can allow intracanal medicaments to penetrate the dentinal tubules for better disinfection . among the different root canal irrigants for removal of smear layer , sodium hypochlorite , ( naocl ) , and ethylene diamine tetra - acetic acid ( edta ) solution
mtad , containing 3% doxycycline , 4.25% citric acid , and detergent ( tween 80 ) , has been shown to be clinically effective in removing the smear layer when used along with naocl .
however , few reports suggest that the microhardness of dentin decreases when they are exposed to naocl or edta , or mtad .
it has been indicated that microhardness determination can provide indirect evidence of mineral loss or gain in the dental hard tissues .
it has been reported that these kinds of chemical irrigants caused alterations in the chemical structure of human dentin and changed the ca : p ratio of the dentin surface .
any change in the ca : p may change the permeability and solubility characteristics of dentin which may also affect the quality of its adhesion to root canal sealers .
moreover , edta and citric acid ( component of mtad ) strongly reacts with sodium hypochlorite , thus rendering the latter agent ineffective .
therefore it is necessary to find a new , safe , and effective irrigating regimen during root canal preparation . a soft chelating irrigation protocol with etidronic acid , also known as 1-hydroxyethylidene-1 , 1-bisphosphonate
( hebp ) or etidronate , has been proposed as a potential alternative to edta or citric acid because of its chelating ability.[1113 ] it shows no short - term reactivity with sodium hypochlorite .
however the effect of hebp on microhardness of root dentin has not been evaluated so far in the literature .
therefore , the purpose of this study was to evaluate the effect of 18% hebp solutions as a final rinse on the microhardness of human root canal dentin in comparison with 17% edta and mtad using vicker 's microhardness test .
forty human single - rooted mandibular premolars , recently extracted for orthodontic reasons , were used for this study .
the teeth were decoronated at the cementoenamel junction sectioned longitudinally starting from cervical with a low speed diamond saw ( isomet , buehler ltd . ,
the separated buccal and lingual root segments were horizontally mounted in autopolymerising acrylic resin so that their dentin was exposed .
the dentin surfaces of the mounted specimens were grounded smooth with a series of increasingly fine emery papers ( shor international corporation , mt .
vernon , ny , usa ) under distilled water to remove any surface scratches , and finally polished with 0.1 m alumina suspension ( ultra - sol r , eminess technologies inc . ,
all the groups were treated with different irrigants as per the following protocol : 
 group i : the specimens were treated with distilled water ( control).group ii : the specimens were treated with 1.3% naocl ( prime dental products ltd . , mumbai , india ) for 20 minutes followed by 17% edta ( dent wash prime dental products ltd . ,
mumbai , india ) for 1 minute.group iii : the specimens were treated with 1.3% naocl for 20 minutes followed by mtad ( dentsply tulsa dental , tulsa , ok , usa ) for 5 minutes.group iv : the specimens were treated with 1.3% naocl for 20 minutes followed by 18% hebp for 5 minutes . 
 
group ii : the specimens were treated with 1.3% naocl ( prime dental products ltd . ,
mumbai , india ) for 20 minutes followed by 17% edta ( dent wash prime dental products ltd . , mumbai , india ) for 1 minute .
group iii : the specimens were treated with 1.3% naocl for 20 minutes followed by mtad ( dentsply tulsa dental , tulsa , ok , usa ) for 5 minutes .
group iv : the specimens were treated with 1.3% naocl for 20 minutes followed by 18% hebp for 5 minutes .
hebp solutions were freshly prepared by mixing the hebp powder ( zschimmer and schwarz mohsdorf gmbh and co. , kg , burgstadt , germany ) with bi - distilled water to w / v concentrations of 18% .
the surface hardness of the root dentin was determined in each specimen with a vicker 's hardness tester ( matsuzawa mmt-7 , matsuzawa seiki co. , ltd . ,
the indentations were made with a vicker 's diamond indenter at a minimum of three widely separated locations .
the locations were chosen in apical , middle , and cervical region of the root canal wall .
the indentations were made on the cut surface of each specimen using 300 g load and a dwell time of 20 seconds .
the microhardness data were tabulated and statistically analyzed by one - way anova and the inter group comparison of means was conducted using a post hoc tukey 's multiple comparison test .
forty human single - rooted mandibular premolars , recently extracted for orthodontic reasons , were used for this study .
the teeth were decoronated at the cementoenamel junction sectioned longitudinally starting from cervical with a low speed diamond saw ( isomet , buehler ltd . ,
the separated buccal and lingual root segments were horizontally mounted in autopolymerising acrylic resin so that their dentin was exposed .
the dentin surfaces of the mounted specimens were grounded smooth with a series of increasingly fine emery papers ( shor international corporation , mt .
vernon , ny , usa ) under distilled water to remove any surface scratches , and finally polished with 0.1 m alumina suspension ( ultra - sol r , eminess technologies inc . ,
all the groups were treated with different irrigants as per the following protocol : 
 group i : the specimens were treated with distilled water ( control).group ii : the specimens were treated with 1.3% naocl ( prime dental products ltd . , mumbai , india ) for 20 minutes followed by 17% edta ( dent wash prime dental products ltd . ,
mumbai , india ) for 1 minute.group iii : the specimens were treated with 1.3% naocl for 20 minutes followed by mtad ( dentsply tulsa dental , tulsa , ok , usa ) for 5 minutes.group iv : the specimens were treated with 1.3% naocl for 20 minutes followed by 18% hebp for 5 minutes . 
 
group ii : the specimens were treated with 1.3% naocl ( prime dental products ltd . ,
mumbai , india ) for 20 minutes followed by 17% edta ( dent wash prime dental products ltd . , mumbai , india ) for 1 minute .
group iii : the specimens were treated with 1.3% naocl for 20 minutes followed by mtad ( dentsply tulsa dental , tulsa , ok , usa ) for 5 minutes .
group iv : the specimens were treated with 1.3% naocl for 20 minutes followed by 18% hebp for 5 minutes .
hebp solutions were freshly prepared by mixing the hebp powder ( zschimmer and schwarz mohsdorf gmbh and co. , kg , burgstadt , germany ) with bi - distilled water to w / v concentrations of 18% .
the surface hardness of the root dentin was determined in each specimen with a vicker 's hardness tester ( matsuzawa mmt-7 , matsuzawa seiki co. , ltd . ,
the indentations were made with a vicker 's diamond indenter at a minimum of three widely separated locations .
the locations were chosen in apical , middle , and cervical region of the root canal wall .
the indentations were made on the cut surface of each specimen using 300 g load and a dwell time of 20 seconds .
the microhardness data were tabulated and statistically analyzed by one - way anova and the inter group comparison of means was conducted using a post hoc tukey 's multiple comparison test .
the mean and standard deviation values of the root dentin microhardness data for the control groups and 17% edta , mtad , and 18% hebp groups are listed in table 1 .
the microhardness values of control ( group i ) , edta treated ( group ii ) , mtad treated ( group iii ) , and hebp treated ( group iv ) groups were 66.65  1.04 , 51.63  0.86 , 42.85  0.99 , and 53.74  1.18 , respectively .
intergroup comparison showed that the reduction in microhardness was statistically significant among the experimental groups as well as between the experimental and control group ( p<0.001 ) .
current concepts of chemo - mechanical preparation imply that chemicals should be applied on instrumented root canal surfaces in order to remove the smear layer following mechanical preparation .
it has been proved that different irrigant activation protocols enhance the action of chelating agents .
but the objective of our investigation was only to assess the chemical action of chelating agent as final rinse on the microhardness of root dentin .
the irrigating regimens in all the experimental groups were standardized to 20 minutes of 1.3% naocl , which represents the working solution , followed by a final rinse 17% edta for 1 minute in group ii mtad for 5 minutes in group iii and 18% hebp for 5 minutes in group iv .
the changes in the apatite / collagen ratio and flexural strength of mineralized dentin were also found to be insignificant with 1.3% naocl for 20 minutes .
the process of the smear layer removal is usually more efficient in the coronal and middle third of the canals in the absence of surfactant . a relatively small canal diameter in the apical one - third exposes the dentin to a lesser volume of irrigants and hence compromising the efficiency of smear layer removal
. therefore tooth specimens were split longitudinally to ensure complete distribution of irrigants throughout the root canal system .
the ability of vicker 's microhardness test to detect surface changes after chemical treatment with edta and citric acid solutions for smear layer removal has been demonstrated .
as microhardness of dentin may vary considerably within the same tooth , three indentations were made in the cervical , middle , and apical root canal wall and the means for each sample were calculated . in our study , the microhardness of the root dentin specimens following exposure with chelating agents reduced drastically when compared with the nontreated specimens ( control group ) .
the microhardness of root dentin following mtad as a final rinse was significantly less when compared to that of edta .
this difference could be attributed to the increased depth of demineralization of mtad ( 812 m ) in relation to edta ( 24 m ) .
it has also been showed that mtad and 5% citric acid had higher demineralization kinetics compared to 17% edta .
this could be attributed to the larger intertubular dentin area available for hybridization when a soft chelating irrigation protocol using hebp is applied .
it has been suggested that the total available area of intertubular dentin is an important aspect in the hybridization process .
the major retention is provided by micromechanical interactions of the bonding agent with the collagen matrix and the underlying mineralized zone in the intertubular dentin .
accordingly , hebp increased the bond strength of resin - based sealers to root canal dentin compared with edta and mtad .
moreover , there is evidence that partial depletion of surface ca may significantly alter the bond strength of some adhesive materials .
the bonding quality of resin - based obturation material to root dentin has been evaluated following a soft chelating irrigation protocol by performing micropush - out and shear bond strength assessment
. however , these bond strength values are useful only in indirect understanding the influence of a different irrigation protocol on dentin demineralization .
the important aspect pertaining to the use of a soft chelating solution is the depth of demineralization which decides the sealing ability .
under the limitations of the study , hebp as a final rinse appears to be a promising irrigation protocol with less impact on the mineral content of root dentin .
however , further studies are required on the depth of demineralization and the sealing ability of resin - based sealers with the radicular dentin to provide more information on the clinical performance of hebp .
 context : evaluation of microhardness of root dentin provides indirect information on the change in mineral content of root dentin thereby providing useful information on the bonding quality of resin - based root canal sealers.aim:this study evaluated the effect of 17% edta , mtad , and 18% hebp solutions on the microhardness of human root canal dentin using the vickers microhardness test.materials and methods : forty human single - rooted teeth were decoronated at the cementoenamel junction and sectioned longitudinally into buccal and lingual segments . 
 eighty specimens were divided into four groups ( n=20 ) . 
 group i was treated with distilled water ( control ) , groups ii , iii , and iv were treated with 1.3% naocl as a working solution for 20 minutes followed by 17% edta , mtad , and 18% hebp respectively . 
 the surface hardness of the root dentin was determined in each specimen with a vicker 's hardness tester . 
 the values were statistically analyzed using the one - way anova and post hoc tukey multiple comparison tests.results:there was a statistical significant difference among all the groups ( one - way anova ; p<0.001 ) . among the experimental groups , hebp showed the highest dentin microhardness ( 53.74 mpa , p<0.001 ) . 
 least microhardness was found with mtad ( 42.85 mpa , p<0.001).conclusions : hebp as a final rinse appears to be a promising irrigation protocol with less impact on the mineral content of root dentin . 
INTRODUCTION
MATERIALS AND METHODS
Specimen preparation
Statistical analysis
RESULTS
DISCUSSION
CONCLUSION