the major cause for the  failure  of primary endodontic therapy is the persistence of intra- and extra - radicular microbial infections . in every failed case , whenever possible , nonsurgical endodontic retreatment should be preferred in comparison with other radical interventions such as apical surgery or extraction because the nonsurgical retreatment is less invasive and has good long - term survival rates . during nonsurgical endodontic retreatment therapy , for the retrieval of filling materials , several techniques such as hand files , rotary files , and ultrasonic instruments either alone or in combination with heat or solvents have been used .
these removal techniques are dependent on the anatomy , size and regions of the root canal , aged , overfilled or overextended , and/or underfilled or underextended fillings . a combination of methods is frequently preferred to achieve a safe , efficient , and potentially complete removal of the filling materials from the root canal system .
gutta - percha along with different endodontic sealers is the most commonly used filling material .
retrieval of gutta - percha usually does not require a great effort while using the aforementioned techniques either alone or in combination .
however , various evidence - based studies till date have reported that filling material residues , especially sealers present on canal walls and in their microscopic ramifications , may either remain inaccessible or resist dissolution .
in such cases , organic solvents play a vital role in the thorough removal of endodontic sealers .
this facilitates the efficient disinfection of the root canal system and thus the probability of long - term treatment success .
although chloroform is considered as the most effective solvent in nonsurgical retreatment , it has been banned by the u.s .
food and drug administration in 1976 due to its carcinogenic potential and toxicity to the tissues . therefore , various alternatives such as halothane , rectified turpentine , endosol r and e benzene , methyl chloroform , ether , xylene , orange oil , and eucalyptol have been suggested and used for softening of filling materials .
xylene ( dimethylbenzene ) is an aromatic compound and has been reported to be a very efficient solvent for root canal obturating materials .
essential oils such as orange oil , eucalyptus oil , and pine oil are able to dissolve most of the endodontic sealers . they have been reported to be safe , biocompatible , noncarcinogenic , and useful for this purpose .
therefore , they could influence and consequently determine the clinical effectiveness of the commonly used organic solvents .
apexit plus has been studied very well regarding their solubility in various solvents . however , there are as yet no studies that show the effectiveness of the aforementioned solvents on endomethasone n and adseal root canal sealers .
therefore , a simple , reproducible , and cost - effective laboratory study was carried out to comparatively evaluate the effectiveness of eucalyptus oil , orange oil , and xylene in dissolving endomethasone n , apexit plus , and adseal .
standardized stainless steel molds ( 8 mm diameter , 2 mm height ) were used to prepare two hundred and forty samples ( eighty for each endodontic sealer ) .
endomethasone n ( septodont , saint maur , france ) , apexit plus ( ivoclar vivadent , schaan , liechtenstein ) , and adseal ( meta biomed co , cheongju , korea ) had been used in this study and their compositions are shown in table 1 .
composition of different endodontic sealers as provided by manufacturers each sealer was mixed according to the manufacturer 's instructions .
freshly mixed materials were carefully poured into the sample molds placed on a glass slab using a 2 ml syringe to prevent air entrapment , and a microscope slide covered with cellophane strip was then pressed onto the upper surface to make the surface flat .
all samples along with their steel molds were then transferred to a chamber with 80% relative humidity and 37c temperature and left untouched to set sealers for 48 h and then removed from the chamber .
the samples were weighed in grams ( up to four decimal places ) 3 times on an analytical balance ( sartorius te214s , sartorius ag , germany ) .
the samples were then divided into four groups of twenty each for immersion in different organic solvents .
solvents used in this study were eucalyptus oil , orange oil , xylene , and distilled water ( negative control group ) .
each group was further subdivided into two equal subgroups ( n = 10 ) for 2 and 10 min of immersion . at room temperature ,
all sealer samples were immersed completely in 20 ml of solvent stored in glass vials .
after the specified immersion period ( 2 and 10 min ) , the samples were removed from glass vial , rinsed with 100 ml of triple distilled water , and then blotted dry with absorbent paper .
samples were allowed to dry for 24 h at 37  1c in an oven and then kept in dehumidifier / desiccators .
thereafter , the samples were weighed 3 times and the mean was calculated . the amount of sealer dissolved was determined as the difference between the original weight of the sealer and its final weight .
data were subjected to statistical analysis of percentage weight loss for each root canal sealer in different solvents at different time intervals and summarized as mean  standard deviation .
all groups were compared by two factor analysis of variance , and significance of mean difference within and between the groups was done by tukey 's post hoc test .
the mean percentage of weight loss of all sealers and their relative solubility in different organic solvents at 2 and 10 min are shown in table 2 and figure 1 .
mean percentage with standard deviation (  ) of weight loss for each endodontic sealer in different organic solvents at 2 and 10 min dissolution of different endodontic sealers in different organic solvents in all the solvent groups , all the three sealers showed more weight loss at 10 min than 2 min .
the weight loss was highest for endomethasone n followed by apexit plus and adseal at both the periods . in the control group ( distilled water ) ,
minimum and insignificant ( p > 0.05 ) weight loss was observed for all sealers at both time periods . in essential oils , both apexit plus and endomethasone n dissolved more ( p < 0.001 ) at 10 min as compared to 2 min . however , adseal showed no significant ( p > 0.05 ) difference in its solubility between the periods . in xylene
, all sealers showed significantly ( p < 0.05 or p < 0.001 ) more weight loss at 10 min compared to 2 min .
for each time period , comparing the effect of eucalyptus oil on sealers , tukey test showed significantly ( p < 0.05 or p < 0.001 ) different and higher weight loss for both apexit plus and endomethasone n as compared to adseal at both 2 and 10 min .
dissolution of apexit plus and endomethasone n did not differ ( p > 0.05 ) at 2 min .
however , at 10 min , weight loss for endomethasone n was significantly ( p < 0.001 ) higher than apexit plus .
similarly , in both orange oil and xylene , endomethasone n dissolved significantly ( p < 0.01 or p < 0.001 ) more than both apexit plus and adseal at both 2 and 10 min .
apexit plus and adseal showed similar behavior in both orange oil and xylene at 2 min .
however , at 10 min , apexit plus dissolved significantly ( p < 0.001 ) more than adseal in both solvents .
apexit plus and endomethasone n showed significantly ( p < 0.001 ) different and higher weight loss at 10 min as compared to 2 min in all solvents except distilled water .
adseal showed significantly ( p < 0.001 ) different and higher weight loss in xylene at 10 min as compared to 2 min .
however , in other solvents , dissolution of adseal was not significantly different ( p > 0.05 ) between 2 and 10 min .
apexit plus dissolved significantly ( p < 0.01 or p < 0.001 ) more in eucalyptus oil , orange oil , and xylene as compared to distilled water at both 2 and 10 min .
however , its dissolution pattern did not differ ( p > 0.05 ) among eucalyptus oil , orange oil , and xylene at both the time periods .
endomethasone n and adseal showed significantly ( p < 0.001 ) different and higher weight loss in eucalyptus oil , orange oil , and xylene as compared to distilled water at both 2 and 10 min . at 2 min ,
their dissolution profile did not differ ( p > 0.05 ) among eucalyptus oil , orange oil , and xylene .
however , at 10 min , both endomethasone n and adseal showed significantly ( p < 0.01 or p < 0.001 ) higher weight loss in xylene as compared to eucalyptus oil and orange oil , in which their dissolution was not statistically significant ( p > 0.05 ) .
in all the solvent groups , all the three sealers showed more weight loss at 10 min than 2 min .
the weight loss was highest for endomethasone n followed by apexit plus and adseal at both the periods . in the control group ( distilled water ) ,
minimum and insignificant ( p > 0.05 ) weight loss was observed for all sealers at both time periods . in essential oils , both apexit plus and endomethasone
n dissolved more ( p < 0.001 ) at 10 min as compared to 2 min . however , adseal showed no significant ( p > 0.05 ) difference in its solubility between the periods . in xylene
, all sealers showed significantly ( p < 0.05 or p < 0.001 ) more weight loss at 10 min compared to 2 min . for each time period , comparing the effect of eucalyptus oil on sealers , tukey test showed significantly ( p < 0.05 or p < 0.001 ) different and higher weight loss for both apexit plus and endomethasone n as compared to adseal at both 2 and 10 min .
dissolution of apexit plus and endomethasone n did not differ ( p > 0.05 ) at 2 min .
however , at 10 min , weight loss for endomethasone n was significantly ( p < 0.001 ) higher than apexit plus .
similarly , in both orange oil and xylene , endomethasone n dissolved significantly ( p < 0.01 or p < 0.001 ) more than both apexit plus and adseal at both 2 and 10 min .
apexit plus and adseal showed similar behavior in both orange oil and xylene at 2 min .
however , at 10 min , apexit plus dissolved significantly ( p < 0.001 ) more than adseal in both solvents .
apexit plus and endomethasone n showed significantly ( p < 0.001 ) different and higher weight loss at 10 min as compared to 2 min in all solvents except distilled water .
adseal showed significantly ( p < 0.001 ) different and higher weight loss in xylene at 10 min as compared to 2 min .
however , in other solvents , dissolution of adseal was not significantly different ( p > 0.05 ) between 2 and 10 min .
apexit plus dissolved significantly ( p < 0.01 or p < 0.001 ) more in eucalyptus oil , orange oil , and xylene as compared to distilled water at both 2 and 10 min .
however , its dissolution pattern did not differ ( p > 0.05 ) among eucalyptus oil , orange oil , and xylene at both the time periods .
endomethasone n and adseal showed significantly ( p < 0.001 ) different and higher weight loss in eucalyptus oil , orange oil , and xylene as compared to distilled water at both 2 and 10 min . at 2 min , their dissolution profile did not differ ( p > 0.05 ) among eucalyptus oil , orange oil , and xylene .
however , at 10 min , both endomethasone n and adseal showed significantly ( p < 0.01 or p < 0.001 ) higher weight loss in xylene as compared to eucalyptus oil and orange oil , in which their dissolution was not statistically significant ( p > 0.05 ) .
during nonsurgical endodontic retreatment , the removal of root canal obturating materials by purely mechanical means may lead to root perforation , canal straightening , or alteration of the original canal outline .
therefore , the use of organic solvents has been anticipated to decrease the resistance of obturating materials inside the canal so that their retrieval can become easier in synergism with instrumentation .
however , clinicians should be very cognizant about the use of removal techniques and materials for the dismantlement of the previous treatment because very strong solvents are capable of softening the enamel and dentin , which may promote canal transportation and chemical pericementitis if penetrated beyond the apex .
there exist no specific standards for the measurement of root canal sealer solubility in organic solvents .
various studies have reported that a mean time of 1.510.8 min is required for the removal of very well - compacted obturating materials by instrumentation with or without solvents . in the present study , application of 2 and 10 min for standardized samples allowed us to demonstrate clear differences in the solubility profiles of the endodontic sealers used in various solvents . to enhance the accuracy of the measurements , one sealer sample was used for just one immersion period , thus excluding its undesirable weight loss because of the repeated drying and immersion .
after the specified immersion period , all samples were washed with distilled water to remove the decomposed loosen debris .
although several studies regarding the solubility of endodontic sealers in various organic solvents have been reported in the literature , the comparison of the effects of sealers on solvents and vice versa was found interesting in this laboratory analysis .
all endodontic sealers used in this study were found to be soluble to some extent in all the four solvents .
xylene was the more effective solvent followed by the essential oils ( eucalyptus and orange oil ) and distilled water the least .
moreover , the effect of all solvents was found gradual and proportional to the contact time with the surface of the sealers .
organic solvents are usually employed in paint industries to soften the coated materials for their easy removal .
these solvents can be applied in retreatment therapy for the retrieval of resistant or strongly adhered sealers in canal irregularities and ramifications .
several organic solvents have been investigated in the literature for their softening or dissolution capability in endodontic retreatment . since all solvents are known for their toxicity to tissues to variable extent , the selection of an ideal organic solvent for any nonsurgical endodontic retreatment requires an equilibrium between its sealer dissolution competency and clinical safety regarding toxicity and belligerence toward the tissues .
the use of essential oils in endodontics is growing because of their safety , biocompatibility , and noncarcinogenicity .
eucalyptus oil is the distilled oil obtained from the leaves of eucalyptus globulus ; a plant of the family myrtaceae native to australia and cultivated worldwide .
orange oil , an extract of the peel of sweet orange fruit ( citrus sinensis ) is an efficient alternative to potentially toxic solvents .
sweet orange oil consists of approximately 90% d - limonene ; a solvent used in various household products .
d - limonene is an efficient cleaning agent with a pleasant smell and is considered environment friendly . there is no evidence for its carcinogenicity or genotoxicity .
further , orange oil is less cytotoxic and more biocompatible than eucalyptol and chloroform . owing to the concerns about the carcinogenicity of chloroform and unpredictable , idiosyncratic hepatic necrosis and toxicities of halothane , xylene and essential oils can be considered as safe alternatives .
it is commonly considered as an efficient solvent for several organic materials such as gutta percha ( alkadienes ; a hydrocarbon ) , polymers ( resilons ; a polycaprolactone ) , resins and sealers .
chloroform dissolves rather than softens the obturating materials , leaving residues on the canal walls and its fast evaporation makes use of more and more solvent , which makes its use messy and inconvenient .
however , the action of xylene is relatively slow , which permits an efficient and biologically safe removal of softened filling materials .
grduysus et al . reported that xylol showed similar behavior in dissolving gutta - percha as chloroform . in the present study ,
it has been reported that both xylol and orange oil were excellent in softening the gutta - percha and sealer cements without any deleterious effects .
orange oil has been shown to be more biocompatible than eucalyptol , xylol , chloroform , and halothane .
eugenol - based sealers was found similar to that of eucalyptol , chloroform , and xylol . however , orange oil and eucalyptol are poor to dissolve the resin - based materials .
mushtaq et al . and martos et al . have stated that dissolving capacity of orange oil is inferior to chloroform and xylene . however , this is in contrast to some studies which showed similar dissolution behavior of orange oil , eucalyptol , chloroform , and xylol .
stated that xylol was the best solvent whereas chloroform , eucalyptol , and orange oil presented a similar solvent profile .
this indicates that both eucalyptol and orange oil could be suitable as solvents for softening or dissolving the endodontic sealers .
the dissolution capacity of eucalyptol is slower than that of other commonly used solvents at room temperature .
furthermore , this solvent can be easily washed out after retrieval of filling materials by irrigation with tensio - active solutions ( sodium laurel sulfate ) . under the experimental conditions of the present study , adseal ( an epoxy resin - based material )
it may be due to the fact that epoxy resin ( adseal ) is a heavily cross - linked , rigid , and strong polymer .
adseal showed significantly higher dissolution in xylene at 10 min than eucalyptus and orange oils .
interestingly , no significant dissolution was observed in eucalyptus oil and orange oil at both time periods .
bodrumlu and kayaoglu in their in vitro study concluded that ah plus ( epoxy resin - based sealer ) dissolved to some extent and more than ketac - endo ( glass ionomer - based sealer ) , using either eucalyptus oil or chloroform as the solvent .
martos et al . reported that the efficacy of eucalyptus oil , orange oil , xylene , and chloroform to dissolve ez - fill ( epoxy resin - based sealer ) was not significantly different from each other at 2 min .
apexit plus , a calcium hydroxide - based sealer has a more convenient delivery form and hydrophilic formulation of apexit .
consequently , the material is more reliable if used in thicker layers . in this investigation , apexit plus had shown more pronounced dissolution in all the organic solvents as compared with distilled water .
no significant difference in its dissolution was observed among eucalyptus oil , orange oil , and xylene at both time periods .
the reason for low solubility could be the more consistent setting reaction forming a more stable complex .
apexit plus has a ph of < 8 , which is not true for other calcium hydroxide - based root canal sealers .
this low ph may be because of less hydroxyl ion concentration which reacts with the acidic phenol group of salicylates subsequent to the dissociation of calcium hydroxide .
mushtaq et al . reported that apexit plus showed the maximum weight loss in xylene .
however , its dissolution in refined orange oil and tetrachloroethylene was found to the same extent .
whitworth and boursin reported that apexit was significantly more soluble in halothane and chloroform as compared to ketac - endo and ah plus .
there are no published data regarding the action of other organic solvents on this material .
therefore , the effective retrieval of this material from the root canal system using these organic solvents can not be assured .
it has been developed to ameliorate the neurotoxic and mutagenic effects of paraformaldehyde present in its predecessor .
its cytotoxicity is approximately 30 times lower than a formaldehyde - containing sealer . in this study
, it showed a higher weight loss than other endodontic sealers and the maximum in xylene followed by orange oil and eucalyptus oil .
this high degree of solubility is probably due to the release of eugenol , and the hydrolysis of hardened zinc eugenolate .
zoe - based materials decompose hydrolytically as follows : zn ( c10h11o2)2 + 2h2o = zn ( oh)2 + 2c10h11o2 this zinc hydroxide is almost insoluble in neutral , but highly soluble in an acidic solution .
eugenol - based sealer ( endofill ) by orange oil , chloroform , and eucalyptus oil in a scanning electron microscope retreatment study .
eugenol - based sealer presented significantly lower solubility in halothane than chloroform , which was 9 times more effective than eucalyptus oil when exposed for 20 min .
the present laboratory investigation did not consider the clinically imposed parameters such as canal system anatomy , temperature , access , volume of exchange , dilution or displacement by biological fluids , or irrigants regarding the action of solvents on root canal sealing cement .
therefore , its result can not be directly extrapolated to clinical scenarios . the search for more effective and biocompatible universal solvent should continue and should not be confined simply to the softening and gross removal of obturating materials .
within the limitations of this laboratory study , the following conclusions had been drawn . 

xylene was the most effective solventorange oil and eucalyptus oil showed no significant difference in their solvent behaviorall the sealers showed more dissolution in all the solvents used at 10 min than 2 minin distilled water , insignificant sealer dissolution was observed . 
 
xylene was the most effective solvent orange oil and eucalyptus oil showed no significant difference in their solvent behavior all the sealers showed more dissolution in all the solvents used at 10 min than 2 min in distilled water , insignificant sealer dissolution was observed .
 objective : the objective of this study was to evaluate the dissolution effectiveness of eucalyptus oil , orange oil , xylene , and distilled water on three different endodontic sealers.materials and methods : about 240 samples of root canal sealers ( eighty for each sealer ) were prepared and divided into four groups of 20 each for immersion in different organic solvents . 
 each group was further subdivided into two subgroups ( n = 10 ) for 2 and 10 min of immersion time . 
 the mean percentage of weight loss was determined for each sealer in each solvent at both time periods . 
 data were statistically analyzed by two factor analysis of variance and significance of mean difference was obtained by tukey 's post hoc test ( p < 0.05).results : the lowest level of solubility was observed for adseal followed by apexit plus and endomethasone n at both time periods in all solvents . 
 apexit plus showed no significant ( p > 0.05 ) difference in its dissolution in all the organic solvents except distilled water at both the time periods . 
 the solubility profile of endomethasone n and adseal did not differ significantly among eucalyptus oil , orange oil , and xylene at 2 min and between eucalyptus oil and orange oil at 10 min . 
 however , at 10 min , endomethasone n and adseal showed a more pronounced solubility in xylene as compared to both eucalyptus oil and orange oil.conclusions:in general , xylene was the most effective in dissolving root canal sealers than other organic solvents . 
 essential oils ( eucalyptus oil and orange oil ) were found similar in their ability to dissolve apexit plus and endomethasone n. 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
Dissolution of different sealers in each solvent
Relative solubility of each sealer in different solvents
DISCUSSION
CONCLUSIONS
Financial support and sponsorship
Conflicts of interest